Skip to main content
NCBI home page
Wiley Open Access Collection logoLink to Wiley Open Access Collection
. 2026 Feb 18;250(3):1424–1437. doi: 10.1111/nph.71024

Fascinating single‐cell red algae: models for evolution and adaptation

Frédéric Berger 1,✉, Debashish Bhattacharya 2, Chung Hyun Cho 1, Seok‐Wan Choi 3, Julia Van Etten 2,4,5, Shunsuke Hirooka 6, Tzu‐Yen Huang 7,8, Kyle J Lauersen 9, Yongsung Lee 3, Shao‐Lun Liu 7, Shin‐ya Miyagishima 6, Stephen D Rader 10, Daniel Schubert 11, Hwan Su Yoon 3
PMCID: PMC13062707  PMID: 41708507

Summary

The unicellular red algae, Cyanidiophyceae, that diverged early during Archaeplastida (algal and plant) evolution, occupy a variety of extreme habitats that are inhospitable for most other eukaryotes. With the use of modern genomics and genetics methods, Cyanidiophyceae show a remarkable taxonomic diversity, share haplodiplophasic life cycles, and are engaged in complex trophic interactions with microbes that occupy geothermal niches. Amenable to molecular engineering, Cyanidiophyceae are excellent models for understanding evolutionary mechanisms that underpin their extremophilic lifestyles. Their unique growth conditions make these choice red algae of high interest for biotechnological exploitation in environments unsuitable for crops.

Keywords: biotechnology, Cyanidiophyceae, ecology, genomics, red algae

Contents
Summary 1424
I. Introduction 1425
II. Cyanidiophyceae systematics and evolution 1425
III. Life cycle of Cyanidiophyceae 1426
IV. Cyanidiophyceae ecology 1428
V. Importance of Cyanidiophyceae in biotechnology 1430
VI. Molecular tools 1432
VII. Molecular responses to stress in Cyanidiophyceae 1432
VIII. Conclusions 1433
Acknowledgements 1433
References 1434
Open in a new tab

I. Introduction

After the first description of Galdieria sulphuraria in 1899 by the Italian scientist A. Galdieri (Galdieri, 1899), various members of the eukaryotic algal class Cyanidiophyceae have since been discovered and their classification has been continuously revised (Cho et al., 2023; Park et al., 2023; Huang et al., 2024). Cyanidiophyceae are dominant in extreme environments such as volcanic areas characterized by high temperatures (> 40°C), acidic waters (pH 0.5–4), and high concentrations of heavy metals (Rothschild & Mancinelli, 2001; Matsuzaki et al., 2004; Misumi et al., 2008). These algae have small genomes (< 20 Mbp, < 8000 genes) and two widely recognized extremophilic species, so far Cyanidioschyzon merolae and G. sulphuraria, can be engineered efficiently (Miyagishima & Tanaka, 2021; Hirooka et al., 2022). Their tolerance to a vast range of temperature, pH, and heavy‐metal concentrations minimizes microbial contaminants in their growth medium (Miyagishima & Tanaka, 2021) and provides opportunities to study mechanisms of detoxification and heat resistance. Beyond their fundamental biological significance, these models are also becoming a focus of research in biotechnology. Here, we review recent progress in the various aspects of research using these fascinating organisms.

II. Cyanidiophyceae systematics and evolution

Following the origin of all red algae c. 1.43 billion years ago (bya), the Cyanidiophyceae lineage diverged from other red algal groups c. 1.3 bya (Fig. 1), making it the earliest diverged branch within this phylum (Yoon et al., 2006). A recent high‐rank taxonomic revision has reclassified Cyanidiophyceae into four orders and four families based on plastid genome data: Galdieriales, Cavernulicolales, Cyanidiales, and Cyanidioschyzonales, whereby Cyanidiales is now restricted to a narrow lineage including Cyanidium rather than the entire class (Park et al., 2023). The diversification of the four orders within Cyanidiophyceae began c. 1 bya, which is contemporaneous with, or even precedes the divergence of other major crown‐group eukaryotes during the Tonian period (Xiao & Tang, 2018).

Fig. 1.

Fig. 1

Open in a new tab

Bayesian time‐calibrated phylogeny of Cyanidiophyceae. Divergence time estimates were obtained using priors from a previous analysis (Yang et al., 2016), which was supplemented with additional genetic data from Cyanidiophyceae species. Bayesian divergence time estimation was conducted with BEAST v.2.6.6 (Bouckaert et al., 2019) using a mixed dataset comprising nucleotides (2623 sites) from two ribosomal genes (LSU, SSU) and amino acids (2054 sites) from five protein‐coding genes (ef2, cox1, psaA, psbA, rbcL). Geological Period and Era abbreviations: C, Carboniferous; Cm, Cambrian; Cr, Cryogenian; Cz, Cenozoic; D, Devonian, Ed, Ediacaran; J, Jurassic; K, Cretaceous; O, Ordovician; S, Silurian; Pm, Permian, Tr, Triassic.

Galdieriales were the first order to diverge c. 1 bya and consist of a single genus, Galdieria, which includes six species that share similar genomic organization. Whereas their plastid genome is relatively similar to other Cyanidiophyceae, their mitochondrial genome shows reduced size and highly diverged sequences (Cho et al., 2020) that make it difficult to reconstruct a mitogenome phylogeny. Nuclear genomic features also distinguish this order from other Cyanidiophyceae. The small genome of these species (13–17 Mb) encompasses 50–60 chromosomes with frequent gene duplication in subtelomeric regions (Schönknecht et al., 2013; Rossoni et al., 2019a; Hirooka et al., 2022; Cho et al., 2023). The peculiar and fluctuating genome organization may enhance fitness in the extreme environments they inhabit via adaptive gene family expansion in the subtelomeric regions (Cho et al., 2023). Another notable characteristic is the versatile heterotrophic ability of Galdieriales, which can utilize > 36 carbon sources (Gross & Schnarrenberger, 1995; Masson et al., 2025). Diploid Galdieriales cells grow up to 10 μm and can form up to 32 autospores (De Luca et al., 1978; Merola et al., 1981; Albertano et al., 2000).

The other three orders (Cavernulicolales, Cyanidiales, and Cyanidioschyzonales) are similar in genome structure. Compared with Galdieriales, all published chromosome‐level genome assemblies from Cyanidiales and Cyanidioschyzonales converge into 20 contigs without exception, contain more intron‐less genes (Matsuzaki et al., 2004; Cho et al., 2023) and encode fewer protein coding genes (c. 5000 vs 7000–8000 in Galdieriales). No genome assemblies are available for Cavernulicolales (as of December 2025). These species also share traits likely to have been inherited from the common ancestor of these lineages such as the arsenic detoxification pathway (Cho et al., 2023), haploid cells that are usually 3–6 μm in diameter, and meiosis that results in 2–4 spores.

Cavernulicolales is a recently proposed order that is composed of so called ‘cave Cyanidium’. It is the earliest diverged order in this lineage, estimated at having split c. 650 million years ago (Ma) (Fig. 1). Subsequently, the divergence of Cyanidiales and Cyanidioschyzonales occurred c. 500 Ma. In contrast to Cyanidiales and Cyanidioschyzonales (Ciniglia et al., 2019), they possess a thick cell wall. Species in this order are not thermoacidophiles; rather, they inhabit humid coastal caves with dim light, mild temperature, and weak acidity (Azúa‐Bustos et al., 2009; Ciniglia et al., 2019). Due to this specificity, cell growth fails in either established media for thermophilic Cyanidiophyceae or conventional culture media for marine and freshwater algae. Consequently, no culture strains are available up to now. The neoproterozoic oxygenation event and increased oxygenation of volcanic emissions may have facilitated the transition of the lineage to mesophilic habitats (Laakso & Schrag, 2017). Further studies are required to elucidate possible mechanisms underlying this physiological adaptation (Box 1).

Box 1. Outlook.

What are the main challenges?

Further studies of Cavernulicolales are required, and uni‐algal cultures made available to scientists to elucidate possible mechanisms underlying this physiological adaptation.

Where do the authors think progress can be made/into which vein should efforts be channeled?

Other geothermal locations in Iceland, Japan, the Middle East, and New Zealand may be home to undiscovered Cyanidiophyceae.

Increased efforts in biotechnological applications are warranted; Galdieria and Cyanidioschyzon merolae could be the algae that appropriately interface with industrial sites. Further genetic engineering of Galdieria for biotechnological application, including engineering its plastid genome, is to be shown. Cyanidioschyzon merolae would rather be a chassis for synthetic genomics applications.

What are the main outstanding questions?

The role of cell ploidy in adaptation to natural habitats, specifically how this trait reflects local selective pressures, needs to be further elucidated.

What is the underlying genetic architecture of species that inhabit neighboring extreme habitats (potentially cryptic species) and what does this teach us about local adaptation and the drivers of this process?

Future investigations of community interactions that involve Cyanidiophyceae to elucidate how they interact with other microbes and to better understand how the community as a whole is functioning/stabilizing as well as to gain insights into mechanisms of past HGT/adaptation.

By what mechanism has the GC content of Galdieria drifted from that of the other Cyanidiophyceae?

Place more interest in the mitochondria and plastidial genomes and more particularly to investigate coordination between the nuclear, plastid, and mitochondrial genomes.

What are the potential generalizable biological insights?

Cyanidioschyzon merolae is a valuable model system for streamlined molecular biology (e.g. splicing and stress responses) and should therefore continue to yield valuable discoveries about the ancestral state of these processes as well as on the minimal composition of components required to maintain functional processes.

Cyanidiales, once used widely to encompass various species in Cyanidiophyceae, now only include the two species, Cyanidium caldarium and Cyanidiofrigus pintoensis. The former has long been used in studies, whereas the latter species was recently described and prefers relatively lower temperatures (20–30°C) and nonaquatic microhabitats (Huang et al., 2024). The recent discovery of Cyanidiofrigus pintoensis points to the value of searching for nonthermophilic species of Cyanidiales that have not been identified using traditional approaches.

Cyanidioschyzonales includes Cyanidiococcus yangmingshanensis and C. merolae; the latter has become the model species to study Cyanidiophyceae because it can be genetically manipulated (Kuroiwa et al., 1994; Matsuzaki et al., 2004). Overlapping exons result in the smallest genome size of Cyanidiophyceae, and this might have accompanied adaptation to high temperatures (Park et al., 2023), which Cyanidioschyzonales best tolerate among Cyanidiophyceae (Huang et al., 2024).

III. Life cycle of Cyanidiophyceae

Since their first description (Galdieri, 1899), Cyanidiophyceae were believed to solely reproduce asexually although their genomes contain genes potentially involved in meiosis (Umen & Coelho, 2019). However, sexual reproduction has recently been discovered in these algae. In Galdieria, the natural and previously known cell‐walled form is diploid (Fig. 2) (Hirooka et al., 2022). When the pH of laboratory cultures is lowered from 2 to 1, these cells undergo meiosis and produce cell‐wall‐less haploids. As with diploids, haploids are also able to proliferate asexually by cell division. The haploids possess two mating types and undergo isogamy, in which morphologically indistinguishable gametes fuse to generate a diploid. In addition, a haploid can generate a diploid by endoreduplication in laboratory culture.

Fig. 2.

Fig. 2

Open in a new tab

Life cycle of Cyanidiophyceae. The ‘default’ state found in natural habitats is the cell‐walled diploid phase. Specific signals (yet unknown) trigger meiosis, leading to transition to the haploid phase with two mating types. Acquisition of competence for mating triggers fertilization and resumes the diploid phase.

Regarding other members (genera) of the Cyanidiophyceae – namely Cyanidioschyzon, Cyanidiococcus, and Cyanidium – several lines of circumstantial evidence, as described below, suggest that previously unrecognized sexual reproduction also occurs in these genera, as in Galdieria. Cyanidioschyzon merolae found in Naples, Italy was first described as the sole cell‐wall‐less species in Cyanidiophyceae (De Luca et al., 1978), and C. merolae 10D has been used as a model organism in which procedures for genetic manipulation have been developed (Miyagishima & Tanaka, 2021). However, genetically closely related strains have been found in Yellowstone National Park, United States but these are cell‐walled and proliferate by forming four daughter cells through two successive cell divisions within the mother cell wall before release (Toplin et al., 2008; Lee et al., 2015), which is similar to Cyanidiococcus and Cyanidium (Jong et al., 2021). Cyanidiococcus yangmingshanensis was first described as a cell‐walled species that proliferates by forming four daughter cells within the mother cell wall, as in Cyanidium (Liu et al., 2020). However, in the same species but different strain, cells morphologically resembling C. merolae 10D and apparently lacking a cell wall have also been observed (Cho et al., 2020). These observations raise the possibility that the cell‐walled form producing four daughter cells within a mother cell represents the diploid phase, whereas the cell‐wall‐less form proliferating by binary fission corresponds to the haploid phase in these three genera.

Under these circumstances, our recent study demonstrated that cell‐walled forms of Cyanidiococcus, Cyanidioschyzon, and Cyanidium give rise to cell‐wall‐less forms when cultures are transferred to lower pH media. Cytological and genomic analyses indicate that the cell‐walled and cell‐wall‐less forms are diploid and haploid, respectively, and that both diploids and haploids can proliferate asexually, representing haplodiplontic life cycles (Fig. 2). Notably, the ACTIN gene (in the case of Galdieria partida, one of four ACTIN genes, ACT3) is specifically expressed in the diploid phase, where actin localizes at the cell division plane and is involved in cytokinesis, whereas cytokinesis in the cell‐wall‐less haploid phase occurs without actin (Hirooka et al., 2022).

Collectively, four genera of Cyanidiophyceae – Galdieria, Cyanidioschyzon, Cyanidiococcus, and Cyanidium – are naturally cell‐walled diploids that form four daughter cells within the mother cell wall through actin‐dependent cytokinesis. Under certain specific environmental stimuli (yet to be identified; although under laboratory conditions haploid cells were generated at low frequency when cultures were transferred to lower pH media), they give rise to isogamous, cell‐wall‐less haploids, which can also proliferate via actin‐independent cell division. Thus, C. merolae 10D is a haploid clone that was probably derived from an originally cell‐walled diploid (Fig. 2).

IV. Cyanidiophyceae ecology

In the geothermal area, Cyanidioschyzonales and Galdieriales exhibit distinct preferences and relative abundances across geothermal microhabitats (Ciniglia et al., 2004; Skorupa et al., 2013; Hsieh et al., 2015). These habitats differ markedly in light intensity, temperature range, and organic carbon availability (Supporting Information Fig. S1; Table 1), enabling spatial differentiation and local adaptation of Cyanidiophyceae along broader environmental gradients. Environmental amplicon‐base surveys demonstrate that Cyanidioschyzonales dominate sunlit aquatic sites such as hot springs and streams, whereas Galdieriales prevail in darker, drier niches including sulfur vents, soils, and endolithic cavities (Ciniglia et al., 2004; Skorupa et al., 2013; Hsieh et al., 2015). This spatial separation reflects their physiology. Cyanidioschyzonales are obligate photoautotrophs tolerant of high temperature (Kobayashi et al., 2014; Huang et al., 2024) and irradiance (Fu & Wang, 2023) but are drought‐sensitive (Pinto et al., 2007); see also our drought simulation assay in Fig. S2. By contrast, Galdieriales are more desiccation‐tolerant (Fig. S2), acclimate to cold (Rossoni & Weber, 2019), and – thanks to prokaryote‐derived horizontal gene transfer (HGT) – use urea and grow mixotrophically/heterotrophically under terrestrial, low light conditions (Qiu et al., 2013; Rossoni et al., 2019a; Schönknecht et al., 2013; see Fig. S1 for likely allochthonous organic sources). Notably, the mixotrophic capacity of Galdieriales helps them withstand photodamage when subjected to higher light conditions (Fu et al., 2019). Together, these findings highlight how spatial differentiation between these two orders is closely linked to their distinct but flexible physiological traits. When organic carbon is available, earlier work showed that no mixotrophy, only heterotrophy, is observed in G. sulphuraria (strain 074G) (Oesterhelt et al., 2007). But more recent work showed that another strain of G. sulphuraria (strain SAG21.92) can grow mixotrophically (Curien et al., 2021). The former strain was later recognized to be G. javensis, a different species from the latter strain now differentiated as G. partita (Park et al., 2023; Huang et al., 2024). In a similar vein, recent work suggests that mixotrophic capacity varies among Galdieriales species and is influenced by the type of organic carbon available (Huang et al., 2024). Some species (G. partita when treated with glucose or glycerol, and G. daedala when treated with glycerol) exhibit enhanced growth under mixotrophic conditions compared to heterotrophy alone, whereas others (G. >daedala and G. javensis when treated with glucose) show little or no benefit. Notably, mixotrophic growth outperformed heterotrophy, highlighting the importance of carbon‐source specificity. Surprisingly, it has been found that elevated carbon dioxide acts as a trigger to promote heterotrophy in multiple Galdieria species. Stable isotope analysis was used to demonstrate this CO2 is not consumed by the cells in this state, but its absence can cause cessation of glucose consumption from the medium (Masson et al., 2025). These differences highlight the need for further investigation into the evolution of mixotrophy in this group and how it contributes to their adaptation to diverse and extreme environments (Box 1).

Table 1.

Environmental characteristics of aquatic and nonaquatic habitats where Cyanidiophyceae biofilms were observed.

Features Aquatic Nonaquatic
Microhabitat Hot springs, pools, streams Soil, sulfur vents, endolithic, epilithic
Temperature 40–63.4°C 19–48°C
pH 1.5–2.6 0.4–1.2
DOC content TOC in stream: 0.71 (μg C ml−1) WEOC in soil: 32.25 (μg C g−1 dry soil)
Open in a new tab

DOC, dissolved organic carbon; TOC, total organic carbon; WEOC, water‐extractable organic carbon.

For aquatic samples (streams), DOC content is represented as TOC. For nonaquatic (soil) samples, it is expressed as WEOC. Data summarized from Hsieh et al. (2015).

Despite broad‐scale spatial differentiation, temporal niche complementarity allows these orders to coexist at fine spatial scales. In the hot springs of Lemonade Creek in Yellowstone National Park (USA), C. merolae (10D‐like) and Galdieria yellowstonensis (previously G. sulphuraria, resembling the strain 5587.1) co‐exist in relatively high abundance across creek biofilm, neighboring acidic soil, and endolithic microhabitats (Skorupa et al., 2013). Yet these species have drastically different genome organization, GC content, and trophic preferences. In addition, they are exposed to pathogens as environmental sample sequencing revealed sequences from (giant) viruses (Felipe Benites et al., 2024). While bacterial pathogens infecting the algae have not been identified yet, several heterotrophic unicellular eukaryotes feeding on Cyanidiophyceae have been uncovered (Reeder et al., 2015; Sunada et al., 2025). This algal assemblage underpins an ecosystem in which organisms from all domains of life cooperate at the community level, driven by photosynthetic output primarily from C. merolae, gene sharing via HGT, and other adaptive mechanisms that lead to complex biotic interactions (Van Etten et al., 2023; Stephens et al., 2024) and enable life in these hostile environments.

Patterns in metagenome, metatranscriptome, and metabolome data over the diurnal cycle in Lemonade Creek show that C. merolae is numerically abundant and most transcriptionally active during the day (Fig. 3, Ecological complementarity) generating photosynthates that are consumed by the rest of the microbial community (Stephens et al., 2024). Galdieria yellowstonensis is most transcriptionally active at night, likely employing its ability to live as a facultative heterotroph, allowing it to take on a scavenging role. This metabolic complementarity explains the coexistence of both algae in this environment and likely explains similar patterns in other geothermal environments like Yangmingshan National Park in Taiwan (Hsieh et al., 2015; Liu et al., 2020) and Sai‐no‐Kawara Park in Kusatsu hot spring, Japan; the latter is dominated by Cyanidiococcus species (sister to C. merolae) with some G. partita also present.

Fig. 3.

Fig. 3

Open in a new tab

Ecological and metabolic interrelationships in the creek biofilm habitat at Lemonade Creek, Yellowstone National Park (USA). (a) Ecological complementarity: schematic representation of relative expression values of plastid genes over the diurnal cycle for Galdieria and Cyanidioschyzon. The bar graphs below show the transcripts per million (TPM) values for plastid‐encoded psbA for these algae, which is a marker for photosynthetic activity. Cyanidioschyzon is the dominant primary producer at Lemonade Creek (Stephens et al., 2024). (b) Metabolic complementarity: a schematic Galdieria cell above a Cyanidioschyzon cell, showing the major genes each encode for arsenic detoxification. The two possible detoxification pathways for Galdieria (extrusion, detoxification) are shown. The diurnal expression patterns in TPM of arsM and arsH genes at Lemonade Creek are summarized below, with Galdieria in orange, Cyanidioschyzon in red, and bacteria in blue. In this pathway, arsM and arsH theoretically work in tandem to convert arsenite to the more toxic methylarsenite and then to the less toxic methylarsenate. Although Galdieria can survive in the presence of arsenic in culture (Van Etten et al., 2024), it only expresses the arsH gene to a detectable level at day's end in nature (Stephens et al., 2024). Cyanidioschyzon dominates arsM expression throughout the day. Images were made in Biorender (https://BioRender.com/l5zy4nt).

The Cyanidiophyceae are well known for harboring a diverse assortment of adaptive HGTs of prokaryotic origin in their genomes, making up c. 1% of their gene inventory (Qiu et al., 2013; Schönknecht et al., 2013; Rossoni et al., 2019a; Cho et al., 2023). These HGTs originated in extremophilic prokaryotes and appear to be ancient acquisitions in the common ancestors of these algal lineages, as demonstrated by their distribution patterns among extant taxa (Rossoni et al., 2019a; Cho et al., 2023). These foreign genes confer salt and osmotic tolerance, carbon and amino acid metabolism, cellular oxidant reduction, and heavy metal resistance and detoxification. By distributing these adaptive functions across domains of life within a single extreme environment, functional redundancies and dependencies are created within populations and communities that provide potential for the evolution of new functions despite selection favoring genome streamlining (Morris et al., 2012; Takeuchi et al., 2024; Van Etten et al., 2024). Using arsenic detoxification as a model for the fates of HGTs, studies have shown how sharing of gene functions by members of the microbial assemblage (Fig. 3, metabolic complementarity) weakened selection on homologs in Cyanidiophyceae, allowing their long‐term persistence via the putative gain of novel functions (Cho et al., 2023; Van Etten et al., 2024). This hypothesis, called the integrated horizontal gene transfer (IHGT) model, can be used to explain broader phenomena and how extremophilic eukaryotes transitioned from their ‘hot start’ milieu by functional innovations driven by the duplication and divergence of genes that originated via IHGT (Van Etten et al., 2024). Here, we see differences in the retention and transfer patterns of heavy metal‐related HGTs in C. merolae and G. yellowstonensis that reflect the gain of new functions, interesting gene retention patterns, and connectivity to diverse (nondetoxification) metabolic pathways. Furthermore, recent work has shown connections between co‐occurring microbes across all domains (and viruses) based on shared DNA that may reflect past ecological connections or lay the foundation for new organismal associations (Van Etten et al., 2025). These results underline the need for in situ studies to gain meaningful evolutionary and ecological insights into ecosystem maintenance (Box 1).

V. Importance of Cyanidiophyceae in biotechnology

The application of algae in biotechnology, in principle, uses the microbes' inherent abilities to convert inorganic chemicals (ammonia, phosphate, and carbon dioxide) into organic chemical value (protein, carbohydrates, lipids, and pigments) in their biomass, generally driven through photosynthesis as an energy source (Zhang et al., 2022). Their cultivation can also be used to remediate wastewaters as the primary goal, with biomasses being a valuable process output (Chen et al., 2018; Nagarajan et al., 2020). Traditional algal biotechnology applies microbial cultivation concepts to unicellular algae by enabling photosynthesis‐driven cultivation in photobioreactors (Fig. 4a,b). Some algae can be cultivated in fermentation infrastructure using organic carbon as a feedstock (Lu et al., 2021; Bürck et al., 2024). After sufficient growth, the microbial broth is harvested and dewatered, resulting in a powdered biomass product that can be used for various applications (Fig. 4c) (Fabris et al., 2020; Torres‐Tiji & Posewitz, 2025). Algal biomass can be a feed additive for animals, a source of specific macromolecules, or specialty chemicals. Each algal species generates a biochemically unique biomass, containing a variable content of macromolecules.

Fig. 4.

Fig. 4

Open in a new tab

The Cyanidiophyceae can be cultivated in extreme environments for its protein‐rich biomass, C‐phycocyanin (C‐PC), and wastewater treatment. (a–e) Various photographs from the Development of Algae Biotechnology in the Kingdom of Saudi Arabia (DABKSA) project funded by the Ministry of Environment Water and Agriculture (MEWA) at King Abdullah University of Science and Technology (KAUST) from 2022 to 2025. Photos graciously provided by Dr Claudio Grünewald. (a) 3× 1000 l Varicon Aqua tubular photobioreactors growing Cyanidioschyzon merolae in August 2022 as previously published (Villegas‐Valencia et al., 2023, used under the terms of CC‐BY 4.0). (b) 2× 80 000 l raceway ponds containing C. merolae; upper, recently inoculated; lower, mature culture. (c) Freeze‐dried flakes C. merolae biomass before milling. (d) Comparison of the colour of water‐soluble C‐PC extracts from Spirulina (Limnospira) (left) and C. merolae (right) which appears lighter blue and with less other chromophores. (e) Cultivation of 125 000 l of C. merolae in flat panel reactors using sparged industrial green‐CO2 in air mixtures. Cultivations in (b) and (e) were performed by Diedrich Vahrenkamp. (f) Plastic bag enclosed raceway system for cultivation of Galdieria in primary settled wastewaters with diagram from (Henkanatte‐Gedera et al., 2015, 2017, used with permission). (g) Various styles of Galdieria cultivation, hanging bags, acrylic panel, and LGEM tubular photobioreactor system. (f, g) Photos provided by Prof. Peter Lammers from Arizona State University (ASU) Arizona Center for Algae Technology and Innovation (AzCATI).

The ability of Cyanidiophyceae to thrive in high‐temperatures and low‐pH environments presents many opportunities for the biotechnologist to use these organisms in conversion of low‐value wastes into higher‐order biochemical outputs (Gross, 2000; Toplin et al., 2008). Their high temperature tolerance opens cultivation potentials to situations that are unsuited for other algae, like geographies with naturally high heat, or industrial facilities. Reducing the need for cooling in large‐scale microbial cultivation can also greatly reduce process costs (Novoveská et al., 2023). The preference of Cyanidiophyceae for low pH opens possibilities of using unconventional acidic waste (water) streams as culture media, permits direct gassing with pure CO2 for carbon delivery, and use of high ammonium concentrations (Hirooka et al., 2022; Villegas‐Valencia et al., 2023; Masson et al., 2025), all of which would cause classical algal cultures to acidify and crash. The highest growth rates are observed with high nitrogen‐to‐carbon ratios (Masson et al., 2025) which align well with the composition of certain industrial effluents that could be used as media (Curien et al., 2021) enabling waste valorization (Russo et al., 2021). The natural biomass compositions of the Cyanidiophyceae have value as both sources of protein and specialty chemicals (Villegas‐Valencia et al., 2023). These algae retain the cyanobacterial water‐soluble, blue‐colored protein complex C‐phycocyanin (C‐PC) phycobiliproteins as part of their photosystems (Yoshida et al., 2021). C‐PC is used as a natural food colorant and normally sourced from the alkaliphile Limnospira sp. (formerly Arthrospira or colloquially ‘Spirulina’). However, Cyanidiophyceae C‐PC is thermo‐ and acid‐tolerant, enabling pasteurization and increasing its applicability in beverages and food industries (Rahman et al., 2017; Masson et al., 2025). The US FDA recently approved C‐PC from Galdieria sp. as an ingredient. In organisms like Galdieria spp. and C. merolae, C‐PC accumulates to c. 3–5% of the cell mass and is part of the water‐soluble protein fraction, facilitating use of the blue color with minimal purification (Yoshida et al., 2021). Many different strains of Galdieria exist, with some exhibiting variability in pigment responses when organic carbon is present in the medium (Masson et al., 2025). The biomass of Galdieria and Cyanidioschyzon are proteinaceous (> 60%), having low triacylglycerol accumulation (<30%) (Muppaneni et al., 2017). Cyanidiophyceae lack alpha‐carotenoids and xanthophyll pigments, exhibiting a minimal carotenoid profile starting from beta‐carotene, with zeaxanthin as the terminal carotenoid. Both these carotenoids have value as provitamins that support macular health (Cunningham et al., 2007).

Recent efforts have demonstrated nuclear genome genetic engineering for carotenoid pathway modification, isoprene biosynthesis, and fatty acid tailoring (Sumiya et al., 2015; Seger et al., 2023; Villegas‐Valencia et al., 2025). Given its high protein content biomass composition, C. merolae could be a promising candidate for conversion of cellular amino acids into tailored chemicals, such as diamines or tyrosine‐derivatives like coumaric acid, melanin, or even vanillin. The feasibility of engineering recombinant protein accumulation or secretion remains open questions in this host (Box 1). Currently, no applications exist for certifying its biomass as a safe food ingredient; however, it could be as valuable as G. sulphuraria in both C‐PC and protein‐rich biomass production.

Together, these genera exemplify the potential of Cyanidiophyceae as robust platforms for new and expanding industrial biotechnology applications. Their unique physiological traits and genetic tractability position them as valuable tools for conducting sustainable resource recovery in existing waste streams. Their native environments are on the extreme edges of eukaryotic life, and they exhibit high tolerance to agents like dissolved metals and strong acidic conditions (Kharel et al., 2023). Industrial sites that already have effluents or that process residuals with these properties could be new avenues to embark on algal‐biotechnology applications using Cyanidiophyceae. For example, acidic mine process wastewater, high‐ammonia content municipal wastewater concentrates, or brewery process wastes are all examples where a Cyanidiophyceae bioprocess could be applied. However, it has been observed in many groups (not shown) that fungal contaminations are common if cultures are lower than 42°C, presenting also the challenge that processes must be built to accommodate thermal regulation. Galdieria spp. present the possibility of converting waste organic carbon products into proteinaceous biomass efficiently, whereas CO2 would be the preferred carbon source for C. merolae, which could be used to valorize industrial process gas emissions. An example of combining extreme Cyanidiophyceae biotechnology to new applications is the growth of G. sulphuraria biomass from primary municipal effluent, and the mixture of its biomass with animal manure to then conduct hydrothermal liquefaction, and application of the resulting hydrocarbon fraction as a binder in road asphalt (Pahlavan et al., 2020).

VI. Molecular tools

Haploid G. partita does not possess a cell wall, enabling DNA delivery and genetic transformation (Hirooka et al., 2022), which will enable further studies of this unique order of Cyanidiophyceae; but most molecular tools have been developed for the unicellular, acidothermophilic red alga C. merolae (Villegas‐Valencia et al., 2025). The development of molecular tools was facilitated by ease of culturing (Suzuki et al., 1994) and transformation (Ohnuma et al., 2008; Villegas‐Valencia et al., 2025). Cell division can be synchronized by alternating light and dark cycles (Suzuki et al., 1994). Under optimal conditions (42°C, pH 1–3, 2% CO2, ≥ 90 μmol light), the doubling time is c. 9 h, and transformants can be isolated in < 2 wk (Villegas‐Valencia et al., 2025). Being haploid and having no cell wall, C. merolae strain 10D allows facile gene modification, deletion, and replacement using selectable markers (Fujiwara et al., 2013a, 2017, 2021; Taki et al., 2015; Zienkiewicz et al., 2017). Episomal DNA (plasmids) is reported to be stably maintained under selection (Ohnuma et al., 2008, 2009). For integration of transgenes, the endogenous homologous recombination machinery (Fujiwara et al., 2017) shows efficiencies of 50–100% depending on the marker and target locus (Villegas‐Valencia et al., 2025). Counterselectable markers such as URA5.3 can be removed if flanked by tandem repeats, allowing marker recycling (Takemura et al., 2018). Most transgenic insertions to date have been targeted to the CMD184/185 intergenic locus that minimally disrupts transcription and has no discernible effect on growth (Fujiwara et al., 2013a).

The ability to modify the genome and introduce novel sequences into cells has accelerated the development of a variety of analytical and cell biological techniques. The most straightforward modification is gene deletion, reported most notably in the case of the URA5.3 gene, which resulted in the useful URA auxotrophic strain T1 (Taki et al., 2015). Although C. merolae promoters have not yet been fully defined, transgene expression can be driven by strong endogenous promoter regions (usually 500 bp upstream of a gene) such as APCCp and CPCCp (Sumiya et al., 2014; Fujiwara et al., 2021), inducible endogenous promoters from the heat shock response pathway (Sumiya et al., 2014), and repressible promoters from the nitrate‐response pathway. It is thought to be important to use different promoters for each transgene to avoid recombination between multiple copies of the same promoter, given the high rates of recombination in C. merolae. Transcription termination is generally achieved using the bacterial NOS terminator (Sumiya et al., 2014). A recent study isolated plastids from C. merolae, owing to its easy lysis and demonstrated these could, for some time, remain viable within intracellular vesicles in mammalian cells.

Genetic engineering in C. merolae has made use of protein tags and various expression reduction techniques (‘knock‐downs’) at the DNA, RNA, and protein level. Protein tags for immunoprecipitation and fluorescence microscopy that have been used in C. merolae include fluorescent proteins, His, protein A, and StrepII (Ohnuma et al., 2009; Villegas‐Valencia et al., 2025), leading to an abundance of cell biological investigations of organelle division (Fujiwara et al., 2013b; Ichinose & Iwane, 2021). 2′Omethyl antisense oligonucleotides have been used successfully to isolate RNP particles from C. merolae whole cell extract. Antisense knockdown of transcription has been reported (Ohnuma et al., 2009), as has rapamycin‐induced protein degradation (Fujiwara et al., 2024). Cyanidioschyzon merolae cells are readily fixed and preserved for fluorescence microscopy and other imaging techniques, including immuno‐electron microscopy (Nishida et al., 2003). Finally, there exist many publications reporting transcriptomic analysis of C. merolae cells under a variety of different light conditions, CO2 levels, nutrient depletion, temperature changes, and so on (Fujiwara et al., 2009; Imamura et al., 2015; Tardu et al., 2016; Rademacher et al., 2017). These treatments enable detailed analysis of gene regulatory pathways in this organism. Recently, transcriptomic analysis has been extended to Ribo‐seq identification of actively translating transcripts in stationary and dividing cells (Mogi et al., 2025). These techniques have been brought together into a method that simultaneously generates tagged genes and gene deletions (Bora & Tanaka, 2025). Having generated valuable strains with gene deletions, gene modifications, transgenes, and so on, the strains can either be preserved in tissue culture flasks at room temperature and ambient light, or cryopreserved in DMSO (Ohnuma et al., 2011).

VII. Molecular responses to stress in Cyanidiophyceae

Organisms can react to stressful environments by basal tolerance mechanisms where the transcriptome and proteome are reshaped after exposure to the stress and can ‘memorize’ previous stress responses to acquire an enhanced stress tolerance for recurring stress (Hilker et al., 2016). The latter has not been shown yet for Cyanidiophyceae (https://refubium.fu‐berlin.de/handle/fub188/37462); however, the red seaweed Bangia fuscopurpurea can acquire memory of sublethal high‐temperature stress, resulting in acquired thermotolerance (Kishimoto et al., 2019).

Cyanidioschyzon merolae optimally grows at 42°C and can survive temperatures up to 60°C. Interestingly, heat shock genes are induced at an exact temperature suggesting a thermal sensing mechanism, which likely activates heat‐protecting mechanisms (Kobayashi et al., 2014; Sumiya et al., 2014). Two of the highly induced genes encode small heat shock proteins (sHSP). These two genes share a common promoter and are highly similar; however, the proteins are predicted to be nuclear and localized to chloroplasts, respectively, suggesting a protective function for the different organelles (Kobayashi et al., 2014). Galdieria sulphuraria has a similar temperature optimum as C. merolae, and reduction in growth temperature from 42°C to 28°C resulted in massive transcriptional changes, including an upregulation of genes involved in protein biosynthesis. While the transcription factors involved in cold responses in higher plants are not conserved in Cyanidiophyceae, G. sulphuraria shows metabolic acclimation to cold stress by synthesis of betaines, which some nonthermophilic organisms also use to acclimate to lower temperatures (Rossoni et al., 2019b).

The responses of Cyanidiophyceae to light conditions vary strongly as their natural habitats range from very low light intensity (e.g. in endolithic habitats) to a high light level for species growing in streams and open ponds. Under high light conditions, reactive oxygen species accumulate and need to be detoxified which is at least partially achieved by ascorbic acid and the activity of ascorbate peroxidases (Fu & Wang, 2023), revealing a conserved mechanisms between algae and higher plants (Yoshimura & Ishikawa, 2024).

Chromatin proteins protect and compact the DNA and influence the expression of the genetic information (Kouzarides, 2007; Li et al., 2007). Covalent modification of chromatin proteins and DNA forms an ‘epigenetic’ information that can be maintained through cell division. This epigenetic information acts as a memory and plays a role in the response to stress in eukaryotes (Ma et al., 2025). The basic unit of eukaryotic chromatin is the nucleosome, comprising two copies of each core histone: two heterodimers of H2A and H2B and one tetramer of H3 and H4. Each of the core histones H2A, H2B, and H3 is strongly diversified in land plants and mammals (Loppin & Berger, 2020; Martire & Banaszynski, 2020). Although H3 and H4 are > 95% conserved among red algae and green plants, H2A showed marked differences. Remarkably, H2A.X is absent in C. merolae, whereas H2A.Z is absent in several isolates of Galdieria, which is truly exceptional, since the complete loss of H2A.Z is nonviable in most eukaryotes. Interestingly, the H2A sequences in C. merolae and Galdieria are very distinct not only from each other but also from other nonthermoacidophilic species. Through their different combinations, histone variants provide a code across the genome that helps to regulate gene expression (Bönisch & Hake, 2012; Loppin & Berger, 2020). For example, in the flowering plant Arabidopsis thaliana, H2A.Z associates with H3K27me3 to repress protein‐coding genes, whereas the histone variant H2A.W associates with H3K9me2 and DNA methylation to repress transposons (Jamge et al., 2023). Transposons in turn have the capacity to carry the epigenetic mark and confer a stress‐sensitive regulation to genes in proximity of their insertion (Thieme et al., 2022). Although H2A.W and DNA methylation are absent in C. merolae, H3K27me3 covers transposons and causes their silencing (Mikulski et al., 2017; Hisanaga et al., 2023). This highlights an ancestral role of this epigenetic mark also found in several other protists (Hisanaga et al., 2023). Although much work remains to be done on the role of chromatin in Cyanidiophyceae, the first studies suggest that together with works in a broader range of eukaryotes (Grau‐Bové et al., 2022; Romero Charria et al., 2025), red algae will provide a glimpse into the ancestral pattern of chromatin regulation in eukaryotes and their roles in adaptation.

VIII. Conclusions

Cyanidiophyceae possess sophisticated stress response systems that enable survival in environments that are lethal to most eukaryotes. These species provide insights into both highly conserved stress resistance mechanisms and the importance of HGT in acquiring novel stress response traits. Whereas extensive genomic resources are now available, comprehensive analyses of transcriptomic, proteomic, and metabolomic responses to diverse stressors are still lacking. In particular, the genetic identification of master regulators governing stress resilience remains a key research gap. Cyanidioschyzon merolae, with its highly reduced genome and available genetic tools, is well suited for such investigations, whereas Galdieria species offer insights into metabolic flexibility and the acquisition of new traits via HGT. The significance of mechanistic studies will be illuminated by a deeper understanding of the ecology of Cyanidiophyceae. To differentiate the particular from general features it will be crucial to place studies in these fascinating organisms in the broader context of the biology and evolution of algae (Goldbecker & de Vries, 2025; Kunz et al., 2025) and more specifically of red algae. This will now be possible with advances in genomics and establishment of the first model multicellular alga (Petroll et al., 2025).

Competing interests

None declared.

Author contributions

Each author contributed to a section of the text. FB coordinated the project and edited the manuscript.

Disclaimer

The New Phytologist Foundation remains neutral with regard to jurisdictional claims in maps and in any institutional affiliations.

Supporting information

Fig. S1 Diversity of Cyanidiophyceae microhabitats and allochthonous carbon sources at GenZiPeng geothermal area, Taiwan.

Fig. S2 Comparative physiological responses of G. partita and C. yangmingshanensis.

Please note: Wiley is not responsible for the content or functionality of any Supporting Information supplied by the authors. Any queries (other than missing material) should be directed to the New Phytologist Central Office.

NPH-250-1424-s001.pdf (1.5MB, pdf)

Acknowledgements

This review developed after a 3‐day workshop on Red Algae that took place in 28–30 November 2024. FB is grateful for the New Phytologist Foundation that provided funding and for the Max Planck Society that hosted us at Schloss Alden. Susana Coelho was the local organizer and made possible the red alga workshop. Additional funding was provided by the National Science and Technology Council, Taiwan (NSTC113‐2628‐M‐029‐001‐MY3) to S‐LL, the National Research Foundation of Korea (RS‐2022‐NR068987, RS‐2022‐NR070837), and the Ministry of Oceans and Fisheries (MOF) (RS‐2025‐02304428) to HSY. FB and CHC were supported by the Austrian Academy of Sciences. CHC is supported by the European Union's Horizon Europe research and innovation programme under the Marie Skłodowska‐Curie Actions grant (101149768) and by the Basic Science Research Program through the National Research Foundation of Korea (RS‐2023‐00248097). SDR was supported by grants from Canada's National Science and Engineering Research Council as well as by UNBC's Office of Research and Innovation. DB was supported by an award from the USDA National Institute of Food and Agriculture Hatch Formula (#NJ01180). KJL is supported by King Abdullah University of Science and Technology Baseline Research Funding. Open Access funding provided by Gregor Mendel Institut fur Molekulare Pflanzenbiologie GmbH/KEMÃ.

References

  1. Albertano P, Ciniglia C, Pinto G, Pollio A. 2000. The taxonomic position of Cyanidium, Cyanidioschyzon and Galdieria: an update. Hydrobiologia 433: 137–143. [Google Scholar]
  2. Azúa‐Bustos A, González‐Silva C, Mancilla RA, Salas L, Palma RE, Wynne JJ, McKay CP, Vicuña R. 2009. Ancient photosynthetic eukaryote biofilms in an Atacama desert coastal cave. Microbial Ecology 58: 485–496. [DOI] [PubMed] [Google Scholar]
  3. Bönisch C, Hake SB. 2012. Histone H2A variants in nucleosomes and chromatin: more or less stable? Nucleic Acids Research 40: 10719–10741. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Bora P, Tanaka K. 2025. Construction of the Gene Tagging and Knock Out system for reliable genetic analysis of nuclear genes in Cyanidioschyzon merolae . Plant & Cell Physiology 66: 374–383. [DOI] [PubMed] [Google Scholar]
  5. Bouckaert R, Vaughan TG, Barido‐Sottani J, Duchêne S, Fourment M, Gavryushkina A, Heled J, Jones G, Kühnert D, De Maio N et al. 2019. BEAST 2.5: An advanced software platform for Bayesian evolutionary analysis. PLoS Computational Biology 15: e1006650. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Bürck M, Lemes AC, Egea MB, Braga ARC. 2024. Exploring the potential and challenges of fermentation in creating foods: a spotlight on microalgae. Fermentation 10: 649. [Google Scholar]
  7. Chen X, Li Z, He N, Zheng Y, Li H, Wang H, Wang Y, Lu Y, Li Q, Peng Y. 2018. Nitrogen and phosphorus removal from anaerobically digested wastewater by microalgae cultured in a novel membrane photobioreactor. Biotechnology for Biofuels 11: 190. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Cho CH, Park SI, Ciniglia C, Yang EC, Graf L, Bhattacharya D, Yoon HS. 2020. Potential causes and consequences of rapid mitochondrial genome evolution in thermoacidophilic Galdieria (Rhodophyta). BMC Evolutionary Biology 20: 112. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Cho CH, Park SI, Huang T‐Y, Lee Y, Ciniglia C, Yadavalli HC, Yang SW, Bhattacharya D, Yoon HS. 2023. Genome‐wide signatures of adaptation to extreme environments in red algae. Nature Communications 14: 10. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Ciniglia C, Cennamo P, De Natale A, De Stefano M, Sirakov M, Iovinella M, Yoon HS, Pollio A. 2019. Cyanidium chilense (Cyanidiophyceae, Rhodophyta) from tuff rocks of the archeological site of Cuma, Italy. Phycological Research 67: 311–319. [Google Scholar]
  11. Ciniglia C, Yoon HS, Pollio A, Pinto G, Bhattacharya D. 2004. Hidden biodiversity of the extremophilic Cyanidiales red algae. Molecular Ecology 13: 1827–1838. [DOI] [PubMed] [Google Scholar]
  12. Cunningham FX, Lee H, Gantt E. 2007. Carotenoid Biosynthesis in the Primitive Red Alga Cyanidioschyzon merolae . Eukaryotic Cell 6: 533–545. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Curien G, Lyska D, Guglielmino E, Westhoff P, Janetzko J, Tardif M, Hallopeau C, Brugière S, Dal Bo D, Decelle J et al. 2021. Mixotrophic growth of the extremophile Galdieria sulphuraria reveals the flexibility of its carbon assimilation metabolism. New Phytologist 231: 326–338. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. De Luca P, Taddei R, Varano L. 1978. «Cyanidioschyzon merolae»: a new alga of thermal acidic environments. Webbia 33: 37–44. [Google Scholar]
  15. Fabris M, Abbriano RM, Pernice M, Sutherland DL, Commault AS, Hall CC, Labeeuw L, McCauley JI, Kuzhiuparambil U, Ray P et al. 2020. Emerging technologies in algal biotechnology: toward the establishment of a sustainable, algae‐based bioeconomy. Frontiers Plant Science 11: 279. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Felipe Benites L, Stephens TG, Van Etten J, James T, Christian WC, Barry K, Grigoriev IV, McDermott TR, Bhattacharya D. 2024. Hot springs viruses at Yellowstone National Park have ancient origins and are adapted to thermophilic hosts. Communications Biology 7: 7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Fu H‐Y, Liu S‐L, Chiang Y‐R. 2019. Biosynthesis of ascorbic acid as a glucose‐induced photoprotective process in the extremophilic red alga Galdieria partita . Frontiers in Microbiology 10: 3005. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Fu H‐Y, Wang M‐W. 2023. Ascorbate peroxidase plays an important role in photoacclimation in the extremophilic red alga Cyanidiococcus yangmingshanensis . Frontiers in Plant Science 14: 1176985. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Fujiwara T, Hirooka S, Miyagishima S. 2021. A cotransformation system of the unicellular red alga Cyanidioschyzon merolae with blasticidin S deaminase and chloramphenicol acetyltransferase selectable markers. BMC Plant Biology 21: 573. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Fujiwara T, Hirooka S, Yamashita S, Yagisawa F, Miyagishima S. 2024. Development of a rapamycin‐inducible protein‐knockdown system in the unicellular red alga Cyanidioschyzon merolae . Plant Physiology 196: 77–94. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Fujiwara T, Misumi O, Tashiro K, Yoshida Y, Nishida K, Yagisawa F, Imamura S, Yoshida M, Mori T, Tanaka K et al. 2009. Periodic gene expression patterns during the highly synchronized cell nucleus and organelle division cycles in the unicellular red alga Cyanidioschyzon merolae . DNA Research 16: 59–72. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Fujiwara T, Ohnuma M, Kuroiwa T, Ohbayashi R, Hirooka S, Miyagishima S‐Y. 2017. Development of a double nuclear gene‐targeting method by two‐step transformation based on a newly established chloramphenicol‐selection system in the red alga Cyanidioschyzon merolae . Frontiers in Plant Science 8: 8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Fujiwara T, Ohnuma M, Yoshida M, Kuroiwa T, Hirano T. 2013a. Gene targeting in the red alga Cyanidioschyzon merolae: single‐ and multi‐copy insertion using authentic and chimeric selection markers. PLoS ONE 8: e73608. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Fujiwara T, Tanaka K, Kuroiwa T, Hirano T. 2013b. Spatiotemporal dynamics of condensins I and II: evolutionary insights from the primitive red alga Cyanidioschyzon merolae . Molecular Biology of the Cell 24: 2515–2527. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Galdieri A. 1899. Su di unálga che cresce intorno alle fumarole della Solfatera. Atti Della Reale Accademia Delle Scienze Fisiche e Matematiche Napoli 3: 160–164. [Google Scholar]
  26. Goldbecker ES, de Vries J. 2025. Systems biology of streptophyte cell evolution. Annual Review of Plant Biology 76: 493–522. [DOI] [PubMed] [Google Scholar]
  27. Grau‐Bové X, Navarrete C, Chiva C, Pribasnig T, Antó M, Torruella G, Galindo LJ, Lang BF, Moreira D, López‐Garcia P et al. 2022. A phylogenetic and proteomic reconstruction of eukaryotic chromatin evolution. Nature Ecology & Evolution 6: 1007–1023. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Gross W. 2000. Ecophysiology of algae living in highly acidic environments. Hydrobiologia 433: 31–37. [Google Scholar]
  29. Gross W, Schnarrenberger C. 1995. Heterotrophic growth of two strains of the acido‐thermophilic red alga Galdieria sulphuraria . Plant & Cell Physiology 36: 633–638. [Google Scholar]
  30. Henkanatte‐Gedera SM, Selvaratnam T, Caskan N, Nirmalakhandan N, Van Voorhies W, Lammers PJ. 2015. Algal‐based, single‐step treatment of urban wastewaters. Bioresource Technology 189: 273–278. [DOI] [PubMed] [Google Scholar]
  31. Henkanatte‐Gedera SM, Selvaratnam T, Karbakhshravari M, Myint M, Nirmalakhandan N, Van Voorhies W, Lammers PJ. 2017. Removal of dissolved organic carbon and nutrients from urban wastewaters by Galdieria sulphuraria: laboratory to field scale demonstration. Algal Research 24(Part B): 450–456. [Google Scholar]
  32. Hilker M, Schwachtje J, Baier M, Balazadeh S, Bäurle I, Geiselhardt S, Hincha DK, Kunze R, Mueller‐Roeber B, Rillig MC et al. 2016. Priming and memory of stress responses in organisms lacking a nervous system. Biological Reviews 91: 1118–1133. [DOI] [PubMed] [Google Scholar]
  33. Hirooka S, Itabashi T, Ichinose TM, Onuma R, Fujiwara T, Yamashita S, Jong LW, Tomita R, Iwane AH, Miyagishima S. 2022. Life cycle and functional genomics of the unicellular red alga Galdieria for elucidating algal and plant evolution and industrial use. Proceedings of the National Academy of Sciences, USA 119: e2210665119. [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Hisanaga T, Romani F, Wu S, Kowar T, Wu Y, Lintermann R, Fridrich A, Cho CH, Chaumier T, Jamge B et al. 2023. The Polycomb repressive complex 2 deposits H3K27me3 and represses transposable elements in a broad range of eukaryotes. Current Biology 33: 4367–4380. [DOI] [PubMed] [Google Scholar]
  35. Hsieh C, Zhan SH, Lin Y, Tang S, Liu S. 2015. Analysis of rbc L sequences reveals the global biodiversity, community structure, and biogeographical pattern of thermoacidophilic red algae (Cyanidiales). Journal of Phycology 51: 682–694. [DOI] [PubMed] [Google Scholar]
  36. Huang T‐Y, Yoon HS, Chiang Y‐R, Fu H‐Y, Watanabe T, Gerung GS, Geraldino PJL, Liu S‐L. 2024. Diversity in Cyanidiophyceae: Cyanidiofrigus pintoensis gen. et sp. nov. within polyextremophilic red algae (Rhodophyta). Phycologia 63: 245–259. [Google Scholar]
  37. Ichinose TM, Iwane AH. 2021. Long‐term live cell cycle imaging of single Cyanidioschyzon merolae cells. Protoplasma 258: 651–660. [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Imamura S, Kawase Y, Kobayashi I, Sone T, Era A, Miyagishima S, Shimojima M, Ohta H, Tanaka K. 2015. Target of rapamycin (TOR) plays a critical role in triacylglycerol accumulation in microalgae. Plant Molecular Biology 89: 309–318. [DOI] [PubMed] [Google Scholar]
  39. Jamge B, Lorković ZJ, Axelsson E, Osakabe A, Shukla V, Yelagandula R, Akimcheva S, Kuehn AL, Berger F. 2023. Histone variants shape chromatin states in Arabidopsis. eLife 12: RP87714. [DOI] [PMC free article] [PubMed] [Google Scholar]
  40. Jong LW, Fujiwara T, Hirooka S, Miyagishima S. 2021. Cell size for commitment to cell division and number of successive cell divisions in cyanidialean red algae. Protoplasma 258: 1103–1118. [DOI] [PubMed] [Google Scholar]
  41. Kharel HL, Shrestha I, Tan M, Nikookar M, Saraei N, Selvaratnam T. 2023. Cyanidiales‐based bioremediation of heavy metals. Biotech 12: 29. [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. Kishimoto I, Ariga I, Itabashi Y, Mikami K. 2019. Heat‐stress memory is responsible for acquired thermotolerance in Bangia fuscopurpurea . Journal of Phycology 55: 971–975. [DOI] [PubMed] [Google Scholar]
  43. Kobayashi Y, Harada N, Nishimura Y, Saito T, Nakamura M, Fujiwara T, Kuroiwa T, Misumi O. 2014. Algae sense exact temperatures: small heat shock proteins are expressed at the survival threshold temperature in Cyanidioschyzon merolae and Chlamydomonas reinhardtii . Genome Biology and Evolution 6: 2731–2740. [DOI] [PMC free article] [PubMed] [Google Scholar]
  44. Kouzarides T. 2007. Chromatin modifications and their function. Cell 128: 693–705. [DOI] [PubMed] [Google Scholar]
  45. Kunz CF, Goldbecker ES, de Vries J. 2025. Functional genomic perspectives on plant terrestrialization. Trends in Genetics 41: 617–629. [DOI] [PubMed] [Google Scholar]
  46. Kuroiwa T, Kawazu T, Takahashi H, Suzuki K, Ohta N, Kuroiwa H. 1994. Comparison of ultrastructures between the ultra‐small eukaryote Cyanidioschyzon merolae and Cyanidium caldarium . Cytologia 59: 149–158. [Google Scholar]
  47. Laakso TA, Schrag DP. 2017. A theory of atmospheric oxygen. Geobiology 15: 366–384. [DOI] [PubMed] [Google Scholar]
  48. Lee J‐H, Heuser JE, Roth R, Goodenough U. 2015. Eisosome ultrastructure and evolution in fungi, microalgae, and lichens. Eukaryotic Cell 14: 1017–1042. [DOI] [PMC free article] [PubMed] [Google Scholar]
  49. Li B, Carey M, Workman JL. 2007. The role of chromatin during transcription. Cell 128: 707–719. [DOI] [PubMed] [Google Scholar]
  50. Liu S, Chiang Y, Yoon HS, Fu H. 2020. Comparative genome analysis reveals Cyanidiococcus gen. nov., a new extremophilic red algal genus sister to Cyanidioschyzon (Cyanidioschyzonaceae, Rhodophyta). Journal of Phycology 56: 1428–1442. [DOI] [PubMed] [Google Scholar]
  51. Loppin B, Berger F. 2020. Histone variants: the nexus of developmental decisions and epigenetic memory. Annual Review of Genetics 54: 121–149. [DOI] [PubMed] [Google Scholar]
  52. Lu Y, Mu D, Xue Z, Xu P, Li Y, Xiang W, Burnett J, Bryant K, Zhou W. 2021. Life cycle assessment of industrial production of microalgal oil from heterotrophic fermentation. Algal Research 58: 102404. [Google Scholar]
  53. Ma L, Xing L, Li Z, Jiang D. 2025. Epigenetic control of plant abiotic stress responses. Journal of Genetics and Genomics 52: 129–144. [DOI] [PubMed] [Google Scholar]
  54. Martire S, Banaszynski LA. 2020. The roles of histone variants in fine‐tuning chromatin organization and function. Nature Reviews. Molecular Cell Biology 21: 522–541. [DOI] [PMC free article] [PubMed] [Google Scholar]
  55. Masson MLP, de Freitas BB, Zybinskii A, Althagafi G, Amad M, Fox MD, Lammers PJ, Lauersen KJ. 2025. Elevated carbon dioxide stimulates efficient organic carbon consumption for the unicellular alga Galdieria. Trends in Biotechnology 44: 547–569. [DOI] [PubMed] [Google Scholar]
  56. Matsuzaki M, Misumi O, Shin‐I T, Maruyama S, Takahara M, Miyagishima S‐Y, Mori T, Nishida K, Yagisawa F, Nishida K et al. 2004. Genome sequence of the ultrasmall unicellular red alga Cyanidioschyzon merolae 10D. Nature 428: 653–657. [DOI] [PubMed] [Google Scholar]
  57. Merola A, Castaldo R, De LP, Gambardella R, Musacchio A, Taddei R. 1981. Revision of Cyanidium caldarium. Three species of acidophilic algae. Giornale Botanico Italiano 115: 189–195. [Google Scholar]
  58. Mikulski P, Komarynets O, Fachinelli F, Weber APM, Schubert D. 2017. Characterization of the polycomb‐group mark H3K27me3 in unicellular algae. Frontiers in Plant Science 8: 607. [DOI] [PMC free article] [PubMed] [Google Scholar]
  59. Misumi O, Sakajiri T, Hirooka S, Kuroiwa H, Kuroiwa T. 2008. Cytological studies of metal ion tolerance in the red algae Cyanidioschyzon merolae . Cytologia 73: 437–443. [Google Scholar]
  60. Miyagishima S‐Y, Tanaka K. 2021. The unicellular red alga Cyanidioschyzon merolae—the simplest model of a photosynthetic eukaryote. Plant & Cell Physiology 62: 926–941. [DOI] [PMC free article] [PubMed] [Google Scholar]
  61. Mogi Y, Matsuo Y, Kondo Y, Higashiyama T, Inada T, Yoshida Y. 2025. Genome‐wide changes of protein translation levels for cell and organelle proliferation in a simple unicellular alga. Proceedings of the Japan Academy, Series B 101: 41–53. [DOI] [PMC free article] [PubMed] [Google Scholar]
  62. Morris JJ, Lenski RE, Zinser ER. 2012. The black queen hypothesis: evolution of dependencies through adaptive gene loss. MBio 3: e00036‐12. [DOI] [PMC free article] [PubMed] [Google Scholar]
  63. Muppaneni T, Reddy HK, Selvaratnam T, Dandamudi KPR, Dungan B, Nirmalakhandan N, Schaub T, Omar Holguin F, Voorhies W, Lammers P et al. 2017. Hydrothermal liquefaction of Cyanidioschyzon merolae and the influence of catalysts on products. Bioresource Technology 223: 91–97. [DOI] [PubMed] [Google Scholar]
  64. Nagarajan D, Lee D‐J, Chen C‐Y, Chang J‐S. 2020. Resource recovery from wastewaters using microalgae‐based approaches: a circular bioeconomy perspective. Bioresource Technology 302: 122817. [DOI] [PubMed] [Google Scholar]
  65. Nishida K, Takahara M, Miyagishima S, Kuroiwa H, Matsuzaki M, Kuroiwa T. 2003. Dynamic recruitment of dynamin for final mitochondrial severance in a primitive red alga. Proceedings of the National Academy of Sciences, USA 100: 2146–2151. [DOI] [PMC free article] [PubMed] [Google Scholar]
  66. Novoveská L, Nielsen SL, Eroldoğan OT, Haznedaroglu BZ, Rinkevich B, Fazi S, Robbens J, Vasquez M, Einarsson H. 2023. Overview and challenges of large‐scale cultivation of photosynthetic microalgae and cyanobacteria. Marine Drugs 21: 445. [DOI] [PMC free article] [PubMed] [Google Scholar]
  67. Oesterhelt C, Klocke S, Holtgrefe S, Linke V, Weber APM, Scheibe R. 2007. Redox regulation of chloroplast enzymes in Galdieria sulphuraria in view of eukaryotic evolution. Plant & Cell Physiology 48: 1359–1373. [DOI] [PubMed] [Google Scholar]
  68. Ohnuma M, Kuroiwa T, Tanaka K. 2011. Optimization of cryopreservation conditions for the unicellular red alga Cyanidioschyzon merolae . The Journal of General and Applied Microbiology 57: 137–143. [DOI] [PubMed] [Google Scholar]
  69. Ohnuma M, Misumi O, Fujiwara T, Watanabe S, Tanaka K, Kuroiwa T. 2009. Transient gene suppression in a red alga, Cyanidioschyzon merolae 10D. Protoplasma 236: 107–112. [DOI] [PubMed] [Google Scholar]
  70. Ohnuma M, Yokoyama T, Inouye T, Sekine Y, Tanaka K. 2008. Polyethylene glycol (PEG)‐mediated transient gene expression in a red alga, Cyanidioschyzon merolae 10D. Plant & Cell Physiology 49: 117–120. [DOI] [PubMed] [Google Scholar]
  71. Pahlavan F, Rajib A, Deng S, Lammers P, Fini EH. 2020. Investigation of balanced feedstocks of lipids and proteins to synthesize highly effective rejuvenators for oxidized asphalt. ACS Sustainable Chemistry & Engineering 8: 7656–7667. [Google Scholar]
  72. Park SI, Cho CH, Ciniglia C, Huang T‐Y, Liu S‐L, Bustamante DE, Calderon MS, Mansilla A, McDermott T, Andersen RA et al. 2023. Revised classification of the Cyanidiophyceae based on plastid genome data with descriptions of the Cavernulicolales ord. nov. and Galdieriales ord. nov. (Rhodophyta). Journal of Phycology 59: 444–466. [DOI] [PubMed] [Google Scholar]
  73. Petroll R, West JA, Ogden M, McGinley O, Craig RJ, Coelho SM, Borg M. 2025. The expanded Bostrychia moritziana genome unveils evolution in the most diverse and complex order of red algae. Current Biology 35: 2771–2788. [DOI] [PubMed] [Google Scholar]
  74. Pinto G, Ciniglia C, Cascone C, Pollio A. 2007. Species composition of Cyanidiales assemblages in Pisciarelli (Campi Flegrei, Italy) and description of Galdieria phlegrea sp. nov. In: Algae and cyanobacteria in extreme environments. Dordrecht, the Netherlands: Springer, 487–502. [Google Scholar]
  75. Qiu H, Price DC, Weber APM, Reeb V, Chan Yang E, Lee JM, Kim SY, Yoon HS, Bhattacharya D. 2013. Adaptation through horizontal gene transfer in the cryptoendolithic red alga Galdieria phlegrea . Current Biology 23: R865–R866. [DOI] [PubMed] [Google Scholar]
  76. Rademacher N, Wrobel TJ, Rossoni AW, Kurz S, Bräutigam A, Weber APM, Eisenhut M. 2017. Transcriptional response of the extremophile red alga Cyanidioschyzon merolae to changes in CO2 concentrations. Journal of Plant Physiology 217: 49–56. [DOI] [PubMed] [Google Scholar]
  77. Rahman DY, Sarian FD, van Wijk A, Martinez‐Garcia M, van der Maarel MJEC. 2017. Thermostable phycocyanin from the red microalga Cyanidioschyzon merolae, a new natural blue food colorant. Journal of Applied Phycology 29: 1233–1239. [DOI] [PMC free article] [PubMed] [Google Scholar]
  78. Reeder WHH, Sanck J, Hirst M, Dawson SC, Wolfe GV. 2015. The food web of Boiling Springs Lake appears dominated by the heterolobosean Tetramitus thermacidophilus strain BSL. Journal of Eukaryotic Microbiology 62: 374–390. [DOI] [PubMed] [Google Scholar]
  79. Romero Charria P, Navarrete C, Ovchinnikov V, Xu L, Sarre LA, Shabardina V, Ksiezopolska E, Casacuberta E, Lara‐Astiaso D, Sebé‐Pedrós A et al. 2025. Adenine DNA methylation associated with transcriptionally permissive chromatin is widespread across eukaryotes. Nature Genetics 57: 3126–3136. [DOI] [PMC free article] [PubMed] [Google Scholar]
  80. Rossoni AW, Price DC, Seger M, Lyska D, Lammers P, Bhattacharya D, Weber AP. 2019a. The genomes of polyextremophilic cyanidiales contain 1% horizontally transferred genes with diverse adaptive functions. eLife 8: e45017. [DOI] [PMC free article] [PubMed] [Google Scholar]
  81. Rossoni AW, Schönknecht G, Lee HJ, Rupp RL, Flachbart S, Mettler‐Altmann T, Weber APM, Eisenhut M. 2019b. Cold acclimation of the thermoacidophilic red alga Galdieria sulphuraria: changes in gene expression and involvement of horizontally acquired genes. Plant & Cell Physiology 60: 702–712. [DOI] [PubMed] [Google Scholar]
  82. Rossoni AW, Weber APM. 2019. Systems biology of cold adaptation in the polyextremophilic red alga Galdieria sulphuraria . Frontiers in Microbiology 10: 927. [DOI] [PMC free article] [PubMed] [Google Scholar]
  83. Rothschild LJ, Mancinelli RL. 2001. Life in extreme environments. Nature 409: 1092–1101. [DOI] [PubMed] [Google Scholar]
  84. Russo GL, Langellotti AL, Oliviero M, Baselice M, Sacchi R, Masi P. 2021. Valorization of second cheese whey through cultivation of extremophile microalga Galdieria sulphuraria . AIMS Environmental Science 8: 435–448. [Google Scholar]
  85. Schönknecht G, Chen W‐H, Ternes CM, Barbier GG, Shrestha RP, Stanke M, Bräutigam A, Baker BJ, Banfield JF, Garavito RM et al. 2013. Gene transfer from bacteria and archaea facilitated evolution of an extremophilic eukaryote. Science (1979) 339: 1207–1210. [DOI] [PubMed] [Google Scholar]
  86. Seger M, Mammadova F, Villegas‐Valencia M, Bastos de Freitas B, Chang C, Isachsen I, Hemstreet H, Abualsaud F, Boring M, Lammers PJ et al. 2023. Engineered ketocarotenoid biosynthesis in the polyextremophilic red microalga Cyanidioschyzon merolae 10D. Metabolic Engineering Communications 17: e00226. [DOI] [PMC free article] [PubMed] [Google Scholar]
  87. Skorupa DJ, Reeb V, Castenholz RW, Bhattacharya D, McDermott TR. 2013. Cyanidiales diversity in Yellowstone National Park. Letters in Applied Microbiology 57: 459–466. [DOI] [PubMed] [Google Scholar]
  88. Stephens TG, Van Etten J, McDermott T, Christian W, Chaverra M, Gurney J, Lee Y, Kim H, Cho CH, Chovancek E et al. 2024. Temporal dynamics in a red alga dominated geothermal feature in Yellowstone National Park. ISME Communications 4: ycae151. [DOI] [PMC free article] [PubMed] [Google Scholar]
  89. Sumiya N, Fujiwara T, Kobayashi Y, Misumi O, Miyagishima S. 2014. Development of a heat‐shock inducible gene expression system in the red alga Cyanidioschyzon merolae . PLoS ONE 9: e111261. [DOI] [PMC free article] [PubMed] [Google Scholar]
  90. Sumiya N, Kawase Y, Hayakawa J, Matsuda M, Nakamura M, Era A, Tanaka K, Kondo A, Hasunuma T, Imamura S et al. 2015. Expression of cyanobacterial acyl‐ACP reductase elevates the triacylglycerol level in the red alga Cyanidioschyzon merolae . Plant & Cell Physiology 56: 1962–1980. [DOI] [PubMed] [Google Scholar]
  91. Sunada Y, Tsujino D, Yamashita S, Hsieh WH, Tamashiro K, Izumi J, Yagisawa F, Zhou B, Hirooka S, Fujiwara T et al. 2025. Heterotrophic unicellular eukaryotes feeding on the unicellular red alga Cyanidiococcus sp. in moderately hot geothermal sulfuric springs. FEMS Microbiology Ecology 101: fiaf048. [DOI] [PMC free article] [PubMed] [Google Scholar]
  92. Suzuki K, Ehara T, Osafune T, Kuroiwa H, Kawano S, Kuroiwa T. 1994. Behavior of mitochondria, chloroplasts and their nuclei during the mitotic cycle in the ultramicroalga Cyanidioschyzon merolae . European Journal of Cell Biology 63: 280–288. [PubMed] [Google Scholar]
  93. Takemura T, Imamura S, Kobayashi Y, Tanaka K. 2018. Construction of a selectable marker recycling system and the use in epitope tagging of multiple nuclear genes in the unicellular red alga Cyanidioschyzon merolae . Plant & Cell Physiology 59: 2308–2316. [DOI] [PubMed] [Google Scholar]
  94. Takeuchi N, Fullmer MS, Maddock DJ, Poole AM. 2024. The Constructive Black Queen hypothesis: new functions can evolve under conditions favouring gene loss. The ISME Journal 18: wrae011. [DOI] [PMC free article] [PubMed] [Google Scholar]
  95. Taki K, Sone T, Kobayashi Y, Watanabe S, Imamura S, Tanaka K. 2015. Construction of a URA5.3 deletion strain of the unicellular red alga Cyanidioschyzon merolae: A backgroundless host strain for transformation experiments. The Journal of General and Applied Microbiology 61: 211–214. [DOI] [PubMed] [Google Scholar]
  96. Tardu M, Dikbas UM, Baris I, Kavakli IH. 2016. RNA‐seq analysis of the transcriptional response to blue and red light in the extremophilic red alga, Cyanidioschyzon merolae . Functional & Integrative Genomics 16: 657–669. [DOI] [PubMed] [Google Scholar]
  97. Thieme M, Brêchet A, Bourgeois Y, Keller B, Bucher E, Roulin AC. 2022. Experimentally heat‐induced transposition increases drought tolerance in Arabidopsis thaliana . New Phytologist 236: 182–194. [DOI] [PMC free article] [PubMed] [Google Scholar]
  98. Toplin JA, Norris TB, Lehr CR, McDermott TR, Castenholz RW. 2008. Biogeographic and phylogenetic diversity of thermoacidophilic cyanidiales in Yellowstone National Park, Japan, and New Zealand. Applied and Environmental Microbiology 74: 2822–2833. [DOI] [PMC free article] [PubMed] [Google Scholar]
  99. Torres‐Tiji Y, Posewitz MC. 2025. Biotechnology of photosynthetic algae for a world demanding sustainable fuels and resources. One Earth 8: 101381. [Google Scholar]
  100. Umen J, Coelho S. 2019. Algal sex determination and the evolution of anisogamy. Annual Review of Microbiology 73: 267–291. [DOI] [PubMed] [Google Scholar]
  101. Van Etten J, Cho CH, Yoon HS, Bhattacharya D. 2023. Extremophilic red algae as models for understanding adaptation to hostile environments and the evolution of eukaryotic life on the early earth. Seminars in Cell & Developmental Biology 134: 4–13. [DOI] [PubMed] [Google Scholar]
  102. Van Etten J, Stephens TG, Bhattacharya D. 2025. Genetic transfer in action: uncovering DNA flow in an extremophilic microbial community. Environmental Microbiology 27: e70048. [DOI] [PMC free article] [PubMed] [Google Scholar]
  103. Van Etten J, Stephens TG, Chille E, Lipzen A, Peterson D, Barry K, Grigoriev IV, Bhattacharya D. 2024. Diverse fates of ancient horizontal gene transfers in extremophilic red algae. Environmental Microbiology 26: e16629. [DOI] [PubMed] [Google Scholar]
  104. Villegas‐Valencia M, González‐Portela RE, de Freitas BB, Al Jahdali A, Romero‐Villegas GI, Malibari R, Kapoore RV, Fuentes‐Grünewald C, Lauersen KJ. 2023. Cultivation of the polyextremophile Cyanidioschyzon merolae 10D during summer conditions on the coast of the Red Sea and its adaptation to hypersaline sea water. Frontiers in Microbiology 14: 1157151. [DOI] [PMC free article] [PubMed] [Google Scholar]
  105. Villegas‐Valencia M, Stark MR, Seger M, Wellman GB, Overmans S, Lammers PJ, Rader SD, Lauersen KJ. 2025. A rapid CAT transformation protocol and nuclear transgene expression tools for metabolic engineering in Cyanidioschyzon merolae 10D. New Biotechnology 85: 39–51. [DOI] [PubMed] [Google Scholar]
  106. Xiao S, Tang Q. 2018. After the boring billion and before the freezing millions: evolutionary patterns and innovations in the Tonian Period. Emerging Topics in Life Sciences 2: 161–171. [DOI] [PubMed] [Google Scholar]
  107. Yang EC, Boo SM, Bhattacharya D, Saunders GW, Knoll AH, Fredericq S, Graf L, Yoon HS. 2016. Divergence time estimates and the evolution of major lineages in the florideophyte red algae. Scientific Reports 6: 21361. [DOI] [PMC free article] [PubMed] [Google Scholar]
  108. Yoon HS, Müller KM, Sheath RG, Ott FD, Bhattacharya D. 2006. Defining the major lineages of red algae (Rhodophyta) 1. Journal of Phycology 42: 482–492. [Google Scholar]
  109. Yoshida C, Murakami M, Niwa A, Takeya M, Osanai T. 2021. Efficient extraction and preservation of thermotolerant phycocyanins from red alga Cyanidioschyzon merolae . Journal of Bioscience and Bioengineering 131: 161–167. [DOI] [PubMed] [Google Scholar]
  110. Yoshimura K, Ishikawa T. 2024. Physiological function and regulation of ascorbate peroxidase isoforms. Journal of Experimental Botany 75: 2700–2715. [DOI] [PubMed] [Google Scholar]
  111. Zhang J, Hansen LG, Gudich O, Viehrig K, Lassen LMM, Schrübbers L, Adhikari KB, Rubaszka P, Carrasquer‐Alvarez E, Chen L et al. 2022. A microbial supply chain for production of the anti‐cancer drug vinblastine. Nature 609: 341–347. [DOI] [PMC free article] [PubMed] [Google Scholar]
  112. Zienkiewicz M, Krupnik T, Drożak A, Golke A, Romanowska E. 2017. Chloramphenicol acetyltransferase‐a new selectable marker in stable nuclear transformation of the red alga Cyanidioschyzon merolae . Protoplasma 254: 587–596. [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Fig. S1 Diversity of Cyanidiophyceae microhabitats and allochthonous carbon sources at GenZiPeng geothermal area, Taiwan.

Fig. S2 Comparative physiological responses of G. partita and C. yangmingshanensis.

Please note: Wiley is not responsible for the content or functionality of any Supporting Information supplied by the authors. Any queries (other than missing material) should be directed to the New Phytologist Central Office.

NPH-250-1424-s001.pdf (1.5MB, pdf)

Articles from The New Phytologist are provided here courtesy of Wiley

RESOURCES