Gamma irradiation shapes high value metabolite responses across microbes microalgae and plants

Summary

Gamma irradiation can function either as an acute physical elicitor that alters redox and metabolic regulation or as a mutagen that generates selectable genetic variation. We compared evidence from bacteria, fungi, microalgae, plants, and plant cell systems using a common framework that links absorbed dose and exposure context to response mode, evidence strength, phenotype stability, and productivity. Across these systems, irradiation can increase metabolite accumulation or support recovery of improved strains and lines, but responses remain strongly dependent on biological material, dosimetry, selection, and cultivation conditions. Heterogeneous dose reporting, inconsistent productivity denominators, limited causal validation, and scarce scale-up data prevent definition of a universal effective dose or mechanism. We therefore distinguish concentration from total yield and volumetric productivity and propose a stage-gated workflow integrating dosimetry, molecular characterization, stability testing, bioprocess evaluation, and safety and economic assessment to support defensible translation.

Graphical abstract

Natural sciences; Biological sciences; Plant biology; Bioactive plant product

Introduction

Bioactive and specialty metabolites support pharmaceutical, nutraceutical, food, agricultural, and materials applications, but many remain difficult to produce consistently because source abundance, growth rate, pathway regulation, and downstream recovery constrain supply.¹ Industrialization, therefore, depends not only on increasing pathway output but also on coordinating biomass formation, product recovery, purity, and batch reproducibility.² Rational metabolic engineering can remove defined bottlenecks, yet it requires sufficient pathway knowledge and may not readily capture distributed regulatory variation.³ Gamma irradiation offers a complementary route by creating broad physicochemical and genetic perturbations from which useful phenotypes can be selected.⁴

The published evidence is fragmented across organismal communities. Plant-centered reviews have emphasized medicinal species, cell cultures, and low-dose elicitation; microbial studies more often treat irradiation as a random strain-improvement step; and microalgal reports frequently combine irradiation with nutrient, light, carbon, or selection pressure. This fragmentation matters because the same phrase—“irradiation-induced enhancement”—may refer to a transient stress response, a selected mutation, altered extractability, or a higher concentration caused by lower biomass. Table 1 maps the closest reviews and shows that a cross-kingdom comparison centered on response mode, evidence strength, productivity, and translation remains underdeveloped.

Table 1.

Positioning of the present review against the closest recent syntheses

Synthesis	Scope	Distinct strength	Unresolved gap	Relation to this review	Reference
Murthy et al., 2024	plant cell and organ cultures; specialized metabolites	focused account of low-dose elicitation and mutation examples	no microbial or microalgal comparison; limited productivity and scale-up analysis	defines the plant-elicitation baseline	Murthy et al.5
da Silva et al., 2025	plant materials; studies from 2019 to 2024	explicit dose-response review with 23 selected studies	plant-centered; limited causal and process-level comparison	confirms the need for dose-aware synthesis	da Silva et al.6
Arifin and Ardo, 2025	secondary metabolites in sustainable agriculture	broad agricultural framing	limited cross-kingdom evidence hierarchy and productivity analysis	provides a recent agriculture-oriented comparator	Arifin and Ardo7
Present review	bacteria, fungi, microalgae, and plants	two response modes, six-level evidence hierarchy, productivity gate, and translation roadmap	narrative rather than quantitative meta-analysis	cross-kingdom mechanistic and translational integration	–

Gamma irradiation has a long record in crop improvement, where induced diversity is evaluated across generations rather than inferred from an immediate biochemical response.⁸ In microbial natural-product research, the analogous opportunity is to select variants with altered pathway regulation or expression of otherwise weak biosynthetic programs.⁹ These traditions share a mutagen but differ in experimental units, selection intensity, generation time, and acceptable proof of stability. The comparison is therefore scientifically useful only when the biological meaning of dose and endpoint is made explicit.

This review introduces a two-mode framework: one for acute elicitation and another for mutation-related strain or line improvement. These are linked through an evidence hierarchy and a productivity gate. The goal is not to claim gamma irradiation’s superiority over methods like genome editing, adaptive laboratory evolution, chemical mutagenesis, ultraviolet irradiation, or electron beams. Instead, it seeks to determine where gamma irradiation offers justifiable value, where the evidence remains correlational, and what measurements are necessary before considering a metabolite response meaningful for translation.

A two-mode framework for gamma-irradiation responses

Primary physicochemical events

Gamma photons deposit energy directly in biomolecules and indirectly via water radiolysis, producing reactive species that can oxidize nucleic acids, proteins, lipids, and low-molecular-weight metabolites.¹⁰ The resulting lesions include base damage, single-strand interruptions, clustered lesions, and double-strand breaks, while the balance among repair routes depends on lesion complexity, cell state, and dose.¹¹ In plants, these primary events are followed by changes in redox metabolism, membrane function, photosynthesis, hormone signaling, and transcription, but the direction and persistence of the response vary with tissue and exposure context.¹²

The immediate presence of reactive oxygen species does not establish that a later metabolite phenotype is caused by redox signaling (Figure 1). Moderate oxidative perturbation can activate antioxidant and defense programs, whereas greater injury can suppress growth, degrade products, or select rare survivors. Low-dose gamma exposure increased antioxidant defense and thymol biosynthesis in thyme under a defined experimental window, illustrating a hormetic pattern rather than a monotonic response.¹⁶ Living mycelium of Fomes fomentarius likewise showed dose-dependent changes in antioxidant-associated compounds after low-dose exposure, but this constitutes biochemical response evidence rather than proof of a stable mutation.¹⁷

Figure 1.

Two mechanistically distinct routes from gamma irradiation to metabolite output

Energy deposition and radiolysis create an early physicochemical perturbation. The upper branch represents acute elicitation, in which redox and regulatory responses are measured over time and need not be inherited. The lower branch represents mutation-associated improvement, in which DNA lesions generate diversity that must be screened and validated across passages or generations. Solid arrows denote established sequence; dashed arrows denote associations that require causal testing. Data are sourced from Ward,¹³ Mladenov et al.,¹⁴ and Suzuki et al.¹⁵

Mode 1: acute elicitation

Acute elicitation refers to a response observed after irradiation, without evidence that the phenotype is genetically determined. It may involve redox-sensitive transcription, enzyme activation, precursor redistribution, altered transport, or changes in tissue extractability. A transcriptomic study of postharvest Lentinula edodes linked irradiation to delayed deterioration and coordinated changes in gene expression, demonstrating an association at the molecular level but not a heritable production phenotype.¹⁸ Metabolomic responses to abiotic stress illustrate more generally that a measured biochemical state can change as redox balance, development, or culture conditions change.¹⁹ Acute elicitation can be useful when the production system itself is short lived, as in harvested biomass, callus, suspension culture, or a scheduled fermentation stage. Its practical unit is the product recovered from a defined batch, not the persistence of a genotype. Accordingly, a valid elicitation study should report the post-irradiation time course, untreated and stress-matched controls, biomass, extraction efficiency, and both concentration- and batch-level yield.

Mode 2: Mutation-associated improvement

Mutation-associated improvement requires irradiation, recovery, screening, isolation, and repeated validation of a phenotype across passages or generations. Random mutagenesis can alter promoters, repressors, transporters, copy number, chromosome structure, or pathway-adjacent physiology, but a high-producing isolate does not reveal which change is causal. Stress-induced mutagenesis research also shows that population state and selection can shape which variants are recovered, making the screening environment part of the evolutionary process.²⁰ The most convincing studies, therefore, combine phenotype stability with molecular characterization and, ideally, genetic reconstruction or complementation. A gamma-derived soybean diversity panel linked altered isoflavone profiles to segregating genomic regions, providing stronger genetic association than a single post-exposure comparison.²¹ Differential expression of isoflavone and fatty-acid pathway genes in selected soybean mutants further connected genotype, transcription, and composition, while still leaving room for causal validation of individual regulators.²²

Evidence hierarchy and claim calibration

We rank evidence in six levels: metabolite observation, biochemical association, molecular association, causal mechanism, stable production phenotype, and translational validation. The hierarchy is not a quality score for the whole article; it specifies the strongest inference supported for a particular claim. Omics can identify coordinated responses, but pathway enrichment or differential expression does not constitute evidence of a regulatory mechanism. Integrated genomic, transcriptomic, proteomic, and metabolomic approaches illustrate both the power of layered measurements and the need to distinguish association from intervention (Table 2).²⁹

Table 2.

Evidence hierarchy used to calibrate mechanistic and translational claims

Level	Evidence type	Minimum observation	Claim permitted	What remains missing	Reference
1	phenomenology	replicated metabolite or activity change	increased or decreased after exposure	identity, biomass denominator, mechanism, stability	Khawory et al.23
2	biochemical association	enzyme, precursor, redox, or flux-proxy response	associated biochemical response	intervention and genetic stability	Liu et al.24
3	molecular association	transcriptomic, proteomic, metabolomic, or genomic correlation	candidate pathway or regulator	causal perturbation	Meriç et al.25
4	causal mechanism	reconstruction, knockout, complementation, or pathway-specific intervention	regulator or pathway contributes causally	stability and process performance	Zhou et al.26
5	stable production phenotype	repeated passages or generations; cryostorage recovery; productivity retained	stable high-producing strain or line	pilot-scale and economic validation	Barten et al.27
6	translation	reactor, field, or process-controlled validation with recovery and quality data	deployment potential in a defined use case	regulatory approval and full-scale economics	Hussain et al.28

Note: Reported values are reproduced as study-specific observations; differences in biological material, dosimetry, and endpoint preclude direct ranking across rows.

Language should follow evidence strength. “Increased after exposure” is appropriate for a controlled concentration change; “associated with” is appropriate for correlated enzyme or omics responses; “contributes to” requires an intervention; and “stable overproduction” requires repeated productivity measurements in a genetically or phenotypically stable line. This calibration resolves much of the apparent conflict among studies, as different reports often support different levels of inference.

Dose biology: From physical exposure to useful output

Absorbed dose is necessary but insufficient

Absorbed dose, expressed in gray (Gy), is energy deposited per unit mass, but equal nominal doses do not ensure equivalent biological exposure. Source geometry, dose rate, sample thickness, water content, oxygenation, temperature, shielding, and dose uniformity can change the spatial and chemical pattern of injury. Plant mutation studies commonly estimate LD₅₀ or GR₅₀ to anchor an initial dose range, yet these values are genotype-, tissue-, and endpoint specific.³⁰ Related work in perennial grasses demonstrates that lethal and growth-reduction metrics can diverge, so the chosen biological endpoint must be stated rather than treated as interchangeable.³¹ Microbial and algal studies often report doses in the kilogray range, whereas many plant elicitation studies operate at tens of gray; this contrast should not be interpreted as an intrinsic kingdom-level constant. Cell aggregation, spores, pigmentation, antioxidant capacity, ploidy, genome organization, growth phase, and the physical state of the irradiated material all affect radiosensitivity. A cross-kingdom comparison should therefore compare normalized survival or growth inhibition, not nominal gray values alone.

The useful window is endpoint dependent

A dose that maximizes mutation frequency may not maximize the recovery of viable, high-producing variants, and a dose that increases metabolite concentration may reduce total product due to biomass loss (Figure 2). Chemical-mutagen dosimetry studies make the broader point that exposure calibration and biological uptake must be separated from the administered treatment, an issue that also applies conceptually to physical mutagens.³⁵ The relevant optimum is thus a multi-objective window bounded by survival, growth, product quality, stability, and the intended production format.

Figure 2.

Dose-response and productivity are related but non-equivalent

A useful exposure window lies between insufficient perturbation and injury-dominated inhibition. The dose that maximizes metabolite concentration per biomass may differ from the dose that maximizes total or volumetric productivity because biomass and recovery can decline as stress increases. Curves are conceptual and are not universal dose functions. Data are sourced from Moffett et al.,³² Hong et al.,³³ and Abo-State et al.³⁴

Concentration is not productivity

Four denominators should be distinguished: product per unit biomass, total batch yield, specific production rate, and volumetric productivity. A treatment can increase milligrams per gram while decreasing grams of biomass per liter, leaving total recovery unchanged or lower. The same caution applies when irradiation improves extractability by fragmenting a matrix: a higher analytical recovery does not necessarily reflect greater biosynthesis. Reviews of irradiation-induced molecular modification of natural compounds show why chemical transformation and biological production must not be conflated.³⁶ Productivity claims should include biomass, culture volume or plant unit, elapsed time, recovery yield, and composition. When only concentration data are available, the appropriate conclusion is “enhanced accumulation” instead of “overproduction.” This key distinction led to the removal of “overproduction” from the title and is fundamental to the interpretative framework discussed in the following text.

Cross-kingdom evidence: Shared logic, different constraints

Bacteria

Bacterial secondary metabolism is often organized in biosynthetic gene clusters controlled by pathway-specific and global regulators (Figure 3). Environmental cues can activate antibiotic production, indicating that pathway output is conditional even in the absence of a new mutation.⁴⁰ Genome mining has revealed many clusters that are silent or weakly expressed under routine culture conditions, but activation by targeted regulatory methods does not prove that irradiation will activate the same cluster.⁴¹ Gamma mutagenesis should therefore be described as generating selectable diversity rather than as a targeted switch for cryptic pathways.

Figure 3.

Cross-kingdom response landscape

Bacteria, fungi, microalgae, and plants share the logic of perturbation, recovery, selection or elicitation, and validation, but differ in population size, cellular organization, repair, culture physics, stability testing, and scale-up. Nominal dose ranges are therefore not directly transferable among systems. Data are sourced from Fouillaud and Dufossé,³⁷ Trovão et al.,³⁸ and Jan et al.³⁹

Classical studies have recovered Streptomyces variants with higher antibiotic output, but their strongest contribution lies in empirical strain improvement rather than in resolving a molecular mechanism. Modern silent-cluster activation uses defined promoters, reporters, or regulators and provides a benchmark against which random irradiation strategies can be evaluated.⁴² Reporter-guided mutant selection demonstrates how high-throughput phenotyping can convert broad variation into pathway-specific discovery.⁴³

Recent work combined irradiation mutagenesis with selection to obtain a Bacillus velezensis strain with higher surfactin production, showing that classical diversity generation can still be productive when paired with analytical screening.⁴⁴ A 2026 study used low-dose gamma irradiation to improve the enzymatic capacity for ochratoxin A detoxification in a soil-derived Bacillus thuringiensis isolate, but the endpoint was biocontrol function rather than a purified metabolite titer.⁴⁵ Gamma-derived Bacillus and Streptomyces mutants have also shown enhanced antagonistic activity against plant pathogens, reinforcing the need to distinguish a functional phenotype from direct chemical quantification.⁴⁶ The bacterial advantage is short generation time and large searchable populations; the main risk is attributing a selected phenotype to a specific pathway without genome-level confirmation. Stability should be tested across nonselective passages, and whole-genome sequencing should be linked to the reconstruction of candidate mutations where causal claims are made. Table 3, therefore, labels most bacterial examples as stable-phenotype evidence only when repeated passage data are available and otherwise retains them at the phenomenological or biochemical level.

Table 3.

Representative gamma-irradiation studies across biological systems; values are study specific and should not be generalized as kingdom-wide optima

System / organism	Exposure	Target endpoint	Reported outcome	Evidence interpretation	Reference
Bacterium / Streptomyces rimosus	∼3 kGy	oxytetracycline	the selected mutant reported ∼19-fold higher production	stable-output claim requires passage and genomic confirmation	Lazim et al.47
Bacterium / Halomonas desertis	∼1 kGy	exopolysaccharide	yield and biological activity increased in the selected variant	biochemical plus genomic association; causality unresolved	Chouchane et al.48
Bacterium / Streptomyces rimosus NRRL 2455	∼4 kGy	paromomycin	selected mutants showed ∼1.4- to 2-fold higher antibiotic activity	functional activity is not identical to the purified product titer	Ibrahim et al.49
Fungus / Acremonium chrysogenum	∼2 kGy	cephalosporin C	optimized mutant/process reported ∼3.46-fold higher production	irradiation and process optimization effects must be separated	Ibrahim et al.50
Fungus / Trichoderma harzianum	250 Gy	xylanase and cellulase	selected variants showed higher enzyme activities	useful strain-screening evidence; pathway causality not established	Askari et al.51
Fungus / Monascus ruber	gamma-derived mutant	red pigment	immobilized mutant culture improved pigment bioprocessing	process conditions and mutant genotype jointly determine output	El-Sayed et al.52
Microalga / Haematococcus pluvialis	5 kGy	astaxanthin	mutant reported ∼66% higher astaxanthin productivity	productivity evidence is stronger than concentration alone	Yang et al.53
Microalga / Botryococcus braunii KMITL	50 Gy	biomass, carotenoids, lipids	biomass increased by 8.7–32.5% with compositional changes	multiple endpoints require product-specific optimization	Jongput et al.54
Plant tissue / Catharanthus roseus	20–40 Gy	vincristine and vinblastine	embryogenic tissues showed higher alkaloid accumulation	acute tissue response should not be labeled heritable without regeneration tests	Mujib et al.55
Plant mutant pool / soybean	gamma-derived lines	isoflavones and fatty acids	differential pathway-gene expression accompanied altered composition	molecular association supports candidates but not single-gene causality	Kim et al.22

Fungi

Fungal natural-product pathways are controlled by cluster-specific factors, chromatin state, development, and global environmental signaling.⁵⁶ Penicillium species illustrate how secondary metabolism is integrated with growth and stress, making yield changes sensitive to both genotype and cultivation state.⁵⁷ Transcriptional regulators can coordinate multiple fungal clusters, so a radiation-derived phenotype may arise from broad regulatory change rather than mutation of a single biosynthetic enzyme.⁵⁸

Epigenetic activation using defined small molecules has revealed silent clusters in endophytic fungi and provided a non-mutational comparator for irradiation-induced changes in expression.⁵⁹ Studies of irradiated endophytic fungi report altered bioactivity and metabolite profiles, but bioassay enhancement does not identify the responsible compound or establish greater process productivity.⁶⁰ Evaluation of gamma-treated Aspergillus terreus endophytes similarly supports screening value while leaving causality and long-term stability as separate questions.⁶¹

Selected fungal mutants have been reported for antibiotic, pigment, and enzyme production, as well as for lovastatin production and degradation. Gamma-derived Agaricus bisporus variants showed changes in enzyme activity and yield-related traits, demonstrating that industrially relevant phenotypes can be selected but may be pleiotropic.⁶² Reports of penicillin and lovastatin enhancement in Penicillium chrysogenum and Aspergillus terreus remain useful case studies, although contemporary replication with genome sequencing, defined titers, and passage stability would strengthen them substantially.^63,64 Compared with bacteria, filamentous fungi add heterokaryosis, multinucleate growth, sporulation, morphology-dependent oxygen transfer, and pellet structure to the interpretation of stability and productivity. Consequently, a high-producing colony should be purified using appropriate single-spore or hyphal-tip procedures, evaluated under nonselective propagation conditions, and retested in controlled fermentation before being treated as a stable strain.

Microalgae and cyanobacteria

Microalgae combine rapid cultivation with photosynthetic carbon capture and can produce carotenoids, phenolics, lipids, polyunsaturated fatty acids, and proteins.⁶⁵ Their response to irradiation is inseparable from light, nutrient availability, carbon supply, mixing, and self-shading, all of which alter redox state and product formation. Reviews of Euglena carotenoid biosynthesis show that pathway capacity is regulated by both cellular state and cultivation environment.⁶⁶ Nuclear irradiation and carbon dioxide stress have been used sequentially to improve Haematococcus pluvialis growth and astaxanthin yield, illustrating how irradiation can provide initial diversity while culture stress supplies selection.⁶⁷ In Chlorella sorokiniana, ultraviolet and gamma exposure induced molecular changes associated with rapid lipid accumulation, but the modality-specific contributions must be distinguished from those of subsequent culture conditions.⁶⁸ Gamma exposure has also altered lipid content and fatty acid composition in Nannochloropsis, an endpoint that should be interpreted alongside biomass and time-normalized productivity.⁶⁹

Recent reports extend the evidence base but also reveal its uneven quality. Gamma-treated microalgae have shown dose-dependent changes in growth, soluble protein levels, stress markers, and biochemical composition, often without corresponding causal genetic validation.⁷⁰ Arthrospira platensis cultures exposed to gamma irradiation showed changes in amino acids, polyphenols, and other phytochemical constituents, but validation across independent cultures and passages is still necessary.⁷¹ A 2026 Algal Research study profiled bioactive compounds in Chlorella sorokiniana under controlled irradiation, adding contemporary analytical depth to this still sparse area.⁷² Adaptive laboratory evolution offers a useful comparator because it applies sustained selection and permits repeated fitness assessment.⁷³ Recent syntheses on microalgal strain engineering emphasize that productivity gains must be balanced against photobioreactor control, robustness, and carbon-use efficiency.⁷⁴ For irradiated algae, the most persuasive workflow is therefore irradiation followed by clone isolation, multi-environment screening, passage stability, and photobioreactor validation rather than a single-flask concentration comparison.

Plants and plant cell systems

Plant evidence spans irradiated seeds, whole plants, callus, suspension cultures, and organ cultures, which represent different biological questions. Earlier reviews documented increases in medicinal-plant metabolites after gamma exposure but also emphasized strong species- and dose-dependent effects.⁷⁵ Milk-thistle callus exposed to gamma irradiation and phenylalanine illustrates how a physical elicitor and a metabolic precursor can interact, making factorial controls essential for attribution.⁷⁶ Acute exposure increased phenolic and antioxidant measures in Curcuma alismatifolia leaves, an elicitation endpoint that, by itself, does not establish inheritance.⁷⁷

Plant cell and organ cultures are particularly suitable for controlled elicitation because tissue age, medium, and post-treatment interval can be standardized. In Centella asiatica, acute gamma irradiation changed physiological traits and flavonoid accumulation, supporting a dose-limited biochemical response.⁷⁸ Catharanthus roseus tissue studies reported altered alkaloid accumulation and tissue responses after irradiation, but comparisons among callus, regenerated plants, and subsequent generations should not be conflated into a single mechanism. Table 2 summarizes a representative case without inferring universal dose thresholds.

Whole-plant mutation breeding requires longer validation. Gamma-derived tomato lines have shown altered phytonutrient capacities, although composition must be considered with agronomic performance.⁷⁹ Earlier, gamma-irradiated soybean material exhibited higher isoflavone concentrations and antioxidant levels, but this phenotype still required genetic and agronomic validation.⁸⁰ Mentha piperita mutants exhibited variation in essential oil yield and quality traits, demonstrating the value of chemotype screening across selected lines.⁸¹ Salvia officinalis in vitro cultures exhibited dose-dependent changes in phenolics, biological activity, and ultrastructure, also demonstrating that biochemical gain can coincide with cellular injury.⁸² Additional plant examples reinforce the need for endpoint-specific language. Gamma irradiation altered gentiopicroside production in Gentiana kurroo cultures under defined in vitro conditions.⁸³ Phaseolus vulgaris leaves exhibited broad metabolite perturbations after exposure, consistent with systems-level stress reprogramming rather than a single pathway switch.⁸⁴ A 2026 tomato transcriptome study detected distinct single-nucleotide variant patterns after low-dose gamma irradiation and cold plasma, but transcript-derived variant calling and low variant counts limit conclusions about genome-wide mutational targeting.⁸⁵

What the cross-kingdom comparison reveals

The shared logic is perturbation, recovery, selection or elicitation, and validation; the biological meaning of each step differs. Bacteria favor large mutant libraries and rapid passage tests; fungi require attention to nuclear and morphological stability; microalgae require integration with light and reactor physics; and plants require separation of acute tissue responses from heritable change. These differences explain more of the reported dose range than kingdom labels alone (Figure 4). Pathway architecture also shapes response. Secondary metabolism is controlled at multiple levels, including precursor supply, enzyme activity, transport, global regulation, and product toxicity.⁹⁰ Microbial biosynthetic gene clusters can sometimes be activated by manipulating regulators, whereas dispersed plant pathways often depend on tissue-specific transcriptional programs and developmental processes.⁹¹ Terpene and isoprenoid production, for example, draws on conserved precursor chemistry but is partitioned differently among organisms and organelles.⁹² Metabolomics can expose these system-wide trade-offs, although it remains an associative tool unless coupled to intervention.⁹³

Figure 4.

Conserved precursor logic and kingdom-specific regulation

Central carbon and reducing power feed major pathway families, including carotenoids and other terpenoids, polyketides, shikimate/phenylpropanoid products, and amino acid-derived metabolites. Gamma irradiation acts upstream through stress and genetic perturbation; it does not target a pathway unless selection or a causal intervention demonstrates specificity. Data are sourced from Paniagua-Michel et al.,⁸⁶ Hertweck,⁸⁷ Shende et al.,⁸⁸ and Tholl.⁸⁹

Table 3 shows that the strongest quantitative examples remain case-specific. The purpose of comparison is not to average across incompatible experiments but to expose which evidence is missing: absorbed-dose detail, biomass-normalized and volumetric output, molecular causality, passage or generation stability, and scale-up.

From laboratory response to translation

A stage-gated workflow

Figure 5 replaces the earlier linear workflow with two response branches and explicit decision gates. Acute elicitation proceeds from time-resolved redox and metabolic measurements to batch-yield validation. Mutation-associated improvement proceeds from survival-calibrated irradiation to clone or line isolation, stability testing, and genotype-to-phenotype analysis. Both branches converge at a productivity gate before process optimization, safety evaluation, and deployment.

Figure 5.

Stage-gated workflow for gamma-irradiation-enabled metabolite development

The workflow begins with dosimetry and response-mode assignment. Acute elicitation and mutation-associated improvement follow separate validation branches before converging at a productivity gate that integrates biomass, specific yield, volumetric productivity, and product quality. Failure at any gate returns the study to dose design, screening, or process optimization rather than allowing a concentration change to be labeled commercial overproduction. Data are sourced from Ma et al.,⁹⁴ LaPanse et al.,⁹⁵ and Cardiff et al.⁹⁶

High-throughput screening is essential because random variation generates many neutral or deleterious outcomes. Microfluidic droplet platforms can evaluate large microbial libraries while retaining genotype-phenotype linkage, although assays must be designed around the target product rather than a convenient proxy. The same principle applies to imaging, fluorescence, or spectroscopic screening in algae and plants: primary screens should be followed by quantitative chemical analysis and independent biological replication. Targeted engineering can be used after irradiation to test or stabilize candidate mechanisms. Metabolic engineering of Nicotiana benthamiana increased taxadiene levels through targeted pathway intervention, illustrating the mechanistic clarity that random mutant studies should aim for.¹⁰⁰ CRISPR-based metabolic editing can modify plant pathway genes or regulators, but its value here is complementary: it can reconstruct a candidate irradiation-derived allele, remove a competing branch, or test causality.¹⁰¹ Machine learning can prioritize multivariate dose-process combinations, yet reliable prediction requires prospective validation and harmonized input data.¹⁰²

Stability, scale-up, and economics

Stability should be defined operationally. Microbial and algal strains require repeated nonselective passages, cryostorage recovery, and performance testing; plant materials require appropriate generations or clonal cycles; and elicited cultures require batch-to-batch reproducibility rather than inheritance. Cryopreservation can reduce drift during storage but cannot substitute for stability testing during active propagation.¹⁰³

Scale-up can reverse laboratory rankings through oxygen transfer, mixing, light gradients, shear, morphology, substrate inhibition, or downstream recovery. A strain that produces more compound in a small flask may be inferior in a reactor if it grows slowly, forms problematic pellets, or produces difficult impurities. Electron-beam-induced structural variation in microbes provides a recent comparator showing that physical mutagenesis platforms should be evaluated by the distribution and functional consequences of variants not only by the mutagen label.¹⁰⁴ A 2026 study of gamma-treated Moringa leaf powder further illustrates a separate translational route—postharvest modulation of functional composition—whose logic differs from that of breeding or strain improvement.¹⁰⁵ Techno-economic value depends on access to irradiation, source maintenance, throughput, sample handling, screening costs, product recovery, regulatory classification, and the value of incremental yield. Gamma sources provide penetration and mature dosimetry infrastructure but may be less accessible than ultraviolet, electron-beam, plasma, or chemical approaches. Direct comparative experiments are needed before superiority is claimed.

Safety, regulation, and product definition

An irradiated production organism, a metabolite purified from an irradiated strain, an irradiated plant-derived ingredient, and a mutation-bred cultivar enter different regulatory pathways. The irradiation process does not automatically make a product radioactive, but a safety assessment must address the specific product, intended use, residual organisms, impurities, genetic stability, and jurisdiction. Radiation mutation-breeding reviews emphasize that regulatory treatment also differs from that of transgenic or genome-edited products.¹⁰⁶ Product identity is equally important. Increased antioxidant activity can result from a different mixture rather than more of the intended compound; an antibiotic or pigment process must therefore assess spectrum, purity, unwanted metabolites, and consistency. Safety and economic gates should be built into development before a high-producing variant is promoted as commercially ready (Figure 6).

Figure 6.

Evidence-to-translation roadmap

Phenomenological responses must progress through biochemical and molecular association, causal testing, stability, process validation, and safety/economic assessment. Targeted metabolic engineering and predictive modeling are complementary tools for testing candidates and optimizing processes; they do not replace prospective validation. Data are sourced from Dasgupta et al.,⁹⁷ Zhao et al.,⁹⁸ and Lawson et al.⁹⁹

Limitations of the study

The literature is heterogeneous with respect to absorbed-dose verification, dose rate, source geometry, biological state, post-exposure interval, and endpoint definition. Many articles report administered settings without dose-uniformity information, use one selected dose without a full response curve, or omit biomass and volumetric yield. This heterogeneity prevents quantitative pooling across kingdoms and makes universal “optimal doses” scientifically indefensible.

Positive-outcome bias is likely because unsuccessful screens, unstable mutants, and neutral metabolite responses are less likely to be published. Some studies quantify total phenolics, antioxidant assays, or inhibition zones without resolving compound identity, while others infer pathway activation from expression alone. The field also lacks enough independent replication, cross-generation or passage tests, and head-to-head comparisons with alternative technologies.

Mechanistic depth remains uneven. Multi-omics can narrow candidate pathways, but causal reconstruction is rare, particularly in microalgae and filamentous fungi. Radiation multi-omics research in other biological settings demonstrates the analytical opportunity, yet study design must remain specific to metabolite production and avoid importing mechanisms across unrelated systems.¹⁰⁷ The narrative design of this review is itself a limitation: it supports conceptual integration but does not provide quantitative estimates of pooled effects or publication bias. The transparent search scope, explicit inclusion logic, evidence hierarchy, and separation of concentration from productivity are intended to make the synthesis auditable without implying that the systematic review is complete.

Research priorities

First, absorbed dose, dose rate, geometry, uniformity, biological material, water content, oxygen status, and temperature should be reported as a minimum set of dosimetric parameters. Second, dose-ranging should be linked to survival, growth, product concentration, total yield, and productivity rather than to lethality alone. Third, time-resolved sampling should distinguish early signaling from stable metabolic or genetic change. Fourth, high-producing variants should undergo whole-genome or appropriate targeted analysis, with independent reconstruction of leading candidate alleles when feasible. Fifth, transcriptomics, proteomics, metabolomics, isotope tracing, and flux analysis should be integrated around pre-specified causal models rather than used as parallel descriptive layers. Sixth, stability criteria should be declared prospectively for passages, generations, cryostorage recovery, and multi-environment testing. Seventh, laboratory optimization should use response-surface or Bayesian designs that jointly consider dose, recovery conditions, and cultivation parameters. Eighth, predictive models should be evaluated prospectively on held-out organisms, strains, or environments, not only by retrospective fit. Ninth, scale-up should include downstream recovery, impurity profiles, batch reproducibility, techno-economic analysis, life cycle assessment, and radiation-facility logistics (Table 4).

Table 4.

Minimum reporting and decision criteria for future studies

Domain	Minimum report	Decision question	Failure signal	Reference
Physical dose	source, absorbed dose, dose rate, geometry, uniformity, exposure time	was the intended exposure delivered reproducibly?	nominal settings without dosimetric verification	Rios et al.108
Biological calibration	survival, growth reduction, recovery interval, biological state	is the range informative without excessive lethality?	one arbitrary dose or endpoint	Ghasemi-Soloklui et al.109
Screening	library size, primary assay, confirmatory chemistry, independent replicates	can the screen recover rare, product-specific phenotypes?	proxy-only selection or no false-positive control	Zhang et al.110
Stability	nonselective passages/generations, cryostorage recovery, multi-environment test	does performance persist without selection?	regression toward parental output	Wu et al.111
Process context	biomass, volume, time, mixing/light/oxygen, recovery yield	does the ranking persist under production conditions?	higher concentration but lower volumetric productivity	Bernard et al.112
Translation	purity, safety, batch variation, throughput, cost, TEA/LCA	is the gain valuable in the intended product pathway?	no product specification or economic boundary	Abdi et al.113

Finally, comparative experiments should compare gamma irradiation with ultraviolet radiation, electron beams, chemical mutagenesis, cold plasma, adaptive laboratory evolution, and targeted engineering, using a shared product-level endpoint. Heavy-ion breeding research shows that radiation quality and mutation spectrum can be compared explicitly, rather than being discussed as interchangeable physical mutagens.¹¹⁴ Integration with elicitation and metabolic engineering should be justified by complementary mechanisms and factorial evidence, not by the assumption that more interventions necessarily produce a better strain.¹¹⁵

Conclusion

Gamma irradiation can contribute to the production of high-value metabolites, but its scientific significance depends on how it is used. As an acute elicitor, it can transiently reshape redox and metabolic regulation; as a mutagen, it can generate diversity from which stable high-producing variants are selected. These modes require different controls, endpoints, and claims. The cross-kingdom comparison reveals no universal beneficial dose and no single conserved route to enhanced output. Instead, organismal structure, repair capacity, culture state, selection design, and process physics determine whether exposure yields useful biology. The most defensible development strategy couples rigorous dosimetry with response-mode identification, evidence-appropriate mechanism claims, stability testing, and product-level productivity.

The field is ready to move beyond catalogs of changes in concentration. Progress will be measured by causal validation, reproducible performance in passage or generation, reactor or field evidence, and transparent safety and economic evaluation. Under those conditions, gamma irradiation can serve as a disciplined platform for discovery and improvement rather than a generalized promise of overproduction.

Acknowledgments

The authors have no additional acknowledgments to report. Funding: this research received no specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Author contributions

Conceptualization, literature curation, visualization, writing – original draft, and writing – review and editing, all authors; supervision and project administration, A.E. All authors reviewed and approved the final manuscript.

Declaration of interests

The authors declare no competing interests.

Declaration of generative AI and AI-assisted technologies in the manuscript preparation process

During the preparation of this work, the authors used ChatGPT (OpenAI) to assist with language editing, structural organization, reference organization, consistency checking, and the preparation of explanatory vector graphics. After using this tool, the authors reviewed and edited the content and artwork as needed and took full responsibility for the publication’s content.