Table 2.
Dynamic and static regulatory strategies used to enhance the cell factory productivities
| Strain | Product | Description | Outcome | Refs. |
|---|---|---|---|---|
| Dynamic regulation | ||||
| E. coli | Bisabolene | An inducer-free Lux QS system | 1.1 g/L | Kim et al. (2018) |
| E. coli | Lycopene | Engineering the Ntr regulon to control intracellular metabolites | 18-fold | Farmer and Liao (2000) |
| E. coli | Zeaxanthin | IPP/FPP-responsive promoter to regulate tuneable intergenic regions (TIGRs) | 2.1-fold | Shen et al. (2016) |
| S. cerevisiae | Linalool and Limonene | An N-degron-dependent protein degradation strategy to downregulate Erg20p | 18 and 76 mg/L, respectively | Peng et al. (2018) |
| S. cerevisiae | Amorpha-4,11-diene | Ergosterol-responsive promoters to regulate Erg9 transcription | 350 mg/L | Yuan and Ching (2015) |
| S. cerevisiae | Lycopene | Growth-phase-dependent dynamic regulation | 1.48 g/L | Su et al. (2020) |
| S. cerevisiae | α-Santalene | Dynamic regulation of Erg9 expression with HXT1 | 92 mg/L | Scalcinati et al. (2012) |
| S. cerevisiae | Nerolidol | An auxin-inducible protein degradation system to decouple growth and production | 3.5 g/L | Lu et al. (2021) |
| S. cerevisiae | Nerolidol | An endoplasmic reticulum-associated protein degradation of Erg9p to redirect flux towards sesquiterpene production | 86% improvement | Peng et al. (2017) |
| B. subtilis | Menaquinone-7 | A bifunctional and modular Phr-60-Rap-60-Spo0A QS system regulated by two endogenous promoters PabrB and PspoiiA | 400-fold | Cui et al. (2019) |
| CRISPR interference (CRISPRi) | ||||
| E. coli | Isoprene, α-bisabolol and lycopene | Development of CRISPRi system for pathway regulation | 2.6-, 10.6-, 8.0-fold increment, respectively | Kim et al. (2016) |
| E. coli | Isopentenol | Combinatorial knockdown of competing pathways with CRISPRi | 98% improvement | Tian et al. (2019) |
| P. putida | Mevalonate | CRISPRi-mediated regulation of glpR, responsible for glycerol utilization | 237 g/L | Kim et al. (2020) |
| C. glutamicum | Decaprenoxanthin | CRISPRi to identify regulatory genes for carotenoid biosynthesis | 43- and ninefold | Göttl et al. (2021) |
| C. glutamicum | Squalene | CRISPRi-mediated repression of competing target genes | 5.2-fold | Park et al. (2019) |
| Synechocystis sp. PCC 6803 | Valencene | Downregulation of crtE with CRISPRi to decrease carotenoid production combined with fusion of ispA and CnVS | 19 mg/g DCW | Dietsch et al. (2021) |
| Methylorubrum extorquens | Carotenoid | CRISPRi-mediated gene mining of phytoene desaturase as well as squalene-hopene cyclase gene repression | 1.9-fold | Mo et al. (2020) |
| Promoter and RBS design | ||||
| E. coli | Geraniol | Optimization of GPP synthase with RBS | 1119 mg/L | Zhou et al. (2015) |
| E. coli | β-carotene | Regulation of atoB, mvaS, and Hmg1 with artificial regulatory parts, MI-46, M-37, and M1-93 | 51% increment | Ye et al. (2016) |
| E. coli | Viridiflorol and Amorphadiene | Transcription and translational optimization of enzymes | 25.7 g/L and 30 g/L, respectively | Shukal et al. (2019) |
| E. coli | Amorphadiene | Combinatorial screening of RBS for translation of pathway enzymes | Fivefold increase | Nowroozi et al. 2014) |
| E. coli | Violaxanthin | RBS optimization of zeaxanthin epoxidase | 231 µg/g DW | Takemura et al. (2019) |
| E. coli | α-Santalene | Promoter replacement to fine-tune the expression of iridoid synthase | 599 g/L | Wang et al. (2021e) |
| E. coli | Steviol | Engineering of 5-UTR and N-terminal of pathway enzymes | 38.4 ± 1.7 mg/L | Moon et al. (2020) |
| E. coli | Salicylate | A combinatorial screening of RBS sequences | 123% | Qian et al. (2019) |
| S. cerevisiae | Sabinene | Downregulating ERG20 with the glucose dependent weak promoter PHXT | 19.4 mg/L | Jia et al. (2020) |
| S. cerevisiae | Squalene-type triterpenoids | Expression of CYP505D13 from Ganoderma lucidum on a yeast expression vector for squalene-type triterpenoids | 3.28 mg/L, 13.77 mg/L, and 12.23 mg/L | Song et al. (2019) |
| S. cerevisiae | Linalool | Downregulating squalene production by replacing the endogenous ERG20 promoter with the sterol-responsive promoter ERG1 | Threefold increment | Zhou et al. (2021) |
| S. cerevisiae | β-amyrin | Employing short synthetic terminators to regulate pathway | 3.16-fold improvement | Ahmed et al. (2019) |
| S. cerevisiae | Lutein | Regulation of pathway enzymes with constitutive promoters as well as temperature-sensitive variant of transcriptional activator Gal4M9 | N. A | Bian et al. (2021) |
| S. cerevisiae | Lycopene | Gal promoter screening | 3.28 g/L | Shi et al. (2019) |
| Y. lipolytica | α-farnesene | Promoter optimization of Sc-tHMG1, IDI and OptFSLERG20 | 2.57 g/L | Liu et al. (2020d) |
| Aspergillus oryzae | Nepetalactol | Promoter replacement to fine-tune the expression of iridoid synthase | 7.2 mg/L | Duan et al. (2021) |
| Rhodobacter capsulatus | Bisabolene | Promoter screening coupled with other pathway engineering strategies | 9.8 g/L | Zhang et al. (2021b) |
| Rhodobacter sphaeroides | Pinene | RBS optimization coupled with fusion of geranyl diphosphate synthase and pinene synthase | N. A | Wu et al. (2021) |
| C. glutamicum | Astaxanthin | Combinatorial RBS, spacer, and start codon library for crtW and crtZ translation | 0.4 mg/L/h | Henke et al. (2016) |
| P. putida | Mevalonate | Development of an inducible CRISPR activation (CRISPRa) system to regulate promoters | 40-fold | Kiattisewee et al. (2021) |
| Chlamydomonas reinhardtii | Carotenoids | Overexpression of wild-type and mutant form of the plant regulatory protein ORANGE under a strong light inducible promoter | Two and threefold, respectively | Yazdani et al. (2021) |
| Synechococcus elongatus UTEX 2973 | Limonene | Fine-tuning GPP synthase expression with synthetic RBS with varying translation rates coupled with crtE mutagenesis | 16.4 mg/L | Lin et al. (2021) |