Candida glabrata Yap6 Recruits Med2 To Alter Glycerophospholipid Composition and Develop Acid pH Stress Resistance

Advances in stress-tolerance elements for microbial cell factories

Microorganisms, particularly extremophiles, have evolved multiple adaptation mechanisms to address diverse stress conditions during survival in unique environments. Their responses to environmental coercion decide not only survival in severe conditions but are also an essential factor determining bioproduction performance. The design of robust cell factories should take the balance of their growing and bioproduction into account. Thus, mining and redesigning stress-tolerance elements to optimize the performance of cell factories under various extreme conditions is necessary. Here, we reviewed several stress-tolerance elements, including acid-tolerant elements, saline-alkali-resistant elements, thermotolerant elements, antioxidant elements, and so on, providing potential materials for the construction of cell factories and the development of synthetic biology. Strategies for mining and redesigning stress-tolerance elements were also discussed. Moreover, several applications of stress-tolerance elements were provided, and perspectives and discussions for potential strategies for screening stress-tolerance elements were made.

Engineering status of protein for improving microbial cell factories

With the development of metabolic engineering and synthetic biology, microbial cell factories (MCFs) have provided an efficient and sustainable method to synthesize a series of chemicals from renewable feedstocks. However, the efficiency of MCFs is usually limited by the inappropriate status of protein. Thus, engineering status of protein is essential to achieve efficient bioproduction with high titer, yield and productivity. In this review, we summarize the engineering strategies for metabolic protein status, including protein engineering for boosting microbial catalytic efficiency, protein modification for regulating microbial metabolic capacity, and protein assembly for enhancing microbial synthetic capacity. Finally, we highlight future challenges and prospects of improving microbial cell factories by engineering status of protein.

Efficient biosynthesis of (R)-mandelic acid from styrene oxide by an adaptive evolutionary Gluconobacter oxydans STA

BACKGROUND

(R)-mandelic acid (R-MA) is a highly valuable hydroxyl acid in the pharmaceutical industry. However, biosynthesis of optically pure R-MA remains significant challenges, including the lack of suitable catalysts and high toxicity to host strains. Adaptive laboratory evolution (ALE) was a promising and powerful strategy to obtain specially evolved strains.

RESULTS

Herein, we report a new cell factory of the Gluconobacter oxydans to biocatalytic styrene oxide into R-MA by utilizing the G. oxydans endogenous efficiently incomplete oxidization and the epoxide hydrolase (SpEH) heterologous expressed in G. oxydans. With a new screened strong endogenous promoter P₁₂₇₈₀, the production of R-MA was improved to 10.26 g/L compared to 7.36 g/L of using P_lac. As R-MA showed great inhibition for the reaction and toxicity to cell growth, adaptive laboratory evolution (ALE) strategy was introduced to improve the cellular R-MA tolerance. The adapted strain that can tolerate 6 g/L R-MA was isolated (named G. oxydans STA), while the wild-type strain cannot grow under this stress. The conversion rate was increased from 0.366 g/L/h of wild type to 0.703 g/L/h by the recombinant STA, and the final R-MA titer reached 14.06 g/L. Whole-genome sequencing revealed multiple gene-mutations in STA, in combination with transcriptome analysis under R-MA stress condition, we identified five critical genes that were associated with R-MA tolerance, among which AcrA overexpression could further improve R-MA titer to 15.70 g/L, the highest titer reported from bulk styrene oxide substrate.

CONCLUSIONS

The microbial engineering with systematic combination of static regulation, ALE, and transcriptome analysis strategy provides valuable solutions for high-efficient chemical biosynthesis, and our evolved G. oxydans would be better to serve as a chassis cell for hydroxyl acid production.

Dynamic regulation of membrane integrity to enhance l-malate stress tolerance in Candida glabrata

Microbial cell factories provide a sustainable and economical way to produce chemicals from renewable feedstocks. However, the accumulation of targeted chemicals can reduce the robustness of the industrial strains and affect the production performance. Here, the physiological functions of Mediator tail subunit CgMed16 at l-malate stress were investigated. Deletion of CgMed16 decreased the survival, biomass, and half-maximal inhibitory concentration (IC₅₀ ) by 40.4%, 34.0%, and 30.6%, respectively, at 25 g/L l-malate stress. Transcriptome analysis showed that this growth defect was attributable to changes in the expression of genes involved in lipid metabolism. In addition, tolerance transcription factors CgUSV1 and CgYAP3 were found to interact with CgMed16 to regulate sterol biosynthesis and glycerophospholipid metabolism, respectively, ultimately endowing strains with excellent membrane integrity to resist l-malate stress. Furthermore, a dynamic tolerance system (DTS) was constructed based on CgUSV1, CgYAP3, and an l-malate-driven promoter P_cgr-10 to improve the robustness and productive capacity of Candida glabrata. As a result, the biomass, survival, and membrane integrity of C. glabrata 012 (with DTS) increased by 22.6%, 31.3%, and 53.8%, respectively, compared with those of strain 011 (without DTS). Therefore, at shake-flask scale, strain 012 accumulated 35.5 g/L l-malate, and the titer and productivity of l-malate increased by 32.5% and 32.1%, respectively, compared with those of strain 011. This study provides a novel strategy for the rational design and construction of DTS for dynamically enhancing the robustness of industrial strains.

Biodegradation of aromatic pollutants meets synthetic biology

Ubiquitously distributed microorganisms are natural decomposers of environmental pollutants. However, because of continuous generation of novel recalcitrant pollutants due to human activities, it is difficult, if not impossible, for microbes to acquire novel degradation mechanisms through natural evolution. Synthetic biology provides tools to engineer, transform or even re-synthesize an organism purposefully, accelerating transition from unable to able, inefficient to efficient degradation of given pollutants, and therefore, providing new solutions for environmental bioremediation. In this review, we described the pipeline to build chassis cells for the treatment of aromatic pollutants, and presented a proposal to design microbes with emphasis on the strategies applied to modify the target organism at different level. Finally, we discussed challenges and opportunities for future research in this field.