One-Step Biosynthesis of Vitamin C in Saccharomyces cerevisiae

Construction of yeast microbial consortia for petroleum hydrocarbons degradation

Microbial degradation of petroleum hydrocarbons plays a vital role in mitigating petroleum contamination and heavy oil extraction. In this study, a Saccharomyces cerevisiae capable of degrading hexadecane has been successfully engineered, achieving a maximum degradation rate of up to 20.42%. However, the degradation ability of this strain decreased under various pressure conditions such as high temperature, high osmotic pressure, and acidity conditions. Therefore, a S. cerevisiae with high tolerance to these conditions has been constructed. And then, we constructed an "anti-stress hydrocarbon-degrading" consortium comprising engineered yeast strain SAH03, which degrades hexadecane, and glutathione synthetic yeast YGSH10, which provides stress resistance. This consortium was able to restore the degradation ability of SAH03 under various pressure conditions, particularly exhibiting a significant increase in degradation rate from 5.04% to 17.04% under high osmotic pressure. This study offers a novel approach for improving microbial degradation of petroleum hydrocarbons.

The ascorbate biosynthesis pathway in plants is known, but there is a way to go with understanding control and functions

Ascorbate (vitamin C) is one of the most abundant primary metabolites in plants. Its complex chemistry enables it to function as an antioxidant, as a free radical scavenger, and as a reductant for iron and copper. Ascorbate biosynthesis occurs via the mannose/l-galactose pathway in green plants, and the evidence for this pathway being the major route is reviewed. Ascorbate accumulation is leaves is responsive to light, reflecting various roles in photoprotection. GDP-l-galactose phosphorylase (GGP) is the first dedicated step in the pathway and is important in controlling ascorbate synthesis. Its expression is determined by a combination of transcription and translation. Translation is controlled by an upstream open reading frame (uORF) which blocks translation of the main GGP-coding sequence, possibly in an ascorbate-dependent manner. GGP associates with a PAS-LOV protein, inhibiting its activity, and dissociation is induced by blue light. While low ascorbate mutants are susceptible to oxidative stress, they grow nearly normally. In contrast, mutants lacking ascorbate do not grow unless rescued by supplementation. Further research should investigate possible basal functions of ascorbate in severely deficient plants involving prevention of iron overoxidation in 2-oxoglutarate-dependent dioxygenases and iron mobilization during seed development and germination.

Metabolic engineering of Escherichia coli for direct production of vitamin C from D-glucose

Background

Production of vitamin C has been traditionally based on the Reichstein process and the two-step process. However, the two processes share a common disadvantage: vitamin C cannot be directly synthesized from D-glucose. Therefore, significant effort has been made to develop a one-step vitamin C fermentation process. While, 2-KLG, not vitamin C, is synthesized from nearly all current one-step fermentation processes. Vitamin C is naturally synthesized from glucose in Arabidopsis thaliana via a ten-step reaction pathway that is encoded by ten genes. The main objective of this study was to directly produce vitamin C from D-glucose in Escherichia coli by expression of the genes from the A. thaliana vitamin C biosynthetic pathway.

Results

Therefore, the ten genes of whole vitamin C synthesis pathway of A. thaliana were chemically synthesized, and an engineered strain harboring these genes was constructed in this study. The direct production of vitamin C from D-glucose based on one-step fermentation was achieved using this engineered strain and at least 1.53 mg/L vitamin C was produced in shaking flasks.

Conclusions

The study demonstrates the feasibility of one-step fermentation for the production of vitamin C from D-glucose. Importantly, the one-step process has significant advantages compared with the currently used fermentation process: it can save multiple physical and chemical steps needed to convert D-glucose to D-sorbitol; it also does not involve the associated down-streaming steps required to convert 2-KLG into vitamin C.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13068-022-02184-0.

Strain Development, Substrate Utilization, and Downstream Purification of Vitamin C

Vitamin C, C6H8O6, is a water-soluble vitamin that is widespread in nature. It is an essential nutrient involved in many biological processes in the living organisms: it enhances collagen biosynthesis, ensures the optimal functioning of enzymes and the immune system, has a major role in lipid and iron metabolism, and it enhances the biosynthesis of l-carnitine. Due to its antioxidant activity, vitamin C can neutralize the tissue-damaging effects of free radicals. Vitamin C is being related to the prevention of cancer and cardiovascular diseases. This review includes current information on the biosynthesis of ascorbic acid, as new methods are now challenging the traditional Reichstein process for vitamin C’s industrial-scale production. Different strains were analyzed in correlation with their ability to synthesize ascorbic acid, and several separation techniques were investigated for a more effective production of vitamin C.

Construction of synthetic microbial consortia for 2-keto-L-gulonic acid biosynthesis

Currently, the establishment of synthetic microbial consortia with rational strategies has gained extensive attention, becoming one of the important frontiers of synthetic biology. Systems biology can offer insights into the design and construction of synthetic microbial consortia. Taking the high-efficiency production of 2-keto-l-gulonic acid (2-KLG) as an example, we constructed a synthetic microbial consortium “Saccharomyces cerevisiae-Ketogulonigenium vulgare” based on systems biology analysis. In the consortium, K. vulgare was the 2-KLG producing strain, and S. cerevisiae acted as the helper strain. Comparative transcriptomic analysis was performed on an engineered S. cerevisiae (VTC2) and a wild-type S. cerevisiae BY4741. The results showed that the up-regulated genes in VTC2, compared with BY4741, were mainly involved in glycolysis, TCA cycle, purine metabolism, and biosynthesis of amino acids, B vitamins, and antioxidant proteases, all of which play important roles in promoting the growth of K. vulgare. Furthermore, Vitamin C produced by VTC2 could further relieve the oxidative stress in the environment to increase the production of 2-KLG. Therefore, VTC2 would be of great advantage in working with K. vulgare. Thus, the synthetic microbial consortium "VTC2-K. vulgare" was constructed based on transcriptomics analyses, and the accumulation of 2-KLG was increased by 1.49-fold compared with that of mono-cultured K. vulgare, reaching 13.2 ± 0.52 g/L. In addition, the increased production of 2-KLG was accompanied by the up-regulated activities of superoxide dismutase and catalase in the medium and the up-regulated oxidative stress-related genes (sod, cat and gpd) in K. vulgare. The results indicated that the oxidative stress in the synthetic microbial consortium was efficiently reduced. Thus, systems analysis confirmed a favorable symbiotic relationship between microorganisms, providing guidance for further engineering synthetic consortia.