Advances in biodegradation of petroleum hydrocarbons / 生物工程学报

Petroleum hydrocarbon pollutants are difficult to be degraded, and bioremediation has received increasing attention for remediating the hydrocarbon polluted area. This review started by introducing the interphase adaptation and transport process of hydrocarbon by microbes. Subsequently, the advances made in the identification of hydrocarbon-degrading strains and genes as well as elucidation of metabolic pathways and underpinning mechanisms in the biodegradation of typical petroleum hydrocarbon pollutants were summarized. The capability of wild-type hydrocarbon degrading bacteria can be enhanced through genetic engineering and metabolic engineering. With the rapid development of synthetic biology, the bioremediation of hydrocarbon polluted area can be further improved by engineering the metabolic pathways of hydrocarbon-degrading microbes, or through design and construction of synthetic microbial consortia.

Biosynthesis of α-lipoic acid in Gluconobacter oxydans increases the production of vitamin C by one-step fermentation / 生物工程学报

In a one-step fermentation system of vitamin C production with Gluconobacter oxydans and Ketogulonicigenium vulgare, a functional module of α-lipoic acid biosynthesis was constructed in G. oxydans. The engineered G. oxydans was co-cultured with K. vulgare to enhance the growth and 2-keto-L-gulonic acid (2-KGA) production of K. vulgare. This one-step fermentation system alleviated the growth inhibition during the mono-culture of K. vulgare and strengthened the interaction between the two bacteria. Moreover, the yield of vitamin C precursor (2-KGA) increased to 73.34 g/L (the control group was 59.09 g/L), and the conversion of D-sorbitol to 2-KGA increased to 86.0%. This study provides a new idea for further optimizing the one-step fermentation system of vitamin C production.

Fitness analysis between the L-sorbosone dehydrogenase modules and Ketogulonigenium vulgare chassis / 生物工程学报

Ketogulonigenium vulgare is an acid-producing strain in the process of two-step vitamin C fermentation. L-sorbosone dehydrogenase (SNDH) is one of the key enzymes during the biosynthesis of 2-keto-L-gulonic acid (2-KGA), the precursor of vitamin C. However, the catalytic mechanism of SNDH is unclear. According to the whole genome sequencing of K. vulgare, two genes encoding sorbosone dehydrogenases, one derived from the chromosome (named as sndhg) and one from plasmid (named as sndhp), were introduced into an industrial strain K. vulgare. The overexpression of gene sndhg had hardly effect on 2-KGA production, and the overexpression of gene sndhp produced an obvious byproduct in the fermentation broth. Combinational expression of sndhg/sndhp with pqqA (obtaining sndhg-pqqA and sndhp-pqqA modules) in K. vulgare resulted in the similar fermentation phenotype to two previous strains. After serial sub-cultivation of co-cultured Bacillus endophyticus with each engineered K. vulgare for 50 d, the conversion rate of 2-KGA increased by 15.4%, 179%, 0.65% and 125% compared with that of the parental K. vulgare with B. endophyticus. This study shows that adaptive evolution of microbial consortium is an effective strategy to increase the fitness between functional modules and chassis, thus quickly getting better strains for production of 2-KGA.

Match of functional module with chassis in 7-dehydrocholesterol synthesis / 生物工程学报

The key challenge to generate engineered cells by synthetic biology for producing 7-dehydrocholesterol (7-DHC) in a high titer is the match between functional module and chassis. Our study focused on solving this problem by combining different promoters and yeast chassis to increase 7-DHC production. To optimize the chassis in order to accumulate zymosterol, the substrate for 7-DHC synthesis, we overexpressed truncated HMG-CoA reductase (tHmglp) and squalene epoxidase (Erglp), both are key genes of yeast endogenous zymosterol biosynthetic pathway. In addition, we knocked out C-24 methyl transferase (Erg6p) and C-22 dehydrogenase (Erg5p) to inhibit the conversion of zymosterol to ergosterol. By introducing heterologous C-24 reductase under three promoters with different strengths, namely TDH3p, PGK1p and TDH1p, we constructed functional modules of diverse activities. Nine engineeredcells were generated based on the combination of these three modules and three chassis. The result shows that the engineered cell composed of functional module regulated by TDH3p and chassis SyBE_000956 had the highest 7-DHC production, indicating a better match than others. This study provides evidences for importance of match and empirical support for rational design of subsequent researches.

Metabolomics analysis of taxadiene producing yeasts / 生物工程学报

In order to study the inherent difference among terpenes producing yeasts from the point of metabolomics, we selected taxadiene producing yeasts as the model system. The changes of cellular metabolites during fermentation log phase of artificial functional yeasts were determined using metabolomics methods. The results represented that compared to W303-1A as a blank control, the metabolites in glycolysis, tricarboxylic acid cycle (TCA) cycle and several amino acids were influenced. And due to the changes of metabolites, the growth of cells was inhibited to a certain extent. Among the metabolites identified, citric acid content in taxadiene producing yeasts changed the most, the decreasing amplitude reached 90% or more. Therefore, citric acid can be a marker metabolite for the future study of artificial functional yeasts. The metabolomics analysis of taxadiene producing yeasts can provide more information in further studies on optimization of terpenes production in heterologous chassis.