山梨酮脱氢酶模块与酮古龙酸杆菌底盘细胞的适配分析

酮古龙酸杆菌Ketogulonigenium vulgare是维生素C二步混菌发酵过程中的产酸菌。山梨酮脱氢酶(L-sorbosone dehydrogenase,缩写为SNDH)作为维生素C直接前体2-酮基-L-古龙酸(2-KGA)合成的关键酶,其作用机制并不十分清楚。借助全基因组测序抽提2个山梨酮脱氢酶基因,分别位于基因组(缩写为sndhg)和质粒(缩写为sndhp)上。通过工程化改造技术在工业产酸菌中构建山梨酮脱氢酶功能模块,比较其对2-KGA产量的影响。研究发现sndhg过表达对菌株产酸影响不明显,sndhp过表达使菌株明显产生副产物。将sndhg和sndhp分别配合辅因子PQQ合成基因pqq A,分别构建sndhg-pqq A和sndhp-pqq A模块,得到的工程菌株产酸情况与之前的结果大致相同。将4株K.vulgare工程菌株分别与内生芽孢杆菌Bacillus endophyticus混合培养传代50 d后,分离菌株进行混菌发酵,其2-KGA的转化率分别提高了15.4%、179%、0.65%和125%。表明混菌适应性进化策略是一种增加功能模块与底盘细胞适配性,进而快速获得优良性状菌种的有效方法。

Fitness analysis between the L-sorbosone dehydrogenase modules and Ketogulonigenium vulgare chassis

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.