镇江香醋醋酸发酵阶段产乳酸功能细菌的物种多样性

Species-level diversity of lactate-producing bacteria in acetic acid fermentation of Zhenjiang aromatic vinegar

乳酸是传统食醋中主要的不挥发性有机酸,具有柔和食醋酸感、增强风味品质等作用,但是目前对于醋酸发酵过程中乳酸形成的微生物机理尚缺少深入研究.首先分析了镇江香醋醋醅中D-乳酸和L-乳酸含量;继而采用宏基因组和宏转录组测序分析了醋醅中L-乳酸脱氢酶(L-LDH)和D-乳酸脱氢酶(D-LDH)基因的相对表达水平;最后利用兼并引物扩增和扩增子测序方法分析了L-LDH和D-LDH基因的物种多样性.结果表明,参与L-LDH和D-LDH合成的微生物均主要分布在Lactobacillus,其相对丰度均占到80%以上;其中与D-LDH相关的微生物主要为Lactobacillus reuteri(67.9%),Lactobacillus pontis(10.2%),Lactobacillus fermentum(4.1%),Lactobacillus helveticus(1.3%),而与L-LDH相关的微生物主要为Lactobacillus helveticus(70.3%),Lactococcus lactis(9.2%),Lactobacillus pontis(8.0%),Lactobacillus casei(1.3%).因此,镇江香醋醋酸发酵阶段乳酸主要由Lactobacillus菌群代谢丙酮酸产生,但D-乳酸和L-乳酸的产量则受到具体菌株的调控,其中D-乳酸可能主要由L.reuteri产生,L-乳酸可能主要由Lactobacillus helveticus产生.本研究结果可为解析醋酸发酵过程中乳酸的生物合成途径提供理论基础.(图7表1参30)

Lactic a cid,one of t he predominant non-volatile organic a cids,is c rucial to t he flavor a nd quality of v inegar.I n this research,we aimed to reveal the configuration of lactic acid in vinegar and analyze the divergent taxonomic distributions related to the two types of key enzymes in the lactic acid metabolic pathway in vinegar Pei.First,the content of D-lactate and L-lactate in vinegar and vinegar Pei was determined.Thereafter,the relative expression levels of D-lactate dehydrogenase(D-LDH)and L-lactate dehydrogenase(L-LDH)genes were compared to those of the DNA and RNA,respectively.The species-level diversities of the D-LDH and L-LDH genes were analyzed by high-throughput sequencing using the designed degenerate primers.Many species scattered in the genus Lactobacillus(>80%)were identified as the main lactate producers.Lactobacillus reuteri(67.9%),Lactobacillus pontis(10.2%),Lactobacillus fermentum(4.1%),and Lactobacillus helveticus(1.3%),which possess the D-LDH gene,might be the major D-lactate producing microorganisms,while Lactobacillus helveticus(70.3%),Lactococcus lactis(9.2%),Lactobacillus pontis(8.0%),and Lactobacillus casei(1.3%)with the L-LDH gene might mainly contribute to the production of L-lactate.Our study revealed the species-level diversity of lactate-producing bacteria during acetic acid fermentation of Zhenjiang aromatic vinegar.Additionally,it demonstrated that L.reuteri might be the main functional strain for the production of D-lactate,while Lactobacillus helveticus might be the main L-lactate producer.