Whole-genome sequencing and genomic-based acid tolerance mechanisms of Lactobacillus delbrueckii subsp.bulgaricus LJJ

The probiotic efficacy and fermentative ability ofLactobacillus delbrueckiisubsp.bulgaricus(L. bulgaricus), a widely used probiotic, is majorly affected by its acid tolerance. Here, we conducted whole-genome sequencing of the high acid-tolerantL. bulgaricusLJJ stored in the laboratory. Compared with the whole genome of low acid-tolerant strainL. bulgaricusATCC11842, the results show that 16 candidate acid-tolerant genes may be involved in the regulation of the acid tolerance ofL. bulgaricusLJJ. Association analysis of candidate acid-tolerant genes and acid-tolerant traits of differentL. bulgaricusstrains revealed that the three genesdapA,dapH, andlysCare the main reasons for the strong acid tolerance ofL. bulgaricusLJJ. The results of real-time quantitative PCR (RT-qPCR) supported this conclusion. KEGG pathway analysis showed that these three acid-tolerant genes are involved in the synthesis of lysine; the synthesis of lysine may conferL. bulgaricusLJJ strong acid tolerance. This study successfully revealed the acid tolerance mechanism ofL. bulgaricusLJJ and provides a theoretical basis for the subsequent selection of strains with high acid tolerance for improved probiotic functions.