Abstract
The probiotic efficacy and fermentative ability of Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus), a widely used probiotic, is majorly affected by its acid tolerance. Here, we conducted whole-genome sequencing of the high acid-tolerant L. bulgaricus LJJ stored in the laboratory. Compared with the whole genome of low acid-tolerant strain L. bulgaricus ATCC11842, the results show that 16 candidate acid-tolerant genes may be involved in the regulation of the acid tolerance of L. bulgaricus LJJ. Association analysis of candidate acid-tolerant genes and acid-tolerant traits of different L. bulgaricus strains revealed that the three genes dapA, dapH, and lysC are the main reasons for the strong acid tolerance of L. bulgaricus LJJ. 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 confer L. bulgaricus LJJ strong acid tolerance. This study successfully revealed the acid tolerance mechanism of L. bulgaricus LJJ and provides a theoretical basis for the subsequent selection of strains with high acid tolerance for improved probiotic functions. KEY POINTS: • Three genes are identified as acid-tolerant genes, respectively, lysC, dapA, and dapH. • LysC and dapA are the major key genes in the synthesis of lysine. • The synthesis of lysine may confer L. bulgaricus LJJ strong acid tolerance.
Highlights
The probiotic efficacy and fermentative ability of Lactobacillus delbrueckii subsp
The raw sequencing data of L. d. bulgaricus LJJ was subjected to quality control based on the three generations of the sequencing data
The gene prediction results of L. d. bulgaricus LJJ showed that a total of 2003 Open reading frame KEGG (ORF) were predicted, with a total length of 1,598,697 bp, an average length of 798.15 bp, accounting for 84.54% of the genome [see Additional file 3,4]
Summary
The probiotic efficacy and fermentative ability of Lactobacillus delbrueckii subsp. Bulgaricus ( L. d. bulgaricus ), a widely used probiotic, is majorly affected by its acid tolerance. Bulgaricus ), a widely used probiotic, is majorly affected by its acid tolerance. A genome-wide sequence of a highly acid-tolerant L. d. Bulgaricus LJJ was supposed to be determined, and we expect to find out the acid tolerance mechanism of L. d. Bulgaricus is widely used in the industrial production of fermented dairy products such as yogurt and cheese It functions in regulating the gut microflora of the human body, maintaining the intestinal micro-ecological balance, inhibiting the growth of pathogenic bacteria, and improving the immunity of the human body [1]. Bulgaricus and the analysis of acid-tolerant mechanisms have become hotspots in the study of lactic acid bacteria [3]. Many researchers have conducted several in-depth studies on the acid tolerance mechanism of lactic acid bacteria through multiple omics methods. This study is based on genome-wide sequencing and comparative genomics analysis of the differences between the
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