Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) is an adaptive immune system that resists foreign genes through nuclease targeting in bacteria and archaea. In this study, we analyzed 68 strains of Lactobacillus casei group from the NCBI GenBank database, and bioinformatic tools were used to investigate the occurrence and diversity of CRISPR system. The results showed that a total of 30 CRISPR loci were identified from 27 strains. Apart from three strains which contained double loci with distinguishable distributed sites, most strains contained only one CRISPR locus. The analysis of direct repeat (DR) sequences showed that all DR could form stable RNA secondary structures. The CRISPR spacers showed diversity, and their origin and evolution were revealed through the investigation of their spacer sequences. In addition, a large number of CRISPR spacers showed perfect homologies to phage and plasmid sequences. Collectively, our results would contribute to researches of resistance in L. casei group, and also provide a new vision on the diversity and evolution of CRISPR/Cas system.
Background: 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. In this study, 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 LJJ by comparative genomics. Results: Functional annotation and pathways of differential genes were determined using bioinformatics. The results in our study showed that the three genes dapA , dapH and lysC identified are implicated in the high acid tolerance of LJJ strain. Thus, they are potentially important as acidtolerant genes of LJJ strain. Conclusions: This study successfully revealed the acid tolerance mechanism of LJJ. Based on the previous research of LJJ in our laboratory, the successful analysis of the acid-tolerant mechanism of L. d. bulgaricus will further lay the foundation for the subsequent breeding of high acid-tolerant strains and greatly enhance their probiotic functions.
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