Abstract
Lactobacillus salivarius has drawn attention because of its promising probiotic functions. Tolerance to the gastrointestinal tract condition is crucial for orally administrated probiotics to exert their functions. However, previous studies of L. salivarius have only focused on the bile salt resistance of particular strains, without uncovering the common molecular mechanisms of this species. Therefore, in this study, we expanded our research to 90 L. salivarius strains to explore their common functional genes for bile salt resistance. First, the survival rates of the 90 L. salivarius strains in 0.3% bile salt solutions were determined. Comparative genomics analysis was then performed to screen for the potential functional genes related to bile salt tolerance. Next, real-time polymerase chain reaction and gene knockout experiments were conducted to further verify the tolerance-related functional genes. The results indicated that the strain-dependent bile salt tolerance of L. salivarius was mainly associated with four peptidoglycan synthesis-related genes, seven phosphotransferase system-related genes, and one chaperone-encoding gene involved in the stress response. Among them, the GATase1-encoding gene showed the most significant association with bile salt tolerance. In addition, four genes related to DNA damage repair and substance transport were redundant in the strains with high bile salt tolerance. Besides, cluster analysis showed that bile salt hydrolases did not contribute to the bile salt tolerance of L. salivarius. In this study, we determined the global regulatory genes, including LSL_1568, LSL_1716 and LSL_1709, for bile salt tolerance in L. salivarius and provided a potential method for the rapid screening of bile salt-tolerant L. salivarius strains, based on PCR amplification of functional genes.
Highlights
Lactobacillus salivarius was first isolated from children’s saliva in Maryland, USA [1].Later studies have shown that it exists in various habitats, including the oral cavity, the gastrointestinal tract, and in the vagina of animals, as well as food materials [2,3,4].In recent years, L. salivarius has drawn attention because of its promising probiotic functions, such as anti-aging, immunoregulation, and bacteriostasis [5]
Homologous sequences of bile salt hydrolases (BSHs) from L. johnsonii PF01 were used as an outgroup to construct the phylogenetic trees (Table 1)
The functional genes obtained through the comparative genomic analysis were related to the survival rates of L. salivarius strains in bile salt solutions
Summary
Lactobacillus salivarius was first isolated from children’s saliva in Maryland, USA [1]. A study indicated that L. salivarius FDB89, isolated from the feces of centenarians, extended the mean life span of Caenorhabditis elegans by up to 11.9% compared to that of the control group [6] Another L. salivarius strain, FXJCJ7-2, was shown to have significant antiinflammatory effects on lipopolysaccharide (LPS)-treated murine macrophages and mice. Research on Bacillus coagulans HS243 based on comparative genomic analysis showed two groups of bile-salttolerance-related genes, including a single-copy chologlycine hydrolase-encoding gene and four chaperone-related genes [21]. Despite this expansion in the use of multi-omics techniques, research on. The result provided a potential method for the rapid screening of bile-salt-tolerant strains based on PCR amplification
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