Abstract
The Lactobacillus acidophilus homology group comprises Gram-positive species that include L. acidophilus, L. helveticus, L. crispatus, L. amylovorus, L. gallinarum, L. delbrueckii subsp. bulgaricus, L. gasseri, and L. johnsonii. While these bacteria are closely related, they have varied ecological lifestyles as dairy and food fermenters, allochthonous probiotics, or autochthonous commensals of the host gastrointestinal tract. Bacterial cell surface components play a critical role in the molecular dialogue between bacteria and interaction signaling with the intestinal mucosa. Notably, the L. acidophilus complex is distinguished in two clades by the presence or absence of S-layers, which are semiporous crystalline arrays of self-assembling proteinaceous subunits found as the outermost layer of the bacterial cell wall. In this study, S-layer-associated proteins (SLAPs) in the exoproteomes of various S-layer-forming Lactobacillus species were proteomically identified, genomically compared, and transcriptionally analyzed. Four gene regions encoding six putative SLAPs were conserved in the S-layer-forming Lactobacillus species but not identified in the extracts of the closely related progenitor, L. delbrueckii subsp. bulgaricus, which does not produce an S-layer. Therefore, the presence or absence of an S-layer has a clear impact on the exoproteomic composition of Lactobacillus species. This proteomic complexity and differences in the cell surface properties between S-layer- and non-S-layer-forming lactobacilli reveal the potential for SLAPs to mediate intimate probiotic interactions and signaling with the host intestinal mucosa.
Highlights
Bacterial cell surface proteins play a critical role in the molecular dialogue between bacteria and their interaction with the host
The L. acidophilus group is a clade of homologous Gram-positive Lactobacillus species that includes L. acidophilus, L. helveticus, L. crispatus, L. amylovorus, L. gallinarum, L. delbrueckii subsp. bulgaricus, L. gasseri, and L. johnsonii [7,8,9,10,11]
S-layer-associated proteins (SLAPs) extractions were performed on two biological replicates, and the SDS-PAGE banding patterns of the SLAPs extracted from each strain did not differ in the major banding patterns between replicates
Summary
Bacterial cell surface proteins play a critical role in the molecular dialogue between bacteria and their interaction with the host For beneficial microbes, such as probiotics, these proteins mediate health-promoting functions through gastrointestinal adhesion, competitive exclusion of pathogens, enhancement of intestinal barrier function, and activation of gut mucosal immunity [1, 2]. Genome sequencing and comparative genomic analyses have clearly established and solidified the current description of the L. acidophilus group [13, 14] These closely related strains can be dichotomized based on their ability to create surface (S)-layer protein arrays as the outermost constituent of the cell wall [15]. NCK56 NCK230 NCK246 NCK338 NCK936 NCK1088 NCK777 NCK953 NCK1351 NCK776 NCK778 NCK1560 NCK1561 NCK334 NCK779 NCK702 NCK125
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