Analysis of a bac operon-silenced strain suggests pleiotropic effects of bacilysin in Bacillus subtilis

Signatures of kin selection in a natural population of the bacteria Bacillus subtilis

Laboratory experiments have suggested that bacteria perform a range of cooperative behaviors, which are favored because they are directed toward relatives (kin selection). However, there is a lack of evidence for cooperation and kin selection in natural bacterial populations. Molecular population genetics offers a promising method to study natural populations because the theory predicts that kin selection will lead to relaxed selection, which will result in increased polymorphism and divergence at cooperative genes. Examining a natural population of Bacillus subtilis, we found consistent evidence that putatively cooperative traits have higher polymorphism and greater divergence than putatively private traits expressed at the same rate. In addition, we were able to eliminate alternative explanations for these patterns and found more deleterious mutations in genes controlling putatively cooperative traits. Overall, our results suggest that cooperation is favored by kin selection, with an average relatedness of r = .79 between interacting individuals.

Comparative biological network analysis for differentially expressed proteins as a function of bacilysin biosynthesis in Bacillus subtilis

The Gram-positive bacterium Bacillus subtilis produces a diverse range of secondary metabolites with different structures and activities. Among them, bacilysin is an enzymatically synthesized dipeptide that consists of L-alanine and L-anticapsin. Previous research by our group has suggested bacilysin's role as a pleiotropic molecule in its producer, B. subtilis PY79. However, the nature of protein interactions in the absence of bacilysin has not been defined. In the present work, we constructed a protein-protein interaction subnetwork by using Omics Integrator based on our recent comparative proteomics data obtained from a bacilysin-silenced strain, OGU1. Functional enrichment analyses on the resulting networks pointed to certain putatively perturbed pathways such as citrate cycle, quorum sensing and secondary metabolite biosynthesis. Various molecules, which were absent from the experimental data, were included in the final network. We believe that this study can guide further experiments in the identification and confirmation of protein-protein interactions in B. subtilis.

Bacilysin within the Bacillus subtilis group: gene prevalence versus antagonistic activity against Gram-negative foodborne pathogens

The Bacillus subtilis group comprises species known for their ability to produce a wide variety of antimicrobial peptides. This work focuses on bacilysin, a broad-spectrum active dipeptide, and its prevalence in the B. subtilis group. In silico genome analysis of strains from Bacillus amyloliquefaciens, Bacillus velezensis, Bacillus licheniformis, Bacillus pumilus and B. subtilis subspecies inaquosorum, spizizenii and subtilis revealed that the bacilysin gene cluster is present in all species except for B. licheniformis. This observation was corroborated by PCR detection of the bacilysin genetic determinants on a collection of 168 food and environmental strains from the B. subtilis group. Phylogenetic analyses also demonstrated that the bacilysin gene cluster sequence showed more than 80 % identity within each species of the B. subtilis group. An in vitro screening of the strain collection was performed against foodborne pathogens. Twenty-three strains were selected for their ability of their Cell-Free Supernatant to inhibit foodborne pathogens. After an ammonium sulphate precipitation of their supernatant, eight strains, all belonging to B. velezensis, exhibited antimicrobial activity against Gram-negative pathogens. Using Ultra High Performance Liquid Chromatography - Mass Spectrometry, the presence of bacilysin was confirmed in these eight precipitates. These findings provide evidence that bacilysin is a major player in the antagonistic activity of B. velezensis against Gram-negative foodborne pathogens.

Impact of spatial proximity on territoriality among human skin bacteria

Bacteria display social behavior and establish cooperative or competitive interactions in the niches they occupy. The human skin is a densely populated environment where many bacterial species live. Thus, bacterial inhabitants are expected to find a balance in these interactions, which eventually defines their spatial distribution and the composition of our skin microbiota. Unraveling the physiological basis of the interactions between bacterial species in organized environments requires reductionist analyses using functionally relevant species. Here, we study the interaction between two members of our skin microbiota, Bacillus subtilis and Staphylococcus epidermidis. We show that B. subtilis actively responds to the presence of S. epidermidis in its proximity by two strategies: antimicrobial production and development of a subpopulation with migratory response. The initial response of B. subtilis is production of chlorotetain, which degrades the S. epidermidis at the colony level. Next, a subpopulation of B. subtilis motile cells emerges. Remarkably this subpopulation slides towards the remaining S. epidermidis colony and engulfs it. A slow response back from S. epidermidis cells give origin to resistant cells that prevent both attacks from B. subtilis. We hypothesized that this niche conquering and back-down response from B. subtilis and S. epidermidis, respectively, which resembles other conflicts in nature as the ones observed in animals, may play a role in defining the presence of certain bacterial species in the specific microenvironments that these bacteria occupy on our skin.