Abstract
Bacterial physiology and adaptation are influenced by the exopolysaccharides (EPS) they produce. These polymers are indispensable for the assembly of the biofilm extracellular matrix in multiple bacterial species. In a previous study, we described the profound gene expression changes leading to biofilm assembly in B. cereus ATCC14579 (CECT148). We found that a genomic region putatively dedicated to the synthesis of a capsular polysaccharide (eps2) was overexpressed in a biofilm cell population compared to in a planktonic population, while we detected no change in the transcript abundance from another genomic region (eps1) also likely to be involved in polysaccharide production. Preliminary biofilm assays suggested a mild role for the products of the eps2 region in biofilm formation and no function for the products of the eps1 region. The aim of this work was to better define the roles of these two regions in B. cereus multicellularity. We demonstrate that the eps2 region is indeed involved in bacterial adhesion to surfaces, cell-to-cell interaction, cellular aggregation and biofilm formation, while the eps1 region appears to be involved in a kind of social bacterial motility. Consistent with these results, we further demonstrate using bacterial-host cell interaction experiments that the eps2 region is more relevant to the adhesion to human epithelial cells and the zebrafish intestine, suggesting that this region encodes a bacterial factor that may potentiate gut colonization and enhance pathogenicity against humans.
Highlights
Bacterial physiology and adaptation are influenced by the exopolysaccharides (EPS) they produce
A previous transcriptomic analysis of B. cereus cells grown under static conditions demonstrated that there were no statistically significant differences in the expression levels of a region homologous to the B. subtilis epsA-O operon between biofilm and planktonic cells 24 and 48 h post-inoculation (Fig. Suppl. 1A)
The data obtained from our study indicate that the two polysaccharides play different, but complementary, roles in B. cereus multicellularity, with EPS1 mainly contributing to motility and EPS2 mainly supporting adhesion, biofilm maturation and interaction with host cells
Summary
Bacterial physiology and adaptation are influenced by the exopolysaccharides (EPS) they produce. Prompted by an interest in the influences of EPS on bacterial physiology and ecology and the divergence in terms of their exact chemical composition and function, in this work we studied the structures of two genomic regions that putatively encode proteins that synthesize two different polysaccharides. We previously reported a transcriptomic analysis in which we showed that an additional region of the B. cereus ATCC14579 genome (containing the genes Bc1583-Bc1591 and referred to as eps2) was overexpressed in biofilm cells compared to its expression level in planktonic cells[36]. This region has been annotated to be involved in capsular polysaccharide production, B. cereus ATCC14579 lacks a capsule. And consistent with these findings, EPS2 seems to be more important for the adhesion of B. cereus cells to human epithelial cells and to the zebrafish gut, a model used to study bacteria-gut interactions
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