Abstract
Like many bacteria, Enterococcus faecalis encodes a number of adhesins involved in colonization or infection of different niches. Two well-studied E. faecalis adhesins, aggregation substance (AS) and endocarditis- and biofilm-associated pili (Ebp), both contribute to biofilm formation on abiotic surfaces and in endocarditis, suggesting that they may be expressed at the same time. Because different regulatory pathways have been reported for AS and Ebp, here, we examined if they are coexpressed on the same cells and what is the functional impact of coexpression on individual cells and within a population. We found that while Ebp are only expressed on a subset of cells, when Ebp and AS are expressed on the same cells, pili interfere with AS-mediated clumping and impede AS-mediated conjugative plasmid transfer during planktonic growth. However, when the population density increases, horizontal gene transfer rates normalize and are no longer affected by pilus expression. Instead, at higher cell densities during biofilm formation, Ebp and AS differentially contribute to biofilm development and structure, synergizing to promote maximal biofilm formation.IMPORTANCE Most bacteria express multiple adhesins that contribute to surface attachment and colonization. However, the network and relationships between the various adhesins of a single bacterial species are less well understood. Here, we examined two well-characterized adhesins in Enterococcus faecalis, aggregation substance and endocarditis- and biofilm-associated pili, and found that they exhibit distinct functional contributions depending on the growth stage of the bacterial community. Pili interfere with aggregation substance-mediated clumping and plasmid transfer under planktonic conditions, whereas the two adhesins structurally complement one another during biofilm development. This study advances our understanding of how E. faecalis, a ubiquitous member of the human gut microbiome and an opportunistic pathogen, uses multiple surface structures to evolve and thrive.
Highlights
Like many bacteria, Enterococcus faecalis encodes a number of adhesins involved in colonization or infection of different niches
Previous studies reported that neither aggregation substance (AS) nor endocarditis- and biofilm-associated pili (Ebp) are expressed on all cells within a population, but both adhesins contribute to biofilm formation [2, 18–20]
We hypothesized that Ebp and AS expression may be coordinated within a population such that different population subsets express different adhesin repertoires for optimal colonization, virulence, or biofilm architecture development
Summary
Enterococcus faecalis encodes a number of adhesins involved in colonization or infection of different niches. Two well-studied E. faecalis adhesins, aggregation substance (AS) and endocarditis- and biofilm-associated pili (Ebp), both contribute to biofilm formation on abiotic surfaces and in endocarditis, suggesting that they may be expressed at the same time. IMPORTANCE Most bacteria express multiple adhesins that contribute to surface attachment and colonization. We examined two well-characterized adhesins in Enterococcus faecalis, aggregation substance and endocarditis- and biofilm-associated pili, and found that they exhibit distinct functional contributions depending on the growth stage of the bacterial community. Pili interfere with aggregation substance-mediated clumping and plasmid transfer under planktonic conditions, whereas the two adhesins structurally complement one another during biofilm development. Most infections start with bacterial adhesion to a biotic or abiotic surface, and E. faecalis encodes multiple adhesins that facilitate attachment to and colonization of different niches within the host. Jb.asm.org 1 be microbial surface component recognizing adhesive matrix molecules (MSCRAMM), only a few, including endocarditis- and biofilm-associated pili (Ebp) and aggregation substance (AS), have been characterized in detail [2, 6–8]
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