Heterogeneous gene expression, metabolic variability and differentiation in Staphylococcus epidermidis biofilms

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Staphylococcus epidermidis is a prototype biofilm-forming bacterium characterised by a pronounced phenotypic variability within biofilm communities. The proposed research aims at an understanding of the biological significance and the factors that trigger and control heterogeneity in S. epidermidis biofilms. In the previous funding period, we established that, within S. epidermidis biofilm populations, phenotypic variants coexist. They vary in terms of biofilm matrix production and metabolic properties, with distinct subpopulations of bacteria undergoing lysis and release of DNA. In addition, biofilm-negative variants arise in high frequencies within the biofilm. Confocal laser scanning microscopy (CLSM) analyses revealed an organised spatial structure of the S. epidermidis biofilms with a significant degree of heterogeneus gene expression patterns and the concentration of various subpopulations in well-defined regions of the biofilm. Most strikingly, a small non-coding RNA (i.e., RsaE) was identified to act as a putative trigger for generating heterogeneity in S. epidermidis biofilm communities. Thus, RsaE is supposed to mediate the (reversible) switch between protein- and polysaccharide-biofilm matrix production, most likely through re-programing of the staphylococcal metabolism. At the same time, the molecule is possibly capable of limiting the frequency of genetic events contributing to biofilm heterogeneity as well. As RsaE itself is heterogeneously expressed, we suggest this riboregulator to function as an important driver for generating and controlling biofilm diversity. To substantiate this, hypothesis we will, in the upcoming funding period, specifically focus on the factors and molecular mechanisms that mediate diversity in S. epidermidis biofilms. Thus, we will investigate the molecular function of RsaE in the process, and study its putative link to other important regulatory circuits such as quorum sensing as well as programmed bacterial lysis and cell death. Moreover, we will continue to analyse the spatiotemporal dynamics of biofilm development by confocal laser scanning microscopy and extend these studies to flow chamber models. Finally, in an joint effort with our collaborators within the consortium, we will establish suitable models to simulate and predict S. epidermidis biofilm development and diversification.