Molecular Control of Extracellular DNA Release and Degradation in Shewanella oneidensis MR-1 Biofilms: The Role of Phages and Nucleases

Under natural conditions, most bacteria tend to form surface-associated multicellular communities that that are commonly referred to as biofilms. Biofilm formation is a complex and highly regulated process that enables bacteria to colonize almost every kind of surface and to resist diverse physical stresses, starvation, and antibiotics. Moreover, surface-associated growth increases virulence in many pathogenic bacteria and allows environmental bacteria to exploit surfaces as nutrient and energy reservoir. Accordingly, bacterial biofilm formation has been shown to be of great medical, ecological, and economical relevance. An essential component of biofilms is the extracellular polymeric matrix that commonly consists of a complex mixture of exopolysaccharides, proteins, and extracellular DNA (eDNA). The significance of eDNA in biofilms has long been disregarded, but a high number of studies has now demonstrated that it is required for structural biofilm formation in most bacteria, including Shewanella oneidensis MR-1. However, mechanisms that regulate and mediate eDNA release on the one hand, and those that control eDNA modulation and degradation (e.g. to induce biofilm dispersal or to exploit eDNA as source of nutrients) on the other hand, are still incompletely understood. These mechanisms were analyzed in the present study by molecular biological, microscopic, and biochemical approaches.