Abstract
Bacterial biofilms are composed of aggregates of cells encased within a matrix of extracellular polymeric substances (EPS). One key EPS component is extracellular DNA (eDNA), which acts as a ‘glue’, facilitating cell–cell and cell–substratum interactions. We have previously demonstrated that eDNA is produced in Pseudomonas aeruginosa biofilms via explosive cell lysis. This phenomenon involves a subset of the bacterial population explosively lysing, due to peptidoglycan degradation by the endolysin Lys. Here we demonstrate that in P. aeruginosa three holins, AlpB, CidA and Hol, are involved in Lys-mediated eDNA release within both submerged (hydrated) and interstitial (actively expanding) biofilms, albeit to different extents, depending upon the type of biofilm and the stage of biofilm development. We also demonstrate that eDNA release events determine the sites at which cells begin to cluster to initiate microcolony formation during the early stages of submerged biofilm development. Furthermore, our results show that sustained release of eDNA is required for cell cluster consolidation and subsequent microcolony development in submerged biofilms. Overall, this study adds to our understanding of how eDNA release is controlled temporally and spatially within P. aeruginosa biofilms.
Highlights
The biofilm mode of growth, in which bacterial aggregates are encased in a matrix of extracellular polymeric substances (EPS), confers many advantages to bacteria, including increased resistance to antibiotics, predators, host cells and mechanical removal [1]
In this study we found that extracellular DNA (eDNA) release through explosive cell lysis determines the sites at which cells begin to cluster to form microcolonies in later stages of submerged biofilm development
Our observations suggest that eDNA released through Lys-m ediated explosive cell lysis is required for the initiation of microcolony formation in submerged biofilms
Summary
The biofilm mode of growth, in which bacterial aggregates are encased in a matrix of extracellular polymeric substances (EPS), confers many advantages to bacteria, including increased resistance to antibiotics, predators, host cells and mechanical removal [1]. The complex EPS component of biofilms, which comprises up to 90 % of the biofilm biomass, consists of polysaccharides, extracellular DNA (eDNA), proteins, lipids and membrane vesicles [5]. Together these components give the biofilm structure, stability and protection. Individual biofilm components have been widely studied in many species [5,6,7,8,9,10,11], there is little understanding of the temporal and spatial production of each component and their roles in different stages of biofilm development. To develop means of preventing biofilm formation and disrupting mature biofilms, the complex interplay between cells, matrix components and the environment needs to be fully elucidated
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