Multiple Holins Contribute to Extracellular DNA Release in Pseudomonas aeruginosa Biofilms

Abstract

Bacterial biofilms are comprised 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.

Bacteriophage infection of Escherichia coli leads to the formation of membrane vesicles via both explosive cell lysis and membrane blebbing

“…These observations are in agreement with our previous observations of explosive cell lysis in P. aeruginosa where we observed MVs forming through curling and selfannealing of shattered membrane fragments from lysed cells [10]. MV formation via explosive cell lysis is mediated by holin-endolysin systems in P. aeruginosa [10,27] and is likely to also be occurring as a consequence of the holin-endolysin systems of lytic T4 and T7 phage in E. coli. This process likely accounts for MV formation in other Gram-negative bacteria.…”

Microbial Musings – April 2021

“…Bryden also presented this work this week at AC2021 in the Genetics and Genomics symposium, so many of you will have heard this explained much better than my attempt at a summary presented here! By now, regular readers of the Microbial Musings will be familiar with the explosive cell lysis phenomenon used by some bacteriophage to exit their hosts, from the papers of Cynthia Whitchurch's group (@Cwhitch), including a paper published in Microbiology early this year [15,16]. Now the group, from the iThree Institute (@ithreeinst), University of Technology Sydney, Australia and the Quadram Institute (@TheQuadram) in Norwich, UK, including Laura Nolan (@LauraNolanLab), are looking in more detail at the formation of membrane vesicles (MVs) during this process during infection of Escherichia coli with T4 or T7 bacteriophage [17].…”