McCaughey, L. C. | bioRxiv Science

bioRxiv2020

Multiple Holins Contribute to Extracellular DNA Release in Pseudomonas aeruginosa Biofilms

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.

microbiology↗

bioRxiv2019

ChpC controls twitching motility-mediated expansion of Pseudomonas aeruginosa biofilms in response to serum albumin, mucin and oligopeptides

Twitching motility-mediated biofilm expansion occurs via coordinated, multi-cellular collective behaviour to allow bacteria to actively expand across surfaces. Type-IV pili (T4P) are cell-associated virulence factors which mediate this expansion via rounds of extension, surface attachment and retraction. The Chp chemosensory system is thought to respond to environmental signals to regulate the biogenesis, assembly and twitching motility function of T4P. In other well characterised chemosensory systems, methyl-accepting chemotaxis proteins (MCPs) feed environmental signals through a CheW adapter protein to the histidine kinase CheA to modulate motility. The Pseudomonas aeruginosa Chp system has two CheW adapter proteins, PilI and ChpC, and an MCP PilJ that likely interacts via PilI with the histidine kinase ChpA. It is thought that ChpC associates with other MCPs to feed environmental signals into the system, however no such signals have been identified. In the current study we show that ChpC is involved in the response to host-derived signals serum albumin, mucin and oligopeptides. We demonstrate that these signals stimulate an increase in twitching motility, as well as in levels of 3-5-cyclic adenosine monophosphate (cAMP) and surface-assembled T4P. Interestingly, our data shows that changes in cAMP and surface piliation levels are independent of ChpC but that the twitching motility response to these environmental signals requires ChpC. Based upon our data we propose a model whereby ChpC associates with an MCP other than PilJ to feed these environmental signals through the Chp system to control twitching motility. The MCP PilJ and the CheW adapter PilI then modulate T4P surface levels to allow the cell to continue to undergo twitching motility. Our study is the first to link environmental signals to the Chp chemosensory system and refines our understanding of how this system controls twitching motility-mediated biofilm expansion in P. aeruginosa.

microbiology↗