Extracellular DNA (eDNA) is a major component of the Pseudomonas aeruginosa biofilm matrix, facilitating cell migration, adhesion and intercellular connectivity^1-2. We have observed that during the early stages of development of hydrated biofilms as well as in actively expanding interstitial biofilms, that a small proportion of cells spontaneously transform into spherical cells before lysing rapidly and releasing cellular content into the extracellular milieu.  We have termed this phenomenon ‘explosive cell lysis’. As this accounts for the production of all eDNA present in these biofilms as well as a number of other ‘public goods’ that benefit the biofilm community, it is important to identify the mechanism mediating this process.

We have found that exposure to exogenous agents that induce oxidative or genotoxic stress dramatically increases the frequency of explosive cell lysis. Interestingly, both internal and external stressors have been reported to stimulate expression of the pyocin gene cluster³. Pyocins are cryptic bacteriophage that function as bacteriocins and are released through cell lysis.  We have found that mutants lacking the pyocin lytic endolysin (PA0629) no longer undergo explosive cell lysis, indicating that this is the mechanism responsible for this phenomenon. We have also found that explosive cell lysis in the early stages of hydrated biofilm development provides a conditioning film for bacterial attachment and microcolony formation.

In summary, we have found that explosive cell lysis can be initiated by exogenous stressors, is mediated through the pyocin endolysin PAO629 and is essential for biofilm development.