Iron triggers ?So prophage induction and release of extracellular DNA in Shewanella oneidensis MR-1 biofilms.

ABSTRACT: Prophages are ubiquitous elements within bacterial chromosomes and affect host physiology and ecology in multiple ways. We have previously demonstrated that phage-induced lysis is required for extracellular DNA (eDNA) release and normal biofilm formation in Shewanella oneidensis MR-1. Here, we investigated the regulatory mechanisms of prophage ?So spatiotemporal induction in biofilms. To this end, we used a functional fluorescence fusion to monitor ?So activation in various mutant backgrounds and in response to different physiological conditions. ?So induction occurred mainly in a subpopulation of filamentous cells in a strictly RecA-dependent manner, implicating oxidative stress-induced DNA damage as the major trigger. Accordingly, mutants affected in the oxidative stress response (?oxyR) or iron homeostasis (?fur) displayed drastically increased levels of phage induction and abnormal biofilm formation, while planktonic cells were not or only marginally affected. To further investigate the role of oxidative stress, we performed a mutant screen and identified two independent amino acid substitutions in OxyR (T104N and L197P) that suppress induction of ?So by hydrogen peroxide (H2O2). However, ?So induction was not suppressed in biofilms formed by both mutants, suggesting a minor role of intracellular H2O2 in this process. In contrast, addition of iron to biofilms strongly enhanced ?So induction and eDNA release, while both processes were significantly suppressed at low iron levels, strongly indicating that iron is the limiting factor. We conclude that uptake of iron during biofilm formation triggers ?So-mediated lysis of a subpopulation of cells, likely by an increase in iron-mediated DNA damage sensed by RecA.

SUBMITTER: Binnenkade L 

PROVIDER: S-EPMC4136115 | biostudies-literature | 2014 Sep

REPOSITORIES: biostudies-literature