Comparative impact of diverse regulatory loci on Staphylococcus aureus biofilm formation

Abstract

The relative impact of 23 mutations on biofilm formation was evaluated in the USA300, methicillin-resistant strain LAC. Mutation of sarA, atl, codY, rsbU, and sigB limited biofilm formation in comparison to the parent strain, but the limitation imposed by mutation of sarA was greater than that imposed by mutation of any of these other genes. The reduced biofilm formation of all mutants other than the atl mutant was correlated with increased levels of extracellular proteases. Mutation of fur- and mgrA-enhanced biofilm formation but in LAC had no impact on protease activity, nuclease activity, or accumulation of the polysaccharide intercellular adhesin (PIA). The increased capacity of these mutants to form a biofilm was reversed by mutation of sarA, and this was correlated with increased protease production. Mutation of sarA, mgrA, and sigB had the same phenotypic effect in the methicillin-sensitive strain UAMS-1, but mutation of codY increased rather than decreased biofilm formation. As with the UAMS-1 mgrA mutant, this was correlated with increased production of PIA. Examination of four additional clinical isolates suggests that the differential impact of codY on biofilm formation may be a conserved characteristic of methicillin-resistant versus methicillin-sensitive strains. In a global analysis of 23 mutants in USA300 strain LAC, mutation of sarA, atl, codY, rsbU, and sigB limited biofilm formation, and in all cases except atl, also resulted in increased levels of extracellular proteases. Mutation of fur and mgrA increased biofilm formation in comparison to the parent strain, but the limitation imposed by mutation of sarA was epistatic to mutation of any of these other genes including those resulting in decreased biofilm formation. While mutation of sigB and mgrA showed similar results in UAMS-1 as they did in LAC, codY demonstrated a strain-dependent increase in biofilm formation, unlike in LAC, mediated by increased amounts of PIA which may be a conserved characteristic of methicillin-resistant versus methicillin-sensitive strains.