Characterisation of the manganese superoxide dismutase of Enterococcus faecium

The manganese superoxide dismutase (SodA) of E. faecium strain AUS0004 has been characterised. It is most closely related to Enterococcus hirae, Enterococcus durans, Enterococcus villorium, and Enterococcus mundtii with 100%, 91,55%, 90,85%, and 90,58% homology, respectively, but more distant from SodA of E. faecalis (81.68%). A sodA deletion mutant has been constructed. Compared to the parental strain, the ΔsodA mutant was affected in aerobic growth and more sensitive to hydrogen peroxide (H₂O₂), cumene hydroperoxide (CuOOH), and the superoxide anion (O₂^•-) generator menadione. The E. faecium strain AUS0004 is part of those bacteria accumulating H₂O₂ to high concentrations (around 5 mM) starting from late exponential growth phase. Accumulation of the peroxide was around 25% less in the mutant suggesting that this part of H₂O₂ is due to the dismutation of O₂^•- by SodA. The sodA gene of E. faecium AUS0004 was induced by oxygen, peroxides and menadione but the corresponding regulator remains hitherto unknown. Finally, we showed that SodA activity is important for virulence in the Galleria mellonella model.