For bacteria, mechanisms of resistance to redox stress are utilised to increase survival. Although B. henselae has the ability to resist redox stress, its genome sequence is characterised by a paucity of genes responsible for redox-stress resistance, particularly hydrogen peroxide degradation systems. However, our results show a surprisingly high resistance to peroxides, given the lack of peroxide disposal systems. To determine how B. henselae achieves resistance to H2O2 stress, the potential role of MbfA (membrane-bound bacterioferritin), which in other α-Proteobacteria is believed to function as an iron exporter, was investigated. The results show that B. henselae has the ability to export iron and that this export activity is promoted by H2O2as export was inhibited by exogenous catalase and anaerobiosis. The form of iron exported was largely ferric. The impact of the iron export process on the resistance to, and degradation of, H2O2, by B. henselae was determined and the results showed that B. henselae mediates a rapid consumption of exogenously supplied H2O2. This degradation was entirely inhibited when iron chelators were included along with the H2O2. The resistance of B. henselae to NO was also tested since NO is generated by phagocytic host cells along with H2O2, and is suggested to potentiate the toxicity of H2O2 towards engulfed bacteria through inhibition of haem-dependent catalases and alkylhydroperoxidases. Our results suggest that NO does not cause a marked increase in H2O2 toxicity for B. henselae, in contrast to E. coli (a haem-catalayse/peroxidase dependent bacterium).

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