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Background  Highly virulent enterohemorrhagic  Escherichia coli  O157:H7 strains possess three  sodC  genes encoding for periplasmic Cu, Zn superoxide dismutases:  sodC , which is identical to the gene present in non-pathogenic  E. coli  strains, and  sodC -F1 and  sodC -F2, two nearly identical genes located within lambdoid prophage sequences. The significance of this apparent  sodC  redundancy in  E. coli  O157:H7 has not yet been investigated.    Results  We report that strains deleted of one or more  sodC  genes are less resistant than the wild type strain to a challenge with hydrogen peroxide, thus confirming their involvement in the bacterial antioxidant apparatus. To understand if the different  sodC  genes have truly overlapping functions, we have carried out a comparison of the functional, structural and regulatory properties of the various  E. coli  O157:H7 SodC enzymes. We have found that the chromosomal and prophagic  sodC  genes are differentially regulated  in vitro .  sodC  is exclusively expressed in aerobic cultures grown to the stationary phase. In contrast,  sodC -F1 and  sodC -F2 are expressed also in the logarithmic phase and in anaerobic cultures. Moreover, the abundance of SodC-F1/SodC-F2 increases with respect to that of SodC in bacteria recovered from infected Caco-2 cells, suggesting higher expression/stability of SodC-F1/SodC-F2 in intracellular environments. This observation correlates with the properties of the proteins. In fact, monomeric SodC and dimeric SodC-F1/SodC-F2 are characterized by sharp differences in catalytic activity, metal affinity, protease resistance and stability.    Conclusion  Our data show that the chromosomal and bacteriophage-associated  E. coli  O157:H7  sodC  genes have different regulatory properties and encode for proteins with distinct structural/functional features, suggesting that they likely play distinctive roles in bacterial protection from reactive oxygen species. In particular, dimeric SodC-F1 and SodC-F2 possess physico-chemical properties which make these enzymes more suitable than SodC to resist the harsh environmental conditions which are encountered by bacteria within the infected host.

bmc microbiology

Regulatory and structural properties differentiating the chromosomal and the bacteriophage-associated Escherichia coli O157:H7 Cu, Zn Superoxide Dismutases