Occurrence of two superoxide dismutases in Aeromonas hydrophila: molecularcloning and differential expression of the sodA and sodB genes

Aeromonas spp., considered as emerging opportunistic pathogens, belong to t he family Vibrionaceae. Among the criteria currently used for their classif ication is the presence of a single FeSOD (iron-containing superoxide dismu tase), which distinguishes them from Enterobacteriaceae. In this paper the cloning of the sodA and sodB genes encoding two different SODs in Aeromonas hydrophila ATCC 7966 is reported. The sodB gene encoded an FeSOD (196 amin o acids, 21.5 kDa), was constitutively expressed and showed 75% homology wi th the E. coli FeSOD. The sodA gene encoded a protein of 206 amino acids (2 2.5 kDa) with MnSOD (manganese-containing SOD) activity and showed 55 % hom ology with the Escherichia coli MnSOD. The MnSOD of A. hydrophila was detec ted only during the stationary phase of growth under high aeration or when induced by lack of iron. Nevertheless, paraquat had no detectable effect on its production. The amino-terminal part of the Mn-containing protein conta ined a putative signal sequence which could permit a periplasmic localizati on.