A Bacillus subtilis sodA recombinant plasmid, pMW-sod, was introduced into a Sod-deficient strain E. coli IM303 (sodA, sodB). The activity of superoxide dismutase in the crude extract of E. coli IM303 bearing pMW-sod was markedly increased by the addition of an inducer, isopropyl-β-D-thiogalactopyranoside, in Mn2+-supplemented medium; in contrast, it was kept at the basal level in Fe2+-supplemented medium. However, the specific activity of B. subtilis SodA purified from this strain was extremely low, compared with that from B. subtilis. An atomic absorption analysis revealed that a relatively high content of Fe2+ was bound to this purified B. subtilis SodA. We further demonstrated that this purified B. subtilis SodA was activated by incubation with manganese salt. These results suggest that B. subtilis SodA was posttranslationally regulated by the manganese in vivo and in vitro.