Cloning of the sodA gene from Corynebacterium melassecola and role of superoxide dismutase in cellular viability

The sodA gene encoding the Corynebacterium melassecola manganese-cofactored superoxide dismutase (SOD) has been cloned in Escherichia coli and sequenc ed. The gene is transcribed monocistronically; the predicted polypeptide is 200 amino acids long and associates in a homotetrameric, manganese depende nt form, able to complement an SOD-deficient E. coli mutant. A second open reading frame, coding for a putative 217 amino acid protein with high homol ogy to peptide methionine sulfoxide reductases from various origins, has be en identified immediately upstream of sodA in the opposite transcription or ientation, The sodA gene was inactivated by insertion of an integrative vec tor carrying a kanamycin resistance gene. The growth rate of the SOD defici ent integrant was only slightly affected in BHI rich medium as well as in B MCG chemically defined medium, but was strongly affected by the presence of the redox-cycling agent paraquat. The SOD deficiency had, on the other han d, a deleterious effect on viability as soon as the culture entered the sta tionary phase of growth in BHI medium. Surprisingly, SOD deficiency was abl e to rescue the dramatic loss of viability observed for the wild-type strai n in BMCG synthetic medium when glucose was not the limiting growth factor.