The Roles of Superoxide Dismutases of a Plant-Beneficial Bacterium, \u3ci\u3ePseudomonas putida\u3c/i\u3e, And a Phytopathogenic Bacterium, \u3ci\u3ePseudomonas syringae\u3c/i\u3e pv. \u3ci\u3esyringae\u3c/i\u3e B728a, During Plant Colonization

Abstract

Both Pseudomonas putida and Pseudomonas syringae produced manganese-superoxide dismutase (MnSOD) and iron-superoxide dismutase (FeSOD). Genes sodB, encoding FeSOD, and sodA, encoding MnSOD, were cloned. The sodB genes were transcribed as monocistronic transcripts, expressed throughout growth phases when iron was available. The sodA genes were part of polycistronic operons, and transcripts of the operons were induced only in iron-deficient conditions. The effect of mutations in the SOD genes was observed during root colonization by Pseudomonas putida. The sodB and sodAsodB mutants were impaired in root colonization in mixed inoculations with wild-type. Growth of the sodB and sodAsodB mutants in aerobic metabolism was impaired. Greater sensitivity to internal oxidative stress was observed in SOD double mutants of both Pseudomonas putida and Pseudomonas syringae, although there was no effect on expression of the SOD genes. However, mutations of SODs in P. syringae did not impair growth on media or pathogenicity on bean