Two distinct manganese-containing superoxide dismutase genes in Bacillus cereus: their physiological characterizations and roles in surviving in wheat rhizosphere.

Rhizosphere inhabitants interact intricately with plant host. Bacillus cereus 905 isolated from wheat rhizosphere colonized wheat rhizosphere with large population size. In this work, the role of superoxide dismutases (SODs) of B. cereus 905 in surviving in wheat rhizosphere was analyzed. Two genes, sodA-1 and sodA-2 encoding two distinct manganese SODs (MnSODs), were isolated from the bacterium. The amino acid sequence similarity between the two peptides is 58.43%. Through homologous recombination, three mutant strains have been created, each lacking either sodA-1, sodA-2 or both. Analysis of these mutant strains revealed differences in transcription and enzymatic activity of SOD. MnSOD2, encoded by sodA-2, plays a more important role in antioxidative stress. MnSOD1, the product of sodA-1 gene, is expressed at lower level. The function of the two MnSODs appears to be essential in colonization of wheat rhizosphere.