Increased oxidative stress tolerance by Superoxide dismutase overexpression in Mesorhizobium loti.

Drought and salinity conditions are the major factors affecting nitrogen fixation by legume-rhizobium symbiosis. A global response to these stress conditions is the increase of intracellular ROS leading to activation of antioxidant system to ensure cellular homeostasis. Under the hypothesis that overexpression of sod gene in M. loti improve tolerance to oxidative stress we decide to investigate the response of constitutive overexpression of the Mesorhizobium loti MAFF303099 sod gene on tolerance to oxidative stress under free-living conditions. The gene mlr7636 was overexpressed constitutively under the nptII promoter of pFAJ1708 plasmid. Our study revealed that the sod overexpressing mutant had five-fold increased SOD activity in periplasmic space and a better tolerance to superoxide and hydrogen peroxide in bacterial killing assays.\n\nIMPORTANCEIn this study, we report that the homologous superoxide dismutase overexpression in Mesorhizobium loti improves its tolerance to oxidative stress under free-living conditions.