Synergism of sodA, sodB and KatG in Aeromonas hydrophila under antioxidative stress

To further explore the mechanism of Aeromonas hydrophila against oxidative stress, the correlations between the expressions of sodA, sodB and KatG in wild-type strain B11 and the gene silencing strains sodA-RNAi, sodB-RNAi and KatG-RNAi under different oxidative stresses were analyzed. Meanwhile, the correlation between the expressions of sodA, sodB and KatG and bacterial growth and survival was also studied. The results indicated that of the three genes (sodA, sodB and KatG), the silencing of any one gene resulted in significantly suppressed expression of the other two genes when they were under no oxidative stress. This indicated that these antioxidant stress genes were closely correlated in expression. Under H₂O₂ stress, silencing of one gene was always coupled with the significant up-regulation of the other two genes. Under MV-induced ROS stress, the expression of sodA and sodB genes in silencing strains was up-regulated, but the expression of KatG in strains sodA-RNAi and sodB-RNAi was down-regulated, indicating that the expression of two SODs genes was essential in resisting MV induced ROS damage. With the increase of H₂O₂ concentration, the survival rate of wild strain B11 remained at a high level, but the survival rate of gene silencing strains sodA-RNAi, sodB-RNAi and KatG-RNAi decreased significantly, and the expression of sodA, sodB and KatG was correlated with the length of the lag phase of A. hydrophila. Under different concentrations of MV stress, the survival rate of wild strain B11 and silencing strain KatG-RNAi remained at a relatively high level, while the survival rate of silencing strains sodA-RNAi and sodB-RNAi decreased significantly. But all the strains still maintained relatively good growth ability. These results suggested that under different oxidative stress conditions, bacteria can resist ROS damage through the synergism of different antioxidant stress genes. Under H₂O₂ stress, KatG is more important for the survival of A. hydrophila. Under MV-induced endogenous ROS stress, the expression of SODs genes contributes more to the survival of A. hydrophila.