Genome-wide transcriptional profiling of Bradyrhizobium japonicum in response to hydrogen peroxide-induced oxidative stress

초록

Bradyrhizobium japonicum is a nitrogen-fixing bacterium found in soil and establishes a symbiotic relationship with the leguminous soybean plant. The host plant produces reactive oxygen species (ROS) to protect itself from the invasion of rhizobial cells as well as pathogens. In this study, we investigated the effects of hydrogen peroxide (H2O2) and paraquat (PQ)-induced oxidative stresses on B. japonicum gene expression. First, we measured the survival rate and growth of B. japonicum at various concentrations of H2O2 and PQ ranging from 100 M to 100 mM. When the cells were exposed to H2O2 and PQ for 2 h, they were able to survive at concentrations up to 10 mM and 5 mM for H2O2 and PQ, respectively. Genome-wide transcriptional profiles revealed that oxidative stress related genes encoding organic hydroperoxide resistance protein (ohr), anti-oxidant protein, and glutathione S-transferase were up-regulated. In addition, other stress-responsive genes including cold-shock proteins and molecular chaperones were also up-regulated. Surprisingly, catalase (katG) gene, which is a primary detoxifier of H2O2 and typically expressed in other bacteria under oxidative stress conditions, was not expressed. However, based on quantitative PCR data, this gene is expressed at an early time. The generation of transcriptional profiles for B. japonicum in the presence of PQ is currently in progress.