Enhanced poly(-glutamic acid) production by H2O2-induced reactive oxygen species in the fermentation of Bacillus subtilis NX-2

Effects of reactive oxygen species (ROS) on cell growth and poly(-glutamic acid) (-PGA) synthesis were studied by adding hydrogen peroxide to a medium of Bacillus subtilis NX-2. After optimizing the addition concentration and time of H2O2, a maximum concentration of 33.9g/L -PGA was obtained by adding 100 mu M H2O2 to the medium after 24H. This concentration was 20.6% higher than that of the control. The addition of diphenyleneiodonium chloride (ROS inhibitor) can interdict the effect of H2O2-induced ROS. Transcriptional levels of the cofactors and relevant genes were also determined under ROS stress to illustrate the possible metabolic mechanism contributing to the improve -PGA production. The transcriptional levels of genes belonging to the tricarboxylic acid cycle and electron transfer chain system were significantly increased by ROS, which decreased the NADH/NAD(+) ratio and increased the ATP levels, thereby providing more reducing power and energy for -PGA biosynthesis. The enhanced -PGA synthetic genes also directly promoted the formation of -PGA. This study was the first to use the ROS control strategy for -PGA fermentation and provided valuable information on the possible mechanism by which ROS regulated -PGA biosynthesis in B. subtilis NX-2. (C) 2015 International Union of Biochemistry and Molecular Biology, Inc.