Adaptive Response of Amphibacillus Xylanus to Normal Aerobic and Forced Oxidative Stress Conditions

Amphibacillus xylanusgrows at the same rate and with the same cell yield under aerobic and anaerobic conditions. Under aerobic conditions, it exhibits vigorous oxygen consumption in spite of lacking a respiratory system and haem catalase. To understand the adaptive response ofA.xylanusto oxidative stresses, a genomic analysis ofA. xylanuswas conducted. The analysis showed thatA. xylanushas the genes of four metabolic systems: two pyruvate metabolic pathways, a glycolytic metabolic pathway and an NADH oxidase (Nox)–AhpC (Prx) system. A transcriptional study confirmed thatA. xylanushas these metabolic systems. Moreover, genomic analysis revealed the presence of two genes for NADH oxidase (nox1andnox2), both of which were identified in the transcriptional analysis. Thenox1gene inA. xylanuswas highly expressed under normal aerobic conditions but that ofnox2was not. A purification study of NADH oxidases indicated that the gene product ofnox1is a primary metabolic enzyme responsible for metabolism of both oxygen and reactive oxygen species.A. xylanuswas successfully grown under forced oxidative stress conditions such as 0.1 mM H2O2, 0.3 mM paraquat and 80 % oxygen. Proteomic analysis revealed that manganese SOD, Prx, pyruvate dehydrogenase complex E1 and E3 components, and riboflavin synthase β-chain are induced under normal aerobic conditions, and the other proteins except the five aerobically induced proteins were not induced under forced oxidative stress conditions. Taken together, the present findings indicate thatA. xylanushas a unique defence system against forced oxidative stress.