Modulation of Anaerobic Energy Metabolism of Bacillus subtilis by arfM ( ywiD )

Abstract

Bacillus subtilis grows under anaerobic conditions utilizing nitrate ammonification and various fermentative processes. The two-component regulatory system ResDE and the redox regulator Fnr are the currently known parts of the regulatory system for anaerobic adaptation. Mutation of the open reading frame ywiDlocated upstream of the respiratory nitrate reductase operonnarGHJI resulted in elimination of the contribution of nitrite dissimilation to anaerobic nitrate respiratory growth. Significantly reduced nitrite reductase (NasDE) activity was detected, while respiratory nitrate reductase activity was unchanged. Anaerobic induction of nasDE expression was found to be significantly dependent on intact ywiD, while anaerobicnarGHJI expression was ywiD independent. Anaerobic transcription of hmp, encoding a flavohemoglobin-like protein, and of the fermentative operonslctEP and alsSD, responsible for lactate and acetoin formation, was partially dependent on ywiD. Expression of pta, encoding phosphotransacetylase involved in fermentative acetate formation, was not influenced byywiD. Transcription of the ywiD gene was anaerobically induced by the redox regulator Fnr via the conserved Fnr-box (TGTGA-6N-TCACT) centered 40.5 bp upstream of the transcriptional start site. Anaerobic induction of ywiDby resDE was found to be indirect viaresDE-dependent activation of fnr. TheywiD gene is subject to autorepression and nitrite repression. These results suggest a ResDE → Fnr → YwiD regulatory cascade for the modulation of genes involved in the anaerobic metabolism of B. subtilis. Therefore,ywiD was renamed arfM for anaerobic respiration and fermentation modulator.