Two-component regulatory proteins ResD-ResE are required for transcriptional activation of fnr upon oxygen limitation in Bacillus subtilis

Bacillus subtilis can grow anaerobically in the presence of nitrate as a terminal electron acceptor. The two component regulatory proteins, ResD and ResE, and an anaerobic gene regulator, FNR, were previously shown to be indispensable for nitrate respiration in B. subtilis. Unlike Escherichia coli fnr, B. subtilis fnr transcription was shown to be highly induced by oxygen limitation. fnr is transcribed from its own promoter as well as from a promoter located upstream of narK, the first gene in the narK-fnr dicistronic operon. DNA fragments containing the hark promoter, the far promoter, and both of the promoters were used to construct three latz fusions to examine the transcriptional regulation of the narK-fnr operon. ResDE was found to be required for transcriptional activation of fnr from the fnr-specific promoter, and FNR was required for activation of narK-fnr transcription from the FNR-dependent nark operon promoter under anaerobiosis. In order to determine if the requirement for ResDE in nitrate respiration is solely to activate far transcription, fnr was placed under control of the IPTG (isopropyl-β-D-thiogalactopyranoside)-inducible promoter, Pspac. The observed defect in anaerobic growth of a Pspac-fnr ΔresDE mutant in the presence of IPTG indicated that resDE has an additional role in B. subtilis anaerobic gene regulation.