Transcriptional regulation and energetics of alternative respiratory pathways in facultatively anaerobic bacteria

Abstract

The facultatively anaerobic Escherichia coli is able to grow by aerobic and by anaerobic respiration. Despite the large difference in the amount of free energy that could maximally be conserved from aerobic versus anaerobic respiration, the proton potential and Δg′ Phos are similar under both conditions. O 2 represses anaerobic respiration, and nitrate represses fumarate respiration. By this the terminal reductases of aerobic and anaerobic respiration are expressed in a way to obtain maximal H + e − ratios and ATP yields. The respiratory dehydrogenases, on the other hand, are not synthesized in a way to achieve maximal H + e − ratios. Most of the dehydrogenases of aerobic respiration do not conserve redox enery in a proton gradient whereas the enzymes from anaerobic respiration do so. Thus transcriptional regulation of the respiratory pathways by electron acceptors has multiple effects on cellular energetics. The transcriptional regulation in response to O 2 is effected by two transcriptional regulators, ArcA/B ( a erobic r espiratory c ontrol) and FNR ( f umarate n itrate reductase r egulator). FNR contains an O 2-sensitive [4Fe4S] 2+ cluster in the sensory domain and is converted to the transcriptional inactive state in the presence of (cytoplasmic) O 2.