TRANSCRIPTIONAL REGULATION AND ENERGETICS OF ALTERNATIVE RESPIRATORY PATHWAYS IN FACULTATIVELY ANAEROBIC-BACTERIA

The facultatively anaerobic Escherichia coli is able to grow by aerobi c and by anaerobic respiration. Despite the large difference in the am ount of free energy that could maximally be conserved from aerobic ver sus anaerobic respiration, the proton potential and Delta G(Phos)' are similar under both conditions. O-2 represses anaerobic respiration, a nd nitrate represses fumarate respiration. By this the terminal reduct ases of aerobic and anaerobic respiration are expressed in a way to ob tain maximal H+/e(-) ratios and ATP yields. The respiratory dehydrogen ases, on the other hand, are not synthesized in a way to achieve maxim al H+/e(-) ratios. Most of the dehydrogenases of aerobic respiration d o not conserve redox energy in a proton gradient whereas the enzymes f rom anaerobic respiration do so. Thus transcriptional regulation of th e respiratory pathways by electron accepters has multiple effects on c ellular energetics. The transcriptional regulation in response to O-2 is effected by two transcriptional regulators, ArcA/B (aerobic respira tory control) and FNR (fumarate nitrate reductase regulator). FNR cont ains an O-2-sensitive [4Fe-4S](2+) cluster in the sensory domain and i s converted to the transcriptional inactive state in the presence of ( cytoplasmic) O-2. (C) 1998 Elsevier Science B.V.