Bioenergetics of acetogenesis in the extremely alkaliphilic homoacetogenicbacteria Natroniella acetigena and Natronoincola histidinovorans

The energy metabolism of the extremely alkaliphilic homoacetogens Natroniel la acetigena and Natronoincola histidinovorans is based on the acetyl-CoA p athway involving CO dehydrogenase, whose activity is manifested at alkaline pH values and is independent of the presence of NaCl and bicarbonate ions. Inhibitory analysis showed that the oxidation of lactate and ethanol by N. acetigena and the oxidation of histidine by Natr. histidinovorans are coup led to ATP synthesis involving the electron transport chain and an H+-ATPas e of the F1F0 type. Cell de-energization by protonophores led to optical ch anges in resting N. acetigena cells; these changes were related to plasmoly sis and subsequent cell lysis as a result of the elimination of the active osmotic barrier. Despite its fermentative metabolism, Natr. histidinovorans proved to be obligately dependent on the activity of ion pumps.