Energy yield of respiration on chloroaromatic compounds in Desulfitobacterium dehalogenans

The amount of energy that can be conserved via halorespiration by Desulfito bacterium dehalogenans JW/IU-DC1 was determined by comparison of the growth yields of cells grown with 3-chloro-4-hydroxyphenyl acetate (CI-OHPA) and different electron donors. Cultures that were grown with lactate, pyruvate, formate, or hydrogen as an electron donor and CI-OHPA as an electron accep tor yielded 3.1, 6.6, 1.6, and 1.6 g (dry weight) per mol of reduction equi valents, respectively. Fermentative growth on pyruvate yielded 14 g (dry we ight) per mol of pyruvate oxidized. Pyruvate was not fermented stoichiometr ically to acetate and lactate, but an excess of acetate was produced. Exper iments with C-13-labeled bicarbonate showed that during pyruvate fermentati on, approximately 9% of the acetate was formed from the reduction of CO2, C omparison of the growth yields suggests that I mol of ATP is produced per m ol of acetate produced by substrate-level phosphorylation and that there is no contribution of electron transport phosphorylation when D. dehalogenans grows on lactate plus CI-OHPA or pyruvate plus CI-OHPA. Furthermore, the g rowth yields indicate that approximately 1/3 mol of ATP is conserved per mo l of CI-OHPA reduced in cultures grown in formate plus CI-OHPA and hydrogen plus CI-OHPA. Because neither formate nor hydrogen nor CI-OHPA supports su bstrate-level phosphorylation, energy must be conserved through the establi shment of a proton motive force. Pyruvate ferredoxin oxidoreductase, lactat e dehydrogenase, formate dehydrogenase, and hydrogenase were localized by i n vitro assays with membrane-impermeable electron acceptors and donors. The orientation of chlorophenol-reductive dehalogenase in the cytoplasmic memb rane, however, could not be determined. A model is proposed, which may expl ain the topology analyses as well as the results obtained in the yield stud y.