Energy Yield of Respiration on Chloroaromatic Compounds in Desulfitobacterium dehalogenans

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Abstract
The amount of energy that can be conserved via halorespiration by Desulfitobacterium dehalogenans JW/IU-DC1 was determined by comparison of the growth yields of cells grown with 3-chloro-4-hydroxyphenyl acetate (Cl-OHPA) and different electron donors. Cultures that were grown with lactate, pyruvate, formate, or hydrogen as an electron donor and Cl-OHPA as an electron acceptor yielded 3.1, 6.6, 1.6, and 1.6 g (dry weight) per mol of reduction equivalents, respectively. Fermentative growth on pyruvate yielded 14 g (dry weight) per mol of pyruvate oxidized. Pyruvate was not fermented stoichiometrically to acetate and lactate, but an excess of acetate was produced. Experiments with 13 C-labeled bicarbonate showed that during pyruvate fermentation, approximately 9% of the acetate was formed from the reduction of CO 2 . Comparison of the growth yields suggests that 1 mol of ATP is produced per mol of acetate produced by substrate-level phosphorylation and that there is no contribution of electron transport phosphorylation when D. dehalogenans grows on lactate plus Cl-OHPA or pyruvate plus Cl-OHPA. Furthermore, the growth yields indicate that approximately 1/3 mol of ATP is conserved per mol of Cl-OHPA reduced in cultures grown in formate plus Cl-OHPA and hydrogen plus Cl-OHPA. Because neither formate nor hydrogen nor Cl-OHPA supports substrate-level phosphorylation, energy must be conserved through the establishment of a proton motive force. Pyruvate ferredoxin oxidoreductase, lactate dehydrogenase, formate dehydrogenase, and hydrogenase were localized by in vitro assays with membrane-impermeable electron acceptors and donors. The orientation of chlorophenol-reductive dehalogenase in the cytoplasmic membrane, however, could not be determined. A model is proposed, which may explain the topology analyses as well as the results obtained in the yield study.

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