Electron transport phosphorylation driven by glyoxylate respiration with hydrogen as electron donor in membrane vesicles of a glyoxylate-fermenting bacterium

Abstract

The syntrophically glycolate-fermenting bacterium in the methanogenic binary coculture F1GlyM was isolated in pure culture (strain F1GlyR) with glyoxylate as sole substrate. This strain disproportionated 12 glyoxylate to 7 glycolate, 10 CO 2, and 3 hydrogen. Glyoxylate was oxidized via the malyl-CoA pathway. All enzymes of this pathway, i.e. malyl-CoA lyase/malate: CoA ligase, malic enzyme, and pyruvate synthase, were demonstrated in cell-free extracts. Glycolate dehydrogenase, hydrogenase, and ATPase, as well as menaquinones as potential electron carriers, were present in the membranes. Everted membrane vesicles catalyzed hydrogen-dependent glyoxylate reduction to glycolate [86-207 nmol min I (mg protein) -1] coupled to ATP synthesis from ADP and Pi [38-82 nmol min -1 (rag protein)q)]. ATP synthesis was abolished entirely by protonophores or ATPase inhibitors (up to 98 and 94% inhibition, respectively) indicating the involvement of proton-motive force in an electron transport phosphorylation driven by a new glyoxylate respiration with hydrogen as electron donor. Measured reaction rates in vesicle preparations revealed a stoichiometry of ATP formation of 0.2-0.5 ATP per glyoxylate reduced.

Genomic Insights into Syntrophy: The Paradigm for Anaerobic Metabolic Cooperation

“…The ferredoxin:NAD + oxidoreductase may function as a reverse electron transfer complex, using the ion gradient to drive the unfavorable reduction of ferredoxin with NADH (7). The fact that ion gradients are needed for hydrogen production by S. wolfei and Syntrophus buswellii (108) and for glyoxylate metabolism by Syntrophobotulus glycolicus (24,25) provides experimental support for reverse electron transport in syntrophic metabolism. …”

Energetic Aspects of Methanogenic Feeding Webs

“…The reaction could even be reverted, as demonstrated through hydrogen-and glyoxylatedependent ATP synthesis with the same membrane vesicle preparations. In both cases, the coupr'ing between the two steps was alleviated by protonophores (Friedrich and Schink, 1995), indicating that they are coupled via a proton gradient system. At least in propionate oxidation, also formate appears to play an important role as an electron carrier (de Bok et aI., 2002).…”

Syntrophism among Prokaryotes

“…The process is even reversible: Membrane vesicles incu bated in the presence of glyoxylate and hydrogen catalyzed a substrate dependent net synthesis of ATP from ADP and P i . The ratio of hydrogen dependent glyoxylate reduction over ATP formation in isolated membrane vesicle preparations (0.2 0.5 mol per mol; Friedrich and Schink 1995) indicates that probably two thirds of an ATP unit can be formed this way per reaction run. Thus, at least with this system, we have rather reliable data on the reaction stoichiometry.…”