Sodium ion-dependent hydrogen production in Acidaminococcus fermentans.
Acidaminococcus fermentans is able to ferment glutamate to ammonia, CO2, acetate, butyrate, and H2. The molecular hydrogen (approximately 10 kPa; E' = -385 mV) stems from NADH generated in the 3-hydroxybutyryl-CoA dehydrogenase reaction (E degrees ' = -240 mV) of the hydroxyglutarate pathway. In contrast to growing cells, which require at least 5 mM Na+, a Na+-dependence of the H2-formation was observed with washed cells. Whereas the optimal glutamate fermentation rate was achieved already at 1 mM Na+, H2 formation commenced only at > 10 mM Na+ and reached maximum rates at 100 mM Na+. The acetate/butyrate ratio thereby increased from 2.0 at 1 mM Na+ to 3.0 at 100 mM Na+. A hydrogenase and an NADH dehydrogenase, both of which were detected in membrane fractions, are components of a model in which electrons, generated by NADH oxidation inside of the cytoplasmic membrane, reduce protons outside of the cytoplasmic membrane. The entire process can be driven by decarboxylation of glutaconyl-CoA, which consumes the protons released by NADH oxidation inside the cell. Hydrogen production commences exactly at those Na+ concentrations at which the electrogenic H+/Na+-antiporter glutaconyl-CoA decarboxylase is converted into a Na+/Na+ exchanger.
Härtel
U
U
Laboratorium für Mikrobiologie, Fachbereich Biologie, Philipps-Universität, D-35032 Marburg, Germany. buckel@mailer.uni-marburg.de
Buckel
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W
D001710:Biotin / Q000378:metabolism; D002262:Carboxy-Lyases / Q000378:metabolism; D003013:Clostridium / Q000378:metabolism; D003470:Culture Media; D005285:Fermentation; D018698:Glutamic Acid / Q000378:metabolism*; D005977:Glutarates / Q000378:metabolism; D006089:Gram-Negative Anaerobic Bacteria / Q000254:growth & development / Q000378:metabolism*; D006859:Hydrogen / Q000378:metabolism*; D006864:Hydrogenase / Q000378:metabolism; D007477:Ions; D009245:NADH Dehydrogenase / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*
D003470:Culture Media; D005977:Glutarates; D007477:Ions; C010971:glutaconic acid; D018698:Glutamic Acid; D001710:Biotin; D006859:Hydrogen; D012964:Sodium; D006864:Hydrogenase; D009245:NADH Dehydrogenase; D002262:Carboxy-Lyases