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Sodium ion-dependent hydrogen production in Acidaminococcus fermentans
1Laboratorium für Mikrobiologie, Fachbereich Biologie, Philipps-Universität, D-35032 Marburg, Germany. buckel@mailer.uni-marburg.de
Archives of Microbiology
|November 1, 1996
Summary
Acidaminococcus fermentans produces hydrogen from glutamate fermentation, a process dependent on sodium ions (Na+). Increased Na+ concentrations enhance hydrogen production and alter the acetate/butyrate ratio, revealing a novel mechanism for microbial energy metabolism.
Area of Science:
- Microbiology
- Biochemistry
- Bioenergetics
Background:
- Acidaminococcus fermentans ferments glutamate into ammonia, CO2, acetate, butyrate, and H2.
- Hydrogen production is linked to NADH generated via the hydroxyglutarate pathway.
Purpose of the Study:
- Investigate the role of sodium ions (Na+) in hydrogen production by A. fermentans.
- Elucidate the mechanism of Na+-dependent hydrogen formation and its impact on fermentation products.
Main Methods:
- Fermentation experiments with washed cells of A. fermentans under varying Na+ concentrations.
- Analysis of hydrogen production rates, acetate/butyrate ratios, and enzyme activities (hydrogenase, NADH dehydrogenase) in membrane fractions.
Main Results:
- While glutamate fermentation is optimal at 1 mM Na+, hydrogen production requires > 10 mM Na+, peaking at 100 mM Na+.
- The acetate/butyrate ratio increased from 2.0 to 3.0 with increasing Na+ concentrations (1 mM to 100 mM).
- A model involving membrane-bound hydrogenase and NADH dehydrogenase explains electron transfer coupled to Na+ gradients, with glutaconyl-CoA decarboxylase acting as an H+/Na+-antiporter.
Conclusions:
- Sodium ions are critical regulators of hydrogen production in A. fermentans, influencing both the rate and the metabolic output.
- The study reveals a novel bioenergetic mechanism where proton motive force, modulated by Na+ and glutaconyl-CoA decarboxylase activity, drives hydrogen evolution.