Abstract
A pathway for conversion of the metabolic intermediate phosphoenolpyruvate (PEP) and the formation of acetate, succinate, formate, and H2 in the anaerobic cellulolytic bacterium Ruminococcus flavefaciens FD-1 was constructed on the basis of enzyme activities detected in extracts of cells grown in cellulose- or cellobiose-limited continuous culture. PEP was converted to acetate and CO2 (via pyruvate kinase, pyruvate dehydrogenase, and acetate kinase) or carboxylated to form succinate (via PEP carboxykinase, malate dehydrogenase, fumarase, and fumarate reductase). Lactate was not formed even during rapid growth (batch culture, µ = 0.35/h). H2 was formed by a hydrogenase rather than by cleavage of formate, and 13C-NMR and14 C-exchange reaction data indicated that formate was produced by CO2 reduction, not by a cleavage of pyruvate. The distribution of PEP into the acetate and succinate pathways was not affected by changing extracellular pH and growth rates within the normal growth range. However, increasing growth rate from 0.017/h to 0.244/h resulted in a shift toward formate production, presumably at the presence of H2. This shift suggested that reducing equivalents could be balanced through formate or H2 production without affecting the yields of the major carbon-containing fermentation endproducts.
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Shi, Y., Weimer, P. & Ralph, J. Formation of formate and hydrogen, and flux of reducing equivalents and carbon in Ruminococcus flavefaciens Fd-1. Antonie Van Leeuwenhoek 72, 101–109 (1997). https://doi.org/10.1023/A:1000256221938
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DOI: https://doi.org/10.1023/A:1000256221938