Enzymes of intermediary metabolism of Butyrivibrio fibrisolvens and Ruminococcus albus grown under glucose limitation

A survey was made of enzyme activities in cell-free extracts prepared from one strain each of Butyrivibrio fibrisolvens and Ruminococcus albus, two anaerobic cellulolytic rumen bacteria, which had been grown in continuous culture on a defined medium under glucose limitation. In both organisms the enzymes of the glycolytic sequence up to the cleavage of hexosediphosphate were demonstrated, except that 6-phosphofructokinase activity in B. fibrisolvens was barely measurable. Instead, 1-phosphofructo-kinase was found in this organism. The role of this enzyme in glucose-grown cells is uncertain. Phosphopyruvate hydratase and pyruvate kinase could not be detected in R. albus extracts and their activities were extremely low in B. fibrisolvens, thus posing a problem as to pyruvate production in these organisms. At least part of the tricarboxylic acid cycle appeared to be functional in both organisms.Since several of the enzymes of this cycle in B. fibrisolvens were NADP-dependent, rather than NAD-dependent, and other workers have shown that fumarate reductase activity exceeds succinate dehydrogenase activity by more than 3:1, it is suggested that the tricarboxylic acid cycle may operate as a reductive cycle in this organism. Both organisms possessed fairly high activities of glutamate dehydrogenase and aspartate aminotransferase. The information obtained is inadequate to map out the pathways leading to the main end products of glucose fermentation.