Production of Enzymes Degrading Plant Cell Walls and Fermentation of Cellobiose by Ruminococcus flavefaciens in Batch and Continuous Culture

Summary: Production of enzymes degrading plant cell walls was studied using media containing cellobiose or ammonium ions (NH4 +) as limiting nutrients. Carboxymethylcellulase (CM-cellulase), xylanase and pectin lyase were primarily cell-associated during exponential growth in batch culture but accumulated in the supernatant during the stationary phase. Activities of CM-cellulase and xylanase were higher in cellobiose-limited than in NH4 +-limited continuous cultures, were inversely related to the growth rate and became progressively more cell-associated as the growth rate increased. The proportion of fermentation products in cellobiose-limited continuous cultures was dependent on the growth rate and the calculated cell yields per mol ATP (Y ATP) varied between 11·92 and 16·39. Glutamate dehydrogenase, an ammonia-assimilating enzyme, was most active in NH4 +-limited continuous cultures. These results are discussed in relation to the growth and metabolism of Ruminococcus flavefaciens in vivo.