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

Abstract

Production of enzymes degrading plant cell walls was studied using media containing cellobiose or 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/mol ATP (YATP) varied between 11.92-16.39. Glutamate dehydrogenase, an NH3-assimilating enzyme, was most active in NH4+-limited continuous cultures. These results are discussed in relation to the growth and metabolism of R. flavefaciens in vivo.