Dilution Rate Increases Production of Plant Cell-wall Degrading Enzymes by Anaerobic Fungi in Continuous-flow Culture

The gut anaerobic fungi,Neocallimastix hurleyensisand aOrpinomyces sp., were grown in 100 mL batch and continuous-flow cultures on wheat straw at a concentration of 80 g dry matter/L of culture liquid. In batch cultures,N. hurleyensisandOrpinomyces sp. degraded only ca. 9% and 5% of the wheat straw, respectively. In continuous-flow cultures, however, the two fungi degraded 52–56% of the apparent dry matter of wheat straw. Both fungi were able to produce greater quantities (up to × 30) of cell-wall degrading enzymes (CMCase, xylanase, β-glucosidase and β-xylosidase) in continuous-flow cultures than in the corresponding batch cultures. Increasing the dilution rate in continuous-flow culture resulted in the production of increased enzyme activity for all the measured cell-wall degrading enzymes, with proportional relationships between dilution rate and the cumulative activities of β-glucosidase and β-xylosidase. Dilution rates, however, had no consistent effect on the cumulative production of the fermentation end-products, acetate, formate, D- and L-lactate from both fungi. In addition to acetate and formate,N. hurleyensisproduced D- and L-lactate in both batch and continuous-flow cultures, whereas only trace amounts of L-lactate were detected in theOrpinomyces sp. cultures.