Growth and survival of anaerobic fungi in batch and continuous-flow cultures

The anaerobic fungus, Neocallimastix hurleyensis, was grown in 100 mi batch and continuous-flow cultures on wheat straw concentrations ranging from 5-80 g dry matter/L of culture fluid. In batch culture, N. hurleyensis could degrade about 45% of the wheat straw, but only if the substrate was provided at 5 g dry matter/L. In cultures containing 10-80 g dry matter/L, progressively less of the straw was degraded as the substrate concentration was increased. At a wheat straw concentration of 80 g dry matter/L, for example, the fungus was able to remove only about 12% of the substrate. Removal of cell wall non-starch polysaccharides was similarly affected in batch cultures with a decline in removal in cultures containing more wheat straw. Likewise, production of fermentation products by the fungus in batch culture did not increase with increasing substrate concentration. These effects in batch culture were attributed to inhibition, probably by fermentation end products or by the development of adverse physiological conditions. Continuous-flow culture is a procedure new to rumen microbiology in which fermentation end products are removed by continuous passage of Liquid medium through the culture vessel at a constant (rumen-like) dilution rate. In this system, N. hurleyensis was able to degrade about 45% of wheat straw at concentrations ranging from 5-40 g dry matter/L. Removal of non-starch polysaccharides from plant cell. walls and production of fermentation products also increased with increasing substrate concentrations. Growth of N. hurleyensis in continuous-flow culture enabled production of greater quantities (up to 20 times larger) of cell wall degrading enzymes (CMCase and beta-glucosidase) and demonstrated the ability of the anaerobic fungus to grow in laboratory culture on levels of recalcitrant particulate substrate much in excess of those used in batch cultures. (C) 1996 Academic Press