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 rangi ng from 5-80 g dry matter/L of culture fluid. In batch culture, N. hur leyensis could degrade about 45% of the wheat straw, but only if the s ubstrate was provided at 5 g dry matter/L. In cultures containing 10-8 0 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 polysaccha rides was similarly affected in batch cultures with a decline in remov al in cultures containing more wheat straw. Likewise, production of fe rmentation products by the fungus in batch culture did not increase wi th increasing substrate concentration. These effects in batch culture were attributed to inhibition, probably by fermentation end products o r by the development of adverse physiological conditions. Continuous-f low culture is a procedure new to rumen microbiology in which fermenta tion end products are removed by continuous passage of Liquid medium t hrough the culture vessel at a constant (rumen-like) dilution rate. In this system, N. hurleyensis was able to degrade about 45% of wheat st raw at concentrations ranging from 5-40 g dry matter/L. Removal of non -starch polysaccharides from plant cell. walls and production of ferme ntation products also increased with increasing substrate concentratio ns. Growth of N. hurleyensis in continuous-flow culture enabled produc tion of greater quantities (up to 20 times larger) of cell wall degrad ing enzymes (CMCase and beta-glucosidase) and demonstrated the ability of the anaerobic fungus to grow in laboratory culture on levels of re calcitrant particulate substrate much in excess of those used in batch cultures. (C) 1996 Academic Press