DIGESTION OF CELL-WALL MONOSACCHARIDES OF RYEGRASS AND ALFALFA HAYS BY THE RUMINAL BACTERIA FIBROBACTER-SUCCINOGENES AND BUTYRIVIBRIO-FIBRISOLVENS

The ruminal bacteria Fibrobacter succinogenes strains S85 and BL2 were grown in monocultures or in coculture with strain D1 of Butyrivibrio fibrisolvens, and the solubilization of ryegrass and alfalfa cell walls (CW) and digestion of CW monosaccharides were measured. Fibrobacter succinogenes monocultures and cocultures with B. fibrisolvens D1 degraded 58-69% of ryegrass CW, solubilizing 67-78% of CW glucose, 65-71% of CW xylose, 69-75% of hemicellulose, and 68-77% of total CW monosaccharides. When grown on alfalfa CW, those cultures degraded 28-39% of alfalfa CW, solubilizing 42-58% of CW glucose, 30-36% of CW xylose, and 37-45% of hemicellulose. With respect to both substrates, F. succinogenes strains solubilized CW carbohydrates better than did B. fibrisolvens D1. Complementary interaction between B. fibrisolvens D1 and the F. succinogenes strains was identified with respect to the utilization of some solubilized carbohydrates, but not with respect to the extent of CW solubilization, which was determined mainly by the F. succinogenes strains. For both substrates, utilization of solubilized cellulose by F. succinogenes monocultures was high (96-98%), whereas that of hemicellulose was lower (24-26% in ryegrass and 49-50% in alfalfa). Under scanning electron microscopy, F. succinogenes bacterial cells attached to and colonized on CW particles were characterized by the appearance of protuberant surface structures that we have identified as ''polycellulosome complexes.''