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 wall s (CW) and digestion of CW monosaccharides were measured. Fibrobacter succinogenes monocultures and cocultures with B. fibrisolvens D1 degra ded 58-69% of ryegrass CW, solubilizing 67-78% of CW glucose, 65-71% o f CW xylose, 69-75% of hemicellulose, and 68-77% of total CW monosacch arides. When grown on alfalfa CW, those cultures degraded 28-39% of al falfa CW, solubilizing 42-58% of CW glucose, 30-36% of CW xylose, and 37-45% of hemicellulose. With respect to both substrates, F. succinoge nes strains solubilized CW carbohydrates better than did B. fibrisolve ns D1. Complementary interaction between B. fibrisolvens D1 and the F. succinogenes strains was identified with respect to the utilization o f some solubilized carbohydrates, but not with respect to the extent o f CW solubilization, which was determined mainly by the F. succinogene s strains. For both substrates, utilization of solubilized cellulose b y F. succinogenes monocultures was high (96-98%), whereas that of hemi cellulose 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 ''polyce llulosome complexes.''