DIGESTION OF STRUCTURAL POLYSACCHARIDES OF PANICUM AND VETCH HAYS BY THE RUMEN BACTERIAL STRAINS FIBROBACTER-SUCCINOGENES BL2 AND BUTYRIVIBRIO-FIBRISOLVENS D1

The rumen bacterial strains Fibrobacter succinogenes BL2 and Butyrivib rio fibrisolvens D1, were grown in monocultures and pair combination o n cell walls (CW) of two tropical hays: Panicum (grass) and vetch (leg ume), and their ability to solubilize and utilize CW structural carboh ydrate was determined. With respect to both substrates, F. succinogene s BL2 was a better solubilizer of CW carbohydrate than B. fibrisolvens D1. However, the solubilization of Panicum constituents by any bacter ial monoculture and co-culture was higher than that of vetch. Compleme ntary interaction between B. fibrisolvens D1 and F. succinogenes BL2 w as identified only with respect to carbohydrate utilization, but not w ith the extent of CW solubilization, which was determined mainly by th e F. succinogenes strain. In both substrates, utilization of solubiliz ed cellulose by BL2 monocultures was high (86.4-97.5%), whereas that o f solubilized xylan and hemicellulose was much lower (35.2-41.6%). Und er scanning electron microscopy visualization, the BL2 bacterial cell mass attached to and colonized on CW particles was characterized by th e appearance of protuberant structures known as ''polycellulosome comp lexes'' on their surface topology.