THE DEGRADATION AND UTILIZATION OF STRUCTURAL POLYSACCHARIDES OF SORGHUM STRAW BY DEFINED RUMINAL BACTERIA

Cell wall (CW) preparations of untreated sorghum straw (SORG) and sulf ur dioxide-treated SORG (T-SORG) were used as substrates for the solub ilization and utilization of CW carbohydrates by pure cultures or pair -combinations of defined rumen bacterial strains. Ruminococcus flavefa ciens FD1 and R. albus 7 monocultures and cocultures with Butyrivibrio fibrisolvens DI had very little solubilizing effect on SORG and even less on T-SORG CW. Fibrobacter succinogenes S85 was the best solubiliz er of SORG CW components. The T-SORG CW was composed of fewer hemicell ulose components and more cellulose and total CW polysaccharides than the SORG CW. Consequently, F. succinogenes S85 and BL2 monocultures an d their cocultures with D1 degraded T-SORG CW saccharides by 21-33% un its better than those of SORG CW, solubilizing 61-66% of T-SORG CW-glu cose, 58-62% of CW-xylose, 58-63% of hemicellulose and 61-65% of total T-SORG structural polysaccharides. Complementary action between B. fi brisolvens D1 and the F. succinogenes strains was identified with resp ect to coculture growth and carbohydrate utilization, but not with res pect to the extent of CW solubilization which was determined mainly by the F. succinogenes strains during 120 h of coculture incubation. In both CW substrates, utilization of solubilized cellulose by F. succino genes S85 and BL2 monocultures was higher than that of CW-xylose and h emicellulose, being 97-98%, 53-69% and 54-75%, respectively. Under sca nning electron microscopic visualization SORG CW particles were less c olonized by attached bacterial cells than T-SORG. In both substrates a ttached F. succinogenes cells were characterized by the appearance of protuberant structures on their surface topology.