INTERACTIONS BETWEEN RUMEN BACTERIAL STRAINS DURING THE DEGRADATION AND UTILIZATION OF THE MONOSACCHARIDES OF BARLEY STRAW CELL-WALLS

Pure cultures and pair-combinations of strains representative of the r umen cellulolytic species Ruminococcus flavefaciens, Fibrobacter succi nogenes and Butyrivibrio fibrisolvens were grown on cell-wall material s from barley straw. Of the pure cultures, R. flavefaciens solubilized straw most rapidly. The presence of B. fibrisolvens, which was unable to degrade straw extensively in pure culture, increased the solubiliz ation of dry matter by R. flavefaciens and the solubilization of cell- wall carbohydrates by both R. flavefaciens and F. succinogenes. During fermentation, both R. flavefaciens and F. succinogenes released bound glucose and free and bound arabinose and xylose into solution. The ac cumulation of these sugars, especially arabinose and xylose, was great ly reduced in co-cultures containing B. fibrisolvens, suggesting that significant interspecies cross feeding of the products of hemicellulos e hydrolysis (particularly soluble bound xylose released by F. succino genes) occurs during straw degradation by mixed cultures containing th is species.