DEGRADATION AND UTILIZATION BY BUTYRIVIBRIO-FIBRISOLVENS H17C OF XYLANS WITH DIFFERENT CHEMICAL AND PHYSICAL-PROPERTIES

Hemicelluloses, mainly xylans, can be a major component of diets consumed by ruminants and undergo various degrees of microbial digestion in the rumen, The ability of Butyrivibrio fibrisolvens, a major xylanolytic ruminal species, to degrade and utilize nine chemically and physically different xylans for growth was examined, The arabinoxylans used included two isolated from corncobs (CCX-A and CCX-B), a native xylan excreted by corn cell tissue cultures (CX), an oxalic acid-treated, arabinose-depleted CX, and oat spelt xylan. Except for CCX-A, these xylans were extensively converted within 3 h of growth to acid-alcohol-soluble forms that remained at high levels for the duration of culture grow;th. These xylans contain mainly xylose and arabinose,vith small amounts of uronic acids, For a given xylan, all three components were used at about the same rate and extent, During the early stages of growth B. fibrisolvens also rapidly solubilized glucuronoxylans from birchwood, larchwood, 4-O-methylglucuronoxylan, and the xylose homopolymer xylan isolated from beechwood (BEWX), In contrast to the findings for the arabinoxylans, little acid-alcohol-soluble carbohydrate remained in these cultures after 9 h of growth, except for BEWX, Initially, with birchwood, larchwood, and 4-O-methylglucuronoxylan the uronic acid components were preferentially used over the xylose, Final xylan utilization measured at 72 h for all xylans varied from 57% for CCX-A to 92% for BEWX and was correlated with the initial 12-h utilization rate for a given xylan, Since CCX-A and BEWX are both highly water insoluble, this aspect did not appear to influence overall utilization, Thus, the type and distribution of xylan side chains are more important to xylan utilization by B. fibrisolvens.