THE ROLE OF RUMINAL CARBOXYMETHYLCELLULASES IN THE DEGRADATION OF BETA-GLUCANS FROM CEREAL GRAIN

The non-cellulolytic ruminal bacterium, Prevotella bryantii, grew rapi dly on water soluble beta-glucans, but a mutant deficient in carboxyme thylcellulase (CMCase) activity could not. Native activity gels prepar ed with CMC and beta-glucan indicated that the CMCase and beta-glucana se activities migrated at similar rates. When a plasmid carrying the P . bryantii CMCase was transferred to Escherichia coli, the clone had C MCase and beta-glucanase activities. P. bryantii grew on mixed beta-1, 3-1,4 glucans, but not on beta-1,3 glucan, and similar results were ob tained with the cellulolytic ruminal bacteria (Fibrobacter succinogene s S85, Ruminococcus flavefaciens FD1 and Ruminococcus albus B199). Mix ed ruminal bacteria from cattle fed hay had twice as much CMCase activ ity as bacteria from cattle fed 90% cereal grain (P < 0.05), and the C MCase and beta-glucanase activities were highly correlated (r(2) = 0.9 3) for the 22 samples tested. The CMCase and beta-glucanase activities of mixed ruminal bacteria migrated slowly through polyacrylamide gels , but the migration distances were approximately the same. When beta-g lucan-utilizing ruminal bacteria were isolated from cattle fed hay or 90% cereal grain, 70 and 38% of the strains, respectively, had CMCase activity. A similar trend was observed with cellobiose-utilizing isola tes (70 and 35%, respectively, were CMCase positive). All CMCase posit ive, cellobiose-utilizing ruminal bacteria could grow on beta-glucan. CMCase activity was not strongly correlated with cellulose utilization , and less than 15% of the CMCase positive isolates grew on ball-mille d cellulose. Based on these results, the cell-associated CMCases of ru minal bacteria provide a mechanism for utilizing water soluble beta-gl ucans from cereal grains. (C) 1998 Published by Elsevier Science B.V. All rights reserved.