Degradation of Bermuda and Orchard Grass by Species of Ruminal Bacteria

Abstract

Fiber degradation in Bermuda grass and orchard grass was evaluated gravimetrically and by scanning and transmission electron microscopy after incubation with pure cultures of rumen bacteria. Lachnospira multiparus D-32 was unable to degrade plant cell wall components. Butyrivibrio fibrisolvens 49 degraded 6 and 14.9% of the fiber components in Bermuda grass and orchard grass, respectively, and Ruminococcus albus 7 degraded 11.4% orchard grass fiber but none in Bermuda grass. Both B. fibrisolvens and R. albus lacked capsules, did not adhere to fiber, and degraded only portions of the more easily available plant cell walls. R. flavefaciens FD-1 was the most active fiber digester, degrading 8.2 and 55.3% of Bermuda and orchard grass fiber, respectively. The microbe had a distinct capsule and adhered to fiber, especially that which is slowly degraded, but was able to cause erosion and disorganization of the more easily digested cell walls, apparently by extracellular enzymes. Results indicated that more digestible cell walls could be partially degraded by enzymes disassociated from cellulolytic and noncellulolytic bacteria, and data were consistent with the hypothesis that the more slowly degraded plant walls required attachment. Microbial species as well as the cell wall architecture influenced the physical association with and digestion of plant fiber.