Fibrolytic capabilities of ruminal bacterium Fibrobacter succinogenes in relation to its phylogenetic grouping

To characterize the fibrolytic function of Fibrobacter succinogenes strains in relation to their phylogenetic grouping, 32 strains were newly isolated from the rumen of sheep. All new strains were classified into phylogenetic groups 1 or 2 including a novel subgroup of group 2. Importantly, the majority of the strains belonging to group 1 were isolated from ruminally incubated hay. Although almost complete degradation of Avicel was observed among all strains, significantly lower digestibility of three different forages was recorded for strain HM2 of group 3 than for the strains of groups 1 and 2. In a comparison of all strains, two group 1 strains showed significantly higher digestibility of alfalfa and orchard grass hays, while two strains of the novel subgroup of group 2 had lower digestibility of orchard grass hay. Adhesion ability of each strain did not necessarily associate with the extent of digestibility. Maximum growth on Avicel was higher in group 1 than in group 2 strains, and two group 1 strains showed a shorter lag time. The results suggest that the ecological prominence of group 1 is due to a mixture of strains that are diverse in their fibrolytic capability making this group highly adaptable to any forage.