Utilization of lactose by Fibrobcter succinogenes, a major cellulolytic bacterium in the rumen

Fibrobacter succinogenes, a major cellulolytic bacterium in the rumen, immediately colonizes the pre-ruminant calf rumen after birth (1-4) and becomes a dominant cellulolytic bacterium after weaning (5). While F. succinogenes vigorously degrades cellulose in the rumen, it seems that there is no or little of its substrate, cellulose, in the rumen of preweaned calves. Little attention, however, has been given to growth characteristics of F. succinogenes on lactose, the most abundant sugar in cow milk. Therefore, we evaluated the ability of F. succinogenes to utilize lactose, a main sugar of milk, with or without the presence of cellobiose. F. succinogenes S85 was grown on media containing 2.5 % lactose combined with 0 %–0.2 % cellobiose or a medium with 0.2% cellobiose but without lactose. The generation times on the 0.2 % cellobiose medium and the 2.5 % lactose medium were greatly different from each other. The bacterium showed rapid growth on cellobiose and diauxic growth on the lactose media containing 0.05 %–0.2 % cellobiose. Moreover, the production of β-galactosidase was low in the presence of 0.1 %–0.2 % cellobiose. These results indicate the possibility that F. succinogenes could colonize pre-ruminant calf rumen, consuming the lactose present in cow milk.