Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2000
Publication Date: N/A
Interpretive Summary: Cattle have bacteria that can digest the cellulose fraction of forages, but the digestibility is generally less than 50%, and rumen microbiologists and nutritionists have sought methods of improving cellulose digestion. Our research indicates that predominant cellulolytic ruminal bacteria already have adequate cellulose activity to digest cellulose a very rapid rate. Cellulose digestion only decreases when the surface of the cellulose is saturated with cells. Research on rumen cellulose digestion has the potential of identifying more efficient and cheaper rations for cattle.
Technical Abstract: Fibrobacter succinogenes S85 grew rapidly on cellobiose (0.31 h-1) and the rate of fermentation acid production was 0.68 h-1. Cultures that were provided with ball-milled cellulose initially produced fermentation acids and microbial protein as fast as those provided with cellobiose, but the cellulose digestion rate eventually declined. If the inoculum size was increased, the kinetics decayed from first to zero order (with respect to cells) even sooner, but in each case the rate declined after only 20 to 30% of the cellulose had been fermented. Congo red binding indicated that the cellulose surface area of individual cellulose particles was not decreasing, but the transition of ball-milled cellulose digestion corresponded with the appearance of unbound cells in the culture supernatant. When bound cells from partially digested cellulose were removed and the cellulose was re-incubated with a fresh inoculum, the initial fermentation rate increased and was as high as the one observed fo undigested cellulose and cellobiose. Based on these results, cellulose digestion by F. succinogenes S85 appears to be constrained by cellulose surface area rather than cellulase activity per se.