Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/11/1995
Publication Date: N/A
Citation: Interpretive Summary: Cellulose is the chief component of forage fiber and its fermentation by bacteria in the rumen is a major contributor to the nutrition of cattle, sheep, and other ruminant animals. Because various species of cellulose- digesting bacteria have different effects on animal performance, we are interested in determining what factors allow individual species to predominate in the rumen. We studied the ability of the three most important species of cellulose-digesting bacteria to grow on each of the sugars that are normally produced during cellulose breakdown. We observed that the general pattern of transporting these sugars into and out of the cells is similar among the three species. However, by fitting the data to mathematical equations, we determined that one species will outcompete the other two species for most of these sugars, regardless of the amounts of these sugars that are available. The results provide a better understanding of how bacteria interact in the rumen.
Technical Abstract: The utilization of soluble cellodextrins was studied in three predominant ruminal cellulolytic bacteria (Fibrobacter succinogenes S85, Ruminococcus flavefaciens FD-1, and Ruminococcus albus 7). Cellodextrins were prepared from microcrystalline cellulose by partial hydrolysis with fuming hydrochloric acid, then separated by chromatography on a charcoal/Celite/stearic acid column to yield purified cellotriose (G3), cellotetraose (G4), cellopentaose (G5), and cellohexaose (G6). Batch culture experiments revealed that although these species can simultaneously hydrolyze cellodextrins and synthesize longer cellodextrins, growth of all three species followed Monod kinetics with respect to substrate concentration. All three ruminal bacteria grew as rapidly on most soluble cellodextrins as they did on glucose (G1) or cellobiose (G2). Statistical analysis revealed that the values of S0.5mmax (substrate concentration permitting growth at half maximum rate) significantly decreased with increasing cellodextrin chain length from G1 to G5 for R. albus 7, but not for R. flavefaciens FD-1. The maximum growth rate (mmax) and S0.5mmax also significantly decreased for F. succinogenes S85 grown on G5 or G6, while it was relatively constant for R. flavefaciens FD-1 and R. albus 7. The concentrations of longer chain cellodextrins needed to sustain growth of R. albus 7 at a given rate were lower than the concentrations needed of G1 or G2. Growth curves predicted from these Monod growth parameters showed that R. flavefaciens FD-1 possesses a greater capacity to compete for soluble cellodextrins than do the other two species.