Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 17, 2002
Publication Date: May 17, 2002
Citation: Weimer, P.J. 2002. The role of competition and amensalism in determining ruminal fibrolytic bacterial populations[abstract]. Joint Grasslands Society of South Africa. p. 1. Technical Abstract: Ruminococcus albus, R. flavefaciens, and Fibrobacter succinogenes are major cellulolytic bacterial species in the rumen. All three have a specialist nutrition based on the degradation of cellulose (and, to a lesser extent, xylan). A common strategy for cellulose degradation based on adherence to fiber, glycocalyx formation, and use of cell-bound cellulase enzymes allow these species to compete effectively for cellodextrins produced during hydrolysis, despite their modest growth rates. Population assessments using species-specific oligonucleotide probes revealed that cellobiose-limited chemostats co-inoculated with the three species yield monocultures of R. albus. By contrast, cellulose-limited chemostats yielded stable tricultues, usually predominated by R. albus, in which individual species exhibit niche specialization. The competitiveness of R. albus is enhanced by its production of at least two bacteriocins (36 kDa and 31 kDa), which we have purified and characterized. Noncellulolytic species (Selenomonas ruminantium or Streptococcus bovis) display variable effects on the outcome of competition among the cellulolytic species. Studies with lactating dairy cows fed diets of varying forage content and forage source (alfalfa silage vs. corn silage) reveal that, while populations of the three cellulolytic species are more similar within cows across diet than among cows within the same diet, R. albus is typically the most abundant of the three cellulolytic species. Moreover, the relative population size of R. albus displays a positive correlation with milk production (r2=0.58, df=14, P<0.05). This is the first demonstration, to our knowledge, of a significant relationship between a production parameter and the population size of a single ruminal microbial species.