Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 10, 2006
Publication Date: January 18, 2007
Citation: Stevenson, D.M., Weimer, P.J. 2007. Dominance of Prevotella and low abundance of classical ruminal bacterial species in the bovine rumen revealed by relative quantification real-time PCR. Applied Microbiology and Biotechnology. 75:165-174. Interpretive Summary: It is known that in natural environments, only a small fraction of the total number of species has been isolated and characterized. The rumen of cattle, sheep, and goats contains a diverse population of different bacterial species, but only about 20 of these species have been studied in detail, and it is not known if these easily-studied species represent a major portion of the rumen bacteral population. We used a specialized gene amplification method to determine what fraction of the bacterial population in the rumen of two dairy cattle was represented by each of 13 of these commonly studied bacteria. In both cows, these species totalled only 5 to 7 per cent of the bacterial population, with several of the species representing less than 0.03 per cent of the total. However, it was determined that related but uncultured members of one group, called Prevotella, represented 40 to 60% of the total bacterial population. Isolation and characterization of these uncultured species should provide new information on the fermentation of feedstuffs by the rumen microbial population. This research represents the first assessment of the percentage contribution of the most widely studied individual species of bacteria in the rumen, and should guide future studies of relating rumen microbial diversity to animal performance.
Technical Abstract: Real time PCR was used with a relative quantification technique to quantify several species of bacteria within bovine ruminal samples. Primer pairs for 1 genus (Prevotella), 3 Prevotella species and 10 non-Prevotella species were designed and tested against pure cultures, and against ruminal samples from two lactating cows, each sampled 3 h after feeding on two successive days after dietary adaptation to mixed silage-grain ration. Abundance of each target taxon was calculated relative to total eubacterial content as determined with a previously designed domain-level eubacterial primer. Eubacterial populations in the rumen showed a clear predominance of members of the genus Prevotella, which comprised 42 to 60% of the bacterial population in the ruminal samples tested. However, only 2 to 4% of the bacterial population was represented by the classical ruminal Prevotella species P. bryantii, P. ruminicola, and P. brevis. Fibrobacter succinogenes, Ruminococcus flavefaciens, Selenomonas ruminantium, and Succinivibrio dextrinosolvens were each generally in the 0.5 to 1% range. Populations of Ruminobacter amylophilus and Eubacterium ruminantium were somewhat lower (0.1 to 0.2%), while Butyrivibrio fibrisolvens, Streptococcus bovis, Ruminococcus albus, Megasphaera elsdenii were even less abundant, each comprising <0.03% of the ruminal bacterial population. The data indicate that, despite the fact that only 5-15% of the total bacterial count in the rumen is typically culturable, a substantial fraction of the uncultured population represents a single bacterial genus.