|Sharp, Richard - NORTHWESTERN UNIV|
|Stern, Marshall - UNIV MINNESOTA|
|Stahl, David - NORTHWESTERN UNIV|
Submitted to: Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 16, 2000
Publication Date: N/A
Interpretive Summary: Digestion in ruminant livestock (e.g., cattle, sheep, and goats) is dependent upon microorganisms that inhabit the forestomach, or rumen, of these animals. Because of this, efforts to improve the efficiency of digestion in agriculturally important species such as beef and dairy cattle focus on modifying the activity of the microorganisms of the rumen. To facilitate the study of the microbiology of the rumen, an in vitro fermenter system was evaluated as a model of the rumen. Chemical and physical measurements of fermenter operation closely matched those found in the rumen. Diagnostic, genetic (oligonucleotide) probes were used to obtain a picture of the microbial populations in the rumen and compared to those in model fermenters. The model rumen was able to maintain important microbial groups, both at the bottom (Fibrobacter) and top (Archaea) of the rumen community. Thus, we anticipate that this model rumen, by maintaining ga suitable simulation of rumen function, should provide results that increase understanding of complex interactions that occur among ruminal microorganisms. The model also provides control of experimental parameters so that methods to modify the activities of rumen microorganisms can be evaluated under laboratory conditions. The information that can be derived from investigations using this model will aid researchers in the development and testing of methods (e.g., feed additives) to manipulate rumen fermentation and improve the efficiency of ruminant livestock production.
Technical Abstract: A model rumen system, dual-flow continuous culture fermenters, was evaluated by two comparative criteria in two experiments using rRNA-targeted DNA probes to compare key microbial groups in samples. The initial experiment measured temporal changes in population structure during adaptation of ruminal microbial populations in fermenters through 240 h. The fermenter inoculum contained 34.9% Bacteria, 60.1% Eucarya, and 6.8% Archaea measured as a fraction of total small subunit (SSU) rRNA quantified using a universal probe. The cellulolytic bacterial genus Fibrobacter comprised 9.5% of total SSU rRNA in the inoculum. After 240 h of fermenter operation, average abundance was 80.9% Bacteria, 6.1% Eucarya, 5.1% Archaea and Fibrobacter genus accounted for 6.6% of total SSU rRNA. Divergence between ruminal and fermenter population structure was evaluated in the second experiment, and samples were classified as ruminal, inoculum, or fermenter (96, 120, 144, and 168 h of fermenter operation). Fermenter samples had higher relative abundances of Bacteria (84.5%) and Archaea (2.1%) and lower relative abundances of Eucarya (1.8%) than ruminal samples (averaging 48.0% Bacteria, 1.3% Archaea, and 61.5% Eucarya). The relative abundance of Fibrobacter was similar in all samples averaging 2.5%. Fermenters were able to maintain a core prokaryotic community structure similar to the native microbial community in the rumen. Although protozoa populations were lost, maintenance of Fibrobacter and archaeal populations indicated that the model system supported a functional community structure remarkably similar to the rumen. This model rumen system may serve as a suitable model for studies of ruminal microbial ecology.