N-225. Functional Microbial Ecology in the Bovine Rumen

E. Hernandez-Sanabria, M. Li, M. Gaenzle, L. L. Guan;
Univ. of Alberta, Edmonton, AB, CANADA.

Background: The rumen is a complex ecosystem consisting of numerous types of microorganisms, with population as high as 10 billion cells per gram of ruminal contents. However, the limitations in traditional isolation and culture of anaerobic ruminal isolates prevent full understanding of the functions of rumen microbes. Culture-independent methodology such as PCR-denaturing gradient gel electrophoresis (PCR-DGGE) has been found to be a powerful tool for characterization of microbiota. This study aims to correlate microbial community to metabolites levels. Methods: Rumen fluid was collected from sixty 10-month old steers, respectively, which were fed with the same high forage diet and raised in the same feedlot. Total DNA was extracted from the rumen fluid and used as a template to amplify bacterial partial 16S rRNA gene products with universal bacterial primers for PCR-DGGE analysis. The obtained profiles were compared using Bionumerics software to identify bacterial diversity in each individual and its association to rumen metabolites. Volatile fatty acids (VFA) concentration in the rumen was determined by GC analysis and the ammonia concentration was measured using a commercial kit. Results: Complex band patterns were observed in the DGGE profiles of individual animal, representing the numerically dominant species of the bacterial population. VFA profiling showed that acetate (p < 0.1), isobutyrate (p < 0.05) and isovalerate (p < 0.1), were significantly correlated with ammonia concentration. The acetate is a product of fermentation of structural carbohydrates by cellulolytic bacteria. Isobutyrate/ isovalerate are known to be involved in amino acid metabolisms and essential for the growth of cellulolytic bacteria, suggesting potential linkage of ruminal microbial community to particular metabolites in the rumen. Conclusion: This is the first study linking microbial diversity identified by culture-independent techniques to the carbohydrate and amino acid metabolites in the bovine rumen.