Abstract:

Ruminants like cows play an essential role in human agriculture. This is particularly important in Wisconsin, where milk and beef production are critical to the state economy. Ruminants, as dominant herbivores in North America, rely on microbial symbionts they harbour in their rumen to degrade plant biomass to ferment nutrients for their host. Due to the domestication efforts of humans, ruminants have become one of the most efficient plant biomass degrading and fermentation systems in nature. As a result, the cow has become a model system for biotechnological applications like the production of advanced biofuels. Moreover, the cow is now being revisited as a model organism for understanding human health, nutrition, and disease, given the development of recent tools like a genome sequence and its genetic tractability. Our own research is focused on characterizing and understanding the complex microbial community found within the rumen. We have been using a combination of 16S rRNA sequencing, whole-genome sequencing, and RNA-seq to characterize what specific microbes are found in the rumen and their potential functional roles. In particular, we are interested in how these microbes influence milk production and the mechanisms through which specific bacteria ferment plant biomass into short chain fatty acids. We show that there are differences in the ruminal microbial community between high and low milk producing cows, particularly in those bacteria that degrade cellulose. Whole-genome sequencing of two of these cellulolytic bacteria, Fibrobacter succinogenes and Rumincococus albus, reveal uniquely different approaches to cellulose degradation. Morever, transcript sequencing of R. albus on cellulose and cellobiose surprisingly revealed that the most highly expressed genes include the tryptophan biosynthesis operon. This has led us to determine that tryptophan is found in greater abundance in proteins associated with cellulose degradation, when compared to other genes in the genome. By applying these approaches we are beginning to understand not only how ruminal bacterial communities are associated with host production, but also how specific members of the community are contributing to the conversion of feed into host-usable nutrients.