Edwards, Holly Danielle (2013-12). Ruminal Characterization of Lipase-producing Bacteria and Immunogenic Inhibition of Ruminal Lipase Activity: Effects on Rumen Microbial Ecology and Beef Quality. Doctoral Dissertation. Thesis uri icon


  • Ruminants saturate up to 80% of dietary unsaturated fatty acids through the microbial processes of lipolysis and biohydrogenation, promoting the accumulation of saturated fatty acids in their meat and milk. Studies were conducted to characterize and define contributors to the ruminal saturation of fatty acids and determine a method to minimize this process. The lipase-producing bacteria Anaerovibrio lipolyticus 5s, Butyrivibrio fibrisolvens 49, Propionibacterium avidum and Propionibacterium acnes were characterized in the presence and absence of glucose, and glycerol. Accumulations of free fatty acids (FFA) were compared between ruminal mixed cultures and each individual pure culture; these ruminal lipase-producing bacteria behaved differently from ruminal mixed cultures. A subsequent study characterized heat-treated ruminal mixed cultures that was selective for Clostridium in the presence and absence of glycerol. Ruminal mixed cultures behaved similarly to heat-treated cultures in the presence of glycerol, suggesting that Clostridium species may contribute appreciably to ruminal lipolysis. In an attempt to reduce ruminal lipolytic activity, antibodies were generated against A. lipolyticus 5s, B. fibrisolvens H17C, P. avidum, and P. acnes. Each antibody was tested against each bacterium in pure culture. An antibody generated against a purified Pseudomonas lipase also was tested against each pure culture to determine if an antibody against a purified lipase would be more effective than antibodies raised against whole cells. All five antibodies were effective at reducing lipolytic activity across all pure cultures of bacteria, with the anti-lipase antibody showing the greatest reduction. A subsequent study examined the four, whole cell antibodies against ruminal mixed cultures and demonstrated that whole cell antibodies also were effective at reducing lipolytic activity of ruminal mixed cultures. Uniquely, B. fibrisolvens participates in both lipolysis and biohydrogenation. Thus, anti-B. fibrisolvens H17C antibody also was examined to determine if it would be effective at reducing biohydrogenation against B. fibrisolvens H17C in pure culture and ruminal mixed cultures. The anti-B. fibrisolvens H17C antibody depressed biohydrogenation in pure and mixed cultures. These studies demonstrated that ruminal bacteria responsible for freeing and hydrogenating ruminal unsaturated fatty acids can be immunologically inhibited in vitro.

publication date

  • December 2013