The role of microbes in rumen lipolysis and biohydrogenation and their manipulation

Abstract

Despite the fact that the ruminant diet is rich in polyunsaturated fatty acids (PUFA), ruminant products -meat, milk and dairy -contain mainly saturated fatty acids (SFA) because of bacterial lipolysis and subsequent biohydrogenation of ingested PUFA in the rumen. The link between SFA consumption by man and coronary heart disease is well established. In contrast, ruminant products also contain fatty acids that are known to be beneficial to human health, namely conjugated linoleic acids (CLAs). The aims of research in this field have been to understand the microbial ecology of lipolysis and biohydrogenation and to find ways of manipulating ruminal microbes to increase the flow of PUFA and CLA from the rumen into meat and milk. This review describes our present understanding of the microbial ecology of ruminal lipid metabolism, including some apparently anomalous and paradoxical observations, and the status of how the metabolism may be manipulated and the possible consequential effects on other aspects of ruminal digestion. Intuitively, it may appear that inhibiting the ruminal lipase would cause more dietary PUFA to reach the mammary gland. However, lipolysis releases the non-esterified fatty acids that form the substrates for biohydrogenation, but which can, if they accumulate, inhibit the whole process. Thus, increasing lipase activity could be beneficial if the increased release of non-esterified PUFA inhibited the metabolism of CLA. Rumen ciliate protozoa do not carry out biohydrogenation, yet protozoal lipids are much more highly enriched in CLA than bacterial lipids. How could this happen if protozoa do not metabolise PUFA? The answer seems to lie in the ingestion of plant organelles, particularly chloroplasts, and the partial metabolism of the fatty acids by contaminating bacteria. Bacteria related to Butyrivibrio fibrisolvens are by far the most active and numerous biohydrogenating bacteria isolated from the rumen. But do we misunderstand the role of different bacterial species in biohydrogenation because there are uncultivated species that we need to understand and include in the analysis? Manipulation methods include dietary vegetable and fish oils and plant-derived chemicals. Their usefulness, efficacy and possible effects on fatty acid metabolism and on ruminal microorganisms and other areas of their metabolism are described, and areas of opportunity identified.Keywords: biohydrogenation, cellulose digestion, lipase, microbial protein synthesis, rumen ImplicationsThe conversion of dietary polyunsaturated fatty acids (PUFA) to saturated fatty acids (SFA) by ruminants has important health implications for human health. However, ruminant products are also rich in conjugated linoleic acids (CLAs), which have positive implications for human health. The transformation from PUFA to SFA (biohydrogenation), and the formation of CLA, is catalysed by the microorganisms that inhabit the rumen. Researchers are finding ways to manipulate biohydrogenation, by identifying the microorganisms responsible and by finding...

Quantitative analysis of ruminal bacterial populations involved in lipid metabolism in dairy cows fed different vegetable oils

“…For example, PUFA are more toxic for biohydrogenating bacteria (e.g. B. fibrisolvens) than monoenoic FA (Lourenco et al, 2010). Consequently, SO, which is a rich source of C18:2 cis n-6, is expected to have strong negative effects on ruminal bacterial populations; this agrees in part with the reduction of total bacteria (copies of 16S rDNA/ml) caused by SO treatment observed in this study.…”

Microbial production of conjugated linoleic and linolenic acids in fermented foods: Technological bottlenecks

“…Many possible biological activities have been ascribed to CLA and CLNA isomers, including positive effects on body composition, cancer, cardiovascular disease, diabetes, bone health and the immune system [1][2][3]. CLA and CLNA isomers occur naturally in several food products, mainly meat and dairy products from ruminants, since they are formed during ruminal biohydrogenation [4]. The CLA content in beef products and dairy foods varies from 3 to 10 mg/g fat [5,6], respectively.…”

Protein Fractionation and Utilization of Soybean and Redbean as Affected by Different Drying Temperature

“…Fat does not contribute to gas production because rumen microbes do not ferment longchain fatty acids. Triglyceride, the main form of fat, undergoes lipolysis in the rumen to result glycerol and fatty acids by the action of Anaerovibrio lipolytica and Butyrivibrio fibrisolvens that release lipolytic enzymes (Lourenco et al, 2010). Unsaturated fatty acids are biohydrogenated to produce various fatty acid isomers with higher saturation degree, but their carbon chains are not degraded and metabolized by rumen microbes (Buccioni et al, 2012).…”