Reindeer Rumens Report
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Research Project on Bacterial Detoxification of Lichen Acids in the Reindeer Rumen

By Prof. Monica A Sundset, Department of Arctic BiologyUniversity of Tromsø, Norway


Ruminants like reindeer depend on symbiotic rumen microorganisms to digest the plants that they eat, resulting in microbial protein and short chain fatty acids that can be absorbed and utilized by the animal. The rumen microbial ecosystem contains bacteria, ciliates and anaerobic fungi and is characterised by its high population density, wide diversity and complexity of interactions. Foregut fermentation in the rumen may have evolved not only as a mechanism to degrade plant cell-wall carbohydrates but also to enable detoxification and thus protection from plant-secondary metabolites. A recent publication by Sundset et al. (2007) (propose that the coevolution of the reindeer rumen with a heterogenous diet of arctic plants has resulted in a unique rumen microbial ecosystem, and the majority of the bacteria (92.5%) described by molecular cultivation-independent methods were found to be previously unknown (novel).


Reindeer are unique because they are able to eat and utilize various lichens as a source of energy and nutrients. Lichens contain a range of secondary metabolites including the usnic acid that protects against herbivory and is generally toxic to most animals including other ruminants. For instance, a few years ago 295 elk died from eating lichens, and ingestion of usnic acid used to aid weight loss in humans were found cause liver failure (requiring liver transplant)complicated by cerebral edema (link to ). Digestibility trials indicate that usnic acid increase the digestion in reindeer, suggesting that reindeer harbour rumen microbes capable of metabolizing this toxic secondary compound. In a research project funded by the Reindeer Husbandry Research Fund (RUF), Norway at Department of Arctic Biology,  University of  Tromsø researchers are now trying to identify bacterial members of this ecosystem responsible for detoxification of the usnic acid.





Student Alexandra Kohn screens our reindeer rumen bacterial culture collection to identify isolates resistant to usnic acid. This bitter, yellow, polyphenolic acid is thought to protect the lichen from sunlight exposure and deter grazing animals with its bitter taste. It was first described in 1844, and has become the most extensively studied lichen metabolite and one of the few that is commercially available. Photo: Monica A Sundset.




The usnic acid is a well known antibiotic agent. This photo shows the inhibition of bacterial growth as zones of clearing around paper discs with usnic acid added at different concentrations. Photo: Monica A Sundset.





Lichens have been shown to accumulate usnic acids when exposed to increased UV-radiation, and predictions indicate that UV-radiation will in fact increase in years to come. It is therefore important to study mechanisms of modification and tolerance to usnic acid that result in detoxification by the symbiotic rumen bacteria in reindeer. Photo: Monica A Sundset.


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