Dietary Supplementation of Usnic Acid, an Antimicrobial Compound in Lichens, Does Not Affect Rumen Bacterial Diversity or Density in Reindeer Trine Glad • Perry Barboza • Roderick I. Mackie • Andre ´-Denis G. Wright • Lorenzo Brusetti • Svein D. Mathiesen • Monica A. Sundset Received: 14 June 2013 / Accepted: 17 December 2013 / Published online: 9 February 2014 Ó Springer Science+Business Media New York 2014 Abstract Reindeer (Rangifer tarandus tarandus) may include large proportions of lichens in their winter diet. These dietary lichens are rich in phenolic secondary com- pounds, the most well-known being the antimicrobial usnic acid. Previous studies have shown that reindeer host rumen bacteria resistant to usnic acid and that usnic acid is quickly detoxified in their rumen. In the present study, reindeer (n = 3) were sampled before, during, and after usnic acid supplementation to determine the effect on their rumen microbial ecology. Ad libitum intake of usnic acid averaged up to 278 mg/kg body mass. Population densities of rumen bacteria and methanogenic archaea determined by real-time PCR, ranged from 1.36 9 10 9 to 11.8 9 10 9 and 9.0 9 10 5 to 1.35 9 10 8 cells/g wet weight, respec- tively, and the two populations did not change significantly during usnic acid supplementation (repeated measures ANOVA) or vary significantly between the rumen liquid and particle fraction (paired t test). Rumen bacterial com- munity structure determined by denaturing gradient gel electrophoresis did not change in response to intake of usnic acid. Firmicutes (38.7 %) and Bacteriodetes (27.4 %) were prevalent among the 16S rRNA gene sequences (n = 62) from the DGGE gels, but representa- tives of the phyla Verrucomicrobia (14.5 %) and Proteo- bacteria (1.6 %) were also detected. Rapid detoxification of the usnic acid or resistance to usnic acid may explain why the diversity of the dominant bacterial populations and the bacterial density in the reindeer rumen does not change during usnic acid supplementation. Introduction Usnic acid is a phenolic secondary compound used as a defense in lichens against bacteria, viruses, fungi, protozoa, insects, herbivores, and UV-radiation [2]. Reindeer utilize lichens as an important source of energy and other nutrients in winter, whereas toxic reactions toward lichens/usnic acid are reported in other ruminants such as sheep and elk [4, 15]. Ruminants rely on symbiotic anaerobic rumen microorganisms to digest their herbivorous diet, but rumen foregut fermentation also allows microbial detoxification [11]. Recent studies suggest that reindeer harbor rumen bacteria resistant to usnic acid [19] and that usnic acid and other phenolic compounds from lichens are rapidly Electronic supplementary material The online version of this article (doi:10.1007/s00284-014-0534-7) contains supplementary material, which is available to authorized users. T. Glad Á M. A. Sundset (&) Department of Arctic and Marine Biology, UiT The Arctic University of Norway, 9037 Tromsø, Norway e-mail: monica.a.sundset@uit.no P. Barboza Institute of Arctic Biology and Department of Biology and Wildlife, University of Alaska, Fairbanks, AK 99775, USA R. I. Mackie Department of Animal Sciences, University of Illinois, Urbana-Champaign, IL 61801, USA A.-D. G. Wright Department of Animal Science, University of Vermont, Burlington, VT 05405, USA L. Brusetti Faculty of Science and Technology, Free University of Bozen, 39100 Bolzano, Bolzano, Italy S. D. Mathiesen The Norwegian School of Veterinary Science, Sjøgata 39, 9000 Tromsø, Norway 123 Curr Microbiol (2014) 68:724–728 DOI 10.1007/s00284-014-0534-7