Production of indolic compounds by rumen bacteria isolated from grazing ruminants

Aim: To screen rumen bacterial cultures and fresh ruminal isolates for indole and skatole production. Methods and Results: Culture collection strains and fresh bacterial isolates from rumen contents of sheep and dairy cows were screened for the production of indolic compounds. Clostridium aminophilum F-T, Peptostreptococcus ssp. S1, Fusobacterium necrophorum D4 produced indole and Clostridium sticklandii SR produced indoleacetic acid. Fresh isolates from sheep (TrE9262 and TrE7262) and dairy cows (152R-1a, 152R-1b, 152R-3 and 152R-4) produced indole, indolepropionic acid, tryptophol and skatole from the fermentation of tryptophan and indoleacetic acid. Glucose altered the indolic compounds produced in some, but not all, isolates. TrE7262 and 152R-4 were identified as Clostridium sporogenes and 152R-1b as a new Cl. aminophilum strain. Isolates TrE9262, 152R-1a and 152R-3 were not closely related to any described species but belong to Megasphaera, Prevotella and Actinomyces genera, respectively. Conclusions: Rumen bacteria that produced a range of indolic compounds were identified. Some isolates are distinct from the previously described bacteria and may represent novel species. Significance and Impact of the Study: These observations will contribute to understanding skatole and indole formation in the rumen and will lead to methods that control the formation of indolic compounds in pasture-grazed ruminants.