Ruminal tryptophan-utilizing bacteria degrade ergovaline from tall fescue seed extract

The objectives of this study were to evaluate degradation of ergovaline in a tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] seed extract by rumen microbiota ex vivo and to identify specific bacteria capable of ergovaline degradation in vitro. Rumen cell suspensions were prepared by harvesting rumen fluid from fistulated wether goats (n = 3), straining, and differential centrifugation. Suspensions were dispensed into anaerobic tubes with added Trypticase with or without extract (~10 μg kg^-1 ergovaline). Suspensions were incubated for 48 h at 39°C. Samples were collected at 0, 24, and 48 h for ergovaline analysis and enumeration of hyper-ammonia producing (HAB) and tryptophan-utilizing bacteria. Ergovaline values were analyzed by repeated measures using the mixed procedure of SAS. Enumeration data were log transformed for statistical analysis. When suspensions were incubated with extract, 11 to 15% of ergovaline disappearance was observed over 48 h (P = 0.02). After 24 h, suspensions with added extract had 10-fold less HAB than controls (P = 0.04), but treatments were similar by 48 h (P = 1.00). However, after 24 h and 48 h, suspensions with extract had 10-fold more tryptophan-utilizing bacteria (P < 0.01) that were later isolated and identified by their 16S RNA gene sequence as Clostridium sporogenes. The isolates and other known rumen pure cultures (Streptococcus bovis JB1, Megasphaera elsdenii B159, Selenemonas ruminatium HD4, Prevotella bryantii B₁₄, Ruminococcus flavefaciens, Clostridium aminophilum F, Clostridium sporogenes MD1, Clostridium sticklandii SR) were evaluated for the ability to degrade ergovaline in vitro. Pure culture cell suspensions were incubated as described above and samples were taken at 0 and 48 h for ergovaline analysis. Data were analyzed using the ANOVA procedure of SAS. All HAB, including the isolates, tested degraded ergovaline (54 to 75%; P < 0.05). Prevotella bryantii B14 was also able to degrade ergovaline but to a lesser capacity (12%; P < 0.05), but all other bacteria tested did not degrade ergovaline. The results of this study indicate which rumen bacteria may play an important role in ergovaline degradation and that microbiological strategies for controlling their activity could have ramifications for fescue toxicosis and other forms of ergotism in ruminants.