Ruminal tryptophan-utilizing bacteria degrade ergovaline from tall fescue seed extract1

Abstract

The objectives of this study were to evaluate degradation of ergovaline in a tall fescue [ (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 ( = 3), straining, and differential centrifugation. Suspensions were dispensed into anaerobic tubes with added Trypticase with or without extract (∼10 μg kg 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 ( = 0.02). After 24 h, suspensions with added extract had 10-fold less HAB than controls ( = 0.04), but treatments were similar by 48 h ( = 1.00). However, after 24 h and 48 h, suspensions with extract had 10-fold more tryptophan-utilizing bacteria ( < 0.01) that were later isolated and identified by their 16S RNA gene sequence as . The isolates and other known rumen pure cultures ( JB1, B159, HD4, B, F, MD1, 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%; < 0.05). B14 was also able to degrade ergovaline but to a lesser capacity (12%; < 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.

Response of Beef Cattle Fecal Microbiota to Grazing on Toxic Tall Fescue

“…The Chloroflexi, Pirellulaceae, and Burkholderiales from the earthworm Eisenia fetida have members previously reported as being capable of degrading ergovaline, the main ergopeptine alkaloid in Eϩ tall fescue (77). Also, ex vivo ruminal sampling of tryptophan-utilizing bacteria demonstrated that Prevotellaceae are not heavily involved in ergovaline degradation, while Clostridiaceae strains degrade the majority of ergovaline (34). Although ergot alkaloids are quickly metabolized in the rumen (42), the changes identified here potentially reflect either ruminal ergot alkaloid selection pressure, as about 30% of OTUs are shared between the rumen, small intestine, and fecal samples (38), or, alternatively, ergot alkaloid bioavailability in the lower GI tract.…”

“…Clavine alkaloids, a major alkaloid type produced by E. coenophialum, and other ergot alkaloid precursors have previously been shown to exhibit antibiotic-like properties (32,33), indicating that they contribute to changes in the microbial populations of animals grazing toxic (Eϩ) tall fescue. Although some previous studies report on how specific ruminal bacteria and/or fermentation profiles shift after exposure to Eϩ fescue or ergot alkaloids (34)(35)(36), understanding the relationship between toxic tall fescue grazing and the fecal microbiota is important, as beef cattle fecal microbiota is dynamic and shifts in response to dietary and/or management strategy changes (12,37). This is particularly important for FT, as rotational grazing is a common management practice to minimize the impact of Eϩ grazing on animal productivity.…”

Beef cattle that respond differently to fescue toxicosis have distinct gastrointestinal tract microbiota

“…Another study has shown degradation of fescue alkaloids by rumen microorganisms without identifying the microbes responsible for the degradation [19]. Tryptophan-utilizing rumen bacteria can be capable of ergovaline degradation as shown for a Clostridium sporogenes, other Clostridium species [36], and a Prevotella bryantii isolate [18]. We did not find Clostridium sporogenes or Prevotella bryantii OTUs in our dataset; however, a number of (abundant) Clostridium OTUs such as OTUs 11 and 15 (both of them were more abundant in the high tolerant cattle at the BBCFL farm considering T*L) were detected.…”

“…The current literature published on the effect of toxic tall fescue effects on gastrointestinal (GI) microbiota is still limited. Most recently, Mote et al, 2019 [17] surveyed fecal bacterial communities of beef cattle during a FT challenge, and described possible connections between the abundance of certain bacterial phylotypes and the host response to FT. Other studies have suggested microbial communities within the cow rumen [18, 19], earthworm’s intestine [20], and soil [21] are able to degrade ergovaline. It is thus conceivable that the GI tract microbiota may be able to alleviate some of the impact of FT symptoms.…”

Effects of endophyte infected tall fescue seed and red clover isoflavones on rumen microbial populations, fiber fermentation, and volatile fatty acidsin vitro

“…Tryptophan is essential for ergovaline synthesis and formation of the ergoline ring structure. It has been hypothesized that bacterial species able to degrade tryptophan may also degrade ergovaline in the rumen [19, 20], proving essential for reducing the effects of tall fescue toxicosis. While a phylogenetically [21] and functionally diverse rumen microbiome is essential to the health and nutritional status of ruminant animals, feed additives or plant-secondary compounds, such as isoflavones, may further improve rumen functionality in tandem with microbial populations.…”