Effects of the Fusarium spp. mycotoxins fusaric acid and deoxynivalenol onthe growth of Ruminococcus albus and Methanobrevibacter ruminantium

The Fusarium spp. mycotoxins fusaric acid and deoxynivalenol (DON) were tes ted for antimicrobial activity against Ruminococcus albus and Methanobrevib acter ruminantium. The growth of both organisms was inhibited by fusaric ac id as low as 15 mu g/mL (84 mu M) but not by DON, at levels as high as 100 mu g/mL (338 mu M) No synergistic inhibitory effect was observed with DON p lus fusaric acid. Neither organism was able to adapt to the fusaric acid an d responses of each organism to the compound were different. The optical de nsity (OD) maximum for R. albus, but not for M. ruminantium, was diminished after 28 days incubation at concentrations of fusaric acid below 240 mu g/ mL. Inhibition of R. albus started before significant growth had occurred, while M. ruminantium doubled twice before the onset of inhibition. Response s to picolinic acid, an analog of fusaric acid, were also dramatically diff erent between the two microorganisms with M. ruminantium exhibiting a sever e lag followed by a complete recovery of growth, while R. albus was only sl ightly inhibited with no lag. These results suggest that the mechanism of f usaric acid inhibition is specific to each microorganism. This is the first demonstration of the common mycotoxin fusaric acid inhibiting the growth o f rumen bacteria.