Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 7/26/1995
Publication Date: N/A
Technical Abstract: Acquisition of tolerance to nitropropanol, the toxin contained in many Astragalus species, by ruminants depends on rates of ruminal nitropropanol metabolism. Our study was undertaken to define conditions which promote increased rates of nitropropanol metabolism and to identify microbes predominantly responsible for this detoxification. Rates of nitropropanol metabolism increased more than 4-fold when mixed ruminal populations were cultured consecutively in a medium containing 40% rumen fluid plus milkvetch forage or alfalfa forage with added nitropropanol but not in medium containing alfalfa and lacking nitropropanol. Rates of nitropropanol metabolism increased more rapidly when the medium also contained the protein component phytone. These results, along with most probable number estimates, suggest that nitropropanol metabolizing bacteria were enriched as a result of selective pressure in the presence of nitropropanol. Enriched populations used H2 as a reductant for nitropropanol metabolism. A nitropropanol metabolizing bacterium was isolated (strain NPOH1) from an enriched population and based on phenotypic and genotypic evidence, the organism appears to be a new species. Growth of strain NPOH1 was supported by nitropropanol, nitropropionic acid, nitrate, nitroethane, or miserotoxin. Sulfate, sulfite, or nitrite did not support growth. This strain's capacity for nitropropanol metabolism suggests that this organism may be an important nitropropanol detoxifying bacterium.