|Allison, Milton - USDA-ARS (RETIRED)|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 7, 1996
Publication Date: N/A
Interpretive Summary: Nitrotoxins are plant chemicals present in many forages that are used throughout the world as feedstuffs for livestock. In the United States, poisonings caused by these toxins occur primarily in the West and result in loss of grazing cattle and sheep. Microbes within the rumen of cattle and sheep are known to degrade these nitrotoxins and animals can be protected from poisoning if these microbes are active. We conducted experiments to find ways to enhance degradation and to determine which microbes are responsible. We found that by gradually adapting cattle to nitrotoxins we could increase the level of toxin degradation and animal protection. A toxin-degrading bacteria was successfully isolated. This bacteria appears to be different from any known microbe. Our research indicates that this bacteria plays an important role in detoxifying nitrotoxins. This bacteria has the potential to be used to protect animals from nitrotoxin poisoning. Lower economic losses to ranchers means that ultimately the savings are passed on to consumers.
Technical Abstract: Astragalus species (Fabaceae) containing the toxins nitropropanol or nitropropionic acid are poisonous and cause considerable loss of productivity in livestock. Ruminants can acquire tolerance to the nitro-toxins when rates of nitropropanol metabolism by ruminal microbes increase; however, the specific microbes responsible for detoxification are not known. We report here the enrichment and isolation of a ruminal bacterium capable of metabolizing substrate levels (more than 3 mM) of nitropropanol. Our evidence from most probable number estimates indicated that before enrichment, nitropropanol metabolizing bacteria were present at approximately 10**4 organisms/ml in bovine ruminal fluid collected from a cow maintained on an alfalfa:corn diet (with no known exposure to nitropropanol). This number was increased 10,000-fold during enrichment, whereas rates of nitropropanol metabolism were increased 8-fold. Our isolation of strain NPOH1 was obtained from such an enriched population. Based on our results, phytone and H2 appeared to be important for the growth of the nitropropanol metabolizing bacteria. Nitropropanol, nitropropionic acid, or nitrate can be used as electron acceptors by the bacterium.