CHARACTERISTICS OF DIHYDROXYPYRIDINE-DEGRADING ACTIVITY IN THE RUMEN BACTERIUM SYNERGISTES JONESII

There are rumen bacteria capable of degrading toxic dihydroxypyridine compounds derived from mimosine, a non-protein amino acid found in the toxic legume Leucaena leucocephala. Activity of degradation of the me tabolite 2,3-dihydroxypyridine (2,3-DHP) can be temporarily or permane ntly lost. In this study we have determined the extension of bacterial growth and degradation of 2,3-DHP under different conditions. Degrada tion of 2,3-DHP started once cultures reached late exponential phase, and complete degradation was achieved in 3 days. If additional 2,3-DHP was added to the cultures, complete degradation occurred within the f ollowing 12 h. Degradation of the 2,3-DHP occurred in medium (saline) containing either pyruvate, rumen fluid or arginine but not in saline supplemented with volatile fatty acids or vitamins. Strict anaerobic c onditions allowed optimal culture growth and degradation of 2,3-DHP. M aintenance of cultures in medium lacking 2,3-DHP for 2 months caused l oss of ability to degrade the compound. When cultured again in medium containing 2,3-DHP, cultures grew normally but only regained activity after a time lag of 4 weeks. Plasmids that could carry fundamental act ivities in the degradation process were not detected. The results of t his work are relevant to the conditions of in vitro screening for 2,3- DHP degradation activity in rumen contents and manipulation of 2,3-DHP degrading cultures in the laboratory.