Characteristics of dihydroxypyridine-degrading activity in the rumen bacterium Synergistes jonesii

Abstract

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 metabolite 2,3-dihydroxypyridine (2,3-DHP) can be temporarily or permanently lost. In this study we have determined the extension of bacterial growth and degradation of 2,3-DHP under different conditions. Degradation 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 following 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 conditions allowed optimal culture growth and degradation of 2,3-DHP. Maintenance of cultures in medium lacking 2,3-DHP for 2 months caused loss 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 activities in the degradation process were not detected. The results of this 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.