Reduction of Heliotrine by A Rumen Microorganism

Abstract

SummaryA small Gram-negative coccus, which brings about the reductive fission of the hepatotoxic pyrrolizidine alkaloids, has been isolated from the rumen contents of Australian Merino sheep. The organism was cultured in a partially defined medium, without rumen fluid, but containing yeast extract. Strictly anaerobic conditions and the presence of carbon dioxide were essential for growth. With limiting quantities of yeast extract, growth was greatly stimulated by any of several carbohydrates or moderately stimulated by the alkaloid heliotrine plus hydrogen. The products of the reductive cleavage of heliotrine were heliotric acid and 7()(-hydroxy-l-methylene-8()(-pyrrolizidine. One mole of hydrogen reduced one mole of heliotrine to produce one mole each of the two products, accounting completely for the substrate consumed. Formate in stoichiometric quantities could replace molecular hydrogen as hydrogen donor in the reaction in which heliotrine acted as hydrogen acceptor. With [UCJformate as hydrogen donor 14CO. was evolved in stoichiometric amounts. The additional growth brought about by the degradation of heliotrine was proportional to the amount of heliotrine degraded, the organism appearing to derive energy from the reaction. Under strictly anaerobic conditions neither growth of the organism nor degradation of heliotrine was dependent on or stimulated by the presence of vitamin B12 in the medium. A method is described for the estimation of heliotrine.

Metabolism of toxic pyrrolizidine alkaloids from tansy ragwort (Senecio jacobaea) in ovine ruminal fluid under anaerobic conditions

“…Some studies have shown that the inhibition of methanogenesis with chloral hydrate or halogenated methanes actually enhanced heliotropine metabolism (24). These results suggest that PA-metabolizing organisms may compete with methanogens for reducing equivalents and that excess electron donors may augment the reductive fractions involved in PA dissimilation (23,24,31). The lack of PA activity in the denitrifying consortium may be due to the fact that either (i) denitrifying bacteria do not metabolize PA or (ii) the presence of nitrate inhibited the methanogenic consortium such that it could not metabolize the amended PA.…”

The Rumen Microbial Ecosystem

“…Two of the potentially toxic alkaloids, heliotrine and lasiocarpine, are reduced to non-toxic I-methylene and 7-hydroxy-lmethyl derivatives in the rumen (Lanigan and Smith, 1970;Russell and Smith, 1968;Dick et al, 1963). These compounds and their metabolites have many pathological effects on the liver, kidney and respiratory systems.…”

Hydrogenation of C18 Unsaturated Fatty Acids by Pure Cultures of a Rumen Micrococcus

“…Finally, these data together with the results of Russell and Smith (1968), who showed that the micrococcus caused a reductive fission of the pyrrolizidine alkaloids, tend to suggest that this bacterium may be non-specific in its hydrogenating capacity.…”

“…Cultures of the rumen miorooooous were isolated from rumen oontents by prooedures outlined previously (Russell and Smith 1968). The organism was inoubated for 24 hr at 38°C under anaerobio oonditions, in oarbon dioxide, in a medium desoribed by Russell and Smith (1968) oontaining [14C]fatty aoid (5 p.Ci, 0·1 p.mole) oomplexed to bovine serum albumin (Kessler, Demeny, and Sobotka 1967, method B).…”

“…The organism was inoubated for 24 hr at 38°C under anaerobio oonditions, in oarbon dioxide, in a medium desoribed by Russell and Smith (1968) oontaining [14C]fatty aoid (5 p.Ci, 0·1 p.mole) oomplexed to bovine serum albumin (Kessler, Demeny, and Sobotka 1967, method B). Vessels oontaining boiled suspensions of the miorooocous were prepared as controls for each acid.…”