USE OF A NOVEL NITROTOXIN-METABOLIZING BACTERIUM TO REDUCE RUMINAL METHANE PRODUCTION

The production of methane by ruminal bacteria involves the conversion of potentially useful energy-rich substrates into a form that cannot b e used by the ruminant host. A possible strategy for reduction of rumi nal methane production is to divert the flow of reducing substrates aw ay from methanogenesis into alternative electron sinks. In this study we examine the potential for nitrocompounds to serve as such electron sinks. When 3-nitropropionate (5, 10, or 20 mM) was added to mixed pop ulations of ruminal microbes incubated under a H-2:CO2 (1:1) atmospher e and with added formate, up to 68% less methane was produced and redu ctant was directed towards increased propionate production. When nitra te (5, 10 or 20 mM) was added to such populations, methane production was inhibited to a lesser degree than with 3-nitropropionate. Addition of cells of a nitropropionate-metabolizing bacterium, strain NPOH1, t o mixed ruminal populations did not change the effect of 3-nitropropio nate on methane production, although more 3-nitropropionate was metabo lized. However the addition of cells of strain NPOH1, which also reduc es nitrate, to such populations drastically changed the effect of nitr ate on methane production. In the latter case, reductant was directed away from methane biosynthesis to the reduction of nitrate by strain N POH1, as evidenced by up to an 18-fold decrease in methane production. These results suggest that 3-nitropropionate and nitrate reduce metha ne production, by different mechanisms. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.