Effects of Nitrate Combined with Fumarate on Methanogenesis, Fermentation, and Cellulose Digestion by Mixed Ruminal Microbes in vitro

Abstract

Mixed ruminal microbes from the rumen of a goat were incubated with nitrate or nitrite in a growth medium containing starch and cellulose. The rate of nitrate reduction was 2.5-fold faster than the rate of nitrite reduction, which brought about the accumulation of nitrite.The increase in nitrate increased the peak nitrite concentration, and prolonged the time for nitrite to disappear. The addition of nitrate decreased methanogenesis partly by the consumption of electrons, but to a greater extent by the suppression of fermentation due to accumulated nitrite.The addition of fumarate increased the rate of nitrate reduction, and to a greater extent increased the rate of nitrite reduction, which alleviated the adverse effect of nitrite on fermentation and cellulose digestion. Consequently, the combination of fumarate and nitrate decreased methanogenesis without the suppression of fermentation or a decrease in propionate production.Animal Science Journal 70 (6): [471][472][473][474][475][476][477][478] 1999 Key words: Ruminal microbes, Fumarate, Nitrate, Methane.Methane production in the rumen implies an energy loss to the host animal.In addition, methane is supposed to contribute to the greenhouse effect, which may affect the global climate2).For these two reasons, it is important to decrease methanogenesis in the rumen.Methanogenesis can be decreased by decreasing the production of H2, which is the major substrate for methanogenesis in the rumen17). Theoretically, H2 production can be decreased by the enhancement of reactions that accept electrons other than H2 formation.Methanogenesis can also be decreased by increasing the utilization of H2 by ways other than methanogenesis.In the latter case, H2 is utilized as an electron donor, and accordingly an increase in H2 utilization implies an increase in electron-accepting reactions. Thus, the two cases are essentially similar in that the enhancement of reductive reactions is important.We reported previously that the addition of fumarate to an in vitro culture of mixed ruminal microbes decreased methanogenesis and increased the production of succinate and propionate1). These results indicate that fumarate is reduced to succinate, and then metabolized to propionate by the consumption of H2, or by the usage of reducing equivalents which are otherwise used to produce H2.Another important reductive reaction in the rumen is the serial reduction of nitrate and nitrite, which finally leads to ammonia production. Theoretically, an increase in nitrate reduction should bring about a decrease in methanogenesis. Many types of plant materials that are ingested by ruminants commonly contain nitrate, and the amount of nitrate-nitrogen is sometimes more than 0.5% on the basis of dry matter, or 37% on the basis of total nitrogen10). As much as 8% nitrate (as KNO3) has been reported to be present in corn stalks and turnip tops7). Nitrate is readily Corresponding: Tsuneo HINO (Fax:+81

Quantification of organic acids in ruminal in vitro batch culture fermentation supplemented with fumarate using a herb mix as a substrate

“…The findings concerning the effect of fumarate on methane, pH, and total and individual SCFA were consistent with other studies with different concentrations (from 8 to 30 mmol L −1 ) of fumarate with varied diets in vitro Iwamoto et al 1999). However, 30 mmol L −1 fumarate had an adverse effect on the IVDMD (30% decrease) of high-concentrate diets.…”

Microbial ecosystem and methanogenesis in ruminants

“…The thermodynamics of the conversion of nitrate into NH 3 is more favourable than the formation of methane and can effectively replace methanogenesis in the rumen if nitrate is available. However, in the rumen nitrate is rapidly reduced into nitrite and the rate of reduction of nitrite into NH 3 is slower (Iwamoto et al, 1999). Nitrite accumulation is undesirable as it is extremely toxic to the host animal.…”

Molecular characterization and transcriptional regulation of nitrate reductase in a ruminal bacterium, Selenomonas ruminantium

“…The rate of nitrate reduction per cell-N was not affected by fumarate. We previously reported that when fumarate was added to cultures of mixed ruminal microbes, the rate of nitrate reduction increased (Iwamoto et al, 1999). At that time, we postulated that nitrate-and fumaratereducing bacteria, such as S. ruminantium, V. parvula, and W. succinogenes grew by obtaining ATP via electron transport phosphorylation coupled with fumarate reduction.…”