Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2008
Publication Date: 6/5/2008
Citation: Anderson, R.C., Krueger, N.A., Stanton, T.B., Callaway, T.R., Edrington, T.S., Harvey, R.B., Jung, Y.S., Nisbet, D.J. 2008. Effects of select nitrocompounds on in vitro ruminal fermentation during conditions of limiting or excess added reductant. Bioresource Technology. 99(18)8655-8661.
Interpretive Summary: Cattle and sheep contain a large population of many different kinds of bacteria within their digestive tract and these bacteria help in the digestion of the feeds they eat. Some of these bacteria produce methane as an end product of the digestive process and this is considered to be economically wasteful for cattle and sheep farmers because it can result in as much as 12% of energy in the food the animal eats being lost from the animal. Methane is also a greenhouse gas and cattle and sheep contribute nearly 20% of the United States’ total annual emission to the atmosphere. We had discovered in earlier studies that certain chemical nitrocompounds significantly inhibit methane production by cattle and sheep but little is known why this occurs. Therefore, we conducted experiments to try and uncover the mode of action of these nitrocompounds. We found that the nitrocompounds significant inhibit two critically important enzymes involved in methane production by bacteria in the cattle gut. The names of these enzymes are formate dehydrogenase and hydrogenase. For instance, when these nitrocompounds were added to mixtures of gut bacteria the chemical reactions carried out by these enzymes were inhibited to such an extent that methane production was reduced by as much as 97%. These results provide much needed information as to how the nitrocompounds work biochemically and will help scientists and producers develop effective strategies to reduce the economic and environmental costs of methane emission from cattle and sheep. Ultimately, these results will benefit the American consumer by helping farmers and ranchers produce safe and wholesome products at less cost.
Technical Abstract: Ruminal methane (CH4) production results in losses of up to 12% of gross energy intake and contributes nearly 20% of the United States’ annual emission of this greenhouse gas. We report the effects of 2-nitro-1-propanol (NPOH), 3-nitro-1-propionic acid (NPA), nitroethane (NE) and 2-nitroethanol (NEOH) on ruminal fermentation after 22 h in vitro incubation (39 deg C) under conditions of limiting or excess added hydrogen (H2), formate or both (each at 60 umol ml**-1). In incubations containing no added reductant, CH4-production was inhibited (P < 0.05) 41% by NPOH and >97% by NPA, NE and NEOH when compared to non-treated controls (4.2 ± 0.2 umol ml**-1) and H2 did not accumulate. With formate as sole added reductant, nitro-treatment reduced (P < 0.05) CH4 production >99% and decreased (P < 0.05) formate catabolizism >42% from that by non-treated controls (13.6 ± 0.9 and 59.5 ± 0.02 umol ml**-1, respectively). Accumulation of H2 was only slightly increased from that of controls (0.1 ± 0.02 umol ml**-1). Nitro-treatment decreased (P < 0.05) CH4 production 57 to 98% from that of controls (11.6 ± 0.9 and 8.4 ± 1.3 umol ml**-1) when reductant was supplied as H2 or formate plus H2. Except for incubations containing added NPA, formate catabolism was decreased 42% from that in controls (>59 umol ml**-1) by nitro-treatment with both formate and H2, with some formate likely consumed for reduction of >50% added NPA. Greater than 97% of the added H2 was catabolized within controls whereas >84% was catabolized in nitro-treated incubations. Accumulations of acetate, propionate and butyrate were unaffected by nitro-treatment irregardless of reductant; however, all nitrocompounds reduced (P < 0.05) isovalerate and all except NPA reduced (P < 0.05) ammonia when incubated in presence of added formate. Effects under other conditions and on isobutyrate and valerate were more variable. These results suggest that nitro-treatment inhibited formate dehydrogenase/formate hydrogen lyase and hydrogenase activity.