Effects of pH and Electron Donors on Nitrate and Nitrite Reduction in Ruminal Microbiota

Abstract

Factors affecting nitrate and nitrite reduction in the rumen were examined. Nitrate and nitrite reduction by mixed microbes harvested from the goat rumen was increased by feeding a high-roughage diet, which contained a much higher amount of nitrate than concentrate . The activities of nitrate reductase and nitrite reductase per bacterial mass appeared to be increased by feeding a high-nitrate diet, suggesting that these enzymes are induced by substrates.Nitrate and nitrite reduction was confirmed to be the fastest at neutral pH and affected by electron supply . The supplementation of electron donors, such as formate, H2, and lactate, stimulated nitrate and nitrite reduction , especially nitrite reduction, which decreased nitrite accumulation . As a result, addition of formate or lactate in the presence of nitrate alleviated the inhibitory effect of nitrite on fermentation , and greatly reduced methanogenesis.

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

“…Reaction was initiated by adding an enzyme sample at room temperature, and terminated by vortexing vigorously for 3 min in the air. The reaction mixture was centrifuged (18,000ϫg, 10 min, 4°C), and the supernatant was subjected to the determination of nitrite by the method described by Iwamoto et al (2001a). Cellular nitrogen (cell-N) was determined by the Kjeldahl method as described previously (Iwamoto et al, 2001b).…”

Molecular Characterization of CcpA and Involvement of This Protein in Transcriptional Regulation of Lactate Dehydrogenase and Pyruvate Formate-Lyase in the Ruminal Bacterium Streptococcus bovis

“…Furthermore, lactate serves as an electron donor for sequential nitrate reduction to ammonia (20,21), which also leads to a decrease in ruminal methanogenesis (19,20). In addition, stimulation of nitrite reduction by lactate may alleviate toxic effects of nitrite (20,21). Hence, it may be beneficial to modulate lactate production so that lactate is always present at appropriate levels in the rumen.…”

“…This is particularly important, because methanogenesis represents an energy loss for ruminants and, in addition, methane contributes to the greenhouse effect. Furthermore, lactate serves as an electron donor for sequential nitrate reduction to ammonia (20,21), which also leads to a decrease in ruminal methanogenesis (19,20). In addition, stimulation of nitrite reduction by lactate may alleviate toxic effects of nitrite (20,21).…”

Molecular Characterization and Expression of Pyruvate Formate-Lyase-Activating Enzyme in a Ruminal Bacterium, Streptococcus bovis

“…Lactate is utilized more effectively for nitrite reduction to ammonia than for nitrate reduction to nitrite (13). Since nitrite reduction is the limiting step in sequential nitrate reduction (8) and nitrite is toxic and mutagenic, stimulation of nitrite reduction is particularly important.…”

“…Furthermore, lactate serves as an electron donor for sequential nitrate reduction to ammonia (13). Lactate is utilized more effectively for nitrite reduction to ammonia than for nitrate reduction to nitrite (13).…”