Abstract
Studies proved that addition of nitrate in rumen could lead to reduction of methane emission. The mechanism of this function was involved in the competition effect of nitrate on hydrogen consumption and the inhibitory effect of generated nitrite on methanogen proliferation. The present study investigated an alternative mechanism that denitrifying anaerobic methane oxidizing (DAMO) bacteria, DAMO archaea and anammox bacteria may co-exist in rumen, therefore, more methane can be oxidized when addition of nitrate. Ruminal batch culture model was used to test the effects of addition of 5 mM NaNO3, 4 mM NH4Cl, or both into the culture substrate on methane production, fermentation patterns, and population of methanogens, NC10 and anaerobic methanotrophic-2d (ANME-2d). Our results showed that NC10 in the ruminal culture was detected by polymerase chain reaction (PCR) when using NC10 special primer sets, and addition of nitrate reduced methane production and the relative proportions of methanogen, whereas increased the relative proportion of NC10. A combined addition of ammonia salt and nitrate did not show further inhibitory effect on methane production but accelerated nitrate removal. We did not detect DAMO archaea in ruminal culture by real-time PCR when using ANME-2d special primer sets. The present study may encourage researchers to pay more attention to methane oxidation performed by anaerobic methanotroph when studying the strategies of inhibiting ruminal methane emission.
Highlights
There are increasing evidences showing the significant inhibitory effect of nitrate on methane production in vitro and methane emission from the rumen in vivo (Zhou et al 2012; Patra and Yu 2014; Elzaiat et al 2014; Olijhoek et al 2016)
It had been reported that denitrifying anaerobic methane oxidation (DAMO) can be extremely accelerated in an anaerobic ammonium oxidation reactor because nitrite produced from nitrate reduction can be jointly reduced to nitrogen when ammonium is oxidized to nitrogen by anammox (Chen et al 2015)
The degradability of dry matter (DM) and acid detergent fiber (ADF) remained similar among the four treatments (P > 0.05), but neutral detergent fiber (NDF) degradability tended to be increased by addition of NaNO3 and by NaNO3 + NH4Cl (P < 0.1)
Summary
There are increasing evidences showing the significant inhibitory effect of nitrate on methane production in vitro and methane emission from the rumen in vivo (Zhou et al 2012; Patra and Yu 2014; Elzaiat et al 2014; Olijhoek et al 2016). ANME-2d and ‘M. oxyfera’ are two anaerobic methanotrophs and exist ubiquitously in the anaerobic environment abundant in methane, such as freshwater sludge, landfill and wastewater (Wu et al 2012). It had been reported that DAMO can be extremely accelerated in an anaerobic ammonium oxidation reactor because nitrite produced from nitrate reduction can be jointly reduced to nitrogen when ammonium is oxidized to nitrogen by anammox (Chen et al 2015). Nitrite produced from nitrate has two pathways to be converted to nitrogen in the mixture reactor of both DAMO and anaerobic ammonium oxidation when provided with nitrate, ammonium salt and methane simultaneously, and nitrite reduced from nitrate in the mixed reactor can be cleaned more rapidly than in the reactor with DAMO system alone. The combined pathways of DAMO and anaerobic ammonium oxidation in the sludge of freshwater were proposed by Haroon et al (2013)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
