Rumen Methanogenesis, Rumen Fermentation, and Microbial Community Response to Nitroethane, 2-Nitroethanol, and...

Nitroethane (NE), 2-nitroethanol (NEOH), and 2-nitro-1-propanol (NPOH) were comparatively examined to determine their inhibitory actions on rumen fermentation and methanogenesis in vitro. Fermentation characteristics, CH₄ and total gas production, and coenzyme contents were determined at 6, 12, 24, 48, and 72 h incubation time, and the populations of ruminal microbiota were analyzed by real-time PCR at 72 h incubation time. The addition of NE, NEOH, and NPOH slowed down in vitro rumen fermentation and reduced the proportion of molar CH₄ by 96.7%, 96.7%, and 41.7%, respectively (p < 0.01). The content of coenzymes F₄₂₀ and F₄₃₀ and the relative expression of the mcrA gene declined with the supplementation of NE, NEOH, and NPOH in comparison with the control (p < 0.01). The addition of NE, NEOH, and NPOH decreased total volatile fatty acids (VFAs) and acetate (p < 0.05), but had no effect on propionate concentration (p > 0.05). Real-time PCR results showed that the relative abundance of total methanogens, Methanobacteriales, Methanococcales, and Fibrobacter succinogenes were reduced by NE, NEOH, and NPOH (p < 0.05). In addition, the nitro-degradation rates in culture fluids were ranked as NEOH (-0.088) > NE (-0.069) > NPOH (-0.054). In brief, the results firstly provided evidence that NE, NEOH, and NPOH were able to decrease methanogen abundance and dramatically decrease mcrA gene expression and coenzyme F₄₂₀ and F₄₃₀ contents with different magnitudes to reduce ruminal CH₄ production.