Inhibiting Methanogenesis Stimulated de novo Synthesis of Microbial Amino Acids in Mixed Rumen Batch Cultures Growing on Starch but Not on Cellulose.

Emilio M Ungerfeld,Emilio D Martínez,M Fernanda Aedo,Marcelo Saldivia,Natalie L Urrutia,Camila Muñoz

doi:10.3390/microorganisms8060799

Emilio M Ungerfeld, Emilio D Martínez + Show 4 more

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https://doi.org/10.3390/microorganisms8060799

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Abstract

Ameliorating methane (CH4) emissions from ruminants would have environmental benefits, but it is necessary to redirect metabolic hydrogen ([H]) toward useful sinks to also benefit animal productivity. We hypothesized that inhibiting rumen methanogenesis would increase de novo synthesis of microbial amino acids (AA) as an alternative [H] sink if sufficient energy and carbon are provided. We examined the effects of inhibiting methanogenesis with 9, 10-anthraquione (AQ) on mixed rumen batch cultures growing on cellulose or starch as sources of energy and carbon contrasting in fermentability, with ammonium (NH4+) or trypticase (Try) as nitrogen (N) sources. Inhibiting methanogenesis with AQ inhibited digestion with cellulose but not with starch, and decreased propionate and increased butyrate molar percentages with both substrates. Inhibiting methanogenesis with 9, 10-anthraquinone increased de novo synthesis of microbial AA with starch but not with cellulose. The decrease in the recovery of [H] caused by the inhibition of methanogenesis was more moderate with starch due to an enhancement of butyrate and AA as [H] sinks. There may be an opportunity to simultaneously decrease the emissions of CH4 and N with some ruminant diets and replace plant protein supplements with less expensive non-protein nitrogen sources such as urea.

Highlights

The abatement of methane (CH4) emissions is key to achieve a rapid mitigation in the emission of greenhouse gases from anthropogenic origin, because CH4, having a shorter atmospheric lifetime than CO2, has an 85-fold Global Warming Potential within a 20-yr timeframe [1,2]
We found that the decrease in the recovery of [2H] when methanogenesis was inhibited was less pronounced with starch compared to cellulose, explained largely by greater recovery of [2H] in butyrate production and amino acids (AA) synthesis
Nitrogen source was included as a factor in the experimental arrangement of treatments to allow distinguishing between the net de Microorganisms 2020, 8, 799 novo synthesis of microbial AA from NH4+ incorporation (NH4+ treatment) and the sum of de novo synthesis of AA plus the uptake of preformed AA supplied by Try to the medium (Try treatment)

Summary

Introduction

The abatement of methane (CH4) emissions is key to achieve a rapid mitigation in the emission of greenhouse gases from anthropogenic origin, because CH4, having a shorter atmospheric lifetime than CO2, has an 85-fold Global Warming Potential within a 20-yr timeframe [1,2]. Enteric CH4 formed in the rumen of domestic ruminants is a major source of anthropogenic CH4 [3]. Decreasing rumen methanogenesis has become an important target to achieve a short term decrease in the emissions of anthropogenic greenhouse gases. Producers are unlikely to increase the costs of animal feed unless inhibiting rumen methanogenesis can enhance animal productivity. The release to the atmosphere of CH4 produced in the rumen is an energy inefficiency, and decreasing energy losses such as CH4 is a potential means to increase ruminant productivity [5,6]. The potential of translating energy saved in CH4 not formed in the rumen into greater animal productivity has not been consistently achieved, with benefits observed in some, but not in all, studies [7]

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