Rumen methanogens and mitigation of methane emission by anti-methanogenic compounds and substances

Abstract

Methanogenic archaea reside primarily in the rumen and the lower segments of the intestines of ruminants, where they utilize the reducing equivalents derived from rumen fermentation to reduce carbon dioxide, formic acid, or methylamines to methane (CH₄). Research on methanogens in the rumen has attracted great interest in the last decade because CH₄ emission from ruminants contributes to global greenhouse gas emission and represents a loss of feed energy. Some DNA-based phylogenetic studies have depicted a diverse and dynamic community of methanogens in the rumen. In the past decade, researchers have focused on elucidating the underpinning that determines and affects the diversity, composition, structure, and dynamics of methanogen community of the rumen. Concurrently, many researchers have attempted to develop and evaluate interventions to mitigate enteric CH₄ emission. Although much work has been done using plant secondary metabolites, other approaches such as using nitrate and 3-nitrooxy propanol have also yielded promising results. Most of these antimethanogenic compounds or substances often show inconsistent results among studies and also lead to adverse effects on feed intake and digestion and other aspects of rumen fermentation when fed at doses high enough to achieve effective mitigation. This review provides a brief overview of the rumen methanogens and then an appraisal of most of the antimethanogenic compounds and substances that have been evaluated both in vitro and in vivo. Knowledge gaps and future research needs are also discussed with a focus on methanogens and methane mitigation.

Keywords: Anti-methanogenic compound; Methanogen; Mitigation; Protozoa; Rumen.

Fig. 1

A taxonomic tree showing rumen archaea. A total of 8623 sequences of rumen archaea were retrieved from the RDP Release 11 (Update 3). Information on sequences recovered from isolates was indicated in parentheses. Cr, Crenarchaeota; Eu, Euryarchaeota; Tha, Thaumarchaeota; Mb, Methanobacteria; Mm, Methanomicrobia; Mp, Methanopyri; The, Thermoplasmata

Fig. 2

Principal coordinates analysis (PCoA) of 16S rRNA PAM gene sequences obtained from two different studies (a) and different rumen ciliate species (b). C = Chagan et al. [28]; T = Tokura et al. [29]; I = Irbis & Ushida [30]; R = Regensbogenova et al. [31]. Cil = Ciliate fraction; Dip = Diplodinium; Ento = Entodinium; Eud = Eudiplodinium; Iso = Isotricha; Meta = Metadinium; Poly = Polyplastron; Oph = Ophryoscolex. Analyses were conducted using 47 sequences recovered from washing single or several ciliate cells based on the Jukes-Cantor model [177] using MEGA6 [178]