Evolving understanding of rumen methanogen ecophysiology

Abstract

Production of methane by methanogenic archaea, or methanogens, in the rumen of ruminants is a thermodynamic necessity for microbial conversion of feed to volatile fatty acids, which are essential nutrients for the animals. On the other hand, methane is a greenhouse gas and its production causes energy loss for the animal. Accordingly, there are ongoing efforts toward developing effective strategies for mitigating methane emissions from ruminant livestock that require a detailed understanding of the diversity and ecophysiology of rumen methanogens. Rumen methanogens evolved from free-living autotrophic ancestors through genome streamlining involving gene loss and acquisition. The process yielded an oligotrophic lifestyle, and metabolically efficient and ecologically adapted descendants. This specialization poses serious challenges to the efforts of obtaining axenic cultures of rumen methanogens, and consequently, the information on their physiological properties remains in most part inferred from those of their non-rumen representatives. This review presents the current knowledge of rumen methanogens and their metabolic contributions to enteric methane production. It also identifies the respective critical gaps that need to be filled for aiding the efforts to mitigate methane emission from livestock operations and at the same time increasing the productivity in this critical agriculture sector.

A reminder—peptidoglycan cell walls indeed occur in the archaeal domain, specifically in the members of Methanobacteria and Methanopyri classes

“…Thus, the versions of this polymer that one finds in the methanogens of the orders of Methanobacteriales and Methanopyrales are not pseudomurein as it does not contain muramic acid but simply another type of peptidoglycan, where glycan strands are connected by peptide linkages. The name archaeal peptidoglycan that has been used recently (Khairunisa et al , 2023 ) is appropriate in this context .…”

“…These advances would facilitate the development of better methods for mitigating methane emission from livestock, manipulating human gut metabolism/microbiome toward better health, and improving processes for methane production and biofuel from renewable resources. Methanobacteriales constitute a great portion of the bovine rumen and human gut methanogen population (Eckburg et al, 2005 ; Borrel et al, 2020 ; Khairunisa et al, 2023 ) and are attractive for industrial bioproduction of methane, as well as amino acids (Pappenreiter et al, 2019 ; Pfeifer et al, 2021 ; Taubner et al, 2023 ).…”