New insights into the enteric methane production based on the archaeal genome map of ruminant gastrointestinal tract

Abstract

Introduction

As one of the important components of ruminant gastrointestinal tract (GIT) microbiome, archaea are involved in many biological processes, especially methanogenesis. However, the diversity and individual metabolic characteristics of archaea in this habitat remain largely understudied, partly due to the lack of a unified reference genome catalog.

Objectives

This study aimed to construct a unified genome map for taxonomic and functional exploration of ruminant GIT archaea in the future.

Methods

We collected archaeal genomes from public sources and new data of this study. We performed phylogenetic analysis, functional genomics analyses, prophages identification based on the genomes. Using collected genomes as a reference, we conducted metagenomic and metatranscriptomic analyses on rumen fluid samples from 18 dairy cows with different methane (CH₄) production.

Results

We constructed the ruminant GIT archaeal genomes (RGAG) by compiling 405 strain-level (160 species) non-redundant archaeal genomes from more than 10 ruminant species. The functional heterogeneity and methanogenic structure within RGAG was investigated. RGAG possessed 1,124 (99.5 %) unknown microbial biosynthetic gene clusters. A survey of RGAG-borne prophages identified 63 prophages with 122 host-beneficial genes and 18 auxiliary metabolic genes (AMGs). The pipeline for both metagenomics and metatranscriptomics generated in the study revealed the roles of archaeal genomes under-assessed in general analyses of muti-omics. The highly expressed genus Methanosphaera was negatively correlated with CH₄ production.

Conclusion

A unified genome map of ruminant GIT archaea is constructed in the study. Functional genomics indicates that the multifaceted functions of RGAG remains undiscovered. Multi-omics analyses reveals the advantages of metatranscriptomics over metagenomics in studying rumen archaeal communities. Differences in rumen archaeal community structure among cattle with different CH₄ production may reflect the balance between rumen hydrogen production and methanogenesis. Our work provides new understanding of archaeal functions in the ruminant GIT and potential targets for future CH₄ reduction.