Methanotrophs from natural ecosystems as biocontrol agents for ruminant methane emissions

Abstract

In ruminant cattle, the anaerobic fermentation of ingested plant biomass results in the production of methane (CH4). This CH4 is subsequently eructated to the environment, where it acts as a potent greenhouse gas and is one of the leading sources of anthropogenic CH4 in Australia. Methane oxidising microorganisms are an important environmental sink for CH4; however the possibility that methanotrophs are native to the rumen has received little attention. This project aimed to characterise methanotrophs from a range of environments, and to subsequently determine the metabolic activity of these microorganisms under in vitro rumen-like conditions. This study is the first to characterise rumen methanotrophs using molecular methodology. Using a combination of denaturing gradient gel electrophoresis and phylogenetic analysis, it was found that simple communities of Proteobacterial methanotrophs can be native residents of the rumen microbial community in grain-fed Bos indicus steers. A putative methanotrophic Gamma-proteobacterial Methylobacter species was also enriched from grain-fed whole rumen contents using novel techniques. However, the activity of these organisms in situ remains to be fully understood. Furthermore, the possibility that a grain-based dietary affect influences the diversity and activity of methanotrophs in situ is intriguing. Future work to address these questions is necessary to evaluate the potential for methanotrophs to act as biocontrol agents for ruminant CH4 emissions.​