Differences Downunder: Methane, Macropodids and Metagenomics

About 16 per cent of Australia's greenhouse gas emissions are attributed to its agricultural sector, which mainly arise from the production and release of methane during rumen fermentation processes. In recent years, there has been a relatively intense focus on better understanding how rumen microbiology, nutrition and (or) animal genetics might be targeted and productively altered to reduce these emissions. Several promising leads with respect to reducing methane output without seriously compromising nutrient availability and animal performance have been identified; but they are still developmental in nature. Less attention has been directed towards the comparative study of herbivores thought to produce small amounts of methane during feed digestion. In that context, the digestive systems of the Australian macropodids (kangaroos and wallabies) have evolved to support the retention of a foregut microbiota that effectively converts plant biomass into nutrients for the host animal; and appears to do so with much less methane emitted. Over the last several years, we have been using methods referred to as metagenomics to characterize the microbiology found in the foregut of the Tammar wallaby (Macropus eugenii). Coupled with a reduced number of methanogenic archaea resident in the macropodid foregut compared to ruminants, metagenomics approaches have identified a suite of “new” bacteria that support feed digestion and fermentation schemes consistent with a low methane emitting phenotype. Metagenomics has also been used to isolate some of these new bacteria, which has provided some insights into what it might take to "reconstruct" the rumen microbiota to reduce methane emissions.