Delving into rumen 'soup': identifying targets to mitigate methane
What's really in a rumen? It's probably something that most people haven't given much thought to. However, in the search for methods and technologies to mitigate methane produced from ruminant animals, this is a key question.
The rumen of a typical NZ ruminant animal contains a complex ‘soup' of chewed-up plant material, saliva, drinking water, plus a vast array of microbial species. Methane, the potent greenhouse gas, is produced in the rumen by microbes known as methanogens. They use hydrogen, another gas that is produced by other microbes like bacteria that break down ingested feed. By converting hydrogen to methane, the methanogens get the energy they need to grow.
Sandra Kittelmann and Henning Seedorf, along with the rest of the rumen microbiology team at AgResearch, have been delving into the rumen contents of a wide range of NZ sheep and cattle to investigate the microbial communities that live there. By accurately identifying and classifying rumen microbes, and looking for similarities and differences in types and abundances between animals, the search for targets and strategies to reduce agricultural methane is being advanced.
A key outcome of the team's work has been the development of a taxonomic framework to enable classification of the methanogens from the rumen, and from other animal and human intestinal tracts. This work has been recently published in PeerJ (http://dx.doi.org/10.7717/peerj.494). Setting up the framework was a long, and sometimes tedious process, with many of the organisms initially unclassified and most requiring new names. However, the completed classification provides a map that allows researchers to identify the methanogen species that are present in a sample from a rumen. "We may not know what they all do yet", says Sandra, "but we can identify what we've got and what we don't have. Sometimes it's incredibly useful to know what we don't know".
The first use of the new classification was to identify the major methanogens present in NZ ruminants. Surprisingly, regardless of species and diet, there turned out to be a limited diversity of methanogens present. This has big implications for vaccine and inhibitor development. If a new vaccine or inhibitor targets and knocks out the major methanogen groups, it has a high likelihood of working across all NZ species. Currently a Global Rumen Census project (funded by the Global Research Alliance) is underway. Led by Gemma Henderson and Peter Janssen, it aims to survey the diversity of microbes present in rumen samples obtained from a range of locations and farming situations around the world. If the same major methanogens turn out to be globally common to ruminants, any new technologies developed in NZ could be used internationally to help make a real impact on agricultural GHGs.
New taxonomic frameworks for rumen microbes have also been instrumental in a recently published study investigating the microbes present in the rumens of naturally high- and low-methane emitting sheep (http://dx.doi.org/10.1371/journal.pone.0103171). The team were hoping to find differences in the communities present, with the expectation that there was something special about the high-emitters. However, unexpectedly the results showed that it was the low-emitters that had additional, different strains of bacteria present.
After some time spent examining the results of the study, it was deduced that there are actually two types of low-emitting sheep. In the more abundant type, bacteria which don't seem to produce hydrogen have muscled their way into the rumen. Less hydrogen means less methane. The animal breeding team, led by John McEwan, have found that the low-emitting sheep tend to have physically smaller rumens, so current thinking suggests that feed passes through the smaller rumens faster, and the non-hydrogen producing species can establish themselves better under these conditions.
As for the second type of low-emitting sheep (as classified by their rumen microbes), the team are still working on an explanation for this. Sandeep Kumar, a PhD student funded jointly by the NZAGRC in NZ and Teagasc in Ireland, is currently unravelling this issue.
Investigation of rumen samples is a pivotal, underpinning part of the NZAGRC-PGgRc methane programme. With major vaccine and inhibitor trials planned during the next year, understanding the effects that these are having on the methanogens present is very important. So Sandra and her team will continue to receive and study as many rumen samples as they can handle for the foreseeable future, feeding back their valuable results and insights to the rest of the methane team.
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