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Belching cows and a tiny bacterium

It may seem like an unusual scientific achievement but a team of scientists from the Pastoral Greenhouse Gas Research Consortium and AgResearch are the first in the world to map the DNA sequence of a very tiny bacterium that lives in cows’ guts.

The results – the first map of a rumen methanogen DNA sequence – were published on 28 January 2010 in the international journal PLoS One (Public Library of Science). The map is significant as it gives scientists worldwide the most detailed view of the bacteria involved in making methane in cows.

Methane from belching ruminant livestock (cows, deer, goats and sheep) makes up a high proportion of New Zealand’s greenhouse gas emissions. Although it is still being debated whether this is significantly contributing to any global warming, there are fears that other countries will use this as an excuse to enforce trade restrictions (that is, they might refuse to buy our meat exports).

Possible methane reduction

By understanding the bacteria involved in methane production, we may be able to reduce methane emissions from our grazing livestock.

The bacteria – of which there are a number of species – remove the hydrogen and carbon dioxide that are released as grass and other plant materials are broken down. The byproduct of this process is methane.

The objective behind sequencing a rumen methanogen – in this case, Methanobrevibacter ruminantium, a bacterium with 2,200 genes and almost 3 million basepairs – is to figure out how to selectively knock them out in ways that will not damage other beneficial bacteria. Possible approaches are vaccines, drenches or even designer forage (grazing food).

Dr Graeme Attwood, AgResearch scientist and leader of the team responsible, says the genome sequence has given them a detailed insight into the bacterium’s lifestyle in the rumen – how the organism lives, behaves and interacts with other rumen microbes. This allows the scientists to identify genes and proteins as targets for methane reduction strategies.

One discovery is large proteins on the surface of the methanogen that may be good candidates for reducing methane production in the rumen. Dr Attwood’s team believe many of these surface proteins are the ‘glue’ that allows the methanogen to interact with other rumen organisms to obtain hydrogen – its energy source. If they could somehow interfere with this association and the methanogen’s ability to get hydrogen, this would hinder its ability to grow in the rumen and lead to lower methane production.

The team has also been able to define the enzymes involved in the methane formation pathway. They’re now aiming to target different steps in this pathway by designing molecules that can bind to these enzymes and prevent their function, thus hampering methane production.

Partnership between farming industry and scientists

Dr Attwood says they are still some years away from delivering on-farm solutions to knock out methane emissions in agriculture but sequencing the genome means they “can now embark on research paths to crack this challenge that is important to the sustainability of New Zealand farming systems and our economy”.

Mark Aspin, Manager of the Pastoral Greenhouse Gas Research Consortium, says the final publication is the result of a great partnership between the farming industry and science over many years. “The genome sequence gives us a blueprint of these unique organisms and will, we believe, enable specific targeting of methanogens which are distinctly different from the microbes responsible for fibre degradation (and hence digestion for the ruminant animal) so that we can reduce the emissions without adversely affecting their productivity.

“This is only one of many species of methanogens in the rumen. The consortium has commenced further sequencing of other predominant methanogens so that we are confident that targets identified in the initial genome have wide application across the whole population of methanogens.”

Activity idea

In relation to this news article, your students may like to watch an animation on the Biotech Learning Hub that gives a step-by-step guide to sequencing DNA in a lab.
www.biotechlearn.org.nz/themes/dna_lab/sequencing_revealing_the_dna_codeexternal link

Useful links

Biotech Learning Hub theme: Barcoding life
www.biotechlearn.org.nz/themes/barcoding_lifeexternal link

Biotech Learning Hub theme: DNA lab
www.biotechlearn.org.nz/themes/dna_labexternal link

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