Image caption The Tammar wallaby is the "model species" for research on kangaroos and their relatives

Scientists have gone some way to explaining why kangaroos produce much less methane in their burps, flatus and manure than farm animals such as cows.

They identified a bacterium in the gut of the Tammar wallaby - a member of the kangaroo family - that processes their food without making methane.

Farm animals are a major source of methane, an important greenhouse gas.

Writing in the journal Science, they suggest the work could show how to cut greenhouse emissions from livestock.

The Tammar wallaby is a fairly small member of the family, found in pockets of Western Australia and on some islands off the coast, and has long been a favourite of biological researchers.

Previous work showed they produce about one-fifth as much methane as cows for each unit of food they ingest; the new research is helping to show why that is.

"The guts of wallabies and cattle have evolved to support the establishment of a complex mixture of microbes, for the 'pre-digestion' of plant materials before the food is exposed to the animal's own digestive processes," said project leader Mark Morrison, of Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO).

"There are differences between the animals in terms of gut anatomy and shape that we think are also an important influence on methane production, as well as the way and the speed at which plant material moves through this 'pre-digestion' step.

"But our knowledge of that microbiology has been pretty limited until now."

Identifying the bacterium - a previously unknown member of the Succinivibrionaceae family - was not a straightforward task, requiring a technique known as "reverse metagenomics".

Using information already available about some aspects of the bacterium's traits and the genes driving those traits, such as the ways it processes nitrogen, they were able to design a culture for growing it that would resemble conditions in the wallaby's gut.

Cultured approach

By experimenting with different ingredients of the culture, eventually the bacterium grew well and the researchers were able to show that the main byproduct of fermentation was not methane, but succinate - a compound of carbon, hydrogen and oxygen.

Image caption Cows and other farm animals produce about as much methane as heavy industry

As well as producing far less methane, processing food this way is more efficient, with more of the available nutrition being extracted from the plants.

Members of the Succinivibrionaceae family are found in many other plant-eating animals, including cattle, though they do not appear to dominate food processing as they do in the wallabies.

The researchers hope to understand what these bacteria are doing inside farm animals, and then find ways of making them more effective.

"Our long-term goal is to redirect feed digestion in livestock away from methane formation, and instead produce more end products that are nutritious for the animal," said Professor Morrison.

"By doing so, we should have a positive impact both on animal productivity and the environment."

The research project was headed from national research agency CSIRO, with contributions from scientists in the US, Norway and Germany.

The CSIRO is in the vanguard of global research efforts to bring down methane emissions from livestock, by methods including changing their diet and selective breeding.

Methane from farm animals accounts for a few percent of global greenhouse gas emissions, and global production of meat and milk is forecast to double over the next half-century.