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Did you know ... ? Reducing methane emissions with kangaroo microbes

Cattle and sheep in Australia account for 11% of Australia’s total greenhouse gas (GHG) emissions. Bacteria called methanogens in the rumen break down otherwise indigestible plant matter, releasing compounds that the animals can digest, but also releasing methane as a waste product. Not only does this contribute to global warming, but it also represents a 15% loss of energy, which equates to farm income.

Two solutions have been proposed. The first is to get rid of the cattle and sheep and to farm kangaroos. We’d all be a lot healthier not eating saturated fats, and the removal of the hard hooves from Australia’s fragile soils would reduce soil erosion and nutrient loss. Dr George Wilson, of the Australian Wildlife Services in Canberra, and colleagues estimated that removing 7 million cattle and 36 million sheep would lower Australia’s GHG emissions by 16 million tonnes, or 3% of annual emissions. But that’s not likely to happen.

The other solution is to replace the bacteria in the cattle’s and sheep’s rumens with the bacteria from kangaroos’ fore-stomachs. On the one hand, cattle belch 250 L of methane a day. On the other hand, kangaroos release less than 400 mL. Instead of methanogens, kangaroo fore-stomachs are populated with different bacteria, called acetogens, that produce acetates. Crucially, acetates are soluble and so are not emitted, but instead are digested.

Dr Athol Klieve, a microbiologist at the DPIF in Brisbane, has recently identified several species of acetogens in the gut of kangaroos. Acetogens are also present in cattle and sheep, so he is now investigating how to replace the methanogens in ruminants with acetogens that can out-compete the methanogens, both reducing GHG emissions and increasing feed conversion efficiency.

Belches versus farts

Nearly all of the methane emitted from cattle and sheep comes from the mouth as belches, not from the gut as farts. Humans, on the other hand, do the reverse.

In humans, most food is broken down in the stomach and small intestine; the remainder passes through to the large intestine. Bacteria here break down carbohydrates and proteins in the food. Some of the byproducts are gases.

The main gas released in farts is nitrogen, the main component of air, which we swallow with our food and drink. CO₂ accounts for up to 30%. Hydrogen, accounting for up to half the composition, and methane, up to 10%, are both flammable ... and can indeed be lit.

The smell is due to reduced sulphur compounds such as hydrogen sulphide (rotten egg smell) and carbonyl sulphide, which are the products of protein breakdown. Foods that contain high levels of insoluble fibre, notably cabbage and beans, take longer to digest and will therefore produce more gas.

Men and women produce the same amount of farts – about 10 to 15 a day, although this depends greatly on diet.

Further information

Wilson GR et al. 2008. Native wildlife on rangelands to minimize methane and produce lower-emission meat: kangaroos versus livestock. Conservation Letters 1(3): 119–128. DOI: 10.1111/j.1755-263X.2008.00023.x

Radio Australia. 2004. Methane In Agriculture.

Hadfield P. 2002. No burps, please. New Scientist 2347: 21.

Trivedi B. 2008. How kangaroo burgers could save the planet. New Scientist 2687: 48–50.

Athol Klieve's page at DFIP.

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