Researchers looking for better ways to make biofuels have turned to experts at breaking down grass - cattle - and found more than a dozen new compounds in their guts that might help make new, cheap sources of energy.
They used new genetic sequencing techniques to find microbes that make enzymes that in turn can break down tough grasses into usable products.
Writing in the journal Science, they said they took samples directly from the rumen - the organ in cattle that ferments and breaks down grass.
"Industry is seeking better ways to break down biomass to use as the starting material for a new generation of renewable biofuels," says Eddy Rubin of the US Department of Energy's Joint Genome Institute in California, which led the study.
"Together with our collaborators, we are examining the molecular machinery used by microbes in the cow to break down plant material."
To make sure they found the right microbes in action, they used a cow that had a hole surgically opened right into its rumen. The researchers needed to find the bacteria that worked in airless environments like a cow's insides.
Rubin's team used metagenomics, a gene-sequencing approach that maps the DNA of a community of organisms instead of one single creature or plant.
Metagenomics are being used to explore the microbes living in and on people, as well as by genome entrepreneur Craig Venter to catalog all the tiniest creatures of the sea.
In this case, the goal was to find microbes that make enzymes that can efficiently break down the toughest fibres in switchgrass, a tough crop that can be used to produce ethanol and which can grow in places where food crops do not grow well.
But switchgrass is very tough to break down.
"Microbes have evolved over millions of years to efficiently degrade recalcitrant biomass," says Rubin.
"Communities of these organisms can be found in diverse ecosystems, such as in the rumen of cows, the guts of termites, in compost piles, as well as covering the forest floor."
Identifying the enzymes that give the tiny bacteria this power could make it easier to turn switchgrass and other plant products into fuel in factories.
Ethanol makers in the US will produce about 49 billion litres of the renewable fuel this year, chiefly from corn. A 2007 law requires annual use of 136 billion litres from 2022 and reserves 80 billion litres of it for 'advanced' biofuels.