Unmasking the methane eaters (10/17/2007)

Soil bacteria that consume the powerful greenhouse gas methane could be important in fighting climate change. A team of European scientists is beginning to understand how communities of them work together in real soils.

Methane is a greenhouse gas 23 times more powerful than carbon dioxide. It is produced naturally in wetlands â€" it is sometimes called marsh gas â€" but it also emanates in quantity from rice fields and cows' guts. Research suggests methane is responsible for around 15% of the anthropogenic greenhouse effect. This is why there is a strong incentive to understand natural processes that can destroy methane.

Methane oxidising bacteria live in all the world's soils. They naturally break down methane, and they are able to use it as a source of energy. In wetlands, these bacteria consume about 80% of the methane that originates in the soil and would otherwise be released to the atmosphere. In some upland soils, they absorb methane directly from the atmosphere.

In the late 1980s, scientists discovered that using fertiliser in upland forest soil can inhibit the uptake of atmospheric methane. The wealth of studies following this discovery showed that the effect is not straightforward. In fact, the reaction to nitrogen fertilisers is different for different types of methane oxidiser, and depends on what species are present in the soil.

Now an international team of scientists led by Peter Frenzel at the Max Planck Institute for Terrestrial Microbiology in Marburg, Germany, is working together to try and establish how communities of these bacteria behave in real soils, and which species are active in different circumstances. The team includes scientists from the Netherlands, Austria, Sweden, France, Finland, Germany, the UK and Norway. It is funded under the European Science Foundation's (ESF) EuroDIVERSITY Programme.

The Austrian group has developed a genetic method called a microarray that can pick up the genetic signatures of all known methane oxidisers in soil. To start with, the project is using this method to test different soils, including those from forests, coasts and the Arctic, to seek out methane oxidisers. "The first outcome is that new types are already turning up," says Paul Bodelier, a member of the team from the Netherlands Institute of Ecology. By testing for RNA, the messenger chemical that helps translate genetic information into proteins, the team plans to show which methane oxidisers are actually consuming methane in different soils. "We are going to find out who is out there, who is really active and what the consequences are for the global methane cycle," says Frenzel.

One part of the project team in Marburg has already made a breakthrough. At the first EuroDIVERSITY conference in Paris in early October, they presented results showing how a newly discovered gene for one enzyme that breaks down methane operates at low levels of methane, like those in the air. The enzymes already known to do this job only work at higher levels of methane, such as you find in flooded soils. The discovery explains how the bacteria in upland soils manage to oxidise methane straight from the atmosphere.

The scientists' ultimate goal is to demonstrate the importance of retaining a variety of species in methane eating communities. Microscopic creatures are entirely overlooked by international species conservation efforts, because they are largely undocumented and difficult to study. "There are no microbes on the red species list," says Bodelier, "and we have no idea whether we have already lost species or whole communities of microbes from the Earth."

Note: This story has been adapted from a news release issued by the European Science Foundation

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