Methane gas makes microbes lively

Life under the sea thanks to anaerobic methane oxidation

Microscopic image of the anaerobic methane oxidizer consortia. Using a special technique, the sulfate-reducing bacteria were stained green and the methane-oxidizing archaea red. Project MUMM, MPI for Marine Microbiology Bremen.
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Gas hydrates at the bottom of the ocean are not only considered as a possible energy source of the future, they are also a veritable feast for microbes. Because these feed on the enclosed in the hydrate methane and do not even need oxygen for their metabolism. But how do the specialists manage to survive in the extreme pressure and temperature conditions in the oceanic sediments?

Methane hydrates are solid, crystalline substances that form from a mixture of gas and water at low temperatures and high pressure. Around 90 percent of naturally occurring hydrates contain natural gas as the central molecule around which the water molecules circling around. In the methane hydrate, however, there are also other gases, such as carbon dioxide and hydrogen sulfide.

Deep sea or permafrost areas

In addition to low temperatures and high pressure, methane is needed to form a gas hydrate. The methane can be produced in different ways - either by biological activity (biogenic gas) or by the thermal decomposition of sedimentary organic material (thermogenic gas).

Optimum conditions for the formation of gas hydrates prevail, for example, in the deep sea or in permafrost areas. Thus, the formation of gas hydrates from methane is spatially very limited. But what about the remaining methane, which is produced permanently, practically everywhere in the world and in the seabed? This gas does not escape into the oceans, but is already mined in the seabed. If this did not happen, the methane gas would first enter the water and then the atmosphere - with catastrophic consequences. Because methane is about 30 times more harmful greenhouse gas than carbon dioxide.

Methane degradation in the sediment

Methane hydrate (white) - trapped between sediment © Gerhard Bohrmann, Marum / University of Bremen

Anaerobic methane oxidation by a consortium of two different groups of microorganisms plays an important role in the degradation of methane in marine sediments. In an unprecedented collaboration, the two groups of microorganisms convert methane with sulfate into carbon dioxide and hydrogen sulfide. Sulphate is dissolved in large quantities in seawater and diffuses into the seabed. In the zone where the sulphate and the rising methane meet, the methane-oxidizing microorganisms feel really well. This only a few centimeters thick layer prevents the escape of large amounts of methane into the oceans. display

Archaea as a "man-eater"

Although the process of anaerobic methane oxidation was described as early as 1974, it was only in 2000 that it was possible to identify the consortia. Since then, many researchers have tried to disentangle the processes in the consortia. One of the most exciting discoveries was that they are composed of two completely different groups of microorganisms: The outer shell is made up of bacteria that oxidize sulfate to hydrogen sulphide, and in the core are archaea, which are actually Produce methane, but be induced by the bacteria to drain their metabolism "backwards" they break down the methane. The amazing thing about it: a consortium consists of several hundred individual cells, but behaves almost like a single cell. It grows and splits when it gets too big.

At the GeoForschungsZentrum Potsdam, the group of organic geochemistry deals with very specific organic molecules called biomarkers. Since these occur only in the "eater moths", this allows the consortia to be proven without the need for elaborate microbiological methods. For example, these investigations were conducted on a permafrost deep well in Mallik, in the far north of Canada. There are large gas hydrate deposits, which are to be mined as a possible source of energy in the future.

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Gas hydrates in the Mackenzie basin

METROL project

(Jens Kallmeyer and Rolando di Primio, GFZ Potsdam, 20.04.2007 - AHE)