Exploring the biodiversity, interactions and controls of prokaryotic communities driving methane flux in marine sediments.

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Methane is a potent greenhouse gas, second in importance only to carbon dioxide. Most methane is produced by microorganisms and methane concentrations in the atmosphere had been increasing rapidly, but now is quite variable. This is important to understand as atmospheric methane increases in the geological past have been linked to global warming. Global methane production in marine sediments is very significant and these sediments contain the largest, global reservoir of methane. This includes huge stores of methane in an ice matrix called hydrates, which might be a future energy store, as well as being a sensitive trigger for rapid climate change. Surprisingly, we know relatively little about the methanogens in ocean sediments that produce this methane, as only a few have been isolated and studied (11 species, representing less than 10% of cultured methanogen species). Also uncultured and little understood, are the microbes related to methanogens, which currently remove approximately 80% of all methane produced in sediments before it can enter the ocean and atmosphere above. These two groups of microbes are intimately connected and together have major influence on the flux of methane from sediments. There are even suggestions that anaerobic methane production and consumption may be due to the same microbes, but nobody knows for sure. Hence, our lack of understanding of the microbes controlling methane flux in marine sediments severely limits our ability to predict controls and future changes in the extremely important global methane cycle. We intend to significantly increase knowledge of the controls on ocean methane flux, and the microorganisms driving this process, by investigating methane production in high-pressure systems. These systems mimic sediment conditions, and within which both methane-producing and methane-consuming microbial communities are active. We will conduct similar experiments with microbial communities from marine gas hydrate sediments to determine their response to temperature and pressure changes, the supply of compounds for methane oxidation or production, and other factors controlling methane concentrations. From these experiments and a range of marine sediments we will isolate a number of methanogens, many of which may be new marine types, as their presence has been indicated by DNA surveys. Study sites include coastal sediments which are strongly influenced by human activity, globally significant gas hydrate sediments and mud volcanoes, which have recently been suggested as being an important potential source of methane. We will identify the physiology and metabolism of these methanogens to significantly increase our knowledge of the biodiversity and function of this important group of microorganisms. This will include, for the first time, investigating their response to high pressure.