Facultative methanotrophs and environmental regulation of methane oxidation

目前大气中甲烷的浓度为1.8 ppm，全球变暖约20%归因于这种强效温室气体。据估计，厌氧土壤和沉积物中的产甲烷细菌每年产生400-640 Tg的甲烷，其中大部分在释放到大气中之前在湿地或上覆的好氧土壤中的好氧-厌氧界面处被氧化，从而减少全球甲烷排放到大气中。因此，湿地和土壤是重要的甲烷汇，估计每年分别消耗27和40 Tg CH 4。这是由需氧甲烷氧化细菌进行的。以甲烷为唯一碳源生长的细菌已从许多环境中获得。培养独立的技术表明，有更多的新甲烷氧化菌的环境中，等待隔离。一般来说，甲烷氧化菌被认为是专性的，即只在甲烷（或甲醇）上生长。最近令人兴奋的发现兼性甲烷氧化菌生长在甲烷和多碳化合物，如乙酸盐，现在使我们必须发展这些新发现的甲烷氧化菌，这似乎是广泛存在于湿地和土壤中，如何调节其甲烷氧化系统，以及它们如何有助于全球甲烷循环的透彻理解。我们建议研究甲烷氧化模式兼性甲烷氧化菌Methylocella silvestris的环境调控。另一个令人兴奋的突破是，我们很快就会获得Methylocella silvestris的基因组序列，这为这种细菌的代谢途径提供了蓝图，使我们能够阐明兼性代谢的途径。我们已经开发了一些生理和分子生物学技术，使我们能够在实验室的培养物中研究这种细菌，并研究乙酸盐利用的途径，并确定哪些环境因素调节这种细菌的代谢。我们还开发了许多尖端的分子生态学工具，使我们能够将实验室培养实验与微观实验相平行，这些微观实验将解决这些兼性甲烷氧化菌在泥炭和垃圾填埋场土壤中的作用，以解决在某些生长环境中兼性甲烷氧化菌比专性甲烷氧化菌具有竞争优势并且它们对甲烷循环做出重大贡献的假设环境中。

The concentration of methane in the atmosphere is currently 1.8 ppm and about 20% of global warming has been attributed to this potent greenhouse gas. It is estimated that 400-640 Tg of methane is produced annually by methanogenic bacteria in anaerobic soils and sediments much of which is oxidised at the aerobic-anaerobic interface in wetlands or overlying aerobic soils before it is released to the atmosphere, thereby mitigating the global emissions of methane into the atmosphere. Wetlands and soils are therefore important sinks for methane, consuming an estimated 27 and 40 Tg CH4 per year respectively. This is carried out by aerobic methane oxidising bacteria. Bacteria which grow on methane as sole carbon source have been obtained from many environments. Cultivation-independent techniques indicate that there are more novel methanotrophs in the environment that await isolation. Generally, methanotrophs have been regarded as obligate, ie only growing on methane (or methanol). Recent exciting discoveries of facultative methanotrophs which grow on both methane and multi-carbon compounds such as acetate now make it imperative that we develop a thorough understanding of how these newly discovered methanotrophs, which appear to be widespread in wetlands and soils, regulate their methane oxidation systems and how they contribute to the global methane cycle. We propose to study the environmental regulation of methane oxidation in a model facultative methanotroph Methylocella silvestris. Another exciting breakthrough is that we will soon have the genome sequence of Methylocella silvestris available to us which provides a blueprint for the metabolic pathways in this bacterium and enables us to elucidate the pathways of facultative metabolism. We have developed a number of physiological and molecular biological techniques to enable us to study this bacterium in cultures in the laboratory and to investigate pathways of acetate utilisation and to determine what environmental factors regulate metabolism in this bacterium. We have also developed a number of cutting edge molecular ecology tools which enable us to parallel the laboratory culture experiments with microcosm experiments which will address the role of these facultative methanotrophs in peat and landfill soils in order to address the hypothesis that in certain growth environments facultative methanotrophs have a competitive edge over obligate methanotrophs and that they make a significant contribution to the cycling of methane in the environment.