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Photomicrographs of culture 6A8. Negatively-stained electron micrographs of uranyl acetate-stained thin rod-shaped (left) and coccoid (right) cells showing notches
(N) in the cell wall and the pilus-like appendages (A) in each. |
Methanogenic Archaea carry out the terminal reactions in the decomposition of organic matter
to methane in natural anaerobic habitats. Because of their limited metabolic repertoire, they are
usually dependent on other organisms, typically Bacteria, to convert complex organic matter into
substrates they can utilize, such as H2/CO2, acetate, or methanol. Methanogens account for a
considerable fraction of the phylogenetic diversity of the Euryarchaeota, and the study of their
biochemistry and physiology has illuminated novel biochemical reactions, many of which were
subsequently found in other organisms.
Methanogens play an important role in the global carbon cycle. Methane is a potent
atmospheric greenhouse gas, and human activities have led to a doubling of atmospheric
methane concentrations over the past 200 years. Among the major sources of atmospheric
methane are natural and cultivated wetlands, and indeed methane was originally called "marsh
gas." Northern peatlands are a crucial but perplexing methanogenic habitat. These systems
have accumulated nearly one-third of the organic matter found in soils worldwide (1), and
account for about 20% of global methane emissions (2). Whether these peatlands will continue
to accumulate atmospheric CO2 or will become CO2 sources, and whether peatland
methanogenesis will increase or decrease in the face of global climate change are important
and unsolved questions facing the global change community. More than half of Northern
peatlands are acidic Sphagnum-dominated bogs, yet our understanding of conversion of carbon
to methane in these bogs is particularly rudimentary.
References
1. Gorham, E. 1991. Northern peatlands role in the carbon cycle and probable responses to climatic warming. Ecol Appl 1.
2. Cicerone, R. J., and R. S. Oremland. 1988. Biogeochemical aspects of atmospheric methane. Global Biogeochem Cycles 2:299-327
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