| Microbes and the Carbon Cycle |
We have classified microorganisms, including archaea, based on their sources of energy and carbon. The cycling of carbon between carbon dioxide and organic compounds is of considerable ecological importance. In addition to eukaryotes (such as plants and algae), autotrophic bacteria (such as cyanobacteria) play an important role in the fixation of carbon dioxide into organic compounds. Consumers, in turn, use organic compounds and release carbon dioxide. Decomposition of plants and animals and their constituent organic compounds is carried out by a large number of bacteria and fungi.
What is taking place in a swamp where you see marsh gas bubbling up though the ooze? A carbon cycle, based on one-carbon compounds, is taking place in the sediments and overlaying water of such freshwater environments. The anoxic sediments harbor archaea, which produce methane as a byproduct of energy metabolism. The methane rises from the sediment and moves into the zone above it. This upper area contains enough oxygen to support methane oxidizers, bacteria that use methane as a source of carbon as well as an energy source.
Methane (CH4) is a greenhouse gas and, according to international agreement, its emissions are controlled. Although it is produced by burning fossil fuel, most enters the atmosphere because of microbial action. How can the latter be limited? One strategy is to drain rice paddies more often, limiting the action of methane producers. Another is to add a layer of soil to landfills to encourage methane-oxidizers. Such approaches to reducing this harmful greenhouse gas are being studied.