Methane - Methane is biologically unique among the gaseous hydrocarbons in two ways. First, it is the only one produced in large amounts through microbial action. Second, it is metabolized by microorganisms that are often inactive on the larger hydrocarbon molecules. Moreover, the status of CH4 as a carbonaceous substrate not having the carbon-carbon linkage typical of biologically synthesized organic molecules provides an interesting problem in the delineation of heterotrophy and chemoautotrophy.
Paddy soils frequently contain a surface film that brings about the oxidation of CH4. To isolate the biological agents of the oxidation from the film, advantage is taken of their capacity to develop in inorganic media incubated in an atmosphere of CH4 and O2. Methane oxidizers also occur in well-drained soils, particularly subsist on the CH4 released from the lower regions of the soil in anaerobic decomposition and they seem to be more abundant a in lower layers than near the surface.
In the process of CH4 oxidation, O2 is consumed and CO2 produced. For each mole of CH4 that disappears, two moles of theoretically are required.
Since CH4 is also a carbonaceous nutrient for the organism, some of the gas will go into the formation of cell substance. The experimental values therefore do not necessarily agree with the theoretical equation because of carbon assimilation. The more efficient the bacterium is in assimilation, that is, efficient in utilizing the energy released by oxidation for cell synthesis, the greater will be the disparity from the theoretical ratio of 1CH4 : 2O2 . However, when CH4 oxidation in nature is proceeding for some time and the population density is large and probably reasonable constant, a ratio of nearly 1:2 is achieved.
Two schools of thought exist on the organism responsible for CH4 oxidation. One school maintains that CH4 utilization is restricted to specialized bacteria that use CH4 and methanol but no other aliphatic hydrocarbon as carbon and energy sources for multiplication. These bacteria, sometimes termed methylotrophs, are strict aerobes of various sizes and shapes, and they are classified in the genera Methylomonas, Methylosinus, Methylobacter and Methylocytic. A few physiologically related but morphologically different CH4-oxidizing bacteria are also known. Although unable to grow on other simple compounds, these organisms may cometabolize them.
A second view holds that other heterotrophs can oxidize CH4. These organisms, many of which are species of Mycobacterium, use CH4 as well as other aliphatic hydrocarbons as carbon sources. In addition, bacteria of a few additional genera as well as fungi like strains of Cephalosporium and Penicillium are reported to use CH4 and many of these are able to grow in media containing sugars or organic acids as carbon sources.
Cell suspensions of CH4, oxidizers metabolize methanol, formaldehyde and formic acid in addition to the gaseous hydrocarbon. Methanol, formaldehyde and formic acid have been found to accumulate if the conditions of incubation are varied or if inhibitors are used. The result of such studies on the oxidation and accumulation of these one-carbon compound indicate that the pathway of CH4 oxidation proceeds as shown in aquation :
Paddy soils frequently contain a surface film that brings about the oxidation of CH4. To isolate the biological agents of the oxidation from the film, advantage is taken of their capacity to develop in inorganic media incubated in an atmosphere of CH4 and O2. Methane oxidizers also occur in well-drained soils, particularly subsist on the CH4 released from the lower regions of the soil in anaerobic decomposition and they seem to be more abundant a in lower layers than near the surface.
In the process of CH4 oxidation, O2 is consumed and CO2 produced. For each mole of CH4 that disappears, two moles of theoretically are required.
CH4 + 2O2 -> CO2 + 2H2O
Since CH4 is also a carbonaceous nutrient for the organism, some of the gas will go into the formation of cell substance. The experimental values therefore do not necessarily agree with the theoretical equation because of carbon assimilation. The more efficient the bacterium is in assimilation, that is, efficient in utilizing the energy released by oxidation for cell synthesis, the greater will be the disparity from the theoretical ratio of 1CH4 : 2O2 . However, when CH4 oxidation in nature is proceeding for some time and the population density is large and probably reasonable constant, a ratio of nearly 1:2 is achieved.
Two schools of thought exist on the organism responsible for CH4 oxidation. One school maintains that CH4 utilization is restricted to specialized bacteria that use CH4 and methanol but no other aliphatic hydrocarbon as carbon and energy sources for multiplication. These bacteria, sometimes termed methylotrophs, are strict aerobes of various sizes and shapes, and they are classified in the genera Methylomonas, Methylosinus, Methylobacter and Methylocytic. A few physiologically related but morphologically different CH4-oxidizing bacteria are also known. Although unable to grow on other simple compounds, these organisms may cometabolize them.
A second view holds that other heterotrophs can oxidize CH4. These organisms, many of which are species of Mycobacterium, use CH4 as well as other aliphatic hydrocarbons as carbon sources. In addition, bacteria of a few additional genera as well as fungi like strains of Cephalosporium and Penicillium are reported to use CH4 and many of these are able to grow in media containing sugars or organic acids as carbon sources.
Cell suspensions of CH4, oxidizers metabolize methanol, formaldehyde and formic acid in addition to the gaseous hydrocarbon. Methanol, formaldehyde and formic acid have been found to accumulate if the conditions of incubation are varied or if inhibitors are used. The result of such studies on the oxidation and accumulation of these one-carbon compound indicate that the pathway of CH4 oxidation proceeds as shown in aquation :
CH4 -> CH3OH -> HCHO -> HCOOH -> CO2
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