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Importance of Methanotrophic Bacteria in the Biosphere and Their Application in Biotechnology

Only thirty years ago methanotrophic bacteria were regarded by most microbiologists as obscure and unimportant organisms. Today, there exists substantial evidence that methanotrophic bacteria constitute one of the major groups of free-living organisms which have an important role in the carbon cycle since methane as their growth substrate is one of the most abundant organic compounds on this planet. Methanotrophic bacteria also play an important role in the nitrogen cycle being able to fix atmospheric nitrogen, oxidize ammonia and reduce nitrite. Recently discovered metabolic activities of some methanotrophic species in the transformation of multicarbon compounds which are not their growth substrates suggest that ubiquitous methanotrophic bacteria may have significant biotechnological potential in other, environmentally crucial bioconversion assignments as well. These cometabolic activities have been described as "fortuitous metabolism" implying that they are merely due to the lack of specificity of methane monooxygenase enzyme system (MMO), whose primary function is to initiate the oxidation of methane to carbon dioxide. Although the metabolic capacity varies between species, the following types of compounds are reported to be oxidized by methanotrophic bacteria: alkanes, alkenes, aromatic and alicyclic hydrocarbons, halogenated alkanes and halogenated aromatic hydrocarbons. At present, there are no profitable processes employed by industries exploiting intact methanotrophic bacteria or enzymes derived therefrom. However, the discovery that methanotrophic bacteria can degrade low-molecular-weight halogenated hydrocarbons at a resonable rate has resulted in research activities that may lead to their biotechnological applications. The use of methanotrophic bacteria for in situ bioremediation of surface and subsurface waters contaminated by halogenated hydrocarbons the widespread, toxic and carcinogenic pollutants, appears to be an attractive possibility.

methanotrophic bacteria; cycling in the biosphere

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