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Methane Oxidising Bacteria as Environmental Indicators

image of Methane Oxidising Bacteria as Environmental Indicators

This report focuses on methane oxidising bacteria (methanotrophs). The key function of methanotrophs as methane consumers and degraders of halogenated hydrocarbons bring them in the perspective of being useful indicators of environmental perturbations. Effects of climate on diversity and temperature adaptation as well as the capacity of different methanotrophs to degrade two atmospheric pollutants (chlorofluoromethanes) was investigated. None of the methanotrophs were found to be adapted for growth at permanently low temperatures although type I methanotrophs grew better at lower temperatures than the type II methanotrophs. Some of the methanotrophs were able to degrade dichlorofluoromethane while chlorodifluoromethane degradation was not demonstrated. No correlation was found between the degradation capacity and the origin of the isolates (landfill or wetland soil), or characteristics of their methane monooxygenase enzymes. The project did not identify a simple correlation between climatic variation or environmental stress and the variation in composition of the methanotroph community. More knowledge about temperature dependent interactions between type I and type II methanotrophs is needed before the composition of methanotrophs can be implemented as an indicator revealing ecological consequences of e.g. changes in climate.

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Capacity of methanotrophs for degradation of HCFC gasses

It has been suggested that methanotrophs play a significant role in dehalogenation of different C-1 and C-2 compounds of anthropogenic origin. Recently published work demonstrates that microbial dehalogenation of HCFC gases occurs in soil layers at Skellingsted landfill, a site that also exhibits a high methane oxidation capacity (Kjeldsen & Fisher 1995, Christophersen et al. 2000, Scheutz & Kjeldsen 2003). The hydrochlorofluorocarbons HCFC-21 and HCFC-22 (Fig.) are supposed to be released either directly from insulation foams typically present in refrigerators, or are products of anaerobic dehalogenation of CFC gases (also present in refrigerators) that are even more harmful to the environment. The two HCFC gases are grouped as class II ozone-depleting substances and are now being phased out. They are harmful to the environment primarily because of their global warming potential rather than their ozone depletion potential. Although the compounds are being phased out, they will persist in the environment due to their stability and their slow release from industrial products, e.g. insulation foams (Kjeldsen & Scheutz, 2003).

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