Methanotrophs are aerobic, Gram-negative bacteria that utilize methane, a potent greenhouse gas, as a sole carbon and energy source. These bacteria oxidise methane through a unique enzyme system known as methane monooxygenase (MMO), thus reducing of the amount of methane released to the Earth’s atmosphere. In methanotrophs, there are two types of MMO; a membrane bound particulate enzyme (pMMO) and a soluble cytoplasmic enzyme (sMMO). The expression of both enzymes is significantly affected by the availability of copper. Under high copper-biomass ratio, the biosynthesis of pMMO is switched on, while sMMO is upregulated during growth at low copper-to biomass ratio. The exact role of copper in regulation of MMO in Methylococcus capsulatus and Methylosinus trichosporium is still unclear. We study the mechanisms and regulation of methane oxidation in methanotrophs using molecular genetics and a combination of post-genomic techniques such as proteomics, transcriptomics. We also study the ecology of methanotrophs in a wide variety of environments including wetlands, landfill cover soil and biofilters, methane seeps, wetlands, Arctic tundra, caves, lakes, the marine environment and extreme environments.