Methane oxidizing bacteria (MOB), or methanotrophs remove 30Tg of methane annually (range 15-45Tg Y-1; ± 6% of global emissions). In addition, these bacteria exhibit a wide range of growing conditions and contain key enzymes with a remarkably broad substrate specificity. Thanks to this versatile character they have a high potential for application in industrial biotechnology, including (i) geoengineering the climate by the fixation of methane from anthropogenic and natural gas to biomass and CO2, (ii) bioremediation of pollutants (eg chlorinated hydrocarbons , aromatic compounds, ... and production of economically relevant metabolites (eg single-cell proteins, ectoine, polyhydroxyalkanoates, .... Nevertheless, there are as yet no applications of MOB widely commercialized, mainly due to the lack of strains with the right properties such as high growth rate and high cell density. Isolation of new strains in this respect is required to expand our knowledge about methanotrophs. So far, most studies focused on terrestrial ecosystems, given the large annual methane emissions, however, marine ecosystems, which annually contribute for 1-20% of the total methane emission were always ignored. As a result little is known about the MOB diversity in these ecosystems. Yet marine systems offer several advantages with regard to biotechnology. Furthermore, knowledge about methanotrophs and their activities is important to understand the microbial mediation of the greenhouse gas methane under climate change and human activities in marine ecosystems.
