Molecular analysis of methanotroph ecology in Lake Washington sediment

Methanotrophs, or methane-oxidizers, are a group of aerobic bacteria of great interest due to their role in global methane cycling and their ability to cometabolize environmental contaminants such as trichloroethylene (TCE). Methanotrophs have historically been divided along phylogenetic lines into Type I strains (γ-proteobacteria) and Type II strains (α-proteobacteria). Many physiological capabilities of methanotrophs have also been thought to fall along these lines. However, this work provides evidence for both soluble methane monooxygenase (sMMO)-production and nitrogen fixation in Type I methanotrophs, physiological activities once thought restricted to Type II strains. Therefore, this work extends the known physiological diversity of methanotrophs. In addition, molecular tools, including oligonucleotides for PCR and hybridization, were developed for the assessment of methanotroph populations. Our PCR and probing data suggest that Type I Methylomonas-like strains are the important sMMO-containing methanotroph population in Lake Washington sediment, in contrast to the long-held belief that Type II strains were the important sMMO-containing methanotrophs in nature. These results may have strong implications for the development of in situ bioremediation protocols involving methanotrophs.