Our research is primarily focused on microbial ecology and covers topics at the community, cellular, genomic, and molecular levels, with a major interest in the molecular biology and ecology of methane-oxidizing bacteria. The present research emphasis is on the genetic basis of their ecological differentiation and on the diversity and seasonal dynamics of atmospheric methane oxidizers in upland soils. Another line of research is to understand how complex microbial communities respond to changes in environmental conditions. This research is majorly based on 'meta-omics' approaches.
Methane is present in the atmosphere at a relatively low concentration (~ 1.8 ppm), but contributes about 20% to the current increase in the greenhouse effect. This is due to the high global warming potential of methane, which is 25 times greater than that of carbon dioxide over a period of 100 years. Aerobic methane-oxidizing bacteria, or methanotrophs, use methane as their major source of carbon and energy. Their activity attenuates methane emission from major sources, such as wetlands, rice paddies, and landfills, and constitutes the only biological sink for atmospheric methane in upland soils. In the methane-oxidation pathway of most methanotrophs, the first step is mediated by particulate methane monooxygenase (pMMO). This key enzyme of methanotrophy converts methane to methanol and is encoded by pmoCAB. Despite the global biogeochemical significance of methanotrophs, there is only limited knowledge about the genetic basis of their ecophysiology. Major drivers of methanotroph diversity in the environment are the methane/oxygen mixing ratio and the nitrogen source. Most likely, specialists for atmospheric methane oxidation are as-yet-uncultivated methanotrophs, among those the "Upland Soil Cluster alpha" (USCα). The type II methanotroph Methylocystis sp. strain SC2 contains two pMMO isozymes (pMMO1, pMMO2) with different methane oxidation kinetics. The pMMO1 is expressed and oxidizes methane only at high concentrations (>600 ppmv), while the novel pMMO2 is constitutively expressed and oxidizes methane at low mixing ratios, even at the trace level of atmospheric methane. The ability of strain SC2 to oxidize atmospheric methane could be improved by expressing environmental pmo genes, such as USCα-pmoCAB. In order to achieve the expression of USCα-pmoCAB in the long run, we currently perform genome-wide transcriptome analyses of Methylocystis sp. SC2 and develop molecular tools for reverse genetic approaches in this strain.