Impact of microorganisms as sinks of atmospheric chloromethane

• Applicants: Professor Dr. Frank Keppler; Professor Dr. Steffen Kolb
• Subject Area: Soil Sciences ; Microbial Ecology and Applied Microbiology
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 258712308

An interdisciplinary consortium of two French and two German partners will combine their expertise and knowledge to address the impact of microorganisms on the global budget of chloromethane (CH3Cl). Anthropogenic emissions of ozone depleting compounds (CFcs) have been strongly reduced since the Montreal protocol came into force in 1989. As a consequence, compounds released from natural sources, such as CH3Cl, have become increasingly relevant in stratospheric ozone depletion. This chlorinated gas is the most abundant halogenated compound in the atmosphere whose primarily source is the terrestrial ecosystems. Release from living and dead vegetation and biomass burning are major sources. The positive linear response with temperature suggests that future warmer climates will likely lead to increased CH3Cl emissions. However, current estimates of the CH3Cl global budget are uncertain and suggest that microorganisms play a more important role in degrading atmospheric CH3Cl than previously thought. Methylotrophic microbes, some with the metabolic capability to degrade CH3Cl, occur in soils, the phyllosphere of many plants, and have recently been reported to be active in water droplets of clouds. The applicants conceive that the main objectives of the proposed project are to reveal quantitative information on process-level and to provide in depth genetic insights into these microbes. The consortium will investigate kinetic and isotope effects during CH3Cl degradation by methylotrophs associated with soils, plants, and clouds. Laboratory experiments with specific CH3Cl degrading methylotrophs will be conducted to measure their effects on isotope composition and to determine temperature effects on kinetic parameters. In various environmental samples the microbial community will be characterized using amplicon-targeted next generation sequencing employing a taxonomical (16S RNA genes) and a functional gene marker for CH3Cl degradation (cmuA). Selected samples of soil, plants, and cloud water will be subjected to 13C-isoptopologue of CH3Cl in order to label the biomass of CH3Cl converting microbes. Metagenomes will then be retrieved using a combination of DNA stable isotope probing, whole genome amplification, and MiSeq (Illumina) high throughput sequencing. These experiments will assess the diversity of the microbial CH3Cl-degrading pathways, and will enable the discovery of novel methyltransferases and further genes involved in CH3Cl metabolic transformation. The metagenomic approach will provide new insights into CH3Cl-degrading microbial communities of temperate terrestrial ecosystems and clouds. Kinetic and isotopic data will resolve the quantitative relevance of microbial sinks for the global CH3Cl budget. A improved quantitative understanding of the sources and sinks of atmospheric CH3Cl will be invaluable for enhancing our predictive capability for stratospheric chlorine chemistry and ozone layer stability.

• DFG Programme: Research Grants
• International Connection: France
• Participating Persons: Dr. Pierre Amato; Dr. Françoise Bringel