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

• Final Report Year: 2018

Final Report Abstract

Chloromethane (CH3Cl) is the most abundant natural chlorine-containing compound in the atmosphere, and is responsible for a significant fraction of natural stratospheric ozone destruction. Current estimates of the global CH3Cl budget are uncertain as the strength of sources and sinks associated with vegetation (either alive such as in plant leaves or decaying such as in topsoil) need to be better characterised. An interdisciplinary consortium of ANR-funded two French (Université de Strasbourg, coordinator F. Bringel; Clermont-Ferrand Fédération de Recherche en Environnement FR3467, resp. P. Amato) and two German DFG-funded partners (Coordinator Heidelberg University, Prof. F. Keppler; Leibniz Centre for Agricultural Landscape Research, resp. S. Kolb) combined their expertise to investigate the impact of atmospheric CH3Cl-degrading microorganisms on the global budget of CH3Cl. To do this, the consortium examined their impact both on process and genetic levels, by using kinetic and isotope effects upon CH3Cl degradation, as well as next-generation sequencing of microbial communities associated with soils, plants, and clouds. CH3Cl biodegradation was affected by soil/plant properties, and temperature, whereas undetected in cloud water. Thus, cloud microbiota was not found to be a major atmospheric CH3Cl sink. No CH3Cl emission was detected from soils, while CH3Cl emissions rates varied between plants, suggesting microbial sink strength differences in the analysed samples. In the microbiota associated with soil and leave CH3Cl sinks, the only characterized cmu pathway for aerobic CH3Cl degradation was not detected. To identify active microbial CH3Cl-utilizing pathways in selected high-degrading forest topsoil and fern leaves samples, whole community genome sequencing of [13C]-labelled CH3Cl microorganisms was performed using the stable isotope probing approach. This will provide the first deep coverage exploration of the bacterial diversity functionally linked with CH3Cl sink. The levels of CH3Cl available to the microbes had a strong effect on stable carbon fractionation. Thus, previously reported values for stable carbon isotope fractionations of CH3Cl such as in soil, as determined under laboratory conditions with CH3Cl concentrations for above ambient concentrations, were probably overestimated when applied to global models.

Publications

• (2017). Chloromethane emissions in human breath. Science of the Total Environment, 605, 405-410
  F. Keppler, J. Fischer, T. Sattler, D. Polag, N. Jaeger, H.F. Schöler, M. Greule
  
• (2018). A transitory habitat for microorganisms in the hyperarid Atacama Desert. Proceedings of the National Academy of Sciences, 115, 2670-2675
  D. Schulze-Makuch, D. Wagner, S.P. Kounaves, K. Mangelsdorf, K.G. Devine, J.-P. de Vera, P. Schmitt-Kopplin, H.-P. Grossart, V. Parro, M. Kaupenjohann, A. Galy, B. Schneider, A. Airo, J. Frösler, A.F. Davila, F.L. Arens, L. Cáceres, F.S. Cornejo, D. Carrizo, L. Dartnell, J. DiRuggiero, M. Flury, L. Ganzert, M.O. Gessner, P. Grathwohl, L. Guan, J. Heinz, M. Hess, F. Keppler, D. Maus, C.P. McKay, R.U. Meckenstock, W. Montgomery, E.A. Oberlin, A.J. Probst, J. Saenz, T. Sattler, J. Schirmack, M.A. Sephton, M. Schloter, J. Uhl, B. Valenzuela, G. Vertergaard, L. Wörmer, P. Zamorano
  
• (2018). Chloromethane degradation in soils - a combined microbial and two-dimensional stable isotope approach. Journal of Environmental Quality, 47, 254-262
  N. Jaeger, L. Besaury, E. Kröber, A.-M. Delort, M. Greule, K. Lenhart, T. Nadalig, S. Vuilleumier, P. Amato, S. Kolb, F. Bringel, F. Keppler
  
• (2018). Chloromethane formation and degradation in the fern phyllosphere. Science of the Total Environment, 634, 1278-1287
  N. Jaeger, L. Besaury, A.N. Röhling, F. Koch, A.-M. Delort, C. Gasc, M. Greule, S. Kolb, T. Nadalig, P. Peyret, S. Vuilleumier, P. Amato, F. Bringel, F. Keppler
  
• (2018). Mass spectrometric measurement of hydrogen isotope fractionation for the reactions of chloromethane with OH and Cl. Atmospheric Chemistry and Physics, 18, 6625–6635
  F. Keppler, E. Bahlmann, M. Greule, H.F. Schöler, J. Wittmer, C. Zetzsch