Natural chloromethane (CH3Cl) sources, mostly from vegetation, are responsible for 16% of the chlorine-dependent fraction of stratospheric ozone destruction with the phasing out of its anthropogenic emissions since the application of the Montreal Protocol in 1987. Atmospheric CH3Cl emissions can be modulated by plant-associated microbial communities [1]. However, the taxonomical and metabolic diversity of the biotic CH3Cl sink remains largely uncharacterized. Under laboratory conditions, CH3Cl-degrading bacteria isolated from leaves and soils harbour the cmu pathway for chloromethane utilization [2]. Bacteria associated with CH3Cl degradation in soils and plant leaves were identified by stable isotope probing [3] following incubation with 13C-labelled CH3Cl. High through put sequencing of the heavy DNA targeted taxonomical and cmu genes as well as metagenomes.

In most experiments, detected taxa did not correspond to known cmu-containing bacteria [4],[5],[6]. In forest soil, taxa closely related to Methylovirgula and Actinobacteria were suggested to be associated with CH3Cl degradation. Ongoing work on 13C-labeled metagenomes of CH3Cl-degrading ferns and soils are expected to provide further information on one-carbon metabolism of the biological CH3Cl sink in the phyllosphere and soil.