Chloromethane (CH(3)Cl) is a toxic gas mainly produced naturally, in particular by plants, and its emissions contribute to ozone destruction in the stratosphere. Conversely, CH(3)Cl can be degraded and used as the sole carbon and energy source by specialised methylotrophic bacteria, isolated from a variety of environments including the phyllosphere, i.e. the aerial parts of vegetation. The potential role of phyllospheric CH(3)Cl-degrading bacteria as a filter for plant emissions of CH(3)Cl was investigated using variants of Arabidopsis thaliana with low, wild-type and high expression of HOL1 methyltransferase previously shown to be responsible for most of CH(3)Cl emissions by A. thaliana. Presence and expression of the bacterial chloromethane dehalogenase cmuA gene in the A. thaliana phyllosphere correlated with HOL1 genotype, as shown by qPCR and RT-qPCR. Production of CH(3)Cl by A. thaliana paralleled HOL1 expression, as assessed by a fluorescence-based bioreporter. The relation between plant production of CH(3)Cl and relative abundance of CH(3)Cl-degrading bacteria in the phyllosphere suggests that CH(3)Cl-degrading bacteria co-determine the extent of plant emissions of CH(3)Cl to the atmosphere.