Correlated production and consumption of chloromethane in the Arabidopsis thaliana phyllosphere.

Chloromethane (CH3 Cl) is a toxic gas mainly produced naturally, in particular by plants, and its emissions contribute to ozone destruction in the stratosphere. Conversely, CH3 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 CH3 Cl-degrading bacteria as a filter for plant emissions of CH3 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 CH3 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 CH3 Cl by A. thaliana paralleled HOL1 expression, as assessed by a fluorescence-based bioreporter. The relation between plant production of CH3 Cl and relative abundance of CH3 Cl-degrading bacteria in the phyllosphere suggests that CH3 Cl-degrading bacteria co-determine the extent of plant emissions of CH3 Cl to the atmosphere.