The use of pesticides contaminates surface and groundwater. Biodegradation is crucial for the fate of pesticides in the environment both in natural attenuation processes in the field and in dedicated bioremediation technologies for mitigating contamination. New pesticides have to comply to stringent requirements regarding biodegradability. Genetic adaptation appears important in the acquisition of novel catabolic pathways for bacterial pesticide degradation. Such pathways apparently evolved by combining individual catabolic gene modules and/or by mutations/rearrangements in genes for degradation of structurally related natural or xenobiotic compounds. However, this knowledge is based on retrospective analysis of individual isolates and was not studied at the community level. This project aims at a better understanding of the genetic adaptation for acquiring pesticide metabolism within bacterial communities by examining to what extent preconditioning with a certain pesticide compound affects the evolutionary pathways for the acquisition of biodegradation of structurally related pesticides. This is relevant since many new pesticide compounds are structural variants of older ones for which the degradation pathways are known. The study includes a profound analysis of the genetics associated with the acquisition of pesticide catabolic capacities in microbial communities in soils and biofilters, using amongst others, an innovative global metagenomic and transcriptomic approach.