Characterization of (R/S)-mecoprop [2-(2-methyl-4-chlorophenoxy) propionicacid]-degrading Alcaligenes sp CS1 and Ralstonia sp CS2 isolated from agricultural soils

The herbicide mecoprop [2-(2-methyl-4-chlorophenoxy) propionic acid] is wid ely applied to corn fields in order to control broad-leaved weeds. However, it is often detected in groundwater where it can be a persistent contamina nt, Two mecoprop-degrading bacterial strains were isolated from agricultura l soils through their capability to degrade (R/S)-mecoprop rapidly, 16S rDN A sequencing of the isolates demonstrated that one was closely related to t he genera Alcaligenes sp. (designated CS1) and the other to Ralstonia sp. ( designated CS2), Additionally, these isolates demonstrated ability to grow on other related herbicides, including 2,4-D (2,4-dichlorophenoxyacetic aci d), MCPA [4-chloro-2-methyl phenoxy acetic acid] and (R/S)-2,4-DP [2-(2,4-d ichlorophenoxy)propionic acid] as sole carbon sources, tfdABC gene-specific probes derived from the 2,4-D-degrading Variovorax paradoxus TV1 were used in hybridization analyses to establish whether tfd-like genes are present in mecoprop-degrading bacteria. Hybridization analysis demonstrated that bo th Alcaligenes sp. CS1 and Ralstonia sp. CS2 harboured tfdA, tfdB and tfdC genes on plasmids that have approximately > 60% sequence similarity to the tfdA, tfdB and tfdC genes of V. paradoxus, It is therefore likely that tfd- like genes may be involved in the degradation of mecoprop, and we are curre ntly investigating this further.