Bacterial diversity in soil enrichment cultures amended with 2 (2‐methyl‐4‐chlorophenoxy) propionic acid (mecoprop)

<jats:title>Summary</jats:title><jats:p>The <jats:italic>tfdA</jats:italic> gene encodes for an α‐ketoglutarate‐dependent dioxygenase enzyme which catalyses the first step of the degradation of phenoxyalkanoic acid herbicides such as 2 (2‐methyl‐4‐chlorophenoxy) propionic acid (mecoprop). The bacterial diversity of soil enrichment cultures containing mecoprop was examined by Denaturing Gradient Gel Electrophoresis (DGGE) and clone libraries of both 16S rRNA genes and <jats:italic>tfdA</jats:italic> genes. The 16S rRNA gene sequences were diverse and clustered with either the <jats:italic>Beta</jats:italic>‐ or <jats:italic>Gammaproteobacteria</jats:italic>. The 16S rRNA gene sequence from a bacterial strain isolated from an enrichment culture, grown on R‐mecoprop, which represented a dominant band in the DGGE profiles, had a high 16S rRNA sequence identity (100%) to <jats:italic>Burkholderia glathei</jats:italic>. This is the first report that <jats:italic>B. glathei</jats:italic> is implicated in mecoprop degradation. PCR amplification of the <jats:italic>tfdA</jats:italic> genes detected class III <jats:italic>tfdA</jats:italic> genes only, and no class I or class II <jats:italic>tfdA</jats:italic> sequences were detected. To understand the genes involved the degradation of specific mecoprop (R‐) and (S‐) enantiomers, oligonucleotide probes targeting the <jats:italic>tfdA</jats:italic>, <jats:italic>rdpA, sdpA</jats:italic> and <jats:italic>cadA</jats:italic> genes were hybridized to DNA extracted from enrichment cultures grown on either R‐mecoprop or (R/S) racemic mecoprop. Strong hybridization signals were obtained with <jats:italic>sdpA</jats:italic> and <jats:italic>tfdA</jats:italic> probes using DNA extracted from cultures grown on racemic mecoprop. A strong hybridization signal was also obtained with the <jats:italic>rdpA</jats:italic> probe with DNA extracted from the cultures grown on R‐mecoprop. This suggests the <jats:italic>rdpA</jats:italic> gene is involved in R‐mecoprop degradation while <jats:italic>tfdA</jats:italic>, <jats:italic>sdpA</jats:italic> and <jats:italic>cadA</jats:italic> genes are involved in the degradation of both R‐ and S‐mecoprop.</jats:p>