Bacterial community changes and enrichment of Burkholderia-like bacteria induced by chlorinated benzoates in a peat-forest soil-microcosm

Bacterial community shifts in a peat-forest soil spiked with 3-chlorobenzoa te (3CBA) or 2,5-dichlorobenzoate (2,5DCB) were monitored by PCR-amplificat ion of the V6 to V8 regions of the 16S rRNA and rDNA, followed by separatio n of the amplicons by temperature gradient gel electrophoresis. 3CBA disapp eared to non-detectable levels after 15 days by a biologically mediated pro cess, while 2,5DCB remained at the initial concentration values. The experi ments were conducted under microcosms sl stems. Addition of the chlorinated benzoates to the soil resulted in a rapid decrease of the microbial divers ity, as judged by a time-dependent reduction in the number of amplicons det ected by temperature gradient gel electrophoresis. Few amplicons specifical ly enriched in the spiked soils were cloned and characterised by sequence a nalysis. The identity of the cloned DNA and the corresponding soil amplicon s was confirmed by hybridisation with a radioactively labelled V6-probe. An alysis of the 16S rDNA sequences indicated that Burkholderia-related bacter ia dominated the enriched soil populations under 3CBA stress. In addition, enrichment cultures growing on 3CBA as sole C-source were obtained from the respective spiked soil, which were found to contain bacteria with identica l 16S rDNA sequences as those induced by 3CBA stress in soil.