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Microbes and Environments
Vol. 22 (2007) No. 3 P 243-256



Regular Papers

Diverse 2,4-D and 2,4,5-T-degrading bacteria were isolated country-wide from ten Vietnamese soils, with or without a history of exposure to Agent Orange. The 353 degraders were phylogenetically grouped into three major categories; Burkholderias spp. (43.3% of all degraders), Sphingomonas spp. (40.2%), and Ralstonia spp. (15.3%) and two minor ones; Bradyrhizobium sp. (0.8%) and Nocardioides sp. (0.3%). The 2,4,5-T degraders, 65% of all degraders, were isolated from all soil samples and their 16S rRNA genes were the most homologous with that of Sphingomonas spp., Burkholderia spp. or Bradyrhizobium sp. The following four degradative genes were found by PCR: tfdA (tfdAα) in the Burkholderia spp., Ralstonia spp., Bradyrhizobium sp., and Nocardioides sp.; tfdB in all degraders; tftA (cadA) in the Sphingomonas spp., Burkholderia sp. and Bradyrhizobium sp.; tftC only in the Burkholderia sp. The degraders among Burkholderia spp. were isolated only from the central and southern sites, while those among Ralstonia spp. were found only at the north sites with one exception. The Sphingomonas spp. were isolated country-wide, but four phylogenetically different groups were found at one site, while only one group was found at the other five sites. At least three different plasmids that carried the tfd genes were found in the Burkholderia spp. and Ralstonia spp. without relation to the sites and the phylogenetic groups. These results suggest that the 2,4-D- and 2,4,5-T-degrading microbial consortia have spread countrywide and are diverse on a genetic as well as geographic basis.

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