title: Enhancement of 2,4-dichlorophenoxyacetic acid (2,4-D) degradation in soil by dissemination of catabolic plasmids.
abstract: Few studies have been done to evaluate the transfer of catabolic plasmids from an introduced donor strain to indigenous microbial populations as a means to remediate contaminated soils. In this work we determined the effect of the conjugative transfer of two 2,4-D degradative plasmids to indigenous soil bacterial populations on the rate of 2,4-D degradation in soil. We also assessed the influence of the presence of 2,4-D on the number of transconjugants formed. The two plasmids used, pEMT1k and pEMT3k, encode 2,4-D degradative genes (tfd) that differ in DNA sequence as well as gene organisation, and confer different growth rates to Ralstonia eutropha JMP228 when grown with 2,4-D as a sole carbon source. In an agricultural soil (Ardoyen) treated with 2,4-D (100 ppm) there were ca. 10(7) CFU of transconjugants per gram bearing pEMT1k as well as a high number of pEMT3k bearing transconjugants (ca 10(6) CFU/g). In this soil the formation of a high number of 2,4-D degrading transconjugants resulted in faster degradation of 2,4-D as compared to the uninoculated control soil. In contrast, only transconjugants with pEMT1k were detected (at a level of ca. 10(3) CFU/g soil) in the untreated Ardoyen soil. High numbers of transconjugants that carried pEMT1k were also found in a second experiment done using forest soil (Lembeke) treated with 100 ppm 2,4-D. However, unlike in the Ardoyen soil, no transconjugants with pEMT3k were detected and the transfer of plasmid pEMT1k to indigenous bacteria did not result in a higher rate of decrease of 2,4-D. This may be because 2,4-D was readily metabolised by indigenous bacteria in this soil. The results indicate that bioaugmentation with catabolic plasmids may be a viable means to enhance the bioremediation of soils which lack an adequate intrinsic ability to degrade a given xenobiotic.
authors.affiliation: Department of Biochemical and Microbial Technology, Faculty of Agricultural and Applied Biological Sciences, University of Ghent, Belgium.
authors.forename: E M
authors.initials: EM
authors.lastname: Top
authors.forename: P
authors.initials: P
authors.lastname: Van Daele
authors.forename: N
authors.initials: N
authors.lastname: De Saeyer
authors.forename: L J
authors.initials: LJ
authors.lastname: Forney
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000378:metabolism*; D001419:Bacteria / Q000235:genetics / Q000378:metabolism; D001673:Biodegradation, Environmental; D003227:Conjugation, Genetic; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development; D018014:Gene Transfer Techniques; D006540:Herbicides / Q000378:metabolism*; D010957:Plasmids / Q000235:genetics*; D012988:Soil Microbiology
chemical_list: D006540:Herbicides; D015084:2,4-Dichlorophenoxyacetic Acid