Enhancement of 2,4-dichlorophenoxyacetic acid (2,4-D) degradation in soil by dissemination of catabolic plasmids |
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Authors: | Eva M. Top Petra Van Daele Nancy De Saeyer Larry J. Forney |
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Affiliation: | (1) Laboratory of Microbial Ecology, Department of Biochemical and Microbial Technology, Faculty of Agricultural and Applied Biological Sciences, University of Ghent, Coupure Links 653, B-9000 Ghent, Belgium;(2) NSF Center for Microbial Ecology, Michigan State University, East Lansing, MI, 48824, U.S.A |
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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. 107CFU of transconjugants per gram bearing pEMT1k as well as a high number of pEMT3k bearing transconjugants (ca. 106 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. 103 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. |
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Keywords: | bio-augmentation 2,4-D catabolic plasmids plasmid transfer soil |
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