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Applied and Environmental Microbiology, August 2000, p. 3399-3407, Vol. 66, No. 8
Department of Microbiology and
Immunology1 and Department of Soil,
Water, and Environmental Science,2
University of Arizona, Tucson, Arizona 85721
Received 20 March 2000/Accepted 31 May 2000
A pilot field study was conducted to assess the impact of
bioaugmentation with two plasmid pJP4-bearing microorganisms: the natural host, Ralstonia eutropha JMP134, and a
laboratory-generated strain amenable to donor counterselection,
Escherichia coli D11. The R. eutropha strain
contained chromosomal genes necessary for mineralization of
2,4-dichlorophenoxyacetic acid (2,4-D), while the E. coli
strain did not. The soil system was contaminated with 2,4-D alone or
was cocontaminated with 2,4-D and Cd. Plasmid transfer to indigenous
populations, plasmid persistence in soil, and degradation of 2,4-D were
monitored over a 63-day period in the bioreactors. To assess the impact
of contaminant reexposure, aliquots of bioreactor soil were reamended
with additional 2,4-D. Both introduced donors remained culturable and
transferred plasmid pJP4 to indigenous recipients, although to
different extents. Isolated transconjugants were members of the
Burkholderia and Ralstonia genera, suggesting multiple, if not successive, plasmid transfers. Upon a second exposure
to 2,4-D, enhanced degradation was observed for all treatments, suggesting microbial adaptation to 2,4-D. Upon reexposure, degradation was most rapid for the E. coli D11-inoculated treatments.
Cd did not significantly impact 2,4-D degradation or transconjugant
formation. This study demonstrated that the choice of donor
microorganism might be a key factor to consider for bioaugmentation
efforts. In addition, the establishment of an array of stable
indigenous plasmid hosts at sites with potential for reexposure or
long-term contamination may be particularly useful.
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Comparison of 2,4-Dichlorophenoxyacetic Acid Degradation and
Plasmid Transfer in Soil Resulting from Bioaugmentation with Two
Different pJP4 Donors
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, Shantz Bldg. No. 38, Rm. 429, University of Arizona, Tucson, AZ 85721. Phone: (520) 626-8292. Fax: (520) 621-1647. E-mail: dnewby{at}ag.arizona.edu.
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