Comparison of 2,4-dichlorophenoxyacetic acid degradation and plasmid transfer in soil resulting from bioaugmentation with two different pJP4 donors

A pilot field study was conducted to assess the impact of bioaugmentation w ith two plasmid pJP4-bearing microorganisms: the natural host, Ralstonia eu tropha JMP134, and a laboratory-generated strain amenable to donor counters election, Escherichia coli D11, The R. eutropha strain contained chromosoma l genes necessary for mineralization of 2,4-dichlorophenoxyacetic acid (2,4 -D), while the E. coli strain did not. The soil system was contaminated,vit h 2,4-D alone or was cocontaminated with 2,4-D anti 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 i mpact of contaminant reexposure, aliquots of bioreactor soil were reamended with additional 2,4-D. Both introduced donors remained culturable and tran sferred plasmid pJP4 to indigenous recipients, although to different extent s, Isolated transconjugants were members of the Burkholderia and Ralstonia genera? suggesting multiple, if not successive, plasmid transfers, Upon a s econd exposure to 2,4-D, enhanced degradation was observed for all treatmen ts, suggesting microbial adaptation to 2,4-D. Upon reexposure, degradation was most rapid for the E, coli D11-inoculated treatments. Cd did not signif icantly impact 2,4-D degradation or transconjugant formation, This study de monstrated 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 reexpo sure or long-term contamination may be particularly useful.