Enhancement of 2,4-Dichlorophenoxyacetic Acid Removal by Gene Bioaugmentation of Activated Sludge

Abstract

 Plasmid-mediated bioaugmentation was demonstrated using sequencing batch reactors (SBRs) for enhancing 2,4-dichlorophenoxyacetic acid (2,4-D) removal by introducing Cupriavidus necator JMP134 and Escherichia coli HB101 harboring 2,4-D-degrading plasmid pJP4. C. necator JMP134 (pJP4) can mineralize and grow on 2,4-D, while E. coli HB101 (pJP4) cannot grow on 2,4-D because it lacks the chromosomal genes to degrade the intermediates. The SBR introduced with C. necator JMP134(pJP4) showed 100% removal against 200 mg/l of 2,4-D just after its introduction, after which 2,4-D removal dropped below 12% on day 7 with decline of the introduced strain. The SBR introduced with E. coli HB101(pJP4) showed low 2,4-D removal, i.e., below 20%, until day 7. Transconjugant strains isolated on day 7 from both SBRs belonged to Pseudomonas plecoglossicida and could not grow on 2,4-D. Both SBRs started removing 2,4-D after day 16, with the appearance of 2,4-D-degrading transconjugants belonging to Burkholderia sacchari.