MICROBIAL REMEDIATION OF SOILS CO-CONTAMINATED WITH 2,4-DICHLOROPHENOXYACETIC ACID AND CADMIUM

摘要

One-third of organically-polluted sites are also contaminated with metals; however, the bioremediation potential of such sites is not clear. While metals are thought to inhibit the abilities of microbial communities to degrade organic pollutants, several microbial-metal resistance mechanisms are known to exist. This study utilizes cadmium-resistant soil microorganisms to enhance the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) in the presence of cadmium. Cadmium-resistant bacteria were isolated from both a 40-year-old metal-contaminated soil and an uncontaminated soil. During growth experiments, it was found that the uncontaminated soil had a greater number of resistant isolates at low concentrations of cadmium, while the cadmium-contaminated soil exhibited higher microbial resistance with increased cadmium concentrations. ERIC PCR fingerprints discriminated among the cadmium-resistant isolates identified by BIOLOG as Bacillus, Corynebacterium, Pseudomonas, and Xanthomonas spp. These isolates were resistant to concentrations ranging from 5 to 275 ppm soluble cadmium. In conventional degradation studies, two resistant isolates, a Bacillus and an unidentified Gram positive rod, supported the degradation of 500 ppm 2,4-D by the cadmium-sensitive 2,4-D degrader Alcaligenes eutrophus JMP 134 in the presence of 20 and 40 ppm soluble cadmium, respectively.