Isolation, Identification and Characteristics of an Efficient PCBs-Degrading Strain

Abstract

An efficient polychlorinated biphenyls (PCBs)-degrading bacteria named ZW was cultivated and isolated from soil suffering from long-term PCBs contamination. The strain was identified as Pseudomonas aeruginosa through 16S rDNA sequence analysis. Experiments were conducted to study the degradation characteristics of the bacteria for PCBs. The study revealed that the strain ZW could grow with PCB77 as the only carbon source and its best 7-day degradation rate in 2 mL culture (OD600 = 1.0) was 50.1%, with the PCB77 concentration at 1.0 mg L−1, pH 7.5, 30 °C and rotating speed 150 r min−1 in a Thermostatic Vibrating Incubator. The influence of additives, including four organic matters and five heavy metals, on the degradation rate was also studied. It was indicated that the degradation rates changed to 65.2, 59.58, 52.3 and 39.8%, respectively, when the same concentration (i.e. 1.0 mg L−1) of Tween-80 or biphenyl or phthalic acid or benzoic acid was introduced. The presence of Cd2+, Cu2+, Ni2+, Cr6+ and Pb2+ had inhibiting effect on the biodegradation rate in a descending order Cd2+ > Cu2+ > Cr6+ > Ni2+ > Pb2+ with the same heave metal ion concentration, and the higher the concentration, the more significant the inhibitory effect was. As the number of chlorine atoms in PCB congeners (PCB18, PCB77, PCB101) increased, the degradation rate changed to 89.6, 49.6 and 23.5%, respectively. The toxicity of PCBs biodegradable system decreased over time and the drop rate showed negative correlation with the number of chlorine atoms in PCBs.