Synergistic removal of phenanthrene and cadmium by two polycyclic aromatic hydrocarbon-degrading bacteria

Abstract:

[Objective] A polycyclic aromatic hydrocarbon (PAH)-degrading strain was isolated from the soil contaminated by PAHs. This strain was mixed with Pseudomonas aeruginosa B6-2 to construct a mixed bacterial system for remediation of the soil or liquid co-contaminated by phenanthrene and cadmium. We investigated the remediation efficiency and the response characteristics of microbial metabolism to Cd at different concentrations, aiming to provide bacterial resources and technology reference for the bioremediation of combined pollution. [Methods] The PAH-degrading strain was screened via enrichment, domestication, isolation, and purification and then identified by physio-biochemical tests and 16S rRNA gene sequence analysis. High performance liquid chromatography and inductively coupled plasma mass spectrometry were employed to evaluate the removal efficiency of phenanthrene and cadmium at different cadmium concentrations. Furthermore, the effects of cadmium stress on phenanthrene biodegradation were analyzed on the basis of cell morphology observed by scanning electron microscopy and metabolic activity. [Results] A novel strain SZ-3 with heavy metal tolerance and high PAH-degrading ability was screened out and identified as Arthrobacter. The mixed system (M) of the two degrading bacteria had high phenanthrene-degrading efficiency and resistance to cadmium stress. The removal rates of M for phenanthrene and cadmium were higher than 85% and 80%, respectively, at the cadmium concentrations of 0.5 mg/L and 10 mg/L. When the cadmium concentrations were 25 mg/L and 50 mg/L, M showed the removal rates higher than 65% for the two pollutants. Cadmium stress increased the surface roughness, led to different degrees of cell deformation, and strengthened the adhesion and aggregation between cells. Both catechol 1,2-dioxygenase activity and electron transport system activity decreased with the increase in cadmium concentration during the reaction cycle, which was consistent with the variation of phenanthrene degradation rate. [Conclusion] Arthrobacter sp. SZ-3 is a strain with high PAH-degrading efficiency, which, together with P. aeruginosa B6-2, can efficiently remediate the soil co-contaminated by phenanthrene and cadmium. The two strains demonstrated significant synergistic effect on the removal of target pollutants.