Isolation of the PCB-degrading bacteria Mesorhizobium sp. ZY1 and its combined remediation with Astragalus sinicus L. for contaminated soil.

A bacterial strain ZY1 capable of utilizing PCBs as its carbon source was isolated from the root nodules of Chinese milk vetch (Astragalus sinicusL.). The strain was identified asMesorhizobiumsp. according to its physiological-biochemical properties and the analysis of its 16S rRNA gene sequence. When the initial OD600 was 0.15, 62.7% of 15 mg L−13,3′,4,4′-TCB in a liquid culture was degraded byMesorhizobiumsp. ZY1 within 10 days.Mesorhizobiumsp. ZY1 also greatly increased the biotransformation of soil PCBs. Pot experiments indicated that the soil PCB concentrations of a single incubation of strain ZY1 (R) and a single planting ofA. sinicus(P) decreased by 20.5% and 23.0%, respectively, and the concentration of PCBs in soil treated withA. sinicusand strain ZY1 decreased by 53.1%. We also observed thatA. sinicus-Mesorhizobiumsp. ZY1 treatment (PR) improved plant biomass and the concentration of PCBs in plants compared with a singleA. sinicusplanting treatment (P). The results suggest that the synergistic association betweenA. sinicusand PCBs-degradingMesorhizobiumsp. ZY1 can stimulate the phytoextraction of PCBs and the rhizosphere microflora to degrade PCBs, and might be a promising bioremediation strategy for PCB-contaminated soil. [ABSTRACT FROM AUTHOR]