Isolation and characterization of Pb-resistant plant growth promoting endophytic bacteria and their role in Pb accumulation by fast-growing trees

Abstract

ABSTRACT Lead (Pb) contamination is one of the major environmental problems on a global scale. Bacterial endophytes have been accepted as a promising technique to assist phytoremediation. In this study, three Pb-tolerant endophytic bacteria were isolated from the roots of Pityrogramma calomelanos. Based on partial 16S rRNA gene sequencing analysis, all isolates were similar to Pseudomonas and tolerated Pb concentration up to 1850mg/L, producing siderophores and solubilized phosphate. Among them, Pc isolate closely related to Pseudomonas psychrophila showed the highest water-soluble Pb in solution (Pb solubilization) and in contaminated soil. This isolate was chosen to study the effects on Pb accumulation in the roots of Acacia mangium and Eucalyptus camaldulensis by a hydroponic experiment. The results showed that, in the Hoagland nutrient solution with no Pb spiking, the roots showed no significant difference (p > 0.05), and the concentration of Pb ranged from 10 to 89 mg/kg. In the nutrient solution in the presence of 30 mg/L Pb, there were no significant changes in Pb contents in roots. However, A. mangium showed an increase in Pb concentration in the roots (6829 ± 697 mg/kg), compared to non-inoculation (6242 ± 272 mg/kg). E. camaldulensis inoculation showed a decrease in Pb content (3763 ± 592 mg/kg), compared to non-inoculation (4233 ± 264 mg/kg). These results suggest that the Pc isolate closely related to P. psychrophila was effective in promoting the phytoremediation potential of A. mangium, but it was not useful for E. camaldulensis.