DOI: 10.14457/tu.the.2017.207
title: Phytoremediation of lead contaminated soil using fast-growing trees inoculated with endophytic bacteria

description: Contamination of Pb in the environment is one of the main problems on a global scale. Phytoremediation is an emerging green technology to restore the contaminated sites. Recently, the use of trees as phytostabilizers has become a popularly powerful tool to remediate heavy metals from the contaminated environments. However, the ability of trees to uptake Pb is low to moderate level. Besides, Pb has low bioavailability making it difficult to remove. The high amount of Pb accumulated in plants causes phytotoxicity reducing the phytoremediation potential. To overcome these limitations, the use of fast-growing trees assisted by endophytic bacteria has been recommended as a promising technique to clean up Pb polluted soils. In this study, the effects of inoculation of the promising plant growth promoting endophytic bacteria (PGPE) on phytostabilization potential of fast-growing trees were studied. Four fast-growing trees with high heating value were firstly screened using hydroponic test. Two species were selected as the new host for bacterial inoculation based on the highest Pb accumulation in roots such as Acacia mangium (49004 mg/kg) and Eucalyptus camaldulensis (40598 mg/kg). To obtain the potent endophytic bacteria, the Pb accumulation in roots of metallophytes was also screened by means of field survey. Pityrogramma calomelanos containing the highest Pb concentration in roots (32633 mg/kg) was chosen as the host of PGPE. Then, three Pb resistant endophytic bacteria were isolated from the roots of their host. Among them, after characterization of plant growth promoting traits (PGPT) and species identification by 16S rRNA partial gene sequencing analysis, Pseudomonas psychrophila Den 03 was chosen as the promising PGPE. It tolerated Pb concentration up to 1850 mg/L. Besides, it exhibited some PGPT such as siderophore production and phosphate solubilization. Moreover, it showed high Pb solubilization from solution and mobilization from soil. After successful inoculation, P. psychrophila could colonize in roots tissues of the new plant hosts, A. mangium and E. camaldulensis. The effect of P. psychrophila on growth, phytotoxicity and Pb accumulation in those plants were evaluated with the absence and presence of Pb in soil. Inoculation of P. psychrophila showed no influence on plant growth and Pb phytotoxicity. Further, P. psychrophila significantly increased Pb accumulation in shoots of A. mangium and E. camaldulensis. Besides, P. psychrophila increased Pb accumulation in roots of A. mangium, but slightly reduced that of E. camaldulensis. With translocation factor (TF) &lt; 1, A. mangium and E. camaldulensis were identified as excluders that are suitable for phytostabilization. Inoculation of P. psychrophila slightly increased bioconcentration factor (BCF) and TF in A. mangium. In addition, inoculation of P. psychrophila in A. mangium showed higher BCF and lower TF values than those in E. camaldulensis. The results of this study suggested that P. psychrophila could promote the phytostabilization potential of A. mangium, which may be used for remediation of Pb contaminated site.