Characterization of Pb-tolerant plant-growth-promoting endophytic bacteria for biosorption potential, isolated from roots of Pb excluders grown in different habitats

Abstract

Bioremediation using metal-tolerant plant-growth-promoting endophytic bacteria has been studied. The biosorption potential of endophytic bacteria isolated from roots of non-metalliferous Pb excluders (Acacia mangium and Eucalyptus camaldulensis), and a metalliferous Pb excluder (Pityrogramma calomelanos) was evaluated. Five isolates were selected and designated as “Pc”, “Pe”, “Ai”, “Aj”, and “El”. Phylogenetic reconstruction suggested that strain Ai was closely related to Serratia proteamaculans, Aj to Pseudomonas sp., El to Bacillus cereus, Pc to Pseudomonas psychrophila, and Pe to Pseudomonas veronii. They could equally tolerate Pb. Most of them had the capacity to produce siderophores and solubilize phosphate, except B. cereus. However, B. cereus showed high capacity of Pb uptake (4.54±0.38 mg/g) and removal (8.36±0.70%) with no significant difference (p>0.05) from the other strains, except P. psychrophila (1.36±0.23 mg/g of Pb uptake, and 2.60±0.44% Pb removal). The results suggest that biosorption capacity may not involve the habitat of a plant host. Plant-growth-promoting traits were not the only factor for biosorption by endophytic bacteria. S. proteamaculans, B. cereus, and P. veronii showed the same Pb biosorption. Strains closely related to P. veronii could be promoted as candidates for the removal of Pb in polluted environments.