Isolation and Characterization of Heavy Metal-Resistant Plant Growth Promoting Rhizobacteria (PGPR) as Candidates for Simultaneous Enhancement of Plant Growth and Bioremediation of Agricultural Metal-Polluted Soils

Application of metal-resistant plant growth-promoting bacteria is an efficient method for enhancing crop yields by improving biomass accumulation and plant tolerance to heavy metals. The present study aimed to isolate and characterize these bacteria from rhizosphere soil and root exudates of plants grown on agricultural soils contaminated with heavy metals. Plant growth-promoting properties of isolated strains were assayed by evaluating their abilities to solubilize insoluble phosphate, produce indole-3-acetic acid (IAA), and fix nitrogen. Resistance to metals toxicity and metal removal potential of the selected strains were investigated by MIC and MBC values determination and atomic absorption spectroscopy (AAS), respectively. Pantoea agglomeransexhibited the maximum solubilization of insoluble phosphate and IAA production. In the case of Cd2+, the highest MIC value belonged to Enterobacter ludwigi. Pseudomonas taiwanensis, P. agglomerans, and E. ludwigi exhibited the greatest MIC value (8mM) in the case of Pb2+. P. agglomerans and E. ludwigi showed the highest MBC of Pb2+(>120mM) and the greatest MBC of Cd2+ (30mM) belonged to P. agglomerans. Also, E. ludwigi exhibited the highest metal removal percentage for Pb2+ as 31.81% and Cd2+ as 37.58%. As results showed, these four isolated strains can be used as novel and efficient agents for improving plant growth, especially in heavy metals polluted agricultural soils.