Role of Pb-solubilizing and plant growth-promoting bacteria in Pb uptake by plants

Phytoextraction of lead (Pb) is a promising green remediation technique of contaminated soils through which Pb ions are absorbed by plant roots and transferred to the shoots, which are easily harvested and removed from the site. However, plant growth and hence the efficiency of phytoextraction is significantly hindered in contaminated soils under the metal stress conditions. In addition, solubility and plant-availability of Pb are typically low in contaminated alkaline soils. To enhance the efficiency of phytoextraction, auxiliary strategies such as the use of plant growth–promoting bacteria (PGPBs) has been adopted. Inoculation of plants with certain strains of PGPBs improves plant growth and biomass production, and thereby assist phytoextraction, through various mechanisms including the exudation of phytohormones, siderophores, and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase enzyme, as well as nitrogen fixation, phosphate solubilization, and antibiotic synthesis. Moreover, various mechanisms, such as acidification, oxidation, reduction, and production of various metal-solubilizing substances by PGPBs can increase Pb solubility and plant uptake, improving the phytoextraction efficiency. In this book chapter, we discuss the underlying mechanisms for the roles of PGPBs in accelerating plant growth and Pb uptake in contaminated soils.