Chapter 23 - Plant growth promoting bacteria (PGPB): applications and challenges in bioremediation of metal and metalloid contaminated soils

Abstract

Plants harbor numerous genera of plant growth promoting bacteria (PGPB). PGPB facilitates metal uptake and promotes growth of plants either as free-living bacteria, binds to plant externally for instance, on roots (rhizosphere) or leaves (phyllosphere), or colonize as endophytic bacteria within internal plant tissues. Plant growth promoting rhizospheric bacteria (PGPR) and plant growth-promoting endophytic bacteria (PGPE) are major categories of PGPB. PGPR on the basis of PGPR host relationship are categorized as intracellular-plant growth promoting rhizobacteria (iPGPR) which live in structural and nonstructural nodules of root cells or extracellular-plant growth promoting rhizobacteria (ePGPR) which colonize rhizosphere over the rhizoplane or superficial intercellular spaces of root cells. The tagline “everything is everywhere, but the environment selects” stands very practical for PGPBs. PGPB produces siderophores, multiply easily, wide action spectrum, harmless to environment, stress-tolerant, and promotes plant growth and health by facilitating the improved nutrient availability, mobilization of nutrients, and assimilation and production of several metabolites. Due to the growing human population and critical world food production challenge of high and stable successful crop yields, the need for smart crop production technologies will increase for sustainable next-generation agriculture. The commercialization of plant-associated microbes is one of the most dynamic fields with a market value of 946.6 million dollars (2015), which will upsurge with 14.08% till end of 2022.