Effectiveness of Plant Growth-Promoting Rhizobacteria in Phytoremediation of Chromium Stressed Soils

Abstract

Chromium pollution is increasing ceaselessly due to unending industrialization. Of the various oxidation states, Cr6+ is highly detrimental due to its mutagenic and carcinogenic nature. Lack of effectiveness of various conventional methods due to economic and technical constraints resulted in a search for an eco-friendly and cost-effective biological techniques for Cr6+ removal from the soil. Phytoremediation came up as an innovative technique to address the problem. However, the effectiveness of phytoremediation process is greatly hindered in high metal contamination environments. Recently, microbial-mediated plant stress improvement has occurred as a major element of metal stress management in plants, and their role in enhancing plant growth and improving phytoremediation process has been well studied. The inoculation of plants with metal-resistant plant growth-promoting rhizobacteria (PGPR) plays an important role in enhancing the efficiency of heavy metal phytoremediation. PGPR improves the plant growth through innumerable mechanisms, such as production of siderophores, solubilization of mineral nutrients, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, and phytohormone production. These microbes transform heavy metals into soluble and bioavailable forms, hence facilitates metal removal through phytoremediation. Correspondingly, application of plant growth-promoting bacteria exhibiting Cr6+ reduction potential when used as an inoculant with phytoremediation plant may result in improved plant growth and chromium remediation efficiency. This chapter focuses on the Cr6+ remediation potential of PGPR through metal–microbe–plant interactions.