Potential of plant growth promoting rhizobacteria to mitigate chromium contamination

Abstract

The main threats to human health and agriculture from heavy metals are associated with exposure to chromium, lead, cadmium, mercury, and arsenic. Among the metals, Chromium is one of the most lethal heavy metals because of its toxicity and hazardous nature. It affects biological activities in soil and metabolism of animals, plants, and human health. Among various forms of chromium, trivalent Cr (III) and hexavalent Cr (VI) are more stable in nature. The higher concentration of Cr (VI) in soil may affect many biochemical and physiological processes and consequently inhibits plant growth. Plant growth promoting rhizobacteria (PGPR) are involved in regulation of seed germination, growth promotion, metabolic rate, and other physiological activities of plants. PGPR may reduce toxic effects of Cr (VI) on plant growth through reducing Cr (VI) to Cr (III). Many recent reports describe the application of heavy metal resistant-PGPRs to enhance agricultural yields without accumulation of metal in plant tissues. This review provides information about the mechanisms possessed by heavy metal resistant-PGPRs that ameliorate metal stress to plants and decrease the accumulation of these metals in plant, and finally gives some perspectives for research on these bacteria in agriculture in the future. • Cr(VI) of industrial effluents impact negatively on human health and environment. • The removal of Cr(VI) from wastewater and soil requires serious and immediate attention. • Biological removal of Cr(VI) is a sustainable and environmentally friendly technology. • Cr(VI)-bioremediation strategies are applied in different systems and scales. • Research is essential to solve the problems associated to the large-scale remediation.