Cadmium Toxicity and Role of Plant Growth Promoting Bacteria in Phytoremediation

Heavy metal contamination has become a household word in recent decades as more and more information about the persistence of such pollutants in soil and water, as well as their toxicity to all life forms is being gained. Anthropogenic practices ranging from agriculture to space science are the main culprits. Lead, nickel, zinc, and copper are the foremost pollutants while cadmium is among the most toxic even at very low concentrations. Cadmium is a rare metal but has been identified as a Group I human carcinogen and a threat to the environment at large. It damages almost every organ system in the long run. Among the various technologies being used to remediate polluted soil and water, phytoremediation is a green, clean method which utilizes plants to accumulate and degrade harmful pollutants from the growth matrix. It is both cost-effective and less invasive. The potential of suitable plants can be further enhanced by addition of amendments like Plant Growth Promoting Bacteria (PGPB). These soil bacteria are found in and around the roots of plants and secrete chemicals which promote plant growth and affect bioavailability of substances like minerals, salts and heavy metals in soil. The chapter discusses all these aspects related to phytoremediation in some detail. A small case study which evaluates the phytoremedial potential of Chenopodium album, and its enhancement in the above context is also described. The two PGPBs used here are Pseudomonas fluorescens and Bradyrhizobium japonicum. The test plant has a good potential for accumulating Cd, especially in synergy with the two bacterial strains. The Cd accumulation patterns along with the physiological and biochemical parameters analysed suggest that plants treated with a combination of the PGPBs performed better than those treated with either one individually. PGPB treatments worked better than non-PGPB treatments as hypothesized.