Abstract
Increasing concentration of heavy metals (HM) due to various anthropogenic activities is a serious problem. Plants are very much affected by HM pollution particularly in contaminated soils. Survival of plants becomes tough and its overall health under HM stress is impaired. Remediation of HM in contaminated soil is done by physical and chemical processes which are costly, time-consuming, and non-sustainable. Metal–microbe interaction is an emerging but under-utilized technology that can be exploited to reduce HM stress in plants. Several rhizosphere microorganisms are known to play essential role in the management of HM stresses in plants. They can accumulate, transform, or detoxify HM. In general, the benefit from these microbes can have a vast impact on plant’s health. Plant–microbe associations targeting HM stress may provide another dimension to existing phytoremediation and rhizoremediation uses. In this review, applied aspects and mechanisms of action of heavy metal tolerant-plant growth promoting (HMT-PGP) microbes in ensuring plant survival and growth in contaminated soils are discussed. The use of HMT-PGP microbes and their interaction with plants in remediation of contaminated soil can be the approach for the future. This low input and sustainable biotechnology can be of immense use/importance in reclaiming the HM contaminated soils, thus increasing the quality and yield of such soils.
Highlights
Heavy metals (HM) are metals of high density
Certain HM are essential for optimum plant growth but excessive amounts are harmful to the plants and other organisms in the food chain
The techniques being used for HM cleanup from contaminated sites include excavation, stabilization or in situ fixation, and soil washing
Summary
Heavy metals (HM) are metals of high density. Regardless of debate on their classification, the term HM in biological sense is more often used for those metals and semimetals with potential human or environmental toxicity (Tchounwou et al, 2012). The techniques being used for HM cleanup from contaminated sites include excavation (physical removal from contaminated sites), stabilization or in situ fixation (stabilization by adding chemicals to alter metal to a state that is not absorbed by plants), and soil washing (reduction of HM by physical or chemical extraction) These physical processes are neither efficient nor cost effective (Schnoor, 1997). In recent past several biological means have been considered (Gavrilescu, 2004; Wuana and Okieimen, 2011) In this context phytoremediation (the use of growing plants reduces the concentration of HM in the soil) and use of rhizospheric microbes have emerged as important alternatives to ensure high efficiency and better performance. The review discusses the utilization of rhizospheric microbes in fighting the HM stress in plants
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