Advances in the Application of Plant Growth-Promoting Rhizobacteria in Phytoremediation of Heavy Metals

Abstract

In this review, we briefly describe the biological application of PGPR for purposes of phytoremediating heavy metals. We address the agronomic practices that can be used to maximize the remediation potential of plants. Plant roots have limited ability ability mental from soil, mainly because metals have low solubility in the soil solution. The phytoavailability of metal is closely tired to the soil properties and the metabolites that are released by PGPR (e.g., siderophores, organ acids, and plant growth regulators). The role played by PGPR may be accomplished by their direct effect on plant growth dynamics, or indirectly by acidification, chelation, precipitation, or immobilization of heavy metals in the rhizosphere. From performing this review we have formed the following conclusions: The most critical factor is determining how efficient phytoremediation of metal-contaminated soil will be is the rate of uptake of the metal by plants. In turn, this depends on the rate of bioavailability. We know from our review that beneficial bacteria exist tha can alter metal bioavailability of plants. Using these beneficial bacteria improves the performance of phytoremediation of the metal-contaminated sites. Contaminated sites are often nutrient poor. Such soil can be nutrient enriched by applying metal-tolerant microbes that provide key needed plant nutrients. Applying metal-tolerant microbes therefore may be vital in enhancing the detoxification of heavy-metal-contaminated soils (Glick 2003). Plant stress generated by metal-contaminated soils can be countered by enhancing plant defense responses. Responses can be enhanced by alleviating the stress-mediated impact on plants by enzymatic hydrolysis of ACC, which is intermediate in the biosynthetic pathway of ethylene. These plant-microbe partnerships can act as decontaminators by improving phytoremediation. Soil microorganisms play a central role in maintaining soil structure, fertility and in remediating contaminated soils. Although not yet widely applied, utilizing a plant-microbe partnership is now being recognized as an important tool to enhance successful phytoremediaton of metal-contaminated sites. Hence, soil microbes are essential to soil health and sustainability. The key to their usefulness is their close association with, and positive influence on, plant growth and function. To capitalize on the early success of this technique and to improve it, additional research is needed on successful colonization and survival of inoculums under field conditions, because there are vital for the success of this approach. In addition, the effects of the interaction of PGPR and plant root-mediated process on the metal mobilization in soil are required, to better elucidate the mechanism that underlines bacterial-assisted phytoremediation is important. Finally, applying PGPR-associated phytoremediation under field conditions is important, because, to date, only locally contaminated sites have been treated with this technique, by using microbes cultured in the laboratory.

Fungal Biosorption for Cadmium and Mercury Heavy Metal Ions Isolated from Some Polluted Localities in KSA

“…They include the bioavailability of the metal to the microbe, concentration of pollutants, electron acceptors, moisture content, nutrients, osmotic pressure, oxygen, pH, redox potential, soil structure, temperature, and water activity. The bioavailability of each metal in soil is influenced by factors such as the buffering capacity, cation exchange capacity, clay minerals content, metal oxide, and organic matter (Tak et al,2013;Mani and Kumar,2014;Brar et al,2006).…”

Alcaligenes faecalisassociated with Mimosa calodendron rizhosphere assist plant survival in arsenic rich soils

“…High levels of trace elements are toxic for any organism due to blockage of biological functions or modification of essential protein structures (Tak et al, 2013). On the other hand, in small amounts, some heavy metals are essential for plant development and the absence of them induce the reduction of the growth rate (Tak et al, 2013).…”

“…On the other hand, in small amounts, some heavy metals are essential for plant development and the absence of them induce the reduction of the growth rate (Tak et al, 2013).…”

“…In contrast, the survival of non-phytoaccumulator plants in metal-rich environments is improved by the presence of a specialized microbial community (Seth et al, 2007). In addition to protect plants from toxic effects, these communities often facilitate nutritional uptake by enhancing plant growth (Tak et al, 2013). It has been demonstrated that As-resistant bacteria associated with Pteris vittata, a hyperaccumulator plant occurring on IQ that improve plant growth and help in metal removal (Han et al, 2016).…”

Chromium uptake by giant reed under rhizobacterial inhibition

“…PGPR can help the improvement of plant growth, plant nutrition, root growth pattern, plant competitiveness and responses to external stress factors. They can also inhibit soilborne plant pathogens by producing growth-promoting chemical substances and inducing plant resistance (Tak et al 2013;Titah et al 2013). Different plant growth-promoting rhizosphere bacteria, including associative bacteria such as Azospirillum, Bacillus, Pseudomonas, Enterobacter group have been used for their beneficial effects on plant growth.…”