Perspectives of plant-associated microbes in heavy metal phytoremediation.

Use of plant growth promoting rhizobacteria (PGPRs) with multiple plant growth promoting traits in stress agriculture: Action mechanisms and future prospects

Bacterial chromate reductase, a potential enzyme for bioremediation of hexavalent chromium: a review.

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 (HMT) plant growth promoting (PGP) microbes in ensuring plant survival and growth in contaminated soils is 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.

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Alleviation of Heavy Metal Stress in Plants and Remediation of Soil by Rhizosphere Microorganisms.

Bacterial mediated alleviation of heavy metal stress and decreased accumulation of metals in plant tissues: Mechanisms and future prospects.

This article reports on the isolation and characterization of a Cr(VI) resistant bacterial strain, having plant growth promoting properties to improve general growth of plant in chromium-contaminated soil through rhizosphere colonization. The strain was isolated from the sludge of waste canal carrying industrial effluents. The minimum inhibitory concentration of chromium to this strain was found to be 450 and 400 mM in complex and minimal media, respectively. The strain also showed varied degree of resistance to Cd, Co, As, Ni and Zn. It exhibited potential Cr(VI) reducing ability under aerobic culture conditions, and the factors affecting Cr(VI) reduction by this strain were evaluated. The optimum pH and temperature required to achieve maximum Cr(VI) reduction values were 7 and 35°C, respectively. Higher concentration of Cr(VI) slowed down the reduction, but with longer incubation time it reduced nearly all detectable amount of Cr(VI). The strain showed positive response to IAA production and phosphate solubilization. It promoted the growth of chilli plants in waste-fed soil with or without additional Cr through its establishment in rhizosphere. The successful establishment of KUCr3 in the rhizosphere of chilli plants helped to reduce Cr uptake by the test plant. This strain shows a promise that the multifarious role of this strain would be useful in the Cr-contaminated rhizosphere soil as a good bioremediation and plant growth promoting agent as well. Through biochemical characterization and 16S rDNA sequence analysis, the strain KUCr3, as the name given to it, was identified as a strain of Cellulosimicrobium cellulans.

Plant growth promotion by a hexavalent chromium reducing bacterial strain, Cellulosimicrobium cellulans KUCr3

Microbial enzymatic reduction of a toxic form of chromium [Cr(VI)] has been considered as an effective method for bioremediation of this metal. This study reports on the in vitro reduction of Cr(VI) using cell-free extracts from a Cr(VI) reducing Bacillus firmus KUCr1 strain. Chromium reductase was found to be constitutive and its activity was observed both in soluble cell fractions (S 12 and S 150 ) and membrane cell fraction (P 150 ). The reductase activity of S 12 fraction was found to be optimal at 40 µM Cr(VI) with enzyme concentration equivalent to 0.493 mg protein/ml. Enzyme activity was dependent on NADH or NADPH as electron donor; optimal temperature and pH for better enzyme activity were 70∞C and 5.6, respectively. The K m value of the reductase was 58.33 µM chromate having a V max of 11.42 µM/min/mg protein. The metabolic inhibitor like sodium azide inhibited reductase activity of membrane fraction of the cell-free extract. Metal ions like

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Chromate reduction by cell-free extract of Bacillus firmus KUCr1.

A chromium resistant bacterial strain KUCr1 exhibiting potential Cr(VI) reducing ability under in vitro aerobic condition is reported. The bacterial strain showed varied degree of resistance to different heavy metals. The MIC of chromium to this strain was found to be 950 mM under aerobic culture condition in complex medium. The factors affecting Cr(VI) reduction by this strain under culture condition were evaluated. Maximal Cr(VI) reduction was observed at the pH 8 to 10 and at a temperature of 35∞C. Higher concentration of Cr(VI) slowed down the reduction, eventually all the metal could be reduced with longer incubation time. Different toxic metals showed differential effect on reduction. Cadmium and zinc were found to inhibit reduction. Cr(VI) reduction and bioremediation were found to be related to the growth supportive condition in terms of carbon, phosphorous and nitrogen supply in wastewater fed with tannery effluent indicating cell mass dependency of Cr(VI) reduction. Through biochemical characterization and 16S rDNA sequence analysis, the strain KUCr1, as the name given to it, was identified as a strain of Bacillus firmus.

Isolation and characterization of a Cr(VI) reducing Bacillus firmus strain from industrial effluents.

In this report, possible utilization of a chromium-reducing bacterial strain Cellulosimicrobium cellulans KUCr3 for effective bioremediation of hexavalent chromium (Cr(VI))-containing wastewater fed with tannery effluents has been discussed. Cr(VI) reduction and bioremediation were found to be related to the growth supportive conditions in wastewater, which is indicative of cell mass dependency for Cr(VI) reduction. Cr(VI) reduction was determined by measuring the residual Cr(VI) in the cell-free supernatant using colorimetric reagent S-diphenylcarbazide. Nutrient availability and initial cell density showed a positive relation with Cr(VI) reduction, but it was inhibited with increasing concentration of Cr(VI) under laboratory condition. The optimum temperature and pH for effective Cr(VI) reduction in wastewater were found to be 35°C and 7.5, respectively. The viable cells of KUCr3 were successfully entrapped in an agarose bead that was used in continuous column and batch culture for assaying Cr(...

Bioremediation of Cr(VI) from Chromium-Contaminated Wastewater by Free and Immobilized Cells of Cellulosimicrobium cellulans KUCr3

This study shows the effect of co-inoculation of three bacterial isolates, viz. Bacillus firmus KUCr1, Cellulosimicrobium cellulans KUCr3 and Pseudomonas aeruginosa KUCd1, on selected growth parameters of amaranth plants. KUCr1 and KUCr3 are reported to be P-solubilizers and indole acetic acid (IAA) producers, and KUCd1 is a siderophore producer. Co-inoculation of the three isolates gave the best results for overall growth of amaranth plants followed by co-inoculation with KUCr1 and KUCd1, then KUCr1 alone. Among the test isolates, KUCr1 and KUCd1 were found to be better rhizosphere colonizers when co-inoculated. KUCr1 and KUCr3 when co-inoculated produced more IAA in liquid medium. Co-inoculation gave insignificant variation in P-solubilization, but siderophore production by KUCd1 was greatly enhanced when inoculated with other isolates in culture conditions. The augmentation of plant growth, whenusing a consortium culture, might be due to better IAA production andsiderophore production by the test isola...

Gopi Ballav Sau

Papers

Plant growth promotion by a hexavalent chromium reducing bacterial strain, Cellulosimicrobium cellulans KUCr3

Chromate reduction by cell-free extract of Bacillus firmus KUCr1.

Isolation and characterization of a Cr(VI) reducing Bacillus firmus strain from industrial effluents.

Bioremediation of Cr(VI) from Chromium-Contaminated Wastewater by Free and Immobilized Cells of Cellulosimicrobium cellulans KUCr3

Effect of co-inoculation of plant growth-promoting rhizobacteria on the growth of amaranth plants