Bacterial Cr(VI) Reduction Concurrently Improves Sunflower (<Emphasis Type="Italic">Helianthus Annuus</Emphasis> L.) Growth

Four Cr(VI)-reducing bacterial strains (Ochrobactrum intermedium, CrT-2, CrT-3 and CrT-4) previously isolated from chromium-contaminated sites were inoculated on to seeds of sunflower (Helianthus annuus var SF-187), which were germinated and grown along with non-inoculated controls with chromate salts (300 μg CrCl₃ or K₂CrO₄ ml⁻¹). Severe reduction (20%) in seed germination was observed in Cr(VI) stress. Plant height decreased (36%) with Cr(VI) when compared with chromium-free control, while O. intermedium inoculation resulted a 20% increment in this parameter as compared to non-inoculated chromium-free control. CrT-3 inoculation resulted a 69% increment in auxin content as compared to non-inoculated control. O. intermedium caused 30% decrease in chromium uptake in sunflower plant roots under Cr(VI) stress as compared to chromium-free control plants.     

Kocuria Flava Induced Growth and Chromium Accumulation in Cicer Arietinum L

In the present investigation a chromate tolerant rhizobacterium Kocuria flava was isolated and inoculated to the Cicer arietinum L to evaluate its effects on growth and chromium accumulation upon exposure of different concentration of chromium (1–10 μg ml^?1) as Cr (VI) for 24 d. K. flava inoculated plant of C. arietinum demonstrated luxuriant growth as compared to non inoculated plant at respective concentration of Cr (VI). K. flava found to ameliorate chromium induced phytotoxicity in terms of chlorophylls, carotenoid and protein contents and thus helps the plant in acquiring higher biomass with high chromium concentration. After 24 d, maximum concentration of chromium recorded in root of C. arietinum (4892.39 μg g^?1dw) inoculated with K. flava as compared to non inoculated plant (1762.22 μg g^?1dw) upon exposure of 5 μg ml^?1Cr (VI). Therefore, application of C. arietinum in association with K. flava could be more efficient in decontamination of chromium polluted site. Moreover, K. flava may be used as a bioresource for developing microbes assisted phytoremediation system due to its compatibility.     

Soil chromium bioremediation: Synergic activity of actinobacteria and plants

The aim of this work was to evaluate a strategy to reduce the bioavailable chromium fraction in soil, using a Cr(VI) resistant microorganism, Streptomyces sp. MC1, under non sterile conditions, with maize plants as bioindicator and/or bioremediator.Soil samples were contaminated with 100, 200 and 400 mg kg⁻¹ of Cr(VI) or Cr(III). Bioavailable chromium (35%) was only detected in samples with Cr(VI). Soil samples with Cr(VI) 200 mg kg⁻¹ were inoculated with Streptomyces sp. MC1, and bioavailable chromium decreased up to 73%.Zea mays seedlings were planted in soil samples contaminated with chromium. Plantlets accumulated chromium mainly as Cr(III), and biomass decreased up to 88%. Streptomyces sp. MC1 was inoculated in soil samples contaminated with 200 mg kg⁻¹ of Cr(VI) and Z.mays seedlings were planted.Streptomyces sp. MC1 caused Z.mays biomass increase (57%), chromium accumulation and bioavailable chromium decreased up to 46% and 96%, respectively.This work constitutes the first contribution of cooperative action between actinobacteria and Z.mays in the bioremediation of Cr(VI) contaminated soil. The large removal capacity of bioavailable chromium by Streptomyces sp. MC1 and Z.mays infers that they could be successfully applied together in bioremediation of soils contaminated with Cr(VI).     

Removal of Cr(VI) from ground water by Saccharomyces cerevisiae

Chromium can be removed from ground water by the unicellular yeast, Saccharomyces cerevisiae. Local ground water maintains chromium as CrO₄ ^2- because of bicarbonate buffering and pH and E _h conditions (8.2 and +343 mV, respectively). In laboratory studies, we used commercially available, nonpathogenic S. cerevisiae to remove hexavalent chromium [Cr(VI)] from ground water. The influence of parameters such as temperature, pH, and glucose concentration on Cr(VI) removal by yeast were also examined. S. cerevisiae removed Cr(VI) under aerobic and anaerobic conditions, with a slightly greater rate occurring under anaerobic conditions. Our kinetic studies reveal a reaction rate (V_max) of 0.227 mg h^-1 (g dry wt biomass)^-1 and a Michaelis constant (Km) of 145 mg/l in natural ground water using mature S. cerevisiae cultures. We found a rapid (within 2 minutes) initial removal of Cr(VI) with freshly hydrated cells [55–67 mg h^-1 (g dry wt biomass)^-1] followed by a much slower uptake [0.6–1.1 mg h^-1 (g dry wt biomass)^-1] that diminished with time. A materials-balance for a batch reactor over 24 hours resulted in an overall shift in redox potential from +321 to +90 mV, an increase in the bicarbonate concentration (150–3400 mg/l) and a decrease in the Cr(VI) concentration in the effluent (1.9-0 mg/l).     

Simultaneous speciation of chromium by spectrophotometry and multicomponent analysis

Abstract

A simple, fast and sensitive spectrophotometric method for the simultaneous determination of Cr(III) and Cr(VI) in effluents and contaminated waters using a UV-visible spectrophotometer, which operates with an advanced software for multicomponent analysis, is proposed. The method consists in the complexation of Cr (III) with EDTA and reaction of Cr(VI) with diphenylcarbazide (DPC). Variables, such as pH and colour stability time, were studied. The effect of concomitant ions on the simultaneous Cr(III) and Cr(VI) determination was also investigated. The sums of the chromium species concentrations obtained by the proposed method were compared with the total chromium concentrations found by electrothermal atomic absorption spectrometry. Recoveries of the chromium species between 75 and 136% were obtained for spiked samples. The linear working range for Cr(III) was 0.5-30 mg L^?1, while for Cr(VI) was 0.005-0.30 mg L^?1. The detection limits were 0.3 mg L^?1 for Cr(III) and 0.003 mg L^?1 for Cr(VI) while the quantification limits were 1.0 mg L^?1 for Cr(III) and 0.01 mg L^?1 for Cr(VI).     

Reduction of Cr(VI) by a Bacillus sp.

A Bacillus sp. RE was resistant to chromium and reduced Cr(VI) without accumulating chromium inside the cell. When Cr(VI) was 10 and 40 μg ml⁻¹, >95% of the total Cr(VI) was reduced in 24 and 72 h of growth, respectively, whereas at 80 μg Cr(VI) ml⁻¹ only 50% of Cr(VI) was reduced. However growth was not affected; the cell mass was 0.7–0.8 mg ml⁻¹ in all cases. The cell-free extract showed Cr(VI) reducing enzyme activity which was enhanced (>5 fold) by NADH and NADPH. Like whole cells the enzyme also reduced Cr(VI) with decreasing efficiency on increasing Cr(VI) concentration. The enzyme activity was optimal at pH 6.0 and 30 °C. The enzyme was stable up to 30 °C and from pH 5.5 to 8, but from pH 4 to 5 the enzyme was severely destabilized. Its K_m and V_max were 14 μm and 3.8 nmol min⁻¹ mg⁻¹ respectively. The enzyme activity was enhanced by Cu²⁺ and Ni²⁺ and inhibited by Hg²⁺. Received 21 September 2005; Revisions requested 5 October 2005; Revisions received 16 November 2005; Accepted 16 November 2005     

Metal-Dependent Root Iron Plaque Effects on Distribution and Translocation of Chromium and Nickel in Yellow Flag (Iris pseudacorus L.)

Iris pseudacorus L. (yellow flag) is a wide-use wetland plant for constructed wetlands for removing metals from wastewater. This study aims to understand effects of root iron plaque on sequestration and translocation of Cr and Ni in yellow flag seedlings using a hydroponic experiment. Yellow flag seedlings (4-week-old seedlings with 4–6 leaves) with or without iron plaque induction (at 50 mg Fe²⁺ L^?1 for 72 hours) were spiked for 6 days in the Hoagland solution with Cr or Ni at 0.5, 5, and 50 mg L^?1, equivalent to 1, 10, 100 times of thresholds of surface water quality, respectively. Results indicated that root iron plaque significantly reduced translocation of Cr and Ni to root but increased from root to shoot. Root iron plaque formation counteracted Cr toxicity to yellow flag seedlings while the control showed Cr toxicity to root at 5 mg L^?1and to shoot at 50 mg L^?1 with significant biomass loss. Neither Ni exposures caused significant biomass loss nor root iron plaque formation significantly changed Ni distribution among plant parts. Our study suggests that root iron plaque effects on metal sequestration and translocation in yellow flag seedlings were metal-dependent.     

Optimization of Chromium(VI) Detoxification by Pseudomonas aeruginosa and Its Application for Treatment of Industrial Waste and Contaminated Soil

The reduction of Cr(VI) to Cr(III) is a potential detoxification process. In this study, seven Pseudomonas spp. were isolated and screened for chromium reduction. Isolate P4 was able to grow in the presence of 8000 μM chromium, in spite of the fact that the isolate was not previously exposed to any metal stress. Isolate P4 was identified as Pseudomonas aeruginosa strain SRD chr3 by 16S rDNA sequence analysis. Shake flask study showed 78% reduction of 1000 μM Cr(VI) after 6 h of incubation. The optimum pH for chromium reduction by the isolate was between 6 and 8. Isolate Pseudomonas aeruginosa gave 50–80% Cr(VI) reduction even in the presence of 100 mM of Cu, Mn, Ni, and Zn and 300–800 mM NaCl in 24 h, compared with the absence of any of these metals. In a 5-L reactor, the isolate showed 84.85% reduction of Cr(VI) even at the 70th cycle, with a hydraulic retention time of 24 h from the effluent of a hard chrome plating (electroplating) industry, which contained 2100 mg L^?1 hexavalent chromium. The chromate-amended soil inoculated with the isolate showed 2800 μM chromium removal from 4000 μM Cr(VI) kg^?1 of soil, which corresponds to 70% removal. The isolate had the ability to degrade stimulated waste containing 10,000 μM chromium.     

Chromium Reducing and Plant Growth Promoting Potential of Mesorhizobium Species under Chromium Stress

Chromium-reducing and plant growth–promoting potential, including production of siderophores by chromium(VI)-resistant Mesorhizobium species RC1 and RC4, isolated from chickpea nodules, was assessed both in the presence and absence of chromium(VI) under in vitro conditions. The Mesorhizobium strains displayed a high level of tolerance to chromium (400 μg ml^{? 1}), and showed a varied sensitivity to antibacterial drugs, on yeast extract mannitol (YEM) agar plates. Mesorhizobium strains RC1 and RC4 reduced chromium(VI) by 84% and 83%, respectively at pH 7 in YEM broth after 120 h of incubation. Mesorhizobial strains RC1 and RC4 produced 27 and 35 μg ml^{? 1} of indole acetic acid (IAA), respectively, in Luria-Bertani broth with 100 μg ml^{? 1} of tryptophan. The IAA production by the mesorhizobial strains did not differ significantly (p ≤ .05) under chromium stress and showed a positive reaction for siderophore, HCN, and ammonia, both in the absence and presence of chromium(VI).The present observations suggest that the chromium reducing and plant growth promoting activities of the Mesorhizobium strains could be exploited for bioremediation of chromium(VI) and to enhance the legume productivity for chromium-contaminated soils.     

The phytoprotective effects of arbuscular mycorrhizal fungi on Enterolobium contorstisiliquum (Vell.) Morong in soil containing coal-mine tailings

The purpose of this study was to evaluate the effects of arbuscular mycorrhizal fungi (AMF) on pacara earpod tree (Enterolobium contorstisiliquum) growth and phytoprotection in soil containing coal-mining waste. A greenhouse experiment was carried out with three inoculation treatment groups (non-inoculated, inoculated with Rhizophagus clarus, and inoculated with Acaulospora colombiana) in two substrates (0 or 30% tailings). After 90 days the seedlings were collected to quantify growth parameters, quality, mycorrhizal root colonization rate, and leaf content of chlorophylls and carotenoids. Macronutrients were quantified in the shoots; Cu, Zn, and Mn levels were measured in the shoots and roots; and glomalin content was measured in the rhizosphere. Colonization by A. colombiana (40%) promoted phytoprotection and better growth in seedlings planted in partial tailing substrate, due to the lower Cu (1.04 mg kg^?1) and Zn (13.4 mg kg^?1) levels in shoot dry mass and reduced translocation of these elements to the shoots. A. colombiana increased soil glomalin concentrations (2.98 mg kg^?1) and the accumulation of nutrients necessary for synthesizing chlorophylls and carotenoids in the leaves. Colonization by R. clarus (81%) produced no phytoprotective effects.     

Antagonistic effects of EDTA against biochemical toxicity induced by Cr(VI) in Hordeum vulgare L. seedlings

The present study aims at the amelioration of chromium Cr(VI) toxicity using ethylenediaminetetraacetic acid (EDTA), and to understand the interactive effects of Cr(VI) and EDTA with respect to seedling growth, lipid peroxidation as assessed from malondialdehyde, pigments and antioxidative enzymes in Hordeum vulgare L. Following multivariate statistical techniques were used to study binary interactions between Cr(VI) and EDTA: 2-way ANOVA, Tukey’s multiple comparison test, multiple regression with interaction between Cr an EDTA, beta coefficients, path analysis and non-metric multidimensional scaling (NMDS). The present study revealed that the EDTA decreases lipid peroxidation induced by Cr(VI) and ameliorates the antioxidative defence system and pigment constitution of seedlings grown in Cr(VI) containing media. EDTA–Cr(VI) interaction decreased the Cr content in the seedlings which may be attributed to the chelating effect of EDTA. The root and shoot bioconcentration factors, the ratio of Cr content in the plant to that in the medium, were decreased by addition of EDTA to Cr(VI), indicating a decrease in the uptake of Cr by the seedlings from the medium. NMDS revealed that the ranking of the studied parameters is maintained by ordination on two axes. The study established that EDTA is antagonistic to Cr(VI) induced biochemical toxicity, and improves the antioxidative defence system, increases the chlorophyll content, and decreases Cr uptake in barley seedlings.     

Mitigating effect of nano-zerovalent iron,iron sulfate and EDTA against oxidative stress induced by chromium in <Emphasis Type="Italic">Helianthus annuus</Emphasis> L.

Due to its wide industrial application, chromium (Cr) is known to be a critical environmental pollutant. Contamination of water and agricultural soil by Cr inhibits crop productivity and their physiological and biochemical processes. The objective of the current work was to investigate the effects of appropriate reducing agents such as EDTA, iron sulfate (Fe²⁺), and zerovalent nano iron (Fe⁰ nanoparticles) on growth and physiology of sunflower plants under Cr(VI) stress. Results showed that the Cr uptake increased by increasing the amount of EDTA, leading to a significant reduction in morphological and physiological parameters except for MDA and H₂O₂ contents. Treatment with Fe⁰ nanoparticles and Fe²⁺ reduced Cr concentration in root and shoot, increased root and shoot dry weight, plastid pigments (chlorophyll and carotenoids) and proline contents; however, the level of MDA and H₂O₂ decreased significantly. All parameters were affected by Fe²⁺ during the first week of sampling; however, Fe⁰ nanoparticles affected all traits until the end of the third sampling stage. A statistically significant and positive correlation was found between root Cr concentration and MDA and H₂O₂ seedlings treated with EDTA, Fe²⁺, and Fe⁰ grown under Cr stress. From the result of this study, it can be concluded that sunflower has the potential for accumulation of Cr as a heavy metal, and treatment with Fe⁰ nanoparticles to prevent Cr uptake is more effective than other employed treatments.     

Different response of Alyssum montanum and Helianthus annuus to cadmium bioaccumulation mediated by the endophyte fungus Serendipita indica

Environmental pollution by heavy metals is a severe issue worldwide. Microbe-assisted phytoremediation is a safe, inexpensive, and promising strategy in refinement of metal-polluted regions. Current in vitro work was installed to study effects of the endophytic fungus Serendipita indica on some physiological traits and cadmium (Cd) bioaccumulation of Alyssum montanum and Helianthus annuus seedlings grown in MS medium, under varying levels of Cd (0, 20, 40 and 60 mg Cd/l medium). Even though Cd stress induced phyto-toxicity in both tested species, but a significant improvement was found in biomass accumulation, photosynthetic pigments content, and chlorophyll fluorescence indicators in inoculated seedlings by S. indica under different doses of Cd in media. The non-infected A. montanum plantlets accumulated more Cd in shoot than root, and illustrated the properties of an accumulator species as evidenced by translocation factor (TF) and bioaccumulation factor of shoot (BFS) higher than 1. Contrary to this, un-colonized H. annuus seedlings had higher amount of Cd in root than shoot and showed a phyto-stabilizer feature, as evidenced by TF˂1 and bioaccumulation factor of root (BFR) higher than 1. Presence of S. indica significantly enhanced Cd accumulation in root, while it noticeably diminished Cd amounts of shoot in both A. montanum and H. annuus seedlings, so that inoculated plants had higher values for BFR against lower values for BFS and TF, in compare to non-inoculated ones. These findings indicated that S. indica can be considered as a bio-fertilizer to improve the physiological characteristics of tested species under Cd stress, as well as a bio-stabilizer of Cd in the roots of A. montanum and H. annuus in the regions exposed to toxic levels of Cd.     

Isolation and characterization of a chromium-resistant bacterium Serratia sp. Cr-10 from a chromate-contaminated site

A novel bacterium, Cr-10, was isolated from a chromium-contaminated site and capable of removing toxic chromium species from solution by reducing hexavalent chromium to an insoluble precipitate. Sequence analysis of 16S rRNA gene of strain Cr-10 showed that it was most closely related to Serratia rubidaea JCM 1240^T (97.68%). Physiological and chemotaxonomic data also supported that strain Cr-10 was identified as Serratia sp., a genus which was never specially reported chromate-resistant before. Serratia sp., Cr-10 was tolerant to a concentration of 1,500 mg Cr(VI) L⁻¹, which was the highest level reported until now. The optimum pH and temperature for reduction of Cr(VI) by Serratia sp. Cr-10 were found to be 7.0 and 37 °C, respectively. The Cr(VI) reduction was significantly influenced by additional carbon sources, and among them fructose and lactose offered maximum reduction, with a rate of 0.28 and 0.25 mg Cr(VI) L⁻¹ h⁻¹, respectively. The cell-free extracts and filtrate of the culture were able to reduce Cr(VI) while concentration of total chromium remained stable in the process, indicating that the enzyme-catalyzed mechanism was applied in Cr(VI) reduction by the isolate. Additionally, it was found that there was hardly any chromium on the cell surface of the strain, further supporting that reduction, rather than bioadsorption, plays a major role in the Cr(VI) removal.     

Isolation and characterization of chromium(VI)-reducing Bacillus sp. FY1 and Arthrobacter sp. WZ2 and their bioremediation potential

Two native bacterial strains, FY1 and WZ2, that showed high chromium(VI)-reducing ability were respectively isolated from electroplating and tannery effluent–contaminated sites and identified as Bacillus and Arthrobacter. The objective of the present study was to evaluate their potential for future application in soil bioremediation. The results showed that both Bacillus sp. FY1 and Arthrobacter sp. WZ2 were tolerant to 1000 mg L^?1 Cr(VI) and capable of reducing 78–85% and 75–82% of Cr(VI) (100–200 mg L^?1) within 24 h, respectively. The Cr(VI) reduction rate decreased with increasing levels of Cr(VI) concentration (200–1000 mg L^?1). The optimum pH, temperature, and inoculum concentration for Cr(VI) reduction were found to be between pH 7.0 and 8.0; 30 and 35°C; and 1 × 10⁸ cells ml^?1, respectively. Further evidence for the bioremediation potential of Bacillus sp. FY1 and Arthrobacter sp. WZ2 was provided by the high capacity to reduce 100, 200, and 500 mg kg^?1 Cr(VI) in contaminated soil by 83–91%, 78–85%, and 71–78% within 7 days, respectively. These findings demonstrated the high potential of Bacillus sp. FY1 and Arthrobacter sp. WZ2 for application in future soil bioremediation.     

Effects of pH on NaCl tolerance of American elm (<Emphasis Type="Italic">Ulmus americana</Emphasis>) seedlings inoculated with <Emphasis Type="Italic">Hebeloma crustuliniforme</Emphasis> and <Emphasis Type="Italic">Laccaria bicolor</Emphasis>

In the present study, we investigated the effects of pH treatments on NaCl tolerance in mycorrhizal and non-mycorrhizal American elm. American elm (Ulmus americana) seedlings were inoculated with Hebeloma crustuliniforme, Laccaria bicolor or with both mycorrhizal fungi and subsequently subjected to different pH solutions (pH 3, 6 and 9) containing 0 mM (control) and 60 mM NaCl for 4 weeks. Inoculation with the mycorrhizal fungi did not have a large effect on seedling dry weights when the pH and NaCl treatments were considered independently. However, when the inoculated seedlings were treated with 60 mM NaCl at pH 3 or 6, shoot to root ratios and root hydraulic conductivity were higher compared with non-inoculated plants, likely reflecting changes in seedling water flow properties. At pH 6, transpiration rates were about twofold lower in non-inoculated plants treated with NaCl compared with non-treated controls. For NaCl-treated H. crustuliniforme- and L. bicolor-inoculated plants, the greatest reduction of transpiration rates was at pH 9. Treatment with 60 mM NaCl reduced leaf chlorophyll concentrations more in non-inoculated compared with inoculated plants, with the greatest, twofold, decrease occurring at pH 6. At pH 3, root Na concentrations were higher in inoculated than non-inoculated seedlings; however, there was no effect of inoculation on root Na concentrations at pH 6 and 9. Contrary to the roots, the leaves of inoculated plants had lower Na concentrations at pH 6 and 9, but not at pH 3. The results point to an interaction between ECM fungi and root zone pH for salt tolerance of American elm.     

Effects of Reductants on Phytoextraction of Chromium (VI) by Ipomoea aquatica

Reductants are often used to reduce Cr(VI) in chemical treatments, yet the effects of the reductants on Cr(VI) phytoremediation are not fully understood. This study investigates the effects of different reductants on Cr(VI) phytoremediation by Ipomoea aquatica in simulated solution with 3 mg L^?1 of Cr(VI), pH₀ of 6, and an incubation time of 5 days. Results indicate that the applications of S₂O₃^2?, Fe⁰, and Fe²⁺ at low doses notably increased root Cr concentrations, which were obviously higher than that those in the control (Cr⁶⁺ alone). However, high reductant concentrations decreased bioaccumulation of Cr in the roots and shoots of the plant.

Statistical results indicate that Cr concentrations were significantly and negatively correlated with Fe concentrations in the roots and shoots of the plant (p < 0.05). This suggest that Fe accumulation inhibited Cr accumulation in the plant. A Cr(VI) concentration of 3 mg L^?1 caused short, brown lateral roots with tip necrosis, leaf chlorosis, and noticeable shoot wilting. The leaf necrosis and shoot wilting is caused by oxidative damage of lateral roots by Cr(VI) rather than by the reactive oxygen species generated by the oxidative stress. Addition of the reductants effectively reduced these plant injuries.     

The ability of 16 ectomycorrhizal fungi to increase growth and phosphorus uptake of Eucalyptus globulus Labill. and E. diversicolor F. Muell.

The effectiveness of 16 fungal isolates in forming ectomycorrhizas and increasing the growth and phosphorus uptake of Eucalyptus globulus Labill. and E. diversicolor F. Muell. seedlings was examined in the glasshouse. Seedlings were grown in yellow sand at 2 phosphorus levels (4 and 12 mg P kg^-1 sand). At the time of harvest (100 days), the non-inoculated seedlings and seedlings inoculated with Paxillus muelleri (Berk.) Sacc. and Cortinarius globuliformis Bougher had a low level of contamination from an unknown mycorrhizal fungi. Seedlings inoculated with Thaxterogaster sp. nov. and Hysterangium inflatum Rodway had developed mycorrhizas of the superficial type whereas Hydnangium carneum Wallr. in Dietr., Hymenogaster viscidus Massee & Rodway, Hymenogaster zeylanicus Petch, Setchelliogaster sp. nov., Laccaria laccata (Scop. ex. Fr.) Berk., Scleroderma verrucosum (Vaillant) Pers., Amanita xanthocephala (Berk.) Reid & Hilton, Descolea maculata Bougher and Malajczuk and Pisolithus tinctorius (Pers.) Coker & Couch formed typical pyramidal ectomycorrhizas. The dry weight of non-inoculated and inoculated E. globulus seedlings at 12 mg P kg^-1 sand did not differ, whereas several isolates caused growth depression of E. diversicolor. By contrast, at 4 mg P kg^-1 sand growth increases ranged from 0–13 times above that of non-inoculated seedlings. P. tinctorius produced the largest growth increase on both eucalypt species. In general, isolates which developed more extensive mycorrhizas on roots produced the largest growth responses to inoculation. Isolates which increased plant growth also increased phosphorus uptake by the plant. Seedlings inoculated with L. laccata and S. verrucosum retained more phosphorus in their roots than plants inoculated with the other fungal isolates.     

Biosorption of hexavalent chromium from aqueous solution by a tropical basidiomycete BDT-14 (DSM 15396)

Summary A tropical white-rot basidiomycete, BDT-14 (DSM 15396) was investigated for its chromium (VI) biosorption potential from an aqueous solution. Pre-treatment of fungal biomass with acid resulted in 100% metal adsorption compared to only 26.64% adsorption without any pre-treatment. Chromium adsorption was a rapid process at early exposure resulting in 60% chromium removal within the first 2 h of exposure. An increase in biomass showed an increase in the total metal ions adsorption but a decrease in specific uptake of metal ions. The concentrations of chromium had a pronounced effect on the rate of adsorption. The adsorption efficiency was 100% when the initial Cr (VI) concentration was 100 mg l⁻¹ with 1,000 mg biomass. Only 47.5% adsorption was observed with 500 mg l⁻¹ Cr (VI) concentration. The adsorption data fit well with the Langmuir and Freundlich isotherm models. Comprehensive characterization of parameters indicates BDT−14 biomass as a promising material for Cr (VI) adsorption.     

Phosphate relieves chromium toxicity in Arabidopsis thaliana plants by interfering with chromate uptake

Soil contamination by hexavalent chromium [Cr(VI) or chromate] due to anthropogenic activities has become an increasingly important environmental problem. Mineral nutrients such as phosphate (Pi), sulfate and nitrate have been reported to attenuate Cr(VI) toxicity, but the underlying mechanisms remain to be clarified. Here, we show that chromate activates the expression of low-Pi inducible reporter genes AtPT1 and AtPT2 in Arabidopsis thaliana transgenic seedlings. Primary-root growth was inhibited by 60 % in AtPT2::uidA-expressing seedlings upon exposure to 140-μM Cr(VI). However, increasing the Pi and sulfate supply to the seedlings that were experiencing Cr(VI) toxicity completely and partially restored the root growth, respectively. This effect correlated with the Cr(VI)-induced AtPT2::uidA expression being completely reversed by addition of Pi. To evaluate whether the nutrient supply may affect the endogenous level of Cr in plants grown under toxic Cr(VI) levels, the contents of Cr were measured (by ICP-MS analyses) in seedlings treated with Cr and with or without Pi, sulfate or nitrate. It was found that Cr accumulation increases tenfold in plants treated with 140-μM Cr(VI) without modifying the phosphorus concentration in the plant. In contrast, the supply of Pi specifically decreased the Cr content to levels similar to those found in seedlings grown in medium without chromate. Taken together, these results show that in A. thaliana seedlings the uptake of Cr(VI) is reduced by Pi. Moreover, our data indicate that Pi and sulfate supplements may be useful in strategies for handling Cr-contaminated soils.