Biotransformation Of Chromium Research Articles

Biotransformation of Chromium (VI) via a Reductant Activity from the Fungal Strain Purpureocillium lilacinum.

Industrial effluents from chromium-based products lead to chromium pollution in the environment. Several technologies have been employed for the removal of chromium (Cr) from the environment, including adsorption, ion-exchange, bioremediation, etc. In this study, we isolated a Cr (VI)-resistant fungus, Purpureocillium lilacinum, from contaminated soil, which could reduce chromium. We also characterized a reductant activity of dichromate found in the cellular fraction of the fungus: optimal pH and temperature, effect of enzymatic inhibitors and enhancers, metal ions, use of electron donors, and initial Cr (VI) and protein concentration. This study also shows possible mechanisms that could be involved in the elimination of this metal. We observed an increase in the reduction of Cr (VI) activity in the presence of NADH followed by that of formate and acetate, as electron donor. This reduction was highly inhibited by EDTA followed by NaN3 and KCN, and this activity showed the highest activity at an optimal pH of 7.0 at 37 °C with a protein concentration of 3.62 µg/mL.

Biotransformation of chromium (VI) by Bacillus sp. isolated from chromate contaminated landfill site

ABSTRACT A potent Cr (VI) resistant bacterial strain DHS-12(7) was isolated from tannery waste landfill site and identified as Bacillus sp. based on pheno- and genotypic methods. The maximum tolerable concentration (MTC) of Cr (VI) was found as 1000 and 250 ppm in nutrient-rich and minimal salt medium, respectively while significant variation of MTC and Cr (VI) reduction efficiency was observed in the solid and liquid medium. The complete reduction of 10 and 25 ppm Cr (VI) was recorded within 18 h and 24 h., respectively in the minimal salt medium and the reduction trend of the strain was bacterial growth-associated. The detection of almost invariable total Cr concentration and the presence of NADH-dependent chromate reductase activity in the cell-free extract, indicated the extracellular Cr (VI) reduction rather than intracellular uptake. Furthermore, chromate reductase (ChrR) gene was amplified, sequenced and the translated amino acid sequence of the ChrR gene showed a high degree of homology with chromate reductase of different organisms. Conclusively, the findings of the present study highlight that Bacillus sp. strain DHS-12(7) can be a potent bioremediation agent for detoxification of Cr (VI) from the contaminated environmental sites for ecological restoration.

Biotransformation of chromium (VI) in liquid effluents by resistant bacteria isolated from the Matanza-Riachuelo basin, in Argentina

ABSTRACTThe aims of this investigation were to evaluate the bacterial resistance to zinc, copper, chromium (VI) and lead in surface water streams from Buenos Aires, Argentina; to select a chromium-resistant strain able to remove the metal in batch process and to evaluate the potential of this strain to remove chromium (VI) in liquid effluents. Bacterial resistance to the metals was evaluated by determining the minimal inhibitory concentration. The kinetic of chromium (VI) removal by one of the resistant strains was studied in nutrient broth with 50 and 100 mg L−1 of the metal, as well as an effluent from an electroplating industry. High resistance to all the metals under study was observed in the bacterial communities of the Matanza-Riachuelo basin. A chromium-resistant strain was isolated and identified as Microbacterium sp. It was able to remove 50 and 100 mg L−1 of Cr (VI) in 36 and 66 h respectively, with efficiency higher than 99%. Experiments with liquid effluents showed the ability of the strain to transform 150 mg L−1 of the metal in 84 h, with efficiency higher than 99%. These results show the potential of this native strain for the treatment of liquid effluents that contain chromium (VI).

Biotransformation of chromium (Cr-VI to Cr III) from tannery effluent using bacteria and fungi

Chromium, a priority pollutant is well known for its mutagenicity, carcinogenicity and teratogenicity in humans, animals and plants. Extensive use of chromium in industries such as leather tanning, stainless -steel production, electroplating and wood preservatives have resulted in extensive chromium contaminated soil and ground water. Microorganisms are involved in the removal of toxic wastes, both in the natural environment and in controlled treatment systems. The present study was undertake n to optimize the chromium reduction capabilities of microbes isolated from the tannery effluents of Dindigul district. About 68 bacterial and 23 fungal isolates were identified based on their microscopic and macroscopic features. The screening was done on minimal salt media incorporated with potassium dichromate. The Bacillus amyloliquefaciensCRB36 strain showed the maximum chromium reduction activity when compared to other bacterial and fungal species isolated in this study. The optimization of chromium reduction was done using various physico-chemical parameters. In the optimization study, the best condition for the reduction of toxic form of chromium was achieved when starch and peptone were supplied as carbon and nitrogen sources at an optimum pH of 7.0 with an incubation temperature of 30°C. Bioremediation is the most promising, eco -friendly and cost effective technology widely used now a days for detoxification of toxic industrial pollutants in soil and water.

Biosorption and biotransformation of chromium by Serratia sp. isolated from tannery effluent

A bacterium isolated from soil and sediment of a leather tanning mill's effluent was identified as Serratia sp. by the analysis of 16S rDNA. Scanning electron microscopy–energy dispersive X-ray analysis (SEM-EDX) and transmission electron microscopy (TEM) were used to assess morphological changes and confirm chromium biosorption in Serratia sp. both in a shake-flask culture containing chromium and in a tannery wastewater. The SEMEDX and the elemental analysis of the chromate-containing samples confirmed the binding of chromium with the bacterial biomass. The TEM exhibited chromium accumulation throughout the bacterial cell, with some granular deposits in the cell periphery and in the cytoplasm. X-ray diffraction analysis (XRD) was used to quantify the chromium and to determine the chemical nature of the metal–microbe interaction. The XRD data showed the crystalline character of the precipitates, which consisted of mainly calcium chromium oxide, chromium fluoride phosphate and related organo-Cr(III) complex crystals. The XRD data also revealed a strong involvement of cellular carboxyl and phosphate groups in chromium binding by the bacterial biomass. The results of the study indicated that a combined mechanism of ion-exchange, complexation, croprecipitation and immobilization was involved in the biosorption of chromium by bacterial cells in contaminated environments.

Use of synchrotron- and plasma-based spectroscopic techniques to determine the uptake and biotransformation of chromium(iii) and chromium(vi) by Parkinsonia aculeata

In this study, a combination of inductively coupled plasma optical emission spectroscopy and X-ray absorption spectroscopy (XAS) was used to study the uptake and speciation of chromium in Parkinsonia aculeata, commonly known as Mexican Palo Verde. Plants were treated for 14 days in a modified Hoagland solution containing chromium(III) or chromium(VI) at several concentrations. The results showed that plants treated with 70 mg Cr(III) L(-1) and 30 mg Cr(VI) L(-1) had similar Cr concentrations in leaves (∼200 mg kg(-1) dry weight, DW). The results also showed that neither Cr(III) nor Cr(VI) affected the uptake of phosphorus and sulfur. However, the concentration of calcium in the stems of plants treated with Cr(VI) at 40 mg L(-1) (about 6000 mg Ca kg(-1) DW) was significantly higher compared to the Ca concentration (about 3000 mg kg(-1) DW) found in the stems of plants treated with 150 mg Cr(III) L(-1). However, no differences were observed in potassium and magnesium concentrations. The iron concentration (about 1000 mg kg(-1) DW) in roots treated with 40 mg Cr(VI) L(-1) was similar to the iron concentration found in the roots of plants treated with 110 mg Cr(III) L(-1). The XAS data showed that Cr(VI) was reduced to Cr(III) in/on the plant roots and transported as Cr(III) to the stems and leaves. The XAS studies also showed that Cr(III) within plants was present as an octahedral complex.

Time-dependent uptake, distribution and biotransformation of chromium(VI) in individual and bulk human lung cells: application of synchrotron radiation techniques

Chromium(VI) is a human carcinogen, primarily affecting the respiratory tract probably via active transport into cells, followed by the reduction to Cr(III) with the formation of DNA-damaging intermediates. Distribution of Cr and endogenous elements within A549 human lung adenocarcinoma epithelial cells, following treatment with Cr(VI) (100 microM, 20 min or 4 h) were studied by synchrotron-radiation-induced X-ray emission (SRIXE) of single freeze-dried cells. After the 20-min treatment, Cr was confined to a small area of the cytoplasm and strongly co-localized with S, Cl, K, and Ca. After the 4-h treatment, Cr was distributed throughout the cell, with higher concentrations in the nucleus and the cytoplasmic membrane. This time-dependence corresponded to approximately 100% or 0% clonogenic survival of the cells following the 20-min or 4-h treatments, respectively, and could potentially be explained by a new cellular protective mechanism. Such processes may also be important in reducing the potential hazards of Cr(III) dietary supplements, for which there is emerging evidence that they exert their anti-diabetic effects via biological oxidation to Cr(VI). The predominance of Cr(III) was confirmed by micro-XANES spectroscopy of intracellular Cr hotspots. X-ray absorption spectroscopy (XANES and EXAFS, using freeze-dried cells after the 0-4-h treatments) was used to gain insight into the chemical structures of Cr(III) complexes formed during the intracellular reduction of Cr(VI). The polynuclear nature of such complexes (probably with a combination of carboxylato and hydroxo bridging groups and O-donor atoms of small peptides or proteins) was established by XAFS data analyses.