Bioremediation Of Chromium Research Articles

Isolation of a methane-oxidizing bacterium that bioremediates hexavalent chromium from a formerly industrialized Suburban River.

Sediment samples were taken from sediment adjacent to a suburban river in Sheffield in Northern England that had suffered heavy metal pollution due to previous activity of the steel industry (between the 17th and 19th centuries). The most abundant heavy metals found in the samples were lead, chromium, nickel, arsenic and cobalt, with maximum concentrations of 412·80, 25·232, 25·196, 8·123 and 7·66mgkg-1 , respectively. Enrichment cultures were set up using methane as carbon and energy source, as a result of which a strain of methanotroph was isolated that was shown via 16S rRNA gene sequencing to be a strain Methylomonas koyamae and given the designation SHU1. M. koyamae SHU1 removed hexavalent chromium from an initial concentration of 10ppm, which was inhibited by the metabolic inhibitor sodium azide or the methane monooxygenase inhibitor phenylacetylene. To the authors' knowledge, this is the first description of a strain of the widely environmentally distributed genus Methylomonas that is capable of remediating hexavalent chromium. SIGNIFICANCE AND IMPACT OF THE STUDY: Aerobic methanotrophic bacteria are known for bioremediation of an increasing range of organic and inorganic pollutants, using methane as carbon and energy source. Previously, one laboratory methanotroph strain, Methylococcus capsulatus Bath, was known to bioremediate toxic chromium (VI) by reducing it to chromium (III). Here, a newly isolated methanotroph strain, Methylomonas koyamae SHU1, has been shown able to remediate chromium (VI). This indicates that chromium (VI) bioremediation is not unique to M. capsulatus and moreover adds weight to the suggestion that methanotrophs may contribute directly to chromium (VI) detoxification in nature and in polymicrobial bioremediation fed with methane.

Microbial Chromate Reductases: Novel and Potent Mediators in Chromium Bioremediation-A Review

Heavy metal pollution from the growing industrialization are a significant cause of environmental concern.Chromium (Cr) is commonly used in the production of stainless steel, textile dyeing, electroplating, as nuclear coolants and largely in chrome tanning of hides and skins. About 90% of leather is produced by chrome tanning and the leather industry contributes to an overload of Cr toxicity in tannery effluents. Accumulation of Cr6+ is carcinogenic, genotoxic and teratogenic to organisms. Biological methods are ‘green’ approaches for chromium bioremediation and microorganisms are the desired candidates for pollution abatement. Microbial chromate reduction is mediated by chromate reductases (ChrRs) which may be expressed constitutively or inducibly. ChrRs have been produced by a number of bacteria, fungi and yeasts and may be extracellular or localized in the membrane or cytosol. ChrRs are dependent on electron donors such as reduced Nicotinamide adenine dinucleotide (NADH) or reduced Nicotinamide adenine dinucleotide phosphate (NADPH) or reduced Glutathione (GSH) as cofactors. In chromate reduction by ChrRs, Cr6+ undergo one electron transfer to produce an unstable Cr5+ radical that is converted to stable and less toxic Cr3+. Putative ChrR genomic sequences have been studied with 99% sequence similarity in Gram negative bacteria. ChrRs are valuable resources in different environments for chromate reduction. This review is to discuss the expression and characteristics of ChrRs and their mechanisms in reduction of Cr6+ toxicity in order to provide a comprehensive understanding of this novel class of enzymes for promisingapplications in Cr bioremediation.

Role of polyphenol in sugarcane molasses as a nutrient for hexavalent chromium bioremediation using bacteria

Biological methods for the removal of hexavalent chromium (Cr(VI)) from contaminated sites are safe and efficient. This is especially true because they employ microorganisms and nutrients. The use of appropriate nutrients is important for the methods to be economically feasible. This paper aims to investigate the role of polyphenol from sugarcane molasses, an inexpensive material derived from the waste of the sugar industry, as a nutrient that efficiently provides carbon for Cr(VI)-removing bacteria. The colored constituents of sugarcane molasses were characterized based on the activity of Cr(VI)-reduction and the support of bacterial growth. Molasses promoted Cr(VI)-reducing activity in a pH dependent manner. The activity was related to the colored constituents, excluding sugar, by using absorbent-column chromatography. Moreover, the activity was closely related to the polyphenol fractions, which were slightly different from those of the colored constituents. Unlike the colored constituents, the isolated sugar was sufficient to support the growth of bacteria. Polyphenols from sugarcane molasses could reduce Cr(VI) with no effect on bacterial growth. The removal of Cr(VI) combining molasses and Cr(VI)-reducing bacteria may present an additive and/or synergistic effect.

Chromium (VI) bioremediation potential of filamentous fungi isolated from Peruvian tannery industry effluents.

The tannery is an important trade in various Peruvian regions; however, tannery effluents are a serious local environmental threat due to its highly toxics components and lack of efficient treatment. The untreated effluents produced by tannery factories in Arequipa Rio Seco Industrial Park (PIRS) have formed a lake in the region nearby. In this work, we study the capability of filamentous fungi species found in this effluents lake with potential for chromium (VI) bioremediation. Fourteen species of filamentous fungi were isolated; only two species were identified Penicillium citrinum and Trichoderma viride, and third strain identified as Penicillium sp. The filamentous fungi showed that are fully tolerant to chromium (VI) concentrations up to 100mg/L. These fungal strains showed significant growth in chromium (VI) concentrations up to 250mg/L. Tolerant index (TI) analysis revealed that P. citrinum and T. viride began adaptation to chromium (IV) concentrations of 250 and 500mg/L, after 6 and 12days, respectively. When exposed to higher Cr (VI) concentrations (1000mg/L), only T. viride was able to show growth (enhance phase). Interestingly, one of the significant responses from these fungal strains to increasing chromium (VI) concentrations was an increment in secreted laccase enzymes. Our results show tolerance and adaptation to elevated concentrations of chromium (VI) of these fungal strains suggesting their potential as effective agents for bioremediation of tannery effluents.

The role of natural Fe(II)-bearing minerals in chemoautotrophic chromium (VI) bio-reduction in groundwater

To date, comparatively little is known about the role of natural Fe(II)-bearing minerals in bioremediation of chromium (VI) contaminated aquifers subject to chemoautotrophic conditions. This work employed four kinds of Fe(II)-bearing minerals (pyrite, mackinawite, wustite, and magnetite) as inorganic electron donors to support Cr(VI) bio-reduction. In batch experiments, mackinawite (FeS) performed best, with Cr(VI) removal efficiency of 98.1 ± 1.21 % in 96 h. Continuous column experiments lasting 180 d implied that groundwater chemistry and hydrodynamics influenced the Cr(VI) removal process. A breakthrough study suggested that biotic and abiotic contributions to Cr(VI) reduction were 76.0 ± 1.12 % and 24.1 ± 1.43 %, respectively. Cr(VI) was reduced to insoluble Cr(III), whereas Fe(II) and S(-II) in mackinawite were finally oxidized to Fe(III) and sulfate. Mackinawite evolved progressively into pyrrhotite. High-throughput 16S rRNA gene sequencing indicated that mackinawite-driven Cr(VI) reduction was mediated through synergistic interactions of microbial consortia; i.e. autotrophs as Acidovorax synthesized volatile fatty acids as metabolic intermediates, which were consumed by Cr(VI) reducers as Geobacter. Genes encoding enzymes for S oxidation (soxB) and Cr(VI) reduction (chrA, yieF) were upregulated. Cytochrome c participating in Fe(II) oxidation increased significantly. This work advances the development of sustainable techniques for Cr(VI) polluted groundwater remediation.

Implications of plant growth promoting Klebsiella sp. CPSB4 and Enterobacter sp. CPSB49 in luxuriant growth of tomato plants under chromium stress

The present study explores the potential of two chromium tolerant and plant growth promoting bacterial strains, Klebsiella sp. and Enterobacter sp. in luxuriant growth of tomato plants under chromium stress conditions. For the assessment of potentiality of the two selected strains, a pot scale experiment was setup with tomato plant under different levels of chromium contamination. In pot experiment, different plant growth parameters, oxidative stress tolerance and chromium bioremediation potential were studied upon inoculation of the selected bacterial strains. The results of pot experiment showed that both the strains were effective in promotion of plant growth and enhanced the plant biomass but Enterobacter sp. was more prominent in enhancement of root length, shoot length, fresh and dry weight, and nutrient uptake in tomato plant. The enhancement of enzymes to combat oxidative stress in tomato plant under chromium stress was also observed for both the strains. Both strains enhanced the levels of superoxide dismutase, catalase, peroxidase, total phenolic, and ascorbic acid in tomato plant under different levels of chromium stress conditions. The chromium phytoremediation potential of tomato plant upon inoculation of both the strains was also studied. The results of phytoremediation showed greater chromium accumulation in roots with poor translocation in shoot upon inoculation of Klebsiella sp. while no significant enhancement in chromium uptake by tomato plant was observed on inoculation of Enterobacter sp. compared to control. Thus, these two strains can effectively be used in luxuriant growth of tomato plant under metal stress conditions.

Exploration on the bioreduction mechanism of Cr(Ⅵ) by a gram-positive bacterium: Pseudochrobactrum saccharolyticum W1

Bioremediation of chromium (Cr(Ⅵ)) contaminations has been widely reported, but the research on its removal mechanism is still scarce. Studies on Cr(Ⅵ) removal by strains affiliated to genus Pseudochobactrum revealed the Cr(Ⅵ) efficiency removal through the reduction of Cr(Ⅵ) to Cr(Ⅲ). However, the location of Cr(Ⅵ) reduction reaction and exact mechanism are still unspecified. In this work, a Gram-positive bacterial strain, Pseudochrobactrum saccharolyticum W1 (P. saccharolyticum W1) was isolated and tested to remove approximately 53.7% of Cr(Ⅵ) (initial concentration was 200 mg L−1) from the MSM medium. Analysis of SEM-EDS and TEM-EDS indicated that chromium-containing particles precipitated both on the cell surface and in the cytoplasm. Batch experiments indicated that the heat-treated bacterial cells almost had no ability to remove Cr(Ⅵ) from solution, while the resting cells could remove 62.0% of Cr(Ⅵ) at the initial concentration of 10 mg L−1. Additionally, at this concentration, 64.8% and 70.8% of Cr(Ⅵ) was reduced by cell envelope components and intracellular soluble substances after 6 h, respectively. These results suggested that the removal of Cr(Ⅵ) by P. saccharolyticum W1 was through direct reduction, which occurred on both cell envelop and cytoplasm. The results also showed that cytoplasm was the main site for Cr(Ⅵ) reduction compared to the cell envelop. Further analysis of FTIR and XPS verified that C–H, C–C, CO, C–OH and C–O–C groups of cells involved in correlation with chromium during Cr(Ⅵ) reduction. The study offered an insight into the Cr(VI) reduction mechanism of P. saccharolyticum W1.

Draft Genome Sequence of Manganese-Oxidizing Bacterium Massilia sp. Strain Mn16-1_5, Isolated from Serpentine Soil in Taitung, Taiwan.

Massilia sp. strain Mn16-1_5 was isolated from serpentine soil. This strain is able to oxidize manganese and has the potential for bioremediation of chromium. Here, we present a 5.53-Mb draft genome sequence of this strain with a G+C content of 64.8% that might provide more information for species delineation and oxidase genes in this strain.

Bioremediation of Chromium Contaminated and Harbor Dredged Soil

Soil contamination is caused by the presence of manmade chemicals in the natural soil environment. It is often caused by some form of industrial activity, agricultural chemicals or the improper disposal of waste. The most common chemicals involved in soil pollution are petroleum hydrocarbons, pesticides and lead and other heavy metals. Heavy metals are among the major environmental pollutants and the accumulation of these metals is a great concern in agricultural production due to the toxic effects it has on crop growth. Remediation of soil is a challenging process but if done perfectly it can yield very good results. Firstly the physical and chemical properties of the soil are tested for understanding the properties of the soil. Test such as sieve analysis, liquid and plastic limit are done to understand the characteristics of the soil. The contaminants and their concentration in the soil can be identified using SEM ANALYSIS and EDAX. The soil is remediated using purpose which suits the nature of the soil. Remediation of soil can be done using either micro organism, chemicals, plants, by passing high voltage current or by other physical purposes. Use of micro organisms is one of the advanced methods of remediation. Micro organisms such as pseudomonas aeruginosa, pseudomonas alcaligenes, and pseudomonas hibisciola are used for remediating the heavy metals of the soil. The micro organisms are inoculated in the contaminated soil and tests such as pH, temperature, UV spectroscopy 620 nm are conducted to understand the effect of micro organisms on the soil. Atomic Absorption Spectroscopy is finally conducted for the 0th hour and 100th hour to understand the amount of heavy metal reduction in the soil samples.

Artificial Neural Networks (ANNs) and Response Surface Methodology (RSM) Approach for Modelling the Optimization of Chromium (VI) Reduction by Newly Isolated Acinetobacter radioresistens Strain NS-MIE from Agricultural Soil.

Numerous technologies and approaches have been used in the past few decades to remove hexavalent chromium (Cr[VI]) in wastewater and the environment. However, these conventional technologies are not economical and efficient in removing Cr(VI) at a very low concentration (1-100 ppm). As an alternative, the utilization of bioremediation techniques which uses the potential of microorganisms could represent an effective technique for the detoxification of Cr(VI). In this study, we reported a newly isolated bacterium identified as Acinetobacter radioresistens sp. NS-MIE from Malaysian agricultural soil. The chromate reduction potential of strain NS-MIE was optimized using RSM and ANN techniques. The optimum condition predicted by RSM for the bacterium to reduce hexavalent chromium occurred at pH 6, 10 g/L ppm of nutrient broth (NB) concentration and 100 ppm of chromate concentration while the optimum condition predicted by ANN is at pH 6 and 10 g/L of NB concentration and of 60 ppm of chromate concentration with chromate reduction (%) of 75.13 % and 96.27 %, respectively. The analysis by the ANN model shows better prediction data with a higher R2 value of 0.9991 and smaller average absolute deviation (AAD) and root mean square error (RMSE) of 0.33 % and 0.302 %, respectively. Validation analysis showed the predicted values by RSM and ANN were close to the validation values, whereas the ANN showed the lowest deviation, 2.57%, compared to the RSM. This finding suggests that the ANN showed a better prediction and fitting ability compared to the RSM for the nonlinear regression analysis. Based on this study, A. radioresistens sp. NS-MIE exhibits strong potential characteristics as a candidate for the bioremediation of hexavalent chromium in the environment.

Potential of novel Dunaliella salina from sambhar salt lake, India, for bioremediation of hexavalent chromium from aqueous effluents: An optimized green approach

The potential of Dunaliella salina isolated from Sambhar Salt Lake (Rajasthan, India) for biosorption of hexavalent chromium Cr(VI) in aqueous solution has been examined under optimized culture conditions. The influence of various process parameters, such as pH (6–11), incubation time (48–120 h), metal concentration (5–25 mgL-1), inoculum dose (2–10% vv−1), and their combination effects during Cr(VI) sorbtion were analyzed by means of Response Surface Methodology (RSM) based on a 3-level Box-Behnken experiment design. Microalgae showed highest chromium biosorption with 66.4% efficiency at optimum pH (8.6) and 10% (vv−1) inoculum size within 120 h. The experimental data obtained were analyzed by analysis of variance (ANOVA) along with lower value of coefficient of variation (34%), indicated the well fitness of quadratic equation as proposed by response surface model. Involvement of the surface morphology of the microalgae biomass and elemental distribution was studied through Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopic (EDS), Fourier-transform infrared spectroscopy (FTIR) and X-ray Diffraction (XRD) analysis. The findings unequivocally corroborates that the novel microalgae inherits immense potential in alleviating the levels of toxic heavy metal, such as Cr(VI) from the hydrosphere at wide range of pH and metal concentrations. The present study provides a workable solution for bioremediation of hazardous heavy metals, in general, and Cr(VI) in specific from the industrial wastes like tannery effluents.

Efficacy of Aspergillus fumigatus MCC 1175 for Bioremediation of Tannery Wastewater

Tannery effluent is characterized by high concentrations of chromium, nitrogen, sulfur compounds, and organic matter such as tannins. Chromium and tannins are considered an important source of contamination due to their toxic nature and large volume of liquid discharged and solid sludge produced. In the present study, bioremediation of chromium and tannic acid is studied in a batch culture system using response surface methodology. Scanning electron microscopy (SEM) coupled with energy‐dispersive X‐ray (EDX) and Fourier‐transform infrared spectroscopy (FTIR) are used to investigate adsorption phenomena. A chromium and tannic acid resistance fungal strain is isolated from tannery effluent, and identified as Aspergillus fumigatus MCC 1175 based on its 18S rDNA gene sequence. The minimum inhibitory condition (MIC) of the isolate against chromium and tannic acid was found to be 0.2 and 10 mg mL−1, respectively. The maximum Cr(VI) removal efficiency of 65.1% is found at optimum condition of pH 7, 96 h incubation period, 2.75% inoculum, and 0.1 mg mL−1 chromium. The maximum degradation of tannic acid (63.0%) occurs at pH 5, 27.5 mg mL−1 tannic acid, 100 rpm agitation speed, and an incubation period of 96 h. FTIR analysis of A. fumigatus MCC 1175 revealed the presence of carboxyl and phosphate groups as possible binding sites.

In situ bioremediation of hexavalent chromium in presence of iron by dried sludge bacteria exposed to high chromium concentration

Stability of chromium in the ferrochrome slag dumps and leachate are affected by pH, redox potential and the presence of other metallic species in the slag. It is desirable to keep chromium in slag dumps in the trivalent [Cr(III)] state because trivalent chromium is 1000 times less toxic to living organisms than the hexavalent form [Cr(VI)]. Due to the low toxicity and low mobility of Cr(III), it is recommended to convert Cr(VI) to Cr(III) wherever possible to protect the health of living organisms. In this study, the role of Cr(VI) reducing organisms for stabilising chromium in slag dumps was evaluated in the presence of iron [oxidation states Fe(II) and Fe(III)]. The study showed that stabilisation of chromium species in the trivalent state was most favourable under aerated conditions. Up to 100 mg/L Cr(VI) was reduced in less than 24 h by cultures grown under aerobic conditions in the presence of Fe(III). A much shorter time (6 h) was required to reduce the same amount of Cr(VI) in the presence of Fe(II). When oxygen was completely excluded, it was only possible to reduce 20 mg/L in about 48 h which was much slower than the removal of 100 mg/L in less than 24 h under aerated conditions. Fe(II) contributed directly to catalytic reduction of Cr(VI) reduction whereas Fe(III) was beneficial to Cr(VI) reduction up to an initial Cr(VI) concentration of 75 mg/L. Evaluation of Cr(VI) reduction kinetics showed that Cr(VI) reduction under aerobic conditions followed the non-competitively inhibited mixed-order reaction. Cr(VI) reduction in sealed reactor vessels, under anaerobic conditions, followed a modified non-competitive inhibition reaction model. The results indicate that chromium stabilisation in ferrochrome slag dumps would require maintenance of a fully aerated dump supplemented by a culture of Cr(VI) reducing organisms.

Bioremediation of chromium contaminated water by diatoms with concomitant lipid accumulation for biofuel production

Hexavalent chromium compounds such as chromate and dichromate, commonly designated as Cr (VI) compounds, are widely used heavy metals in different industries and are considered highly toxic to most life forms. Unfortunately, they have become a major pollutant of groundwater and rivers around dichromate using industries. Bioremediation is widely used to decrease the amount of dichromate in wastewater but requires large amounts of precious fresh water. Here we tested two marine micro-algal species, Phaeodactylum tricornutum strain CCY0033 and Navicula pelliculosa strain CCMP543, for their ability of dichromate bioremediation and concomitantly producing lipids that can serve as biofuel. Dichromate tolerance of the strains was investigated under different growth conditions in order to obtain high biomass yields, high lipid accumulation and high dichromate removal from the medium. Both algal strains grew well and produced high biomass in media containing up to 1 mg of dichromate per liter. Variations in growth conditions revealed that dichromate removal from the medium correlated positively with biomass yield. Dichromate removal using living cells was in the same order of magnitude as with autoclaved dead cells or when using extracted extracellular polymeric substances (EPS). This suggests biosorption of dichromate to cell-associated polymeric substances as the major mechanism of the bioremediation process. For both strains, optimal dichromate removal and lipid production were achieved at a light intensity of 55 μmol m−2s−1 and at a sodium nitrate concentration of 3 mM. The optimal temperature for dichromate removal and lipid production was 23 °C for P. tricornutum and 27 °C for N. pelliculosa. Compared to P. tricornutum strain CCY0033, N. pelliculosa strain CCMP543 produced an overall higher lipid yield under these conditions.

Bioremediation of hexavalent chromium by endophytic fungi; safe and improved production of Lactuca sativa L

One of the main problems of the industrialized world is the accumulation of chromium (Cr) in soil, which is a serious threat to the crops. Complete removal of Cr from the contaminated soils poses a great challenge. However, this issue can be minimised by using plant growth promoting microbes as a bioremediation tool. In the present study, healthy plants established near the University campus in Mardan were selected for the isolation of Cr resistant endophytes. From the designated plants, 114 species of endophytic fungi were isolated. Among the 114 isolated strains, 4 strains have induced resistance in L. sativa against Cr. The strains were identified as Aspergillus fumigatus, Rhizopus sp., Penicillium radicum and Fusarium proliferatum based on ITS region (18 S rDNA) homology. The isolates have removed Cr from soil and culture media as well as bio-transformed it from highly toxic hexavalent to least toxic trivalent form, thus helped the Cr stressed L. sativa to restore its normal growth. The Rhizopus Sp. CUC23 has mainly accrued Cr and detoxified intracellularly, whereas A. fumigatus ML43 and P. radicum PL17 has detoxified up to 95% of Cr extracellularly. From the results, it is concluded that the selected endophytic strains might be used as biofertilizer for healthy and safe crop production in Cr contaminated soils.

Multiple metal resistance and Cr6+ reduction by bacterium, Staphylococcus sciuri A-HS1, isolated from untreated tannery effluent

A chromium-resistant bacterium was isolated indigenously from tannery effluent and identified as Staphylococcus sciuri. The optimum growth was observed at 37 °C and pH 7. S. sciuri was able to resist Cr6+ (25 mM) and other heavy metals such as As2+ (19 mM), Pb2+ (18.5 mM), Zn2+ (17 mM), Cu2+ (2.5 mM), Cd2+ (3 mM), and Ni2+ (1.5 mM). Biochemical characterization of chromate reductase revealed its optimal pH as 8.0 and temperature as 40 °C. The enzyme activity was stimulated only by Mg2+ among other heavy metals tested. S. sciuri showed chromium biosorption proficiency (q) after 2, 4, 6 and 8 days as 42, 73, 85 and 31 mM/g, respectively. Cr6+ did not stimulate activities of APOX, SOD and CAT significantly, however, only POX showed marked production (86%). Also, enhanced production of glutathione and other non-protein thiols significantly combat metal induced oxidative stress. Pilot study verified that S. sciuri was able to remove 93% Cr6+ from tannery effluent within 6 days of incubation. Thus, S. sciuri could act as a potential candidate for the bioremediation of hexavalent chromium contaminated environmental sites.

Magnesium-induced biofilm development in Arthrobacter sp. SUK 1201 and removal of hexavalent chromium

This study reports the influence of Mg ions on the development and architecture of biofilms by a chromium resistant and reducing bacterium Arthrobacter sp. SUK 1201 and their utilization in the removal of toxic hexavalent chromium. Among the different metal ions tested, Mg(II) greatly influenced the biofilm growth in peptone yeast extract glucose medium. Both Scanning and Confocal Laser Scanning Microscopy revealed that biofilms formed under the induction of Mg(II) had characteristic higher cell densities. The cells remain embedded in thick porous layers of extracellular polymeric substances as evident from the fluorescein isothiocyanate labeled lectin concanavalin A and 4, 6- diamino-2-phenylindole staining. COMSTAT analysis also indicated maximum thickness and roughness coefficient of the biofilm grown in presence of Mg(II). Biofilms of Arthrobacter sp. SUK 1201 developed under such Mg (II) influenced condition showed complete removal of 0.5 mM Cr(VI) in mineral salts medium. The biofilm of this isolate grown in presence of Mg(II) was also able to remove 60µM Cr(VI) from mine seepage water suggesting its possible implication in effective bioremediation of chromium polluted environments.

Optimization of chromium and tannic acid bioremediation by Aspergillus niveus using Plackett\u2013Burman design and response surface methodology

A chromium and tannic acid resistance fungal strain was isolated from tannery effluent, and identified as Aspergillus niveus MCC 1318 based on its rDNA gene sequence. The MIC (minimum inhibitory concentration) of the isolate against chromium and tannic acid was found to be 200 ppm and 5% respectively. Optimization of physiochemical parameters for biosorption of chromium and tannic acid degradation was carried out by Plackett–Burman design followed by response surface methodology (RSM). The maximum chromium removal and tannic acid degradation was found to be 92 and 68% respectively by A. niveus. Chromium removal and tannic acid degradation was increased up to 11 and 6% respectively after optimization. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) was used to investigate biosorption phenomena.

Chromium bioremediation by Alcaligenes sp. strain newly isolated from chromite mine of Sabzevar

In this work, CKCr-6A strain was found to be highly resistant to some toxic heavy metals such as Cr+6, Cr+3, Cu+2, Co+2, Cd+2, Pb+2, Hg+2, U+6, tellurium, and selenite. Herein, high chromate tolerance of an isolated strain is reported with a high minimum inhibitory concentration value of 80,000 mg/L and the effective parameters (pH, temperature, shaking, and glucose concentration) were selected for Cr(VI) removal by this isolated strain. Cr(VI) elimination by the target strain increased with glucose addition to the culture medium. We optimized the possible parameters and their interactions using design experimental software. After optimization, this strain showed high efficiency in detoxifying chromate; this could reduce up to 100 mg/L of Cr(VI) to Cr(III) over 3 h. The CKCr-6A strain exhibited ability to in vitro reduction after 3 h and repeated removing of Cr(VI) without any amendment of nutrients, suggesting its possible application in continuous bioremediation.

Bioremediation of chromium(VI) by Stenotrophomonas maltophilia isolated from tannery effluent

Bioremediation of chromates using bacteria primarily involves the removal/reduction of heavy metals in effluent using indigenous micro-organisms such as chromium reducing bacteria as biosorbents for cleaner and healthier environment. In the present study, the removal of hexavalent chromium by micro-organisms isolated from acclimatized tannery effluent was investigated. Biochemical assays and molecular sequencing revealed strain SRS05 to be Stenotrophomonas maltophilia. Resistance to chromium was determined by agar and broth dilution assays followed by determination of minimal inhibitory concentration. Strain SRS05 was able to resist 400 mg/ml of chromium which reflects that the heavy metal could be utilized by the micro-organism for its growth. Results by atomic absorption spectroscopy, Fourier transform infrared spectroscopic analysis and scanning electron microscopy revealed effective biosorption of chromium by S. maltophilia SRS05 with no intracellular changes morphologically indicating the stability of the organism in the presence of chromium. It is therefore recommended that this bacterium can be used widely for remediation of hexavalent chromium although the genetic basis for observations concluded in this study is to be confirmed.