Bioremediation Of Cr Research Articles

Chromium in Environment, Its Toxic Effect from Chromite-Mining and Ferrochrome Industries, and Its Possible Bioremediation

Chromium has long been recognized as a toxic, mutagenic and carcinogenic metal. It is toxic to microorganism, plants, animals and humans. Chromium exists in environment in two stable forms: Cr(VI) and Cr(III). Cr(III) is less toxic and insoluble, while Cr(VI) is extremely toxic and highly soluble. Chromium is used in many industrial applications, but it poses a threat to local environment. The effluents and solid wastes from the mining, chrome-plating, leather-tanning, and dye-manufacturing industries are high in chromium concentration and identified as a major health hazard because of pollution to the environment. Industrial waste is used in landfilling, which causes the seepage, and the leaching of toxic chromium from soil into water bodies poses a threat to the environment. Ferrochrome industry is one of the biggest contributors of the chromium pollution to the water bodies. South Africa has the world’s largest chromium reserve. The waste materials produced by ferrochrome industry are slag, dust and processed water. These wastes have high chromium concentration that can cause pollution to the environment. Inhalation is the major exposure route of the Cr(VI) toxicity in humans. The bioremediation of Cr(VI) to Cr(III) in the polluted site is a cost-effective and ecofriendly solution for preventing chromium detoxification. Bioremediation can be in situ or ex situ, and choice of remediation method depends upon the extent of pollution and the nature of the site. This paper summarizes the chromium pollution caused by ferrochrome industries, current remediation method adopted by ferrochrome industries, and the possible new methods for effective bioremediation. This paper focuses mainly on bioremediation techniques to convert the high-toxic form of chromium to less-toxic and mobile form of chromium.

Identification of the main mechanisms involved in the tolerance and bioremediation of Cr(VI) by Bacillus sp. SFC 500-1E.

Chromium pollution is a problem that affects different areas worldwide and, therefore, must be solved. Bioremediation is a promising alternative to treat environmental contamination, but finding bacterial strains able to tolerate and remove different contaminants is a major challenge, since most co-polluted sites contain mixtures of organic and inorganic substances. In the present work, Bacillus sp. SFC 500-1E, isolated from the bacterial consortium SFC 500-1 native to tannery sediments, showed tolerance to various concentrations of different phenolic compounds and heavy metals, such as Cr(VI). This strain was able to efficiently remove Cr(VI), even in the presence of phenol. The detection of the chrA gene suggested that Cr(VI) extrusion could be a mechanism that allowed this strain to tolerate the heavy metal. However, reduction through cytosolic NADH-dependent chromate reductases may be the main mechanism involved in the remediation. The information provided in this study about the mechanisms through which Bacillus sp. SFC 500-1E removes Cr(VI) should be taken into account for the future application of this strain as a possible candidate to remediate contaminated environments.

Characterization of Product and Potential Mechanism of Cr(VI) Reduction by Anaerobic Activated Sludge in a Sequencing Batch Reactor

Bioremediation of Cr(VI) and nitrate is considered as a promising and cost-effective alternative to chemical and physical methods. However, organo-Cr(III) complexes in effluent generally causes environmental concerns due to second-pollution. Here, Cr(VI) reduction and immobilization efficiencies of anaerobic activated sludge were investigated. Anaerobic activated sludge showed strong reduction ability of Cr(VI) and possessed a great potential of Cr(III) immobilization. Almost 100.0 mg l−1 Cr(VI) could be completely reduced and immobilized by anaerobic activated sludge in a sequencing batch reactor in 24 h. And most generated Cr(III) was accumulated outside of sludge cells. Extracellular polymeric substances (EPS) could bind to Cr(VI) and form EPS-Cr(VI) interaction to reduce the toxic effect of Cr(VI) and promote the Cr(VI) reduction. Protein-like and humic-like substances were responsible for binding with Cr(VI), meanwhile the process was a thermodynamically favorable binding reaction. Then Cr(VI) was reduced to Cr(III) by membrane-associated chromate reductase of sludge. Eventually, the generated Cr(III) might exist as poly-nuclear Cr(III) complexes adhered to sludge surfaces.

Treatment of Chromium Pollution by the Reductase Enzyme Generated by a Chromium-Resistant Bacterium Isolated in Dewatering Sludge

An efficient Cr (VI)-resistant and reducing bacterial strain was successfully isolated in dewatering sludge collected from a sewage treatment plant, and characterized in vitro Cr (VI) reduction through a reductase enzyme. Phylogenetic analysis using 16S rDNA gene sequencing revealed that the newly isolated strain namely Pf-1 was closely related to Bacillus cereus. The strain almost reduced 0.17 mM Cr (VI) within 24h incubation and the presence of different substrates such as glucose, sucrose, or acetate significantly enhanced the reduction rate of Cr (VI) to Cr (III). However, addition of the same substrate at the stationary phase of the microbial growth increased the reduction rate as well as bacterial growth. Additionally, raising the concentration of thiosulfate in the medium doubled the reduction rate under similar conditions. Assay with different fractions of the cells demonstrated that the reductase enzyme activity was mainly associated with the cytoplasmic fraction. The maximum activity was 23.3 µM h-1 mg-1 protein and was obtained at the Cr (VI) concentration of 2 mM. The promising strain can be efficiently employed for bioremediation of Cr (VI) polluted sites.

Hexavalent Chromium Reduction by Microbacterium oleivorans A1: A Possible Mechanism of Chromate -Detoxification and -Bioremediation.

Hexavalent chromium (Cr(6+)) contamination is one of the mejor problems of environmental protection for its carcinogenic effect on human health. Remediation of Cr(6+) contaminated environment thus becomes highest priority. A Gram positive tiny rod shaped chromate (Cr(6+)) reducing bacterium strain A1 was isolated from uranium ore collected from Jaduguda, East Singhbhum, Jharkhand. The strain was identified and characterized in terms of its potential to reduce more toxic Cr(6+) to its less toxic form for its application in bioremediation of Cr(6+) contaminated environments. 16S rRNA gene based phylogentic analysis identified the strain as Microbacterium oleivorans. Along with Cr(6+), the strain showed resistance to other heavy metals including Ag, Cu, Co, Hg, Ni and Zn also. Complete reduction of Cr(6+) (750 µM) was achieved within 84 h with optimum reduction at pH 9 and 30°C. Effect of different parameters including cell mass concentration, pH, induction with Cr(6+), SO4 = ion, heavy metals, etc. on Cr(6+) reduction were studied thoroughly at resting cell condition to study its potential towards Cr(6+) bioremediation. Chromate reductase gene (chrA) was detected within this strain. Along with presence of appropriate genetic determinant, efficient Cr(6+) reduction ability of the strain indicated its potential for developing redox based Cr(6+) remediation system for varied concentrations of Cr6+ under a wide range of environmental conditions. Patent data have suggested the efficient application of Cr(6+) reducing bacteria in cleaning up of Cr(6+) contaminated environments.

In vitro evaluation of bioremediation capacity of a commercial probiotic, Bacillus coagulans, for chromium (VI) and lead (II) toxicity.

Introduction:The bioaccumulation of heavy metals including chromium (VI) (Cr (VI)) and lead (II) (Pb (II)) causes fatal toxicity in humans. Some naturally occurring bacterial genera such as Bacillus and Pseudomonas help in bioremediation of these heavy metals and some of the species of Bacillus are proven probiotics. However, no study has been conducted on Bacillus coagulans, which is a proven probiotic species of genus Bacillus.Objectives:The primary objective of the present study was to assess the potential of a proven probiotic, B. coagulans, marketed as “Sporlac-DS,” to survive in the presence of Cr (VI) and Pb (II) and its ability to reduce its concentration in vitro.Materials and Methods:The Minimum inhibitory concentration (MIC) of the organism for Cr (VI) and Pb (II) was determined followed by its biochemical and morphological characterization. Its antibiotic sensitivity and probiotic efficacy were assessed. Further, its bioremediation capacity was observed in vitro by determining the residual Cr (VI) and Pb (II) concentration after 72 h.Results:B. coagulans could tolerate up to 512 ppm concentration of Cr (VI) and had an MIC of 128 ppm for Pb (II). After 72 h, the organism reduced 32 ppm Cr (VI) and 64 ppm Pb (II) by 93% and 89%, respectively. When B. coagulans was studied before and after growing on Cr (VI) and Pb (II) for 24 h, an increase was seen in sensitivity toward the tested antibiotics whereas no change was observed in morphological and biochemical characters. It also showed no change in their bile and acid tolerance, indicating that it retains its probiotic efficacy.Conclusion:The tested probiotic B. coagulans may have a potential role in bioremediation of Cr (VI) and Pb (II), in vivo.

Bioremediation of Cr(VI) by Enterobacter amnigenus EA31 isolated from tannery waste contaminated soil

A novel chromium resistant and reducing bacterium was isolated from tannery waste contaminated soil. On the basis of different morphological, biochemical characteristics and 16S rRNA gene analysis the strain was identified as Enterobacter amnigenus EA31. The strain reduced Cr(VI) under a wide range of concentrations from 100 to 400 mg/L with a maximumat 100 mg/L. Optimum temperature and pH being 37°C and 9 respectively for maximum chromium reduction. The bacterial culture were repeatedly added with 25 mg/L Cr(VI) until saturation in Cr(VI) reduction was observed. Repeated detoxification of 25 mg/L Cr(VI) could be achieved up to three consecutive inputs. The suspended culture repeatedly reduced 25 mg/L Cr(VI) within 6 h up to three consecutive inputs. The reduction of chromium occurred even in the presence of high concentration of other heavy metals. Assay with resting and permeabilised cells (treated with toluene and Triton X-100) demonstrated that Cr(VI) reduction activity was soluble and not tightly bound to the cell membrane. Inoculation with E. amnigenus improved the growth parameters of wheat and clover under chromium stress. The results suggest that E. amnigenus can be exploited for bioremediation of chromium under various environmental conditions.

Bioremediation of Cr(VI) by Enterobacter amnigenus EA31 isolated from tannery waste contaminated soil

A novel chromium resistant and reducing bacterium was isolated from tannery waste contaminated soil. On the basis of different morphological, biochemical characteristics and 16S rRNA gene analysis the strain was identified as Enterobacter amnigenus EA31. The strain reduced Cr(VI) under a wide range of concentrations from 100 to 400 mg/L with a maximumat 100 mg/L. Optimum temperature and pH being 37°C and 9 respectively for maximum chromium reduction. The bacterial culture were repeatedly added with 25 mg/L Cr(VI) until saturation in Cr(VI) reduction was observed. Repeated detoxification of 25 mg/L Cr(VI) could be achieved up to three consecutive inputs. The suspended culture repeatedly reduced 25 mg/L Cr(VI) within 6 h up to three consecutive inputs. The reduction of chromium occurred even in the presence of high concentration of other heavy metals. Assay with resting and permeabilised cells (treated with toluene and Triton X-100) demonstrated that Cr(VI) reduction activity was soluble and not tightly bound to the cell membrane. Inoculation with E. amnigenus improved the growth parameters of wheat and clover under chromium stress. The results suggest that E. amnigenus can be exploited for bioremediation of chromium under various environmental conditions.

Alleviation of toxic hexavalent chromium using indigenous aerobic bacteria isolated from contaminated tannery industry sites

ABSTRACTIn the last decade, much attention has been paid to bioremediation of Cr(VI) using various bacterial species. Cr(VI) remediation by indegeneous bacteria isolated from contaminated sites of a tannery industry located in Tamil Nadu, India, was investigated in this study. Three Cr(VI) resistant bacterial strains (TES-1, TEf-1, and TES-2) were isolated and selected based on their Cr(VI) reduction ability in minimal salt medium. Among these three bacterial strains, TES-1 was found to be most efficient in bioreduction, while TES-2 was only found to be Cr(VI) resistant and showed negligible bioreduction, whereas TEf-1 was observed to be most Cr(VI) tolerant. Potential for bioremediation of TES-1 and TEf-1 was further investigated at different concentrations of Cr(VI) in the range of 50 to 350 mg L−1. TEf-1 showed prominent synchronous growth throughout the experiment, whereas TES-1 took a longer acclimatization time. Minimum inhibitory concentrations (MIC) of Cr(VI) for TES-1 and TEf-1 were approximated as 600 mg L−1 and 750 mg L−1, respectively. The kinetic behavior of Cr(VI) reduction by TES-1 and TEf-1 exhibited zero- and first-order removal kinetics for Cr(VI), respectively. The most efficient strain TES-1 was identified as Streptomyces sp. by gene sequencing of 16S rRNA.

Versatility of Streptomyces sp. M7 to bioremediate soils co-contaminated with Cr(VI) and lindane

The aim of this work was to study the impact of environmental factors on the bioremediation of Cr(VI) and lindane contaminated soil, by an actinobacterium, Streptomyces sp. M7, in order to optimize the process.Soil samples were contaminated with 25µgkg−1 of lindane and 50mgkg−1 of Cr(VI) and inoculated with Streptomyces sp. M7. The lowest inoculum concentration which simultaneously produced highest removal of Cr(VI) and lindane was 1gkg−1. The influence of physical and chemical parameters was assessed using a full factorial design. The factors and levels tested were: Temperature: 25, 30, 35°C; Humidity: 10%, 20%, 30%; Initial Cr(VI) concentration: 20, 50, 80mgkg−1; Initial lindane concentration: 10, 25, 40µgkg−1.Streptomyces sp. M7 exhibited strong versatility, showing the ability to bioremediate co-contaminated soil samples at several physicochemical conditions. Streptomyces sp. M7 inoculum size was optimized. Also, it was fitted a model to study this process, and it was possible to predict the system performance, knowing the initial conditions. Moreover, optimum temperature and humidity conditions for the bioremediation of soil with different concentrations of Cr(VI) and lindane were determined. Lettuce seedlings were a suitable biomarker to evaluate the contaminants mixture toxicity. Streptomyces sp. M7 carried out a successful bioremediation, which was demonstrated through ecotoxicity test with Lactuca sativa.

Comparative Studies on the Bioremediation of Hexavalent and Trivalent Chromium using Citrobacter freundii: Part I-Effect of parameters controlling Biosorption

The potential of Citrobacter freundii, a Gram negative bacteria for the remediation of hexavalentchromium (Cr(VI)) and trivalent chromium (Cr(III)) from aqueous solutions was investigated. Bioremediationof Cr(VI) involved both biosorption and bioreduction processes, as compared to only biosorption processobserved with respect to Cr(III) bioremediation. In the case of Cr(VI) bioremediation studies, about 59 %biosorption was achieved at an equilibrium time of 2 h, initial Cr(VI) concentration of 4 mg/L, pH 1 and abiomass loading of 5x1011 cells/mL. The remainder, 41 %, was found to be in the form of Cr(III) ions owing tobioreduction of Cr(VI) by the bacteria resulting in the absence of Cr(VI) ions in the residue, there by meetingthe USEPA specifications. Similar studies were carried out using Cr(III) solution for an equilibrium time of 2h, Cr(III) concentration of 4 mg/L, pH 3 and a biomass loading of 6.3x1011 cells/mL, wherein a maximumbiosorption of about 30 % was achieved.

Bacterial community dynamics during bioremediation of Cr(VI)-contaminated soil

Pannonibacter phragmitetus BB was utilized to intensify the remediation of Cr(VI)-contaminated soil. The dynamics of indigenous bacterial community and the role of exogenous P. phragmitetus BB in the bioremediation process were investigated. Water soluble Cr(VI) and pH of the contaminated soil were 518.84 and 8.64mgkg−1, respectively. Cr(VI) in contaminated soil and leachate were completely reduced within two days. Restriction fragment length polymorphism (RFLP) revealed that the relative abundance of P. phragmitetus BB ranged from 35.5 to 74.8% during the bioremediation process, which was dominant in the soil bacterial community. Real-time quantitative PCR revealed that the population of P. phragmitetus BB in soil maintained relatively stable within the first 48h (about 2.0×109cells per gram soil), and the concentration of P. phragmitetus BB increased dramatically after the first 48h. The results suggest that P. phragmitetus BB can play a key role and get competitive advantages in the remediation Cr(VI) contaminated soil.

Aerobic Cr(VI) Reduction by an Indigenous Soil Isolate Bacillus thuringiensis BRC-ZYR2

Chromium (Cr) may cause losses in the yield of field plant, which is one of the favorite habitats of Bacillus thuringiensis (Bt). The purposes of our study were to assess the Cr(VI)-resistance and Cr(VI)-reducing abilities of an indigenous soil isolate of Bt and to determine the factors governing Cr(VI) reduction. Towards this end a novel dichromate-reducing Bt BRC-ZYR2, characterized with insecticidal crystal proteins (ICPs), was isolated from a uranium deposit. Minimum inhibitory concentrations (MICs) of Cr(VI) were determined by broth dilution method and the concentrations of Cr(VI) and total Cr in the supernatant were quantified colorimetrically using 1,5-diphenylcarbazide (DPC) reagent and a mixture of sulfuric-nitric acids, respectively. The isolate contained five ICP genes (cry1Ba, cry1Bb, cry1Be/cry1Bf, cry9Ca and cry9Da) and exhibited a high level of Cr(VI) resistance with MICs of 150 mg L−1 at pH 7.0 and 30 °C, and 500 mg L−1 under optimal conditions (pH 9.0 and 40 °C). The total Cr concentration was similar to initial concentration of Cr(VI) under the optimal condition, suggesting that the essential removal of the Cr(VI) was dependent on Bt reduction. Under optimal conditions, the initial Cr(VI) concentrations from 25 to 75 mg L−1 significantly decreased in 24 h after incubation. Addition of Mn2+, Co2+, Mo2+ and Cu2+ activated Bt-mediated Cr(VI) reduction, while Zn2+, Ni2+ and glucose were found to inhibit the reduction. Our results indicated that this isolate could be a promising biopesticide with the potential for both insect biocontrol and Cr bioremediation in the field.

Estimation of Kinetic Parameters for Bioremediation of Cr(VI) from Wastewater Using Pseudomonas taiwanensis, an Isolated Strain from Enriched Mixed Culture

ABSTRACTAn aerobic mixed culture collected in the form of activated sludge was enriched for Cr(VI) reduction. An indigenous microorganism was isolated from the enriched aerobic mixed culture and identified as Pseudomonas taiwanensis. Bioremediation studies were carried out for treating Cr(VI)-contaminated wastewater using the indigenous microorganism. The kinetic studies were carried out for initial Cr(VI) concentrations ranging from 20 to 200 mg L−1. The maximum consumption of Cr(VI) obtained was 108.3 mg L−1 for an initial Cr(VI) concentration of 150 mg L−1 at a solution pH of 7.0. The effect of nutrient dosage and pH were studied to get their optimum values. The same isolated bacterial strain was also used to treat Cr(VI)-contaminated industrial wastewater collected from a local plating industry. Various growth kinetic models, such as Monod, Powell, Haldane, Luong, and Edward models, were fitted with the obtained experimental data. The obtained results for different growth kinetic models indicate that the growth kinetics of Pseudomonas taiwanensis for bioremediation of Cr(VI) can be better understood by the Luong model (R2 = .913). The rate kinetic analysis was performed using zero-order and three-half-order kinetic models. The three-half-order kinetic model was found to be suitable for the present bioremediation study.

Biosensing and bioremediation of Cr(VI) by cell free extract of Enterobacter aerogenes T2

Hexavalent chromium or Cr(VI) enters the environment through several anthropogenic activities and it is highly toxic and carcinogenic. Hence it is required to be detected and remediated from the environment. In this study, low-cost and environment-friendly methods of biosensing and bioremediation of Cr(VI) have been proposed. Crude cell free extract (CFE) of previously isolated Enterobacter aerogenes T2 (GU265554; NII 1111) was prepared and exploited to develop a stable biosensor for direct estimation of Cr(VI) in waste water, by using three electrodes via cyclic voltammetry. For bioremediation studies, a homogeneous solution of commercially available sodium alginate and CFE was added dropwise in a continuously stirred calcium chloride solution. Biologically modified calcium alginate beads were produced and these were further utilized for bioremediation studies. The proposed sensor showed linear response in the range of 10–40 μg L−1 Cr(VI) and the limit of detection was found to be 6.6 μg L−1 Cr(VI). No interference was observed in presence of metal ions, e.g., lead, cadmium, arsenic, tin etc., except for insignificant interference with molybdenum and manganese. In bioremediation studies, modified calcium alginate beads showed encouraging removal rate 900 mg Cr(VI)/m3 water per day with a removal efficiency of 90%, much above than reported in literature. The proposed sensing system could be a viable alternative to costly measurement procedures. Calcium alginate beads, modified with CFE of E. aerogenes, could be used in bioremediation of Cr(VI) since it could work in real conditions with extraordinarily high capacity.

Anthraquinone 2-sulfonic acid-mediated reduction of Cr(VI) by Bacillus sp. BT1

Bacillus sp. BT1 exhibited enhanced efficiency as well as rate of Cr(VI) reduction in the presence of anthraquinone-2-sulfonic acid (AQS), a quinone compound analogous to humic acid. The culture exhibited 5.67-fold higher Cr(VI) reduction rate in Luria broth containing 100 mg Cr(VI)/L augmented with 1mM AQS. Furthermore, in the absence of AQS, Bacillus sp. BT1 reduced only 100 mg Cr(VI)/L, whereas in the presence of AQS, it reduced a total of 400 mg Cr(VI)/L, added in form of repeated spikes of 100 mg Cr(VI)/L in each cycle. The activation energy of mediated Cr(VI) reduction was found to be 2.1-fold lower in comparison to nonmediated Cr(VI) reduction. The Cr(VI) and AQS, both induced intracellular quinone and chromate reductases in Bacillus sp. BT1. The results demonstrate the potential of AQS-mediated Cr(VI) reduction by Bacillus sp. BT1 in bioremediation of Cr(VI) containing wastewaters.

Bioaugmentation of chromium-polluted soil microcosms withCandida tropicalisdiminishes phytoavailable chromium

Localization of Cr(VI) removal activity in Candida tropicalis strain and the study of its Cr(VI) removal capacity in soil. Candida tropicalis strain HE650140 showed a remarkable capacity to completely reduce 50mgl(-1) of Cr(VI) in 48h under aerobic conditions; however, a small change in total content of chromium in the culture liquid was detected, which can be explained by the formation of Cr(III). Fractionation of the cells showed that chromium removal activity was present in both the cytoplasm and membrane. The bioaugmentation of Cr(VI)-contaminated soil microcosms by live and dead biomass showed that yeast inoculation diminishes phytoavailable chromium from soils, improving different growth parameters of clover. The Cr(VI) removal activity was found in both cytoplasmic and membrane fractions. Both live and dead biomass of C.tropicalis were capable to reduce Cr(VI) in the soil and limit the toxicity of this metal to clover seedlings. This study is one of the few documents that present the ability of dead yeast to limit phytoavailability of Cr(VI) from soil. This is of great significance in bioremediation of Cr(VI)-contaminated soil.

Bioremediation of Cr(VI) Polluted Wastewaters by Sorption on Heat Inactivated Saccharomyces cerevisiae Biomass

The potential of heat inactivated Saccharomyces cerevisiae in the bioremoval and reduction ofCr (VI) ions from wastewaters was evaluated in terms of metal uptake in time and at equilibrium, andbiosorption efficiency, by varying pH, biosorbent doses, contact time and temperature, in batch mode. During the sorption process, the heat inactivated biomass of the yeast Saccharomyces cerevisiae is capable of reducing Cr(VI) to Cr(III). Different kinetic models based on adsorption and reduction are used to represent the kinetic data of Cr(VI) bioremoval by S. cerevisiae, in explaining the biosorption mechanism of heavy metals and potential rate-controlling steps, in the perspective of full-scale process design. The results indicated some potential differences in the Cr(VI) removal mechanism at different experimental conditions. FTIR and SEM analysis were performed as well as to elucidate the mechanism of metal bioremoval by S. cerevisiae. FTIR spectra indicate that heavy metal bioremoval process doesn’t imply in this case the formation of stable covalent bonds, but it is predominantly based on chemical interactions, ion-exchange type. The SEM micrographs of Cr-loaded yeast, indicates that the surface morphology doesn’t change much after chromium ions were uptaken. This leads to the conclusion that Cr(VI) reduction occurs at the interface of the adsorbent.

Bioremediation of chromium by novel strains Enterobacter aerogenes T2 and Acinetobacter sp. PD 12 S2

This study had an objective to identify the most potent chromium-resistant bacteria isolated from tannery effluent and apply them for bioremediation of chromium in tannery effluents. Two such strains (previously characterized and identified by us)--Enterobacter aerogenes (NCBI GenBank USA Accession no. GU265554) and Acinetobacter sp. PD 12 (NCBI GenBank USA Accession no. GU084179)--showed powerful chromium resistivity and bioremediation capabilities among many stains isolated from tannery waste. Parameters such as pH, concentration of hexavalent chromium or Cr (VI), and inoculum volume were varied to observe optimum bioconversion and bioaccumulation of Cr (VI) when the said strains were grown in M9 minimal salt media. E. aerogenes was used to remediate chromium from tannery effluents in a laboratory level experiment. Observation by Scanning Electron Microscope and chromium peak in Energy Dispersive X-ray Spectroscopic microanalysis revealed that E. aerogenes helped remediate a moderate amount of Cr (VI) (8-16 mg L(-1)) over a wide range of pH values at 35-37°C (within 26.05 h). High inoculum percentage of Acinetobacter sp. PD 12 also enabled bioremediation of 8-16 mg L(-1) of Cr (VI) over a wide range of temperature (25-37°C), mainly at pH 7 (within 63.28 h). The experiment with real tannery effluent gave very encouraging results. The strain E. aerogenes can be used in bioremediation of Cr (VI) since it could work in actual environmental conditions with extraordinarily high capacity.

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).