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Journal ArticleDOI

Cr(VI) reduction by Bacillus coagulans isolated from contaminated soils

01 Dec 1998-Journal of Environmental Engineering (American Society of Civil Engineers)-Vol. 124, Iss: 12, pp 1165-1170
TL;DR: In this article, the authors compared the performance of Bacillus coagulans and Pseudomonas aeruginosa with Bacillus circulans, a pure culture obtained from the Institute of Microbial Technology.
Abstract: Investigation on Cr(VI) reduction was conducted using bacteria isolated from soil samples receiving electroplating wastewater. Chromium reduction capacity of these isolates was compared with that of Pseudomonas aeruginosa, a pure culture procured from the Institute of Microbial Technology, as well as Bacillus circulans, a laboratory isolate from garden soil. Bacillus coagulans, isolated and identified from chromium polluted soil, gave maximum reduction potential among all organisms studied. Malate was found to yield maximum biotransformation out of four electron donors employed. B. coagulans was able to reduce Cr(VI) even at 10 mM initial Cr(VI) concentration. With an increase in initial cell density, Cr(VI) reduction capacity was also increased; however, maximum specific biotransformation occurred at low cell densities. The optimum pH for Cr(VI) reduction was 7. Sulphates and nitrates did not compete with Cr(VI) for accepting the electrons. The presence of respiratory inhibitors like DNP and NaN3 margina...
Citations
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Journal ArticleDOI
TL;DR: This review article focuses on chromium pollution problem, its chemistry, sources, effects, remediation strategies by biological agents and detailed chromium detoxification mechanism in microbial cell.
Abstract: Chromium (VI) is one of the most common environmental contaminant due to its tremendous industrial applications. It is non-biodegradable as it is a heavy metal, and hence, of major concern. Therefore, it is pertinent that the remediation method should be such that brings chromium within permissible limits before the effluent is discharged. Several different strategies are adopted by microorganisms for Cr (VI) removal mostly involving biosorption and biotransformation or both. These mechanisms are based on the surface nature of the biosorbent and the availability of reductants. This review article focuses on chromium pollution problem, its chemistry, sources, effects, remediation strategies by biological agents and detailed chromium detoxification mechanism in microbial cell. A summary of applied in situ and ex situ chromium bioremediation technologies is also listed. This can be helpful for developing technologies to be more efficient for Cr (VI) removal thereby bridging the gap between laboratory findings and industrial application for chromium remediation.

488 citations

Journal ArticleDOI
TL;DR: The present review discusses on the types of chromate reductases found in different bacteria, their mode of action and potential applications in bioremediation of hexavalent chromium both under free and immobilize conditions.
Abstract: Hexavalent chromium is mobile, highly toxic and considered as a priority environmental pollutant. Chromate reductases, found in chromium resistant bacteria are known to catalyse the reduction of Cr(VI) to Cr(III) and have recently received particular attention for their potential use in bioremediation process. Different chromate reductases such as ChrR, YieF, NemA and LpDH, have been identified from bacterial sources which are located either in soluble fractions (cytoplasm) or bound to the membrane of the bacterial cell. The reducing conditions under which these enzymes are functional can either be aerobic or anaerobic or sometimes both. Enzymatic reduction of Cr(VI) to Cr(III) involves transfer of electrons from electron donors like NAD(P)H to Cr(VI) and simultaneous generation of reactive oxygen species (ROS). Based on the steps involved in electron transfer to Cr(VI) and the subsequent amount of ROS generated, two reaction mechanisms, namely, Class I "tight" and Class II "semi tight" have been proposed. The present review discusses on the types of chromate reductases found in different bacteria, their mode of action and potential applications in bioremediation of hexavalent chromium both under free and immobilize conditions. Besides, techniques used in characterization of the Cr (VI) reduced products were also discussed.

363 citations

Journal ArticleDOI
TL;DR: The present work reviews in a critical way the published literature on chromium effects on activated sludge, and on the operation of wastewater treatment plants, and concludes that clear conclusions cannot be derived about the critical chromium concentrations that affectactivated sludge growth.
Abstract: Chromium is a heavy metal of commercial importance, thus significant amounts are released in wastewaters. Chromium in wastewaters and in the aquatic environment is primarily encountered in oxidation stages +3 (Cr (III) ) and +6 (Cr (VI) ). Recent publications suggest that Cr (VI) compounds are more toxic than Cr (III) ones, while Cr (III) has been identified as trace element, at least for complex organisms. With respect to chromium species mobility, Cr (VI) can cross cellular membranes, which then may be oxidized to Cr (III) and react with intracellular biomolecules. Clear conclusions cannot be derived about the critical chromium concentrations that affect activated sludge growth, as the latter is a function of a number of factors. Broadly, may be supported that activated sludge growth is stimulated at Cr (III) concentrations up to 15 mg L −1 , above which is inhibited, with lethal doses lying above 160 mg Cr (III) L −1 . On the other hand, literature data on Cr (VI) effects on activated sludge are even more controversial. A number of reports support that Cr (VI) is toxic to activated sludge at concentrations above 5 mg L −1 , while others report growth stimulation at concentrations up to 25 mg L −1 . However, all reports agree that Cr (VI) is definitely an activated sludge growth inhibitor at higher concentrations, while 80 mg Cr (VI) L −1 have been identified as lethal dose. A number of factors have been identified to influence chromium toxicity on activated sludge, such as, pH, biomass concentration, presence of organic substances or other heavy metals, acclimation process, exposure time, etc. Naturally, the presence of chromium species in wastewaters may affect the performance of wastewater treatment plants often causing malfunctions, particularly for industrial wastewaters containing relatively high chromium concentrations. The present work reviews in a critical way the published literature on chromium effects on activated sludge, and on the operation of wastewater treatment plants.

200 citations

Journal ArticleDOI
TL;DR: This study showed that bioremediation is a viable, environmental friendly technology for cleaning-up the chromium contaminated site at TCCL, Ranipet, Tamil Nadu, India, and optimal operating conditions under laboratory conditions were evaluated.
Abstract: Bacterial strains were isolated and enriched from the contaminated site of Tamil Nadu Chromates and Chemicals Limited (TCCL) premises, Ranipet, Tamil Nadu, India. The strain which was isolated from the highly contaminated location had shown high Cr(VI) reduction potential. Cr(VI) reduction was evaluated both in aerobic and anaerobic conditions. Though the aerobic system performed better than the anaerobic one, further study were carried out in the anaerobic condition due to its economic viability. At higher initial concentration, Cr(VI) reduction was not complete even after 108 h, however, specific Cr(VI) reduction, unit weight of Cr reduced/unit weight of biomass was greater at higher concentration. It was found that a bacterial concentration of 15 ± 1.0 mg/g of soil (wet weight) 50 mg of molasses/g of soil as carbon source were required for the maximum Cr(VI) reduction. The bioreactor operated at these conditions could reduce entire Cr(VI) (5.6 mg Cr(VI)/g of soil) in 20 days. The Cr(III) thus formed was found to be strongly attached to the soil matrix and the mobility of Cr(III) was negligible as evident from the low concentration of Cr(III) in the leachate. This study showed that bioremediation is a viable, environmental friendly technology for cleaning-up the chromium contaminated site at TCCL, Ranipet, Tamil Nadu, India, and optimal operating conditions under laboratory conditions were evaluated.

188 citations

Journal ArticleDOI
TL;DR: In this paper, the main machinery of the process, the microbes, and their conditions, which decide the fate of this heavy metal, should be appropriate for efficient bioremoval of hexavalent chromium [Cr(VI) by bacteria.
Abstract: The anthropogenic inputs of hexavalent chromium [Cr(VI)] have increased enormously during the past few decades and has become a challenge for life on earth and hence removal of this carcinogen has become the need of the hour. Cr(VI) removal through common physicochemical techniques is highly expensive and inappropriate at low concentration. Microbial reduction of Cr(VI) to trivalent form is considered a favorable technique for Cr(VI) removal from wastewater, as it reduces the highly toxic form of Cr to less toxic form and therefore the article conveys essential fundamental information on removal of Cr(VI) by bacteria. For efficient bioremoval of Cr(VI),the main machinery of the process, the microbes, and their conditions, which decide the fate of this heavy metal, should be appropriate. Hence, the authors cover vast information about the isolation of chromium-resistant bacteria from various environment and their Cr(VI) resistance capability. An extensive report is given on information pertaining to the fa...

176 citations


Cites background from "Cr(VI) reduction by Bacillus coagul..."

  • ...Glucose showed maximum reduction in B. coagulans (Philip et al., 1998), E. coli (Bae et al., 2000), and Bacillus sp (Kathiravan et al., 2010a; Liu et al., 2006) because it is catabolized to pyruvate through glycolysis process, that enters the TCA cycle, whereas the other electron donors such as…...

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  • ...The reduction rate of hexavalent chromium by microorganisms are influenced by the initial cell, Cr(VI), and salt concentrations along with pH and temperature (Philip et al., 1998; Shen and Wang 1994a)....

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  • ...Philip et al. (1998) also found that the presence of sulfate or nitrate up to 1000 mg/l did not affect Cr(VI) reduction by Bacillus coagulans....

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References
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Journal ArticleDOI
TL;DR: Neither sulfate nor nitrate affected chromate reduction either in vitro or with intact cells, and Chromate reductase activity was associated with soluble protein and not with the membrane fraction.
Abstract: Reduction of hexavalent chromium (chromate) to less-toxic trivalent chromium was studied by using cell suspensions and cell-free supernatant fluids from Pseudomonas putida PRS2000. Chromate reductase activity was associated with soluble protein and not with the membrane fraction. The crude enzyme activity was heat labile and showed a Km of 40 microM CrO4(2-). Neither sulfate nor nitrate affected chromate reduction either in vitro or with intact cells.

390 citations

Journal ArticleDOI
TL;DR: An Enterobacter cloacae strain (HO1) capable of reducing hexavalent chromium (chromate) was isolated from activated sludge and was resistant to chromate under both aerobic and anaerobic conditions.
Abstract: An Enterobacter cloacae strain (HO1) capable of reducing hexavalent chromium (chromate) was isolated from activated sludge. This bacterium was resistant to chromate under both aerobic and anaerobic conditions. Only the anaerobic culture of the E. cloacae isolate showed chromate reduction. In the anaerobic culture, yellow turned white with chromate and the turbidity increased as the reduction proceeded, suggesting that insoluble chromium hydroxide was formed. E. cloacae is likely to utilize toxic chromate as an electron acceptor anaerobically because (i) the anaerobic growth of E. cloacae HO1 accompanied the decrease of toxic chromate in culture medium, (ii) the chromate-reducing activity was rapidly inhibited by oxygen, and (iii) the reduction occurred more rapidly in glycerol- or acetate-grown cells than in glucose-grown cells. The chromate reduction in E. cloacae HO1 was observed at pH 6.0 to 8.5 (optimum pH, 7.0) and at 10 to 40°C (optimum, 30°C).

329 citations

Journal ArticleDOI
TL;DR: Comparison of the rates of chromate reduction by chromate grown cells and cells grown without chromate indicated that the chromate reductase activity is constitutive, and studies with cell-free extracts show that the reduct enzyme is membrane-associated and can mediate the transfer of electrons from NADH to chromate.
Abstract: Pseudomonas fluorescens LB300 is a chromateresistant strain isolated from chromium-contaminated river sediment Chromate resistance is conferred by the plasmid pLHB1 Strain LB300 grew in minimal salts medium with as much as 1000 μg of K2CrO4 ml−1, and actively reduced chromate to Cr(III) while growing aerobically on a variety of substrates Chromate was also reduced during anaerobic growth on acetate, the chromate serving as terminal electron acceptor P fluorescens LB303, a plasmidless, chromatesensitive variant of P fluorescens LB300, did not grow in minimal salts medium with more than 10 μg of K2CrO4 ml−1 However, resting cells of strain LB303 grown without chromate reduced chromate as well as strain LB300 cells grown under the same conditions Furthermore, resting cells of chromate-sensitive Pseudomonas putida strain AC10, also catalyzed chromate reduction Evidently chromate resistance and chromate reduction in these organisms are unrelated Comparison of the rates of chromate reduction by chromate grown cells and cells grown without chromate indicated that the chromate reductase activity is constitutive Studies with cell-free extracts show that the reductase is membrane-associated and can mediate the transfer of electrons from NADH to chromate

292 citations

Journal ArticleDOI
TL;DR: Washed cells of Enterobacter cloacae HO1 reduced hexavalent chromium (chromate: CrO4(2-) anaerobically and showed high chromate reductase activities when ascorbate-reduced phenazine methosulfate was added as an electron donor.
Abstract: Washed cells of Enterobacter cloacae HO1 reduced hexavalent chromium (chromate: CrO4(2-) anaerobically. Chromate reductase activity was preferentially associated with the membrane fraction of the cells. Right-side-out membrane vesicles prepared from E. cloacae cells showed high chromate reductase activities when ascorbate-reduced phenazine methosulfate was added as an electron donor.

204 citations

Journal ArticleDOI
TL;DR: In this paper, Pseudomonas fluorescens LB300 was shown to reduce hexavalent chromium, Cr(VI), aerobically at neutral pH (pH 7.0) with citrate as carbon and energy source.
Abstract: Batch and continuous cultures of Pseudomonas fluorescens LB300 were shown to reduce hexavalent chromium, Cr(VI), aerobically at neutral pH (pH 7.0) with citrate as carbon and energy source. The product of Cr(VI) reduction was previously shown and confirmed in this work to be trivalent chromium, Cr(III), by quantitative reoxidation to Cr(VI) with KMnO4. In separate batch cultures (100 ml) containing initial Cr(VI) concentrations of 314.0, 200.0 and 112.5 mg Cr(VI) L−1, the organism reduced 61%, 69% and 99.7% of the Cr(VI), respectively. In a comparison of stationary and shaken cultures, the organism reduced 81% of Cr(VI) in 147 h in stationary culture and 80% in 122 h in shaken culture. In continuous culture, the organism lowered the influent Cr(VI) concentration by 28% with an 11.7-h residence time, by 39% with a 20.8-h residence time and by 57% with a 38.5-h residence time. A mass balance of chromium in a continuous culture at steady state showed an insignificant uptake of chromium by cells of P. fluorescens LB300.

129 citations