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Modeling of Chromium (VI) Accumulation in Gordonia polyisoprenivorans VH2 Using Response Surface Methodology
Abstract
An experimental design technique was carried out to investigate the bioaccumulation of chromium VI by the rubber degrading nocardioform actinomycete Gordonia polyisoprenivorans VH2. Response Surface Methodology (RSM) was adopted to acquire the best level of four variables namely, pH, FeSO<SUB>4</SUB>, NaNO<SUB>2</SUB> and Cr (VI) which have been optimized to bring about maximum chromium biosorption percentage. In this respect, the 3-level Box-Behnken design was employed. A polynomial model has been created to correlate the relationship between the four variables and chromium biosorption. The optimal combination of those variables for chromium biosorption evaluated from the non-linear optimization algorithm of EXCEL-Solver was as follows (mg L<sup>-1</SUP>): FeSO<SUB>4</SUB>, 18; NaNO<SUB>2</SUB>, .75; Cr (VI), 41.25 at pH 6.7. Based on the predicted model, an experimental verification of the optimal conditions revealed chromium biosorption percentage of 90%, which is more than 3 folds the basal medium.
... In a biocatalytic microbial fuel cell (MFC) anodic reactions (the transfer of electrons from the microorganism to the anode) are used for the production of current while the cathodic reactions (transfer of electrons from the cathode to the microorganism) have been recently applied for current consumption 8 . The biocathodes may be a better alternative to abiotic catalysis, because the bacteria are used as biocatalysts on low cost carbon cathodes 16 and are able to accept electrons and reduce compounds which, in their oxidized form, are potential environmental pollutants, such as Cr(VI), NO 3 − , chloroethenes, 2-chlorophenol, ClO 4 − , U(VI) and CO 2 17 . Recently, biocatalytic MFCs have shown promising results for the reduction of Cr(VI) to less toxic Cr(III) 43 . ...
... The investigation was conducted employing, for the first time, a fluorescent Cr(III) probe, with a naphthalimide-rhodamine base, in order to perceive Cr(III) ions. The investigation showed that although Cr(VI) is reduced to Cr(III), forming Cr(OH) 3 and Cr 2 O 3 precipitates on the surface of cathodic electroactive bacteria, there is, at this point in time, no information about the occurrence of intracellular Cr(VI) reduction. ...
... K 2 HPO 4 (7.0), NH 4 Cl (0.1), NaHCO 3 (24). For the cathode chamber, 300 ml of the macronutrient solution was employed, as described by Huang et al. 18 (g/l): KH 2 PO 4 (4.4), ...
Although Cr(VI)-reducing and/or tolerant microorganisms have been investigated, there is no detailed information on the composition of the microbial community of the biocathode microbial fuel cell for Cr(VI) reduction. In this investigation, the bacterial diversity of a biocathode was analyzed using 454 pyrosequencing of the 16S rRNA gene. It was found that most bacteria belonged to phylum Proteobacteria (78.8%), Firmicutes (7.9%), Actinobacteria (6.6%) and Bacteroidetes (5.5%), commonly present in environments contaminated with Cr(VI). The dominance of the genus Pseudomonas (34.87%), followed by the genera Stenotrophomonas (5.8%), Shinella (4%), Papillibacter (3.96%), Brevundimonas (3.91%), Pseudochrobactrum (3.54%), Ochrobactrum (3.49%), Hydrogenophaga (2.88%), Rhodococcus (2.88%), Fluviicola (2.35%), and Alcaligenes (2.3%), was found. It is emphasized that some genera have not previously been associated with Cr(VI) reduction. This biocathode from waters contaminated with tannery effluents was able to remove Cr(VI) (97.83%) in the cathodic chamber. Additionally, through use of anaerobic sludge in the anodic chamber, the removal of 76.6% of organic matter (glucose) from synthetic waste water was achieved. In this study, an efficient biocathode for the reduction of Cr(VI) with future use in bioremediation, was characterized.
... They reported that Cr(VI)-reducing biofilm systems could effectively reduce Cr(VI), 100 % at the optimum conditions of initial metal concentration of 100 mg/L, nutrient supplementation of 20 % and flowrate of 3 mL/min. The 3-level Box-Behnken design was employed by Berekaa et al. (2006) for Cr(VI) accumulation by Gordonia polyisoprenivorans VH2. They reported that FeSO 4 , 18 mg/L; NaNO 2 , 3.75 mg/L; Cr(VI), 41.25 mg/L at pH 6.7 were optimal for Cr(VI) accumulation. ...
Hexavalent chromium Cr(VI) is regularly introduced into the environment through diverse anthropogenic activities. It is highly toxic, mutagenic and carcinogenic, and because of its solubility in water, chromate contamination can be difficult to contain. Bacteria can reduce chromate to insoluble and less toxic trivalent chromium Cr(III), and thus increasing attention is paid to chromate bioremediation to reduce its ecotoxicological impacts. In this study, the factorial design 23 was employed to optimize critical parameters responsible for higher Cr(VI) removal by a bacterial consortium. The factors considered were pH, temperature, and inoculum size at two markedly different levels. All three dependent variables have significant effect on Cr(VI) reduction. Optimal Cr(VI) removal by the bacterial consortium occurred at pH 9, temperature 37°C, and inoculum size OD = 3. Analysis of variance (ANOVA) showed a high coefficient of determination (R2) value of 0.984, thus ensuring a satisfactory adjustment of the second-order regression model with the experimental data. In addition, the effect of bioaugmentation of Cr(VI)-polluted soil microcosms with the bacterial consortium was investigated using the best factor levels. Contaminated soil by 20 and 60 mg/Kg of Cr(VI) showed reductions of 83% and 65% of initial Cr(VI) by the bacterial consortium, suggesting that this bacterial consortium might diminish phytoavailable Cr(VI) in soil and be useful for cleaning up chromium-contaminated sites.
Water saving technologies such as non-flooded irrigation have been introduced in many rice production during the past decade. Water balance analysis is needed to quantify water supply, loss and consumption for maximization rice production under such irrigation. However, hydrological data are often limited because acquisition of measurements in the field is costly, complicated and time consuming, hence methods that can estimate water balance components based on the combined use of available measurement data and an appropriate model are required. This study presents the estimation method using excel solver to estimate non-measurable water balance components, i.e., irrigation water, crop evapotranspiration, percolation and runoff, in a paddy field under non-flooded irrigation. The method was examined in two cultivation periods under different weather conditions. The model validation, indicated by coefficient of determination (R2) values, was greater than 0.86 (p<0.01) between observed and calculated values of soil moisture. Furthermore, when relationships among precipitation and estimated runoff was compared, the reliability of the model was shown by the significant linear correlations with correlation coefficient (R2) higher than 0.98 (p<0.01). These results indicate the reliability and applicability of the proposed method for estimating non-measurable water balance components for rice production when only limited data of measurable components are available.
The Streptomyces strains CHR3 and CHR28, isolated from the Baltimore Inner Harbor, contained two and one, respectively, giant linear plasmids which carry terminally bound proteins. The plasmids pRJ3L (322 kb), from CHR3, and pRJ28 (330 kb), from CHR28, carry genes homologous to the previously characterized chromosomal Streptomyces lividans 66 operon encoding resistance against mercuric compounds. Both plasmids are transmissible (without any detectable rearrangement) to the chloramphenicol-resistant S. lividans TK24 strain lacking plasmids and carrying a chromosomal deletion of the mer operon. S. lividans TK24 conjugants harboring pRJ3L or pRJ28 exhibited profiles of mercury resistance to mercuric compounds similar to those of Streptomyces strains CHR3 and CHR28.
Strains designated R22 and R25, isolated from Salí River sediments, Argentina, were highly resistant to chromium. These strains were shown by 16S rRNA sequencing studies to be Streptomyces spp.; this affiliation was consistent with morphological and chemical characteristics. Growth of strains R22 and R25 in medium containing 100 mg l(-1) chromate was reduced by only 23% and 34%, respectively, compared with growth in medium without added chromium. Streptomyces sp. strains R22 and R25 both accumulated chromium with yields of 10.0 and 5.6 mg Cr g(-1) of dry weight, respectively, and a chromate concentration of 50 mg ml(-1). Cell fractionation studies with strain R22 showed that the great majority of the chromium were associated with the cell wall fraction. Streptomyces strains R22 and R25 may have applications in bioremediation of chromium contamination.
The study presented in this article investigated the influence of different Cr(III) and Cr(VI) compounds in the cultivation medium on the uptake and localization of chromium in the cell structure of the yeast Candida intermedia. The morphology of the yeast cell surface was observed by the scanning electron microscopy. Results demonstrated that the growth inhibitory concentration of Cr(III) in the cultivation medium induced changes in the yeast cell shape and affected the budding pattern, while inhibitory concentration of Cr(VI) did not cause any visible effects on morphological properties of the yeast cells. The amount of total accumulated chromium in yeast cells and the distribution of chromium between the yeast cell walls and spheroplasts were determined by atomic absorption spectroscopy. No significant differences were found neither in total chromium accumulation nor in the distribution of chromium in yeast cell walls and spheroplasts between the two of Cr(VI) compounds. Conversely, substantial differences between Cr(III) compounds were demonstrated in the total uptake as well as the localization of chromium in yeast cells.
Two actinomycete strains, CHR3 and CHR28, were isolated from metal-contaminated sediments from Baltimore Inner Harbor. The isolates were classified as Streptomyces spp. Agar diffusion assays showed both isolates to be resistant to mercuric chloride and phenylmercuric acetate. Hybridization experiments indicated that genes homologous to the mercuric reductase and organomercurial lyase of Streptomyces lividans 1326 were present in strains CHR3 and CHR28. Strain CHR28 grew at both low and high salt concentrations; however, strain CHR3 showed enhanced growth in the presence of salt, evidence of its habitat being marine or estuarine sediment.
Chromium (Cr) was first discovered in Siberian red lead ore (crocoite) in 1798 by the French chemist, Vauquelin. Named for the bright colors of its compounds, Cr has since found an extremely wide variety of industrial uses that exploit these colors, as well as various other characteristics of Cr, such as strength, hardness and corrosion resistance of the metal, and the oxidizing capabilities of certain Cr species. Not surprisingly, large volumes of Cr waste in various chemical forms are generated from industrial processes and discharged into the environment. While Cr, in trace amounts, is essential for human life, exposure to some Cr compounds can pose a major health risk to all forms of life. This review will discuss some of the environmental impacts of chromium, including novel bioremediation techniques currently under development for detoxifying Cr-contaminated water and soils.
A Gram-negative bacterium (CRB5) was isolated from a chromium-contaminated site that was capable of reducing hexavalent chromium to an insoluble precipitate, thereby removing this toxic chromium species from solution. Analysis of the 16S rRNA from the isolate revealed that it was a pseudomonad with high similarity to Pseudomaonas synxantha. CRB5 was tolerant to high concentrations of chromate (500 mg l(-1)) and can reduce Cr(VI) under aerobic and anaerobic conditions. It also exhibited a broad range of reduction efficiencies under minimal nutrient conditions at temperatures between 4 degrees C and 37 degrees C and at pH levels from 4 to 9. As reduction increased, so did total cellular protein, indicating that cell growth was a requirement for reduction. Under low nutrient conditions with CRB5 or when using non-sterile contaminated groundwater from the site, reduction of Cr(VI) was followed by a increase in solution turbidity as a result of the formation of fine-grained Cr(III) precipitates, most probably chromium hydroxide mineral phases such as Cr(OH)3. Chromium adsorption and precipitation, as observed by transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (TEM/EDS), revealed that the surfaces of the cells were uniformly stained with bound Cr(III) and amorphous precipitates (as determined by selected area electron diffraction; SAED). A mass balance of chromium in a batch bioreactor revealed that up to 30% of the total Cr was as settable precipitates or bound to cells.
Bacterial strains, previously isolated from a chromium-polluted soil, were identified on the basis of Gram reaction and biochemical characteristics (Biolog system). Moreover, chromate MICs, chromate reduction capability, multiple heavy metal tolerance, and antibiotic susceptibility were tested for each isolate. All strains but one were Gram-positive and resistant to high concentrations of chromate. The most Cr(VI)-resistant isolate (22m M) was identified as Corynebacterium hoagii. All Cr(VI)-resistant strains except the isolate ChrC20 were capable of catalyzing the reduction of Cr(VI) to Cr(III), a less toxic and less water-soluble form of chromium. The only isolate Cr(VI)-sensitive, attributed to the Pseudomonas genus, also exhibited Cr(VI)-reduction. Isolates were also screened for the presence of plasmid DNA. The strains ChrC20 and ChrB20 harbored one and two plasmids of high molecular mass, respectively. This approach permitted selection of some bacterial strains, which could be used for bioremediation of Cr(VI)-polluted environments.