Browsing by Author "Sani, Rajesh K."

Now showing 1 - 10 of 10

Assessment of lead toxicity to desulfovibrio desulfuricans g20: influence of components of lactate c medium
(2001-08) Sani, Rajesh K.; Geesey, Gill G.; Peyton, Brent M.
The bioavailability and toxicity of lead (Pb) to Desulfovibrio desulfuricans G20 is greatly influenced by aqueous phase chemical composition. Apparent Pb toxicity is reduced by precipitation and complexation with chemicals found in standard growth media for sulfate-reducing bacteria (SRB). To determine the influence of medium composition on observed Pb toxicity, a new medium was developed to more accurately assess the toxicity of Pb to Desulfovibrio desulfuricans. The new medium, metal toxicity medium (MTM), eliminates abiotic Pb precipitation and minimizes formation of Pb complexes in solution. Significant growth of Desulfovibrio desulfuricans was observed on MTM in the absence of Pb, while no measurable growth was observed at 3 mg/1 Pb as PbCl2. For comparison, in Lactate C medium (Burlage et al., 1998) abiotic Pb precipitation was apparent, and the specific growth rate at 100 mg/1 Pb was only reduced by 8.1% compared to the Pb-free control. Toxicity was measured in terms of longer lag times and slower growth rates (including no growth) as compared to Pb-free controls. This report describes the effects of specific medium components on Pb toxicity to Desulfovibrio desulfuricans and provides a better baseline for comparison of natural and industrial waters for observing heavy metal toxicity on SRB.
Heavy metal-mineral associations in Coeur d'Alene River sediments: A synchrotron-based analysis
(2009-12) Moberly, James G.; Borch, Thomas; Sani, Rajesh K.; Spycher, Nicolas; Şengör, S. Sevinç; Ginn, Timothy R.; Peyton, Brent M.
Nearly a century of mining activities upstream have contaminated Lake Coeur d’Alene and its tributaries with Pb, Zn, and other heavy metals. Heavy metal concentrations in sediments of the Coeur d’Alene watershed have been shown to be inversely proportional to the sediment size fraction; thus, analysis on a very small scale is essential to determine the mobility and stability of heavy metals in this environment. Micron-scale synchrotron-based methods were used to determine the association of heavy metals with solid phases in sediments of the Coeur d’Alene River. Bulk X-ray diffraction (XRD), extended X-ray absorption fine structure spectroscopy, and synchrotron-based microfocused XRD combined with microfocused X-ray fluorescence mapping indicate the presence of crystalline Pb- and Zn-bearing mineral phases of dundasite [Pb2Al4(CO3)4(OH)8·3H2O], coronadite [PbMn8O16], stolzite [PbWO4], mattheddleite [Pb10(SiO4)3.5(SO4)2Cl2], bindheimite [Pb2Sb2O7], and smithsonite [ZnCO3]. Likely phases for Zn and Pb adsorption were ferrihydrite, diaspore [AlO(OH)], manganite [Mn(III)O(OH)], muscovite [KAl2(Si3Al)O10(OH,F)2], biotite [K(Fe,Mg)3AlSi3O10(F,OH)2], and montmorillonite [Na0.3(Al,Mg)2Si4O10(OH)2·8H2O]. The large predominance of Fe and Mn (hydr)oxides over other sorbent minerals suggests that the metal sorption behavior is dominated by these (hydr)oxide phases.
Impact of different environmental conditions on the aggregation of biogenic U(IV) nanoparticles synthesized by Desulfovibrio alaskensis G20
(2016-12) Şengör, S. Sevinç; Singh, Gursharan; Dohnalkova, Alice; Spycher, Nicolas; Ginn, Timothy R.; Peyton, Brent M.; Sani, Rajesh K.
This study investigates the impact of specific environmental conditions on the formation of colloidal U(IV) nanoparticles by the sulfate reducing bacteria (SRB, Desulfovibrio alaskensis G20). The reduction of soluble U(VI) to less soluble U(IV) was quantitatively investigated under growth and non-growth conditions in bicarbonate or 1,4-piperazinediethanesulfonic acid (PIPES) buffered environments. The results showed that under non-growth conditions, the majority of the reduced U nanoparticles aggregated and precipitated out of solution. High resolution transmission electron microscopy revealed that only a very small fraction of cells had reduced U precipitates in the periplasmic spaces in the presence of PIPES buffer, whereas in the presence of bicarbonate buffer, reduced U was also observed in the cytoplasm with greater aggregation of biogenic U(IV) particles at higher initial U(VI) concentrations. The same experiments were repeated under growth conditions using two different electron donors (lactate and pyruvate) and three electron acceptors (sulfate, fumarate, and thiosulfate). In contrast to the results of the non-growth experiments, even after 0.2 μm filtration, the majority of biogenic U(IV) remained in the aqueous phase resulting in potentially mobile biogenic U(IV) nanoparticles. Size fractionation results showed that U(IV) aggregates were between 18 and 200 nm in diameter, and thus could be very mobile. The findings of this study are helpful to assess the size and potential mobility of reduced U nanoparticles under different environmental conditions, and would provide insights on their potential impact affecting U(VI) bioremediation efforts at subsurface contaminated sites.
Influence of chelating agents on biogenic uraninite reoxidation by Fe(III) (Hydr)oxides
(2013-01) Stewart, B. D.; Giradot, Crystal L.; Spycher, Nicolas; Sani, Rajesh K.; Peyton, Brent M.
Microbially mediated reduction of soluble U(VI) to U(IV) with subsequent precipitation of uraninite, UO2(S), has been proposed as a method for limiting uranium (U) migration. However, microbially reduced UO2 may be susceptible to reoxidation by environmental factors, with Fe(III) (hydr)oxides playing a significant role. Little is known about the role that organic compounds such as Fe(III) chelators play in the stability of reduced U. Here, we investigate the impact of citrate, DFB, EDTA, and NTA on biogenic UO2 reoxidation with ferrihydrite, goethite, and hematite. Experiments were conducted in anaerobic batch systems in PIPES buffer (10 mM, pH 7) with bicarbonate for approximately 80 days. Results showed EDTA accelerated UO2 reoxidation the most at an initial rate of 9.5 Î¼M dayâˆ’1 with ferrihydrite, 8.6 Î¼M dayâˆ’1 with goethite, and 8.8 Î¼M dayâˆ’1 with hematite. NTA accelerated UO2 reoxidation with ferrihydrite at a rate of 4.8 Î¼M dayâˆ’1; rates were less with goethite and hematite (0.66 and 0.71 Î¼M dayâˆ’1, respectively). Citrate increased UO2 reoxidation with ferrihydrite at a rate of 1.8 Î¼M dayâˆ’1, but did not increase the extent of reaction with goethite or hematite, with no reoxidation in this case. In all cases, bicarbonate increased the rate and extent of UO2 reoxidation with ferrihydrite in the presence and absence of chelators. The highest rate of UO2 reoxidation occurred when the chelator promoted both UO2 and Fe(III) (hydr)oxide dissolution as demonstrated with EDTA. When UO2 dissolution did not occur, UO2 reoxidation likely proceeded through an aqueous Fe(III) intermediate with lower reoxidation rates observed. Reaction modeling suggests that strong Fe(II) chelators promote reoxidation whereas strong Fe(III) chelators impede it. These results indicate that chelators found in U contaminated sites may play a significant role in mobilizing U, potentially affecting bioremediation efforts.
Influence of pH and inorganic phosphate on toxicity of zinc to Arthrobacter sp. isolated from heavy-metal-contaminated sediments
(2010-10) Moberly, James G.; Staven, A.; Sani, Rajesh K.; Peyton, Brent M.
Because of its high solubility over a wide range of pH conditions, zinc is found in many natural and human-impacted systems. Zinc speciation is critical in assessing zinc toxicity to microorganisms because it varies considerably with pH and is dependent on other aqueous constituents. Combined results of thermodynamic modeling, statistical analysis, and batch culture studies using Arthrobacter sp. JM018 suggest that the toxic species may not be solely limited to the free ion, but also includes ZnHPO40(aq). Cellular uptake of ZnHPO40(aq) through the inorganic phosphate transporter (Pit family), which requires a neutral metal phosphate complex for phosphate transport, may explain the observed toxicity. Based on visual MINTEQ (v3.0) modeling, at 50 Î¼M total zinc, ZnHPO40(aq) constitutes 33, 70, and 76% of the neutral metal phosphate pool at pH 6, 7, and 8, respectively. At 50 Î¼M total zinc, cultures supplied with organic phosphate (glycerol-3-phosphate) show no significant response to pH (p=0.13) while inhibition of inorganic phosphate-supplemented cultures, whose neutral metal phosphates are increasingly dominated by ZnHPO40(aq), show significant pH dependence (p=9.45 x 10-7). Using sodium to decrease the distribution of ZnHPO40(aq) in the neutral metal phosphate pool also decreased the pH dependent toxicity, further supporting this mechanism.These findings show the important role of minor zinc species in organism toxicity and have wider implications because the Pit inorganic phosphate transport system is widely distributed in Bacteria, Archaea, and Eukarya.
Molecular analysis of prokaryotic diversity in the deep subsurface of the former Homestake Gold Mine, South Dakota, USA
(2009-08) Rastogi, Gurdeep; Stetler, Larry D.; Peyton, Brent M.; Sani, Rajesh K.
A culture-independent molecular phylogenetic analysis was carried out to study the prokaryotic diversity in two soil samples collected from the subsurface (1.34 km depth) of the former Homestake gold mine, Lead, South Dakota, USA at two sites, the Ross shaft and number 6 Winze. Microbial community analyses were performed by cloning and sequencing of 16S rRNA genes retrieved directly from soil samples. Geochemical characterization of soils revealed high amount of toxic metals such as As, Cd, Co, Cr, Cu, Ni, Pb, Zn, and U at both the sites. Phylogenetic analyses showed that soil samples were predominantly composed of phylotypes related to phylum Proteobacteria. Other phyla detected in libraries were Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Chlorobi, Firmicutes, Gemmatimonadetes, Nitrospirae, Planctomycetes, Verrucomicrobia, and candidate divisions OP10 and TM7. The majority (>95%) of the phylotypes retrieved in the libraries were most closely related to environmental sequences from yet-uncultured bacteria representing a hitherto unidentified diversity. The archaeal communities at both the sites exhibited lower diversity and were most closely affiliated to uncultivated species within the Crenarchaeota. Results showed the existence of diverse microbial populations in deep subsurface environment of the Homestake gold mine. Statistical analyses demonstrated that each site harbored phylogenetically distinct microbial populations that were more diverse at Ross site compare to winze site.
Multiple mechanisms of uranium immobilization by Cellulomonas sp. strain ES6
(2011-02) Sivaswamy, V.; Boyanov, M. I.; Peyton, Brent M.; Viamajala, Sridhar; Gerlach, Robin; Apel, William A.; Sani, Rajesh K.; Dohnalkova, Alice; Kemner, K. M.; Borch, Thomas
Removal of hexavalent uranium (U(VI)) from aqueous solution was studied using a gram-positive facultative anaerobe, Cellulomonas sp. strain ES6, under anaerobic, non-growth conditions in bicarbonate and PIPES buffers.Inorganic phosphate was released by cells during the experiments providing ligands for formation of insoluble U(VI) phosphates. Phosphate release was most probably the result of anaerobic hydrolysis of intracellular polyphosphates accumulated by ES6 during aerobic growth. Microbial reduction of U(VI) to U(IV) was also observed. However, the relative magnitudes of U(VI) removal by abiotic (phosphate-based) precipitation and microbial reduction depended on the buffer chemistry. In bicarbonate buffer, X-ray absorption fine structure (XAFS) spectroscopy showed that U in the solid phase was present primarily as a non-uraninite U(IV) phase, whereas in PIPES buffer, U precipitates consisted primarily of U(VI)-phosphate. In both bicarbonate and PIPES buffer, net release of cellular phosphate was measured to be lower than that observed in U-free controls suggesting simultaneous precipitation of U and POâ‚„Â³â ». In PIPES, U(VI) phosphates formed a significant portion of U precipitates and mass balance estimates of U and P along with XAFS data corroborate this hypothesis. High-resolution transmission electron microscopy (HR-TEM) and energy dispersive X-ray spectroscopy (EDS) of samples from PIPES treatments indeed showed both extracellular and intracellular accumulation of U solids with nanometer sized lath structures that contained U and P. In bicarbonate, however, more phosphate was removed than required to stoichiometrically balance the U(VI)/U(IV) fraction determined by XAFS, suggesting that U(IV) precipitated together with phosphate in this system. When anthraquinone-2,6-disulfonate (AQDS), a known electron shuttle, was added to the experimental reactors, the dominant removal mechanism in both buffers was reduction to a non-uraninite U(IV) phase.Uranium immobilization by abiotic precipitation or microbial reduction has been extensively reported; however, the present work suggests that strain ES6 can remove U(VI) from solution simultaneously through precipitation with phosphate ligands and microbial reduction, depending on the environmental conditions. Cellulomonadaceae are environmentally relevant subsurface bacteria and here, for the first time, the presence of multiple U immobilization mechanisms within one organism is reported using Cellulomonas sp. strain ES6
Reduction of uranium (VI) under sulfate-reducing conditions in the presence of Fe(III)-(hydr)oxides
(2004-06) Sani, Rajesh K.; Peyton, Brent M.; Amonette, James E.; Geesey, Gill G.
Hexavalent uranium [U(VI)] dissolved in a modified lactate-C medium was treated under anoxic conditions with a mixture of an Fe(III)-(hydr)oxide mineral (hematite, goethite, or ferrihydrite) and quartz. The mass of Fe(III)-(hydr)oxide mineral was varied to give equivalent Fe(III)-mineral surface areas. After equilibration, the U(VI)-mineral suspensions were inoculated with sulfate-reducing bacteria, Desulfovibrio desulfuricans G20. Inoculation of the suspensions containing sulfate-limited medium yielded significant G20 growth, along with concomitant reduction of sulfate and U(VI) from solution. With lactate-limited medium, however, some of the uranium that had been removed from solution was resolubilized in the hematite treatments and, to a lesser extent, in the goethite treatments, once the lactate was depleted. No resolubilization was observed in the lactate-limited ferrihydrite treatment even after a prolonged incubation of 4 months. Uranium resolubilization was attributed to reoxidation of the uraninite by Fe(III) present in the (hydr)oxide phases. Analysis by U L3-edge XANES spectroscopy of mineral specimens sampled at the end of the experiments yielded spectra similar to that of uraninite, but having distinct features, notably a much more intense and slightly broader white line consistent with precipitation of nanometer-sized particles. The XANES spectra thus provided strong evidence for SRB-promoted removal of U(VI) from solution by reductive precipitation of uraninite. Consequently, our results suggest that SRB mediate reduction of soluble U(VI) to an insoluble U(IV) oxide, so long as a suitable electron donor is available. Depletion of the electron donor may result in partial reoxidation of the U(IV) to soluble U(VI) species when the surfaces of crystalline Fe(III)-(hydr)oxides are incompletely reduced.
The toxicity of lead to Desulfovibrio desulfuricans G20 in the presence of goethite and quartz
(2010-04) Sani, Rajesh K.; Rastogi, Gurdeep; Moberly, James G.; Dohnalkova, Alice; Ginn, Timothy R.; Spycher, Nicolas; Shende, Rajesh V.; Peyton, Brent M.
An aqueous mixture of goethite, quartz, and lead chloride (PbCl2) was treated with the sulfate reducing bacterium, Desulfovibrio desulfuricans G20 (D. desulfuricans G20), in a medium specifically designed to assess metal toxicity. In the presence of 26 Î¼M of soluble Pb, together with the goethite and quartz, D. desulfuricans G20 grew after a lag time of 5 days compared to 2 days in Pb-, goethite-, and quartz-free treatments. In the absence of goethite and quartz, however, with 26 Î¼M soluble Pb, no measurable growth was observed. Results showed that D. desulfuricans G20 first removed Pb from solutions then growth began resulting in black precipitates of Pb and iron sulfides. Transmission electron microscopic analyses of thin sections of D. desulfuricans G20 treated with 10 Î¼M PbCl2 in goethite- and quartz-free treatment showed the presence of a dense deposit of lead sulfide precipitates both in the periplasm and cytoplasm. However, thin sections of D. desulfuricans G20 treated with goethite, quartz, and PbCl2 (26 Î¼M soluble Pb) showed the presence of a dense deposit of iron sulfide precipitates both in the periplasm and cytoplasm. Energy-dispersive X-ray spectroscopy, selected area electron diffraction patterns, or X-ray diffraction analyses confirmed the structure of precipitated Pb inside the cell as galena (PbS) in goethite- and quartz-free treatments, and iron sulfides in treatments with goethite, quartz, and PbCl2. Overall results suggest that even at the same soluble Pb concentration (26 Î¼M), in the presence of goethite and quartz, apparent Pb toxicity to D. desulfuricans G20 decreased significantly. Further, accumulation of lead/iron sulfides inside D. desulfuricans G20 cells depended on the presence of goethite and quartz.
Uranium immobilization by sulfate-reducing biofilms
(2004-04) Beyenal, Haluk; Sani, Rajesh K.; Peyton, Brent M.; Dohnalkova, Alice; Amonette, James E.; Lewandowski, Zbigniew
Hexavalent uranium [U(VI)] was immobilized using biofilms of the sulfate-reducing bacterium (SRB) Desulfovibrio desulfuricans G20. The biofilms were grown in flat-plate continuous-flow reactors using lactate as the electron donor and sulfate as the electron acceptor. U(VI)was continuously fed into the reactor for 32 weeks at a concentration of 126 microM. During this time, the soluble U(VI) was removed (between 88 and 96% of feed) from solution and immobilized in the biofilms. The dynamics of U immobilization in the sulfate-reducing biofilms were quantified by estimating: (1) microbial activity in the SRB biofilm, defined as the hydrogen sulfide (H2S) production rate and estimated from the H2S concentration profiles measured using microelectrodes across the biofilms; (2) concentration of dissolved U in the solution; and (3) the mass of U precipitated in the biofilm. Results suggest that U was immobilized in the biofilms as a result of two processes: (1) enzymatically and (2) chemically, by reacting with microbially generated H2S. Visual inspection showed that the dissolved sulfide species reacted with U(VI) to produce a black precipitate. Synchrotron-based U L3-edge X-ray absorption near edge structure (XANES) spectroscopy analysis of U precipitated abiotically by sodium sulfide indicated that U(VI) had been reduced to U(IV). Selected-area electron diffraction pattern and crystallographic analysis of transmission electron microscope lattice-fringe images confirmed the structure of precipitated U as being that of uraninite.