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Equilibrium sorption and desorption experiments were conducted with clinoptilolite to evaluate the potential sorption/desorption of iron during different pH conditions. Sorption experiments indicated a partitioning of 0% to 17% of the iron in solution given pH of 2 to 4. The pH 2 solution was able to desorb 70% of the iron that was captured from a pH 3 solution. The largest desorption and sorption of iron and corresponding pH represent the end points of iron capture primarily by sorption/exchange. These endpoints are the estimated pHpzc of 2.5 and the initial precipitation point of iron(II) at pH ~3.5. This acidity range is where clinoptilolite is able to capture iron without precipitation or the occurrence of full surface protonation. The inability of the highest acidity to remove all sorbed iron represents the greater bound iron that will not readily desorb with a change in pH. This retained iron creates a metastable state of the clinoptilolite that has a lower sorption capacity but reflects the ability of clinoptilolite to retain a sorbed transition metal with changes in pH. As pH varies, clinoptilolite may evolve in a sequence of metastable states reflective of its ability to capture or retain metals. PRACTITIONER POINTS: Clinoptilolite is a capable reactive substrate, but its sorption/exchange effectiveness at low and variable pH and ability to retain captured metals was unknown. Clinoptilolite retains its metal capture properties to a pH of 2.5 where surface protonation and mineral degradation likely occurs. The ability of clinoptilolite to retain captured iron under greater acidity reflects an evolution of its sorption/retention capacity.

Passive treatment systems provide lower cost alternatives for remediation of mine drainage; however, acidic drainage increases treatment difficulty because of higher metal concentrations and proton competition for reactive substrates. A silica fiber functionalized with (3-aminopropyl) triethoxysilane (Si + APTES) and a naturally-occurring, microporous silicate mineral (clinoptilolite of the zeolite family) were evaluated in the laboratory as potential reactive substrates for passive treatment of mild (≥ pH of 3) acid rock drainage. Column permeability experiments with spun, 10-µm median diameter, silica fiber and loosely packed, 3.6-mm median diameter clinoptilolite indicate greater permeability and stability of clinoptilolite under flowing conditions. Batch sorption experiments with silica fiber (Si), Si + APTES, and clinoptilolite in a synthetic Fe(II)–SO4, pH 3.0 solution indicate an Fe specific sorption efficacy of Si + APTES > clinoptilolite > Si at equivalent surface areas. Specific sorption normalized to packing densities indicate greater sorption per volume for clinoptilolite. Sorption results for Si + APTES and clinoptilolite did not produce isotherms described by the Langmuir or Freundlich models, likely because of surface heterogeneity and precipitation reactions. Column sorption experiments under flowing conditions indicate an Fe removal efficacy of clinoptilolite > Si + APTES for permeable packing densities. Si + APTES demonstrated high specific sorption of Fe in batch sorption experiments and has potential use in low-flow, passive treatment of mildly acidic solutions. The balance of minimal surface preparation, greater permeability, structural stability, large surface area, micropore structure, and ion-exchange properties make clinoptilolite a better reactive substrate for passive treatment of mildly acidic solutions in high- or low-flow conditions.

The efficacy of passive treatment systems for remediating acid rock drainage can be limited by the seasonal flux of discharge and metal concentrations that may not have been considered during treat...

Methylmercury (MeHg) is a bioaccumulative toxic contaminant in many ecosystems, but factors governing its production are poorly understood. Recent work has shown that the anaerobic microbial conversion of mercury (Hg) to MeHg requires the Hg-methylation genes

The oxidation state of sulfur [S] is a primary control on mobility of metals in sediments impacted by legacy mining practices. Coeur d&rsquo, Alene Lake of northern Idaho, USA, has been impacted by upstream legacy mining practices that deposited an estimated 75 Mt of metal(loid)- and S-rich sediments into the lake. Future lake conditions are expected to include algal blooms, which may alter S and metal remobilization during the seasonal euxinic environment. Cores of the lake sediments were exposed to anoxic and anoxic + algal detritus conditions for eight weeks at 4.5 &deg, C through introduction of a N2 atmosphere and addition of algal detritus. At a location 2.5 cm below the sediment-water interface, anoxic conditions promoted a shift in S species to continually larger concentrations of reduced species and an associated shift in the bonding environment reflective of increased S&ndash, metal bonds. Anoxic + algal detritus conditions suppressed the increasing trend of reduced S species and induced greater release of Mn compared to the anoxic-only conditions but did not appear to enhance the release of As, Cd, or Fe. The addition of algal detritus to the sediment-water interface of these Fe- and S-rich sediments enhanced mobilization of Mn likely because of dissimilatory metal reduction where the anaerobic oxidation of the algal detritus stimulated Mn reduction. Results of the study indicate that future metal release from the lake sediments will be altered with the likely deposition of algal detritus, but the effect may not enhance the release of acutely toxic metals, such as As or Cd, or substantially impact Fe cycling in the sediments.

Rare earth elements (REEs) are widely used across different industries due to their exceptional magnetic and electrical properties. In this work Cupriavidus necator (C. necator) is characterized using dielectrophoretic ultra-high frequency measurements, typically in MHz range to quantify the properties of cytoplasm in C. necator for its metal uptake / bioaccumulation capacity. C. necator, a gram-negative bacteria strain is exposed to REEs like europium, samarium, and neodymium in this study. Dielectrophoretic crossover frequency experiments were performed on the native C. necator species pre- and post-exposure to the REEs at MHz frequency range. The net conductivity of native C. necator, C-europium, C-samarium, and C-neodymium are 15.95 ± 0.029 μS/cm, 16.15 ± 0.028 μS/cm, 16.05 ± 0.029 μS/cm, 15.61 ± 0.005 μS/cm respectively. The estimated properties of the membrane published by our group are used to develop a microfluidic sorter by modeling and simulation to separate REE absorbed C. necator from the unabsorbed native C. necator species using COMSOL Multiphysics commercial software package v5.5. This article is protected by copyright. All rights reserved.

This work presents the dielectric characterization of rare earth elements (REEs) biosorption by Cupriavidus necator using dielectrophoretic crossover frequency measurements. Traditional means of characterizing biomass for biosorption is limited and time consuming. In this research we are presenting, for the first time, an electrokinetic method termed as dielectrophoresis (DEP) for the characterization of biosorption (uptake) of rare earth elements (REEs) by gram negative bacteria - Cupriavidus necator. To characterize, a 3mm-diameter point and planar microwell device platform is used to measure the DEP crossover frequency that yields the dielectric properties of the targeted biosorbents. Quantified dielectric properties of native Cupriavidus necator (REE−) and those exposed to rare earth elements (REE+): europium, neodymium, and samarium revealed a substantial change in the surface characteristics of the Cupriavidus necator after exposure to the REE solution. The response of C. necator to changes in REE exposure is substantially different for europium but similar between neodymium and samarium. Statistically both the REE+ and REE− groups dielectric signatures were significantly different proving that the REEs were absorbed by the bacteria. This research will revolutionize and impact the researchers and industrialists in the field of biosorption seeking for economical, greener, and sustainable means to recover REEs.

BACKGROUND: Four parallel continuous stirred tank reactors were used to investigate the single and joint exposure of Zn and Cu to Arthrobacter sp. JM018, in terms of the impact on the adenosine triphosphate (ATP) pool and microbial tolerance. RESULTS: ATP, optical density (OD), and substrate concentration measurements indicated that Cu was more toxic than Zn under all conditions studied. The results showed that although both OD and ATP measurements individually reflected a decrease in microbial growth rate after the addition of metals for the reactors exposed to Cu, specific ATP (i.e. ATP/OD) showed only a temporary reduction followed by a monotonic return to pre‐exposure levels within 100 h. The latter implied tolerance and recovery in the energy status of these cells, after the initial shock due to the exposure to Cu. CONCLUSION: Specific ATP is an important quantity to be considered as a measure of the activity or energy status of microbial biomass surviving after exposure to toxic metals or other unfavorable conditions. The study provides insights for maintaining metal‐tolerant microbial communities and to explore both quantitatively and experimentally the dynamics of ATP pool and microbial tolerance in metal‐contaminated environments. © 2018 Society of Chemical Industry

Additions to the popular evaporation rate determination laboratory of alcohol-based hand-rub sanitizers are described here. Significantly, inquiry-driven protocols for formulating hand-rub sanitizers, falling-ball viscometry, and sanitizer efficacy are included. Incorporation of familiar substances (“molecular relevance”) enables students to assimilate knowledge and connect to and recognize interrelated disciplines. To stimulate engagement and project ownership, students were given the opportunity to alter sanitizer formulations by varying the amount and molecular weight of the gelling agent. Viscosities were determined using a falling-ball viscometer to integrate physics and fluid dynamics concepts into these experiments. Lastly, to stress microbiological applications and determine the efficacy of their hand sanitizers, students tested the formulated hand sanitizers for qualitative efficacy using agar plating of skin secretions and comparing colonies formed from sanitized versus nonsanitized hands. Chemi...

The formation and transport of geogenic metal nanoparticles in mining-impacted environments is a developing concern because of their potential for greater distribution compared to larger particles. Discharge from the abandoned Gem Mine in the Coeur d'Alene Mining District of northern Idaho was examined for the presence of metal nanoparticles from weathering of an ore body of galena [PbS] and sphalerite [(Zn,Fe)S] with associated carbonate zones of siderite [FeCO3] and ankerite [Ca(Fe,Mg,Mn)(CO3)2] in intruded quartz veins. Analysis of this circumneutral discharge from the abandoned mine and groundwater in the receiving shallow aquifer indicate poor-quality mine drainage containing nanophase Zn-CO3 form(s) that dissociate into smaller particles or ions with release into the new geochemical environment of the aquifer. The nanoparticles were identified through acid titrations and dynamic light scattering analysis of 450-nm-filtered mine water. The stability of the nanoparticles was estimated through ζ potential analysis of mine water and groundwater, which indicated limited stability of the nanoparticles that was sufficient for transport in the mine drainage but insufficient for transport in the aquifer. The release of the nanophase Zn-CO3 form(s) likely occurs through weathering of secondary carbonate minerals in the mined areas of the Gem-Gold Hunter deposit through water-rock interaction → crystal repulsion → particle detachment → solution entrainment → and limited dissociation during transport as opposed to crystal formation in solution with mineral-phase saturation.

The heterogeneity and anisotropy of fractured-rock aquifers, such as those in the Columbia River Basalt Province, present challenges for determining groundwater recharge. The entrance of recharge to the fractured-basalt and interbedded-sediment aquifer in the Palouse region of north-central Idaho is not well understood because of successive basalt flows that act as restrictive barriers. It was hypothesized that a primary recharge zone exists along the basin’s eastern margin at a mountain-front interface where eroded sediments form a more conductive zone for recharge. Potential source waters and groundwater were analyzed for δ18O and δ2H to discriminate recharge sources and pathways. Snowpack values ranged from −22 to −12‰ for δ18O and from −160 to −90‰ for δ2H and produced spring-time snowmelt ranging from −16.5 to −12‰ for δ18O and from −120 to −90‰ for δ2H. With the transition of snowmelt to spring-time ephemeral creeks, the isotope values compressed to −16 and −14‰ for δ18O and −110 and −105‰ for δ2H. A greater range of values was present for a perennial creek (−18 to −13.5‰ for δ18O and −125 to −98‰ for δ2H) and groundwater (−17.5 to −13‰ for δ18O and −132 to −105‰ for δ2H), which reflect a mixing of seasonal signals and the varying influence of vapor sources and sublimation/evaporation. Inverse modeling and the evaluation of matrix characteristics indicate conductive pathways associated with paleochannels and deeper pathways along the mountain-front interface. Depleted isotope signals indicate quicker infiltration and recharge pathways that were separate from, or had limited mixing with, more evaporated water that infiltrated after greater time/travel at the surface.

The distorted title square-planar silver(I) complex was obtained in very good yield after gentle mixing of solutions of the N,N-di­ethyl­phenyl­azo­thio­formamide (ATF) ligand with silver hexa­fluorido­phosphate in tetra­hydro­furan. In the crystal, one sulfur atom from an ATF ligand of a neighboring complex coordinates to the silver atom, with a bond distance of 2.9884 (14) Å. This creates a polymeric zigzag chain propagating along the c-axis direction., The structure of the title complex, [Ag(C11H15N3S)2]PF6, has monoclinic (P21/c) symmetry, and the silver atom has a distorted square-planar geometry. The coordination complex crystallized from mixing silver hexa­fluorido­phosphate with a concentrated tetra­hydro­furan solution of N,N-di­ethyl­phenyl­azo­thio­formamide [ATF; systematic name: 3,3-diethyl-1-(phenyl­imino)­thio­urea] under ambient conditions. The resultant coordination complex exhibits a 2:1 ligand-to-metal ratio, with the silver(I) atom having a fourfold AgN2S2 coordination sphere, with a single PF6 counter-ion. In the crystal, however, one sulfur atom from an ATF ligand of a neighboring complex coordinates to the silver atom, with a bond distance of 2.9884 (14) Å. This creates a polymeric zigzag chain propagating along the c-axis direction. The chains are linked by C—H⋯F hydrogen bonds, forming slabs parallel to the ac plane.

Redox-active azothioformamides ligands rapidly coordinate to transition metals and are excellent substrates for monitoring host–guest binding interaction mechanisms as they can exhibit unique coordination complexes while producing an increase in extinction coefficient upon addition of metal salt. Herein, an alkyl derivative, N,N-diethyl-t-butylazothioformamide, was synthesized and fully characterized, including X-ray crystallography. Crystalline coordination complexes were prepared with various copper(I) salts (CuBr, CuI and [(CH3CN)4Cu]BF4 producing both 1:1 µ-X dimers from copper(I) halides and a distorted tetrahedral 2:1 species with non-coordinative tetrafluoroborate salt. Bond distances and angles suggest neutrally bound alkyl azothioformamide ligands with copper(I), indicating no redox activity upon binding. UV–Vis titration studies with copper(I) salts and subsequent data evaluation with both 1:1 and 2:1 non-linear regression binding models suggest inconsistent mechanisms with copper(I) salts.

National Science Foundation under Grant No. 0628258; Defense University Research Instrumentation Program (DURIP, Contract Number: W911NF0510255); MSU Thermal Biology Institute from the NASA Exobiology Program (Project NAG5-8807)

Formation of dissolved metal particles (

Redox-active ligands lead to ambiguity in often clearly defined oxidation states of both the metal centre and the ligand. The arylazothioformamide (ATF) ligand class represents a redox-active ligand with three possible redox states (neutral, singly reduced, and doubly reduced). ATF-metal interactions result in strong colorimetric transitions allowing for the use of ATFs in metal detection and/or separations. While previous reports have discussed dissolution of zerovalent metals, the resulting oxidation states of coordination complexes have proved difficult to interpret through X-ray crystallographic analysis alone. This report describes the X-ray crystallographic analysis combined with computational modelling of the ATF ligand and metal complexes to deconvolute the metal and ligand oxidation state of metal-ATF complexes. Metal(ATF)2 complexes that originated from zerovalent metals were found to exist as dicationic metal centers containing two singly reduced ATF ligands. When employing Cu(I) salts instead of Cu(0) to generate copper-ATF complexes, the resulting complexes remained Cu(I) and the ATF ligand remained “innocent”, existing in its neutral state. Although the use of CuX (where X = Br or I) or [Cu(NCMe)4]Y (where Y = BF4 or PF6) generated species of the type: [(ATF)Cu(μ-X)]2 and [Cu(ATF)2]Y, respectively, the ATF ligand remained in its neutral state for each species type.

The release of nanophase metal particles from sulfide mineral decomposition in mining-impacted environments is a growing concern because of the potential for the transport of nanoscale particles that could increase the distribution of the metals and their environmental impact. An analysis of total (unfiltered) and dissolved (450-nm filtered) metal concentrations in the mining-impacted Coeur d&rsquo, Alene River indicates the leaching of dissolved metal forms from sediments and transport to and within the river. The distribution of metals between total and dissolved forms is driven by seasonal temperatures, hydraulic gradients, and ligand availability. Cd and Zn were the least influenced by changes in gradient and biological productivity between the upper and lower basins. Cd and Zn primarily travel as dissolved forms, with the lowest ratio of dissolved-to-total concentrations in spring and the highest in summer. Fe and Pb primarily travel as suspended particles, but their dissolved forms were greater during all seasons in the lower basin. A principal components analysis of upper basin data indicates that temperature and conductivity were correlated with dissolved Cd and Zn, and total Fe and Pb were correlated with streamflow. In the lower basin, dissolved Cd and Zn, conductivity, and temperature were correlated, and suspended sediment, total metals, and dissolved Pb, but not streamflow, were correlated. The correlation of metals and sediment in the lower basin is not from erosion but the availability of organic matter and Fe that form a range of dissolved to suspended metal particles. The summer decrease in surface water levels releases sediment porewater containing nanoscale-to-microscale metal particles that are transported to open water, where they may impact human and wildlife health. Such releases are unmitigated with current remediation strategies of sediment stabilization.

OriginLab’s newest version update to Origin and OriginPro includes ease-of-use features, like Origin Central updates and creation of an App Center, as well as larger changes like the addition of Unicode characters, alteration to how user files are stored and visually searched, and user input formula in cells within worksheets. These features add additional value to an already powerful data analysis and plotting software package.

Neurotoxic methylmercury (MeHg) is produced by anaerobic Bacteria and Archaea possessing the genes hgcAB , but it is unknown how organic substrate and electron acceptor availability impacts the distribution and abundance of these organisms. We evaluated the impact of organic substrate amendments on mercury (Hg) methylation rates, microbial community structure, and the distribution of hgcAB + microbes with sediments. Sediment slurries were amended with short-chain fatty acids, alcohols, or a polysaccharide. Minimal increases in MeHg were observed following lactate, ethanol, and methanol amendments, while a significant decrease (∼70%) was observed with cellobiose incubations. Postincubation, microbial diversity was assessed via 16S rRNA amplicon sequencing. The presence of hgcAB + organisms was assessed with a broad-range degenerate PCR primer set for both genes, while the presence of microbes in each of the three dominant clades of methylators ( Deltaproteobacteria , Firmicutes , and methanogenic Archaea ) was measured with clade-specific degenerate hgcA quantitative PCR (qPCR) primer sets. The predominant microorganisms in unamended sediments consisted of Proteobacteria , Firmicutes , Bacteroidetes , and Actinobacteria . Clade-specific qPCR identified hgcA + Deltaproteobacteria and Archaea in all sites but failed to detect hgcA + Firmicutes . Cellobiose shifted the communities in all samples to ∼90% non- hgcAB -containing Firmicutes (mainly Bacillus spp. and Clostridium spp.). These results suggest that either expression of hgcAB is downregulated or, more likely given the lack of 16S rRNA gene presence after cellobiose incubation, Hg-methylating organisms are largely outcompeted by cellobiose degraders or degradation products of cellobiose. These results represent a step toward understanding and exploring simple methodologies for controlling MeHg production in the environment. IMPORTANCE Methylmercury (MeHg) is a neurotoxin produced by microorganisms that bioacummulates in the food web and poses a serious health risk to humans. Currently, the impact that organic substrate or electron acceptor availability has on the mercury (Hg)-methylating microorganisms is unclear. To study this, we set up microcosm experiments exposed to different organic substrates and electron acceptors and assayed for Hg methylation rates, for microbial community structure, and for distribution of Hg methylators. The sediment and groundwater was collected from East Fork Poplar Creek in Oak Ridge, TN. Amendment with cellobiose (a lignocellulosic degradation by-product) led to a drastic decrease in the Hg methylation rate compared to that in an unamended control, with an associated shift in the microbial community to mostly nonmethylating Firmicutes . This, along with previous Hg-methylating microorganism identification methods, will be important for identifying strategies to control MeHg production and inform future remediation strategies.

The biogeochemical transformations of mercury are a complex process, with the production of methylmercury, a potent human neurotoxin, repeatedly demonstrated in sulfate- and Fe(III)-reducing as well as methanogenic bacteria. However, little is known regarding the morphology, genes, or proteins involved in methylmercury generation. Desulfovibrio africanus strain Walvis Bay is a Hg-methylating δ-proteobacterium with a sequenced genome and has unusual pleomorphic forms. In this study, a relationship between the pleomorphism and Hg methylation was investigated. Proportional increases in the sigmoidal (regular) cell form corresponded with increased net MeHg production but decreased when the pinched cocci (persister) form became the major morphotype. D. africanus microarrays indicated that the ferrous iron transport genes (feoAB), as well as ribosomal genes and several genes whose products are predicted to have metal binding domains (CxxC), were up-regulated during exposure to Hg in the exponential phase. Whereas no specific methylation pathways were identified, the finding that Hg may interfere with iron transport and the correlation of growth-phase-dependent morphology with MeHg production are notable. The identification of these relationships between differential gene expression, morphology, and the growth-phase dependence of Hg transformations suggests that actively growing cells are primarily responsible for methylation, and so areas with ample carbon and electron-acceptor concentrations may also generate a higher proportion of methylmercury than more oligotrophic environments. The observation of increased iron transporter expression also suggests that Hg methylation may interfere with iron biogeochemical cycles.

BACKGROUND: Microbial behavior in batch reactors may be different from that in continuous flow reactors, which is expected to affect microbial response to heavy metal exposure. Four parallel continuous flow reactors and batch growth tests were used to investigate the single and joint toxicity of Zn and Cu to Artrobacter sp. JM018. RESULTS: The results indicated that Cu is more toxic than Zn under all conditions. In the batch reactors, all Zn concentrations showed a stimulatory effect on microbial growth. However in the continuous system, 125 µmol L−1 Zn exposure produced inhibition. In the case of mixed Zn and Cu exposures in the batch system, the presence of Zn reduced the severity of Cu inhibition, with a net impact of reduced growth in all cases, whereas in the continuous system microbial growth and substrate utilization rates sharply decreased and ceased. CONCLUSION: The results clearly showed that growth in batch reactors underestimated significantly the heavy metal inhibition, compared with the continuous system. Therefore, the results of batch reactor tests should not be used directly when heavy metal inhibition is to be interpreted for continuous flow systems. Copyright © 2011 Society of Chemical Industry

The prokaryotic diversity associated with highly metal-contaminated sediment samples collected from the Coeur d'Alene River (CdAR) was investigated using a cultivation-independent approach. Bacterial community structure was studied by constructing an RNA polymerase beta subunit (rpoB) gene library. Phylogenetic analysis revealed that 75.8% of the rpoB clones were associated with beta-Proteobacteria while the remaining 24.2% were with gamma-Proteobacteria. All phylotypes showed close similarity to previously reported cultivable lineages from metal or organic contaminant-rich environments. In an archaeal 16S rRNA gene library, 70% of the clones were affiliated to Crenarchaeota, while 30% belonged to Euryarchaeota. Most of the Euryarchaeota sequences were related to acetoclastic lineages belonging to Methanosarcinales. A single phylotype within the Euryarchaeota showed no association with cultivable euryarchaeotal lineages and might represent novel taxon. Diversity indices demonstrated greater diversity of Bacteria compared to Archaea in CdAR sediments. Sediment characterization by the X-ray fluorescence spectroscopy revealed high amount of toxic metals. To our knowledge, this is the first culture-independent survey on the prokaryotic diversity present in mining-impacted sediments of CdAR.

Despite over three decades of progress, extraction of high molecular weight (HMW) DNA from high clay soils or iron oxide cemented clay has remained challenging. HMW DNA is desirable for next generation sequencing as it yields the most comprehensive coverage. Several DNA extraction procedures were compared from samples that exhibit strong nucleic acid adsorption. pH manipulation or use of alternative ion solutions offered no improvement in nucleic acid recovery. Lysis by liquid N2 grinding in concentrated guanidine followed by concentrated sodium phosphate extraction supported HMW DNA recovery from clays high in iron oxides. DNA recovered using 1 M sodium phosphate buffer (PB) as a competitive desorptive wash was 15.22±2.33 µg DNA/g clay, with most DNA consisting of >20 Kb fragments, compared to 2.46±0.25 µg DNA/g clay with the Powerlyzer system (MoBio). Increasing PB concentration in the lysis reagent coincided with increasing DNA fragment length during initial extraction. Rarefaction plots of 16S rRNA (V1–V3 region) pyrosequencing from A-horizon and clay soils showed an ∼80% and ∼400% larger accessed diversity compared to the Powerlyzer soil DNA system, respectively. The observed diversity from the Firmicutes showed the strongest increase with >3-fold more operational taxonomic units (OTU) recovered.

The determination of the success of in situ bioremediation strategies is complex. By using controlled laboratory conditions, the influence of individual variables, such as U(VI), Cr(VI), and electron donors and acceptors on community structure, dynamics, and the metal-reducing potential can be studied. Triplicate anaerobic, continuous-flow reactors were inoculated with Cr(VI)-contaminated groundwater from the Hanford, WA, 100-H area, amended with lactate, and incubated for 95 days to obtain stable, enriched communities. The reactors were kept anaerobic with N 2 gas (9 ml/min) flushing the headspace and were fed a defined medium amended with 30 mM lactate and 0.05 mM sulfate with a 48-h generation time. The resultant diversity decreased from 63 genera within 12 phyla to 11 bacterial genera (from 3 phyla) and 2 archaeal genera (from 1 phylum). Final communities were dominated by Pelosinus spp. and to a lesser degree, Acetobacterium spp., with low levels of other organisms, including methanogens. Four new strains of Pelosinus were isolated, with 3 strains being capable of Cr(VI) reduction while one also reduced U(VI). Under limited sulfate, it appeared that the sulfate reducers, including Desulfovibrio spp., were outcompeted. These results suggest that during times of electron acceptor limitation in situ , organisms such as Pelosinus spp. may outcompete the more-well-studied organisms while maintaining overall metal reduction rates and extents. Finally, lab-scale simulations can test new strategies on a smaller scale while facilitating community member isolation, so that a deeper understanding of community metabolism can be revealed.

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 ZnHPO(4)(0)(aq). Cellular uptake of ZnHPO(4)(0)(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 μM total zinc, ZnHPO(4)(0)(aq) constitutes 33, 70, and 76% of the neutral metal phosphate pool at pH 6, 7, and 8, respectively. At 50 μM 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 ZnHPO(4)(0)(aq), show significant pH dependence (p = 9.45 × 10(-7)). Using sodium to decrease the distribution of ZnHPO(4)(0)(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.

An aqueous mixture of goethite, quartz, and lead chloride (PbCl(2)) 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 muM 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 microM 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 microM PbCl(2) 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 PbCl(2) (26 microM 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 PbCl(2). Overall results suggest that even at the same soluble Pb concentration (26 microM), 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.

The behavior of metal ions' leaching and precipitated mineral phases of metal-rich fly ash (FA) was examined in order to evaluate microbial impacts on carbon sequestration and metal immobilization. The leaching solutions consisted of aerobic deionized water (DW) and artificial eutrophic water (AEW) that was anaerobic, organic- and mineral-rich, and higher salinity as is typical of bottom water in eutrophic algae ponds. The Fe- and Ca-rich FAs were predominantly composed of quartz, mullite, portlandite, calcite, hannebachite, maghemite, and hematite. After 86 days, only Fe and Ca contents exhibited a decrease in leaching solutions while other major and trace elements showed increasing or steady trends in preference to the type of FA and leaching solution. Ca-rich FA showed strong carbon sequestration efficiency ranging up to 32.3 g CO(2)/kg FA after 86 days, corresponding to almost 65% of biotic carbon sequestration potential under some conditions. Variations in the properties of FAs such as chemical compositions, mineral constituents as well as the type of leaching solution impacted CO(2) capture. Even though the relative amount of calcite increased sixfold in the AEW and the relative amount of mineral phase reached 37.3 wt% using Ca-rich FA for 86 days, chemical sequestration did not accomplish simultaneous precipitation and sequestration of several heavy metals.