Search

The photosynthetic amoeba, Paulinella provides a recent (ca. 120 Mya) example of primary plastid endosymbiosis. Given the extensive data demonstrating host lineage‐driven endosymbiont integration, we analysed nuclear genome and transcriptome data to investigate mechanisms that may have evolved in Paulinella micropora KR01 (hereinafter, KR01) to maintain photosynthetic function in the novel organelle, the chromatophore. The chromatophore is of α‐cyanobacterial provenance and has undergone massive gene loss due to Muller's ratchet, but still retains genes that encode the ancestral α‐carboxysome and the shell carbonic anhydrase, two critical components of the biophysical CO2 concentrating mechanism (CCM) in cyanobacteria. We identified KR01 nuclear genes potentially involved in the CCM that arose via duplication and divergence and are upregulated in response to high light and downregulated under elevated CO2. We speculate that these genes may comprise a novel CO2 delivery system (i.e., a biochemical CCM) to promote the turnover of the RuBisCO carboxylation reaction and counteract photorespiration. We posit that KR01 has an inefficient photorespiratory system that cannot fully recycle the C2 product of RuBisCO oxygenation back to the Calvin‐Benson cycle. Nonetheless, both these systems appear to be sufficient to allow Paulinella to persist in environments dominated by faster‐growing phototrophs. [ABSTRACT FROM AUTHOR]

• legacy mercury in upper Berry's Creek has a δ202Hg value of −0.29‰. • organic matter content was used to identify a low δ202Hg pool of mercury that dilutes legacy contaminant mercury. • upper Berry's Creek contributes 21%–82% of mercury to the Hackensack River estuary. • legacy mercury may affect marsh habitats far from sites of primary contamination. Spatial redistribution of legacy mercury (Hg) contamination in the Hackensack River estuary (New Jersey, USA) was evaluated using mercury stable isotopes. Total Hg varied from 0.06 to 3.8 μg g−1 in sediment from the tidal Hackensack River and from 15 to 154 μg g−1 near historically contaminated sites in upper Berry's Creek, a tributary of the Hackensack River. δ202Hg values for total Hg from Berry's Creek and Hackensack River estuaries varied over a fairly narrow range (−0.44‰ to −0.21‰), but were highest for sediment from upper Berry's Creek. Isotope mixing plots show that residual legacy mercury from upper Berry's Creek is partially diluted by a low concentration and low δ202Hg pool of mercury associated with low organic matter content sediments similar to those in Newark Bay. Based on an isotope mixing model, we estimate that upper Berry's Creek contributes 21%–82% of the mercury in sediments in the Hackensack River estuary and its tidal tributaries, including upstream marsh habitats far from the primary source. Our results show that mercury stable isotopes can be used to track the redistribution of mercury in tidal ecosystems and highlight the potentially large areas which may be affected by legacy mercury contamination in estuaries. [ABSTRACT FROM AUTHOR]

Methylmercury (MeHg), a neurotoxic substance that accumulates in aquatic food chains and poses a risk to human health, is synthesized by anaerobic microorganisms in the environment. To date, mercury (Hg) methylation has been attributed to sulfateand iron-reducing bacteria (SRB and IRB, respectively). Here we report that a methanogen, Methanospirillum hungatei JF-1, methylated Hg in a sulfide-free medium at comparable rates, but with higher yields, than those observed for some SRB and IRB. Phylogenetic analyses showed that the concatenated orthologs of the Hg methylation proteins HgcA and HgcB from M. hungatei are closely related to those from known SRB and IRB methylators and that they cluster together with proteins from eight other methanogens, suggesting that these methanogens may also methylate Hg. Because all nine methanogens with HgcA and HgcB orthologs belong to the class Methanomicrobia, constituting the late-evolving methanogenic lineage, methanogenic Hg methylation could not be considered an ancient metabolic trait. Our results identify methanogens as a new guild of Hg-methylating microbes with a potentially important role in mineral-poor (sulfate- and iron-limited) anoxic freshwater environments. [ABSTRACT FROM AUTHOR]

The role of a C4 pathway in photosynthetic carbon fixation by marine diatoms is presently debated. Previous labeling studies have shown the transfer of photosynthetically fixed carbon through a C4 pathway and recent genomic data provide evidence for the existence of key enzymes involved in C4 metabolism. Nonetheless, the importance of the C4 pathway in photosynthesis has been questioned and this pathway is seen as redundant to the known CO2 concentrating mechanism of diatoms. Here we show that the inhibition of phosphoenolpyruvate carboxylase (PEPCase) by 3,3-dichloro-2-dihydroxyphosphinoylmethyl-2-propenoate resulted in a more than 90% decrease in whole cell photosynthesis in Thalassiosira weissflogii cells acclimated to low CO2 (10 μM), but had little effect on photosynthesis in the C3 marine Chlorophyte, Chlamydomonas sp. In 3,3-dichloro-2-dihydroxyphosphinoylmethyl-2-propenoate-treated T. weissflogii cells, elevated CO2 (150 μM) or low O2 (80–180 μM) restored photosynthesis to the control rate linking PEPCase inhibition with CO2 supply in this diatom. In C4 organic carbon-inorganic carbon competition experiments, the 12C-labeled C4 products of PEPCase, oxaloacetic acid and its reduced form malic acid suppressed the fixation of 14C-labeled inorganic carbon by 40% to 50%, but had no effect on O2 evolution in photosynthesizing diatoms. Oxaloacetic acid-dependent O2 evolution in T. weissflogii was twice as high in cells acclimated to 10 μM rather than 22 μM CO2, indicating that the use of C4 compounds for photosynthesis is regulated over the range of CO2 concentrations observed in marine surface waters. Short-term 14C uptake (silicone oil centrifugation) and CO2 release (membrane inlet mass spectrometry) experiments that employed a protein denaturing cell extraction solution containing the PEPCKase inhibitor mercaptopicolinic acid revealed that much of the carbon taken up by diatoms during photosynthesis is stored as organic carbon before being fixed in the Calvin cycle, as expected if the C4 pathway functions as a CO2 concentrating mechanism. Together these results demonstrate that the C4 pathway is important in carbon accumulation and photosynthetic carbon fixation in diatoms at low (atmospheric) CO2. [ABSTRACT FROM AUTHOR]

Examines the bioaccumulation, subcellular distribution and trophic transfer of copper in a coastal marine diatom Thalassiosira weissflogii. Increase of intracellular copper quotas per decade increase in free copper ion concentration; Assimilation efficiency of copper in marine copepods fed T. weissflogii.

Presents evidence that carbon[sub4] photosynthesis supports carbon assimilation in the marine diatom Thalassiosira weissflogii, thus providing a biochemical explanation for carbon-dioxide-insensitive photosynthesis in marine diatoms. Speculation that carbon[sub4] photosynthesis may account for a significant portion of carbon fixation and export in the ocean and would explain the enrichment of carbon in diatoms compared with other classes of phytoplankton; Possibility that unicellular carbon[sub4] plants predated multicellar ones.

Metabolic responses to the subacute toxicities (non-growth-rate inhibiting) of Cd, Cu, and Zn were measured in the coastal marine diatom Thalassiosira weissflogii using calorespirometry. Respiratory heat production and oxygen consumption rates were measured in diatom cells grown with concentrations of Cd2+ (10-12 to 10-8 M), Cu2+ (10-13.8 to 10-9.8 M), and Zn2+ (10-10.9 to 10-6.9 M) that are typical of urban and suburban coastal waters. These trace metals did not significantly inhibit diatom growth rates in high-nutrient, high-light laboratory cultures except for the highest concentrations of Cd (Cd2+ = 10-8 M) and Zn (Zn2+ = 10-6.9 M). Respiratory heat rates in cells grown with elevated, but on-growth-rate-inhibiting free Cu2+ ion concentrations (10-11.8 to 10-9.8 M) were up to 40% higher and oxygen consumption rates were 50 to 75% lower than control ([Cu2+] = 10-10.8 M) cells indicating a subacute depression of respiratory efficiency in Cu-exposed cells. Exposure to elevated free Cd2+ concentrations (10-10 to 10-8 M) caused dramatic short-term (hours) increases (five- to eight-fold) in respiratory oxygen consumption rates, which returned to normal in acclimated cells, suggesting a transient disruption of metabolism upon Cd exposure. Zinc did not significantly affect either respiratory parameter up to a free Zn concentration of 10-7.9 M, above which diatom growth rate was significantly reduced. The subacute toxic effects of Cd and Cu were more pronounced in low Mn than in Mn-replete cells, consistent with proposed Mn- Cd, -Cu antagonisms in marine phytoplankton. The range of free Cu2+ ion concentrations in coastal waters is similar to that found to cause a decrease in respiratory efficiency in T. weissflogii, th... [ABSTRACT FROM AUTHOR]

Assesses the bioavailability of inorganic silver species and the importance of the low polarity AgCl complex to biological uptake. Determination of the octanol-water partition coefficient of silver over a range of chloride concentration representatives of fresh to brackish water; AgCl as the principal bioavailable species of inorganic silver in phytoplankton.

Examines the primary mechanisms controlling the accumulation of methylmercury and inorganic mercury in aquatic food chains. Partition coefficients; Mercury uptake experiments; Cellular reactivity of mercury and methylmercury; Trophic transfer; Chemical analyses; Mercury speciation and accumulation; Cell fractionation; Hydrophobicity.

Significant calcium enrichment relative to seawater was observed in bulk and size-segregated aerosols in the marine atmospheric boundary layer over the Arctic Ocean in summer. The calcium enrichment factor generally increased with decreasing particle size (aerodynamic diameter) in the fine mode (particle size <1.8 μm), especially within the particle size ranges of 1.8 μm to 0.56 μm and 0.18 μm to 0.1 μm. Potassium was slightly enriched and showed a similar trend of enrichment in fine mode particles. No positive enrichment was observed for magnesium. Calcium bound to certain organic compounds and possibly calcareous debris from marine organisms may have contributed to the calcium enrichment in aerosols. Model results predict that observed calcium enrichments would increase hygroscopic growth in both coarse (10 μm and 5.6 μm) and fine (0.56 μm and 1 μm) aerosol particles. Possible alteration of this model result due to interactions with anions notwithstanding, increases in hygroscopic growth would be particularly important in the Arctic summer when sea-salts constitute the major fraction of aerosol dry mass. This study provides unique insights into ocean-atmosphere chemical interactions in the high-latitude Arctic Ocean. • Calcium enrichment relative to seawater occurred in both bulk and size-segregated aerosols. • Calcium enrichment increased with decreasing particle size. • Calcium bound possibly to calcareous debris from marine organisms may have been the source of aerosol calcium enrichment. [ABSTRACT FROM AUTHOR]

• Long-term volumetric Hg TSP concentration was decreasing in Beijing. • Mass-based concentrations of Hg TSP were not reduced during emission control. • Industrial emission control has limited change in Hg isotope ratios of TSP. We investigated the effect of the temporary ban of local industrial activities during the Asia-Pacific Economic Cooperation (APEC) summit (4th–14th Nov 2014) in Beijing, China on total suspended particulate mercury (Hg TSP) concentrations and isotope compositions. We measured Hg concentrations and isotope ratios in 33 TSP samples from central Beijing, including 21 samples collected from Jun 2012 to Apr 2014, and 12 samples collected from 14th Oct–19th Nov 2014. Volumetric concentrations of both TSP and Hg TSP during the APEC summit were a factor of 2 lower than during the pre-APEC period, indicating substantial reductions in total particulate matter and Hg TSP as a result of emissions controls. However, mass-normalized concentrations and mercury isotope ratios of Hg TSP did not vary significantly between samples collected before, during, or after the APEC summit. These results show that local emissions are important sources of particle bound mercury (PBM) in Beijing and that their control can be used to immediately lower the volumetric concentration of Hg TSP. They also indicate that a similarly complex mixture of sources contributed to PBM in Beijing before and during emissions controls were put in place and that PBM concentrations in Beijing are primarily controlled by emissions and secondarily by photoreduction. [ABSTRACT FROM AUTHOR]

We examined mercury (Hg) accumulation in juvenile and adult subpopulations of Antarctic krill (Euphausia superba) collected west of the Antarctic Peninsula. Samples were collected along a northern cross-shelf transect beginning near Anvers Island and farther south near the sea ice edge in the austral summers of 2011, 2013, 2014, and 2015. Regardless of geographical position, mean concentrations of total Hg and methylmercury (MeHg), the form of Hg that biomagnifies in marine food webs, were significantly higher in juvenile than adult krill in all years. In 2013, juvenile Antarctic krill collected along the coast near Anvers Island had significantly higher MeHg concentrations than krill collected farther offshore, and in 2013 and 2014, coastal juvenile krill exhibited some of the highest MeHg concentrations of all subpopulations sampled. Across all sampling years, collection in northern (sea ice-free) or southern (sea ice edge) transects did not affect MeHg concentrations of juvenile or adult krill, suggesting similar levels and routes of MeHg exposure across the latitudes sampled. Developmental stage, feeding near the coast, and annual variations in sea ice-driven primary and export production were identified as potentially important factors leading to greater MeHg accumulation in juvenile than adult krill. Krill-dependent predators feeding primarily on juveniles may thus accumulate more MeHg than consumers foraging on older krill. These results report MeHg concentrations in Antarctic krill and will be useful for predicting Hg biomagnification in higher-level consumers in this productive Antarctic ecosystem. Unlabelled Image • THg and MeHg were measured in coastal populations of Antarctic krill. • Concentrations of THg and MeHg were higher in juvenile than adult krill. • MeHg accumulation was similar in krill from sea ice covered and ice-free transects. • Annual sea ice may indirectly affect krill Hg accumulation through POM formation. [ABSTRACT FROM AUTHOR]

Abstract Cadmium (Cd) and arsenic (As) are nonessential and toxic elements in rice that often occur together in contaminated paddy field soils. To understand whether rice has a common molecular response mechanism against Cd and As toxicity, 30-day seedlings (Oryza sativa L. indica) were exposed separately to Cd and As3+ in hydroponic cultures for up to 7 days. Root transcriptomic analysis of plants exposed to Cd and As for 3 days revealed that a total of 2224 genes in rice roots responded to Cd stress, while 1503 genes responded to As stress. Of these, 841 genes responded to both stressors. The genes in common to Cd and As stress were associated with redox control, stress response, transcriptional regulation, transmembrane transport, signal transduction, as well as biosynthesis and metabolism of macromolecules and sulfur compounds. In plants exposed to Cd and As separately or in combination for 3 and 7 days, qRT-PCR verification revealed that the glutathione metabolism associated gene Os09g0367700 was significantly up-regulated with respect to unexposed controls and had a positive synergistic effect under combined Cd and As stress. In addition, the redox control related genes Os06g0216000 , Os07g0638300 and Os01g0294500 , the glutathione metabolism related gene Os01g0530900 , the cell wall biogenesis related genes Os05g0247800 , Os11g0592000 and Os03g0416200 , the expression regulation related genes Os07g0597200 and Os02g0168200 , and the transmembrane transport related genes Os04g0524500 , also varied significantly with respect to an unexposed control and displayed synergistic effects after 7 days of simultaneous exposure to Cd and As. Our identification of a novel set of genes in rice which responded to both Cd and As3+ stress may be of value in mitigating the toxicity of co-contaminated soils. These results also provide a deeper understanding of the molecular mechanisms involved in response to multi-metal/loids stress, and may be used in the genetic improvement of rice varieties. Graphical abstract Unlabelled Image Highlights • Cd- and As- stressed plants shared a broad array of stress response genes. • Most common response genes were upregulated and belong to five metabolic categories. • A novel set of common response genes in Cd- and As- stressed plants was identified. • Some genes related to the alleviation of metal/loid toxicity responded synergistically. • Common detoxification mechanisms were characterized and discussed. [ABSTRACT FROM AUTHOR]

Of the six elements incorporated into the major polymers of life, phosphorus is the least abundant on a global scale [E. Anders, M. Ebihara, Geochim. Cosmochim. Acta 46, 2363–2380 (1982)] and has been described as the “ultimate limiting nutrient” [T. Tyrrell, Nature 400, 525–531 (1999)]. In the modern ocean, the supply of dissolved phosphorus is predominantly sustained by the oxidative remineralization/recycling of organic phosphorus in seawater. However, in the Archean Eon (4 to 2.5 Ga), surface waters were anoxic and reducing. Here, we conducted photochemical experiments to test whether photodegradation of ubiquitous dissolved organic phosphorus could facilitate phosphorus recycling under the simulated Archean conditions. Our results strongly suggest that organic phosphorus compounds, which were produced by marine biota (e.g., adenosine monophosphate and phosphatidylserine) or delivered by meteorites (e.g., methyl phosphonate) can undergo rapid photodegradation and release inorganic phosphate into solution under anoxic conditions. Our experimental results and theoretical calculations indicate that photodegradation of organic phosphorus could have been a significant source of bioavailable phosphorus in the early ocean and would have fueled primary production during the Archean eon. [ABSTRACT FROM AUTHOR]

Sources of methylmercury (MeHg) in adult Pacific bluefin tuna (Thunnus orientalis, PBT) from the western North Pacific Ocean (WPO) were examined using mercury stable isotopes. Significant increases in δ202Hg and Δ199Hg values with PBT size and age, along with those of potential prey, indicate a shift in the source of MeHg accumulated by PBT as they age. Among adults from the WPO, this shift likely involves greater accumulation of MeHg from epipelagic prey in the Kuroshio extension in large vs. small and medium-sized PBT. For all adults, little MeHg is accumulated in the spawning grounds near Taiwan. Significantly lower Δ199Hg/Δ201Hg ratios in adult PBT and their prey from the WPO than from the central and eastern North Pacific indicate different sources or transformations of MeHg prior to accumulation in the WPO food web than further east. Our results show that MeHg sources to oceanic food webs vary across the North Pacific Ocean and regionally within the WPO. [ABSTRACT FROM AUTHOR]

We measured short-term uptake rates of copper using the gamma-emitting radioisotope 67Cu in seven algal species in natural and artificial seawater. Cellular net uptake of Cu was typically rapid over periods of 2-20 min. Net uptake ceased after about 60 min. The most copper-sensitive species examined, Synechococcus sp., exhibited 2-3 orders of magnitude higher carbon and surface-area-normalized Cu-accumulation rates (46 µmol Cu mol C-1 min-1 and 1,100 zmol Cu µm-2 min-1) (zmol X 10-21 moles) than those measured in diatoms, chlorophytes, a dinoflagellate, and a coccolithophore. Cu-accumulation rates for Thalassiosira weissflogii were three times faster in natural seawater than in EDTA-buffered artificial seawater containing an inorganic Cu concentration of 28 pmol L-1. Calculations showing that the diffusive flux of inorganic Cu was insufficient to account for observed short-term uptake rates suggest that some of the Cu bound to naturally occurring organic ligands is released through the rapid dissociation of those complexes in the cell's boundary layer. [ABSTRACT FROM AUTHOR]

Redox cycling between elemental [Hg(0)] and divalent [Hg(II)] mercury is a key control on the fate and transport of Hg in groundwater systems. In this study, we tested the ability of anaerobic bacteria to oxidize dissolved Hg(0) to Hg(II). Controlled laboratory experiments were carried out with the obligate anaerobic bacterium Geothrix fermentans H5, and the facultative anaerobic bacteria Shewanella oneidensis MR-1 and Cupriavidus metallidurans AE104. Under anoxic conditions, all three bacterial strains reacted with dissolved gaseous Hg(0) to form non-purgeable Hg. In mass balance experiments, the formation of non-purgeable Hg corresponded to the loss of volatile Hg. To determine if the non-purgeable Hg was oxidized, we performed ethylation experiments on Hg(0)-reacted cell suspensions and X-ray absorption near edge structure (XANES) spectroscopy on Hg(0)-reacted cells. Derivatization of non-purgeable Hg to diethylmercury and the Hg LIII-edge position of the XANES spectra demonstrated that the reacted bacterial samples contained Hg(II). XANES analysis also revealed that cell-associated Hg(II) was covalently bound to bacterial functional groups, most likely to thiol moieties. Finally, experiments with metabolically active and heat-inactivated cells indicated that both live and dead cells oxidized Hg(0) to Hg(II). Hg(0) oxidation rates for metabolically active cultures increase in the order S. oneidensis MR-1 (1.6×10−4 fg/cell/min), C. metallidurans AE104 (2.5×10−4 fg/cell/min), and G. fermentans H5 (23.1×10−4 fg/cell/min). The results of this study suggest that reactivity towards Hg(0) is widespread among diverse anaerobic bacteria, and passive microbial oxidation of Hg(0) may play an important role in the redox transformation of mercury contaminants in subsurface environments. [ABSTRACT FROM AUTHOR]

• Surface species content was used to construct species-informed model. • The equilibrium and kinetic data were used to train species-informed model. • The optimal species-informed model showed excellent predictability. • LIME values helped explain species-informed model's surface species content. • Species-informed modeling framework could be applied to other adsorption systems. This study aimed to develop surface complexation modeling-machine learning (SCM-ML) hybrid model for chromate and arsenate adsorption on goethite. The feasibility of two SCM-ML hybrid modeling approaches was investigated. Firstly, we attempted to utilize ML algorithms and establish the parameter model, to link factors influencing the adsorption amount of oxyanions with optimized surface complexation constants. However, the results revealed the optimized chromate or arsenate surface complexation constants might fall into local extrema, making it unable to establish a reasonable mapping relationship between adsorption conditions and surface complexation constants by ML algorithms. In contrast, species-informed models were successfully obtained, by incorporating the surface species information calculated from the unoptimized SCM with the adsorption condition as input features. Compared with the optimized SCM, the species-informed model could make more accurate predictions on pH edges, isotherms, and kinetic data for various input conditions (for chromate: root mean square error (RMSE) on test set = 5.90 %; for arsenate: RMSE on test set = 4.84 %). Furthermore, the utilization of the interpretable formula based on Local Interpretable Model-Agnostic Explanations (LIME) enabled the species-informed model to provide surface species information like SCM. The species-informed SCM-ML hybrid modeling method proposed in this study has great practicality and application potential, and is expected to become a new paradigm in surface adsorption model. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The transformation of inorganic mercury (Hg) to methylmercury (MeHg) plays a key role in determining the amount of Hg that is bioaccumulated in aquatic food chains. An accurate knowledge of Hg methylation mechanisms is required to predict the conditions that promote MeHg production in aquatic environments. In this study, we conducted experiments to examine the oxidation and methylation of dissolved elemental mercury [Hg(0)] by the anaerobic bacterium Desulfovibrio desulfuricans ND132. Anoxic cultures of D. desulfuricans ND132 were exposed to Hg(0) in the dark, and samples were collected and analyzed for the loss of Hg(0), formation of non-purgeable Hg, and formation of MeHg over time. We found that D. desulfuricans ND132 rapidly transformed dissolved gaseous mercury into non-purgeable Hg, with bacterial cultures producing approximately 40μg/L of non-purgeable Hg within 30min, and as much as 800μg/L of non-purgeable Hg after 36h. Derivatization of the non-purgeable Hg in the cell suspensions to diethylmercury and analysis of Hg(0)-reacted D. desulfuricans ND132 cells using X-ray absorption near edge structure (XANES) spectroscopy demonstrated that cell-associated Hg was dominantly in the oxidized Hg(II) form. Spectral comparisons and linear combination fitting of the XANES spectra indicated that the oxidized Hg(II) was covalently bonded to cellular thiol functional groups. MeHg analyses revealed that D. desulfuricans ND132 produced up to 118μg/L of methylmercury after 36h of incubation. We found that a significant fraction of the methylated Hg was exported out of the cell and released into the culture medium. The results of this work demonstrate a previously unrecognized pathway in the mercury cycle, whereby anaerobic bacteria produce MeHg when provided with dissolved Hg(0) as their sole Hg source. [Copyright &y& Elsevier]

Abstract: Mercury (Hg) is a trace metal with potentially serious public health consequences, especially when its neurotoxic form, monomethylmercury (MMHg), accumulates in aquatic and terrestrial food chains. Given the variation in Hg stable isotope abundances (up to 6‰ in δ202/198Hg and 11‰ in Δ201/198Hg) in natural environmental samples and evidence for Hg isotopic fractionation during microbial (e.g., reduction of Hg(II), degradation and formation of MMHg) and abiotic processes (e.g., photo-degradation of MMHg and volatilization, evaporation and diffusion of Hg(0)), Hg isotope biogeochemistry is currently being developed as a tool to study sources, sinks, and transformations of Hg in the environment. The use of Hg stable isotopes to identify sources of MMHg in aquatic and terrestrial food chains depends on the knowledge of reasonably precise fractionation factors for individual Hg transformations that influence speciation and accumulation of Hg. Microbial transformations are critical to the formation of MMHg and Hg(0) and to the degradation of MMHg. This article a) highlights the importance of experimental determination of microbial fractionation factors for the development of Hg stable isotope systematics because of the limitations of theoretical calculations; b) provides a summary of the current understanding of microbial stable isotope fractionation of Hg, especially during kinetically controlled processes; and c) demonstrates the various factors likely to affect cell-level fractionation during microbial transformations through use of an iterative finite-step model. We also identify future directions, conditions and controls that could help rigorously advance the development of mass-dependent Hg isotope systematics at the enzymatic, cellular and ecosystem level. [Copyright &y& Elsevier]

The concentrations of Ag, Cd, Cu, Hg(II), monomethylmercury (MeHg), Pb, and Zn were measured and modeled in calanoid copepods collected from the Hudson River plume in April 2005 and May 2006. Copepods in the buoyant plume were significantly (p < 0.05) enriched in Ag, Cu, Pb, Zn, and MeHg (2- to 25-fold), but depleted in Cd (by 25-40%) relative to oceanic copepods. Median burdens of Ag, Cu, and Hg(II) differed in plume copepods collected in April 2005 and May 2006 by factors of 1.5 to 3, reflecting the influence of river discharge and associated physical processes on plankton dynamics and metal bioaccumulation. Only the concentrations of Cu and Zn in plume copepods clearly showed the expected trend of highest levels near the mouth of the Hudson River and lower levels offshore. Spatial trends in concentrations of Ag and Hg(II) in plume copepods were strikingly different from those in suspended particles and the dissolved phase, apparently reflecting differences in metal bioavailability because of shifts in available food types. Modeled concentrations of Cd, Cu, Pb, and Zn in plume copepods were within less than a factor of two of measured values, but model results showed that Hg(II) was less bioavailable, and Ag and MeHg were more bioavailable in the Hudson River plume than laboratory results would predict. Zooplankton from urban river plumes may accumulate potentially toxic levels of trace metals or act as a trophic link between metal contamination in polluted estuaries and pelagic ecosystems. [ABSTRACT FROM AUTHOR]

Superoxide dismutase (SOD) catalyzes the transformation of superoxide to molecular oxygen and hydrogen peroxide. Of the four known SOD isoforms, distinguished by their metal cofactor (iron, manganese [Mn], copper/zinc, nickel), MnSOD is the dominant form m the diatom Thalassiosira pseudonana. We cloned the MnSOD gene, sodA, using the expression vector pBAD, overexpressed the product in Escherichia coli, and purified the mature protein (TpMnSOD). This recombinant enzyme was used to generate a polyclonal antibody in rabbit that recognizes MnSOD in T. pseudonana. Based on quantitative immunoblots, we calculate that in vivo concentrations of TpMnSOD are approximately 0.9 amol cell-1 using the recombinant protein as a standard. Immunogold staining indicates that TpMnSOD is localized in the chloroplasts, which is in contrast to most other eukaryotic algae (including chlorophytes and embryophytes) where MnSOD is localized exclusively in mitochondria. Based on the photosynthetic Mn complex in photosystem II, cellular Mn budgets cannot account for 50% to 80% of measured Mn within diatom cells. Our results reveal that chloroplastic MnSOD accounts for 10% to 20% of cellular Mn, depending on incident light intensity and cellular growth rate. Indeed, our analysis indicates that TpMnSOD accounts for 1.4% (±0.2%) of the total protein in the cell. The TpMnSOD has a rapid turnover rate with an apparent half-life of 6 to 8 h when grown under continuous light. TpMnSOD concentrations increase relative to chlorophyll, with an increase in incident light intensity to minimize photosynthetic oxidative stress. The employment of a Mn-based SOD, linked to photosynthetic stress in T. pseudonana, may contribute to the continued success of diatoms in the low iron regions of the modern ocean. [ABSTRACT FROM AUTHOR]

The curious phenomenon of similar levels of methylmercury (MeHg) accumulation in fish from contaminated and pristine environments may be explained by the observation that the proportion of total mercury (Hgr) present as MeHg is inversely related to Hgr in natural waters. We hypothesize that this "MeHg accumulation paradox" is explained by the quantitative induction of bacterial enzymes that are encoded by the mercury resistance (met) operon, organomercury lyase (MerB), and mercuric reductase (MerA) by inorganic Hg (Hg[ll]). We tested this hypothesis in two ecosystems in New Jersey: Berry's Creek in the Meadowlands (ML) and Pine Barren (PB) lakes. Across all sites, an inverse correlation (r² = 0.80) between the concentration of Hgr (ML 113-4220 ng L-1 PB, 0.3- 5.4 ng L-1) and the proportion of Hgr as MeHg (MeHg in ML and PB ranged from 0.08 to 1.6 and from 0.03 to 0.34 ng L-1, respectively) was observed. The planktonic microbial community in Meadowlands surface waters exhibited adaptation to mercury, the presence of mer genes and mRNA transcripts, and high rates of reductive demethylation (kdeg = 0.19 day-1). In contrast, the microbial community of PB was not adapted to mercury and demonstrated low rates of oxidative demethylation (kdeg = 0.01 day-1). These results strongly support our hypothesis and show that the degradation of MeHg by mer-encoded enzymes by the water column microbiota of contaminated environments can significantly affect the amount of MeHg that is available for entry into the aquatic food web. [ABSTRACT FROM AUTHOR]

• Si reverses Cd- and As-driven inhibition of rice plant growth via shared mechanisms. • Shared transcriptomic mechanisms were involved in the Si-mediated stress response. • Si may play a fundamental, active role in heavy metal/loid stress amelioration. • Metal/loid translocation and ROS production were alleviated by Si treatment. • MYB transcription factor and thionin may be involved in Si-mediated defense response. The inessential heavy metal/loids cadmium (Cd) and arsenic (As), which often co-occur in polluted paddy soils, are toxic to rice. Silicon (Si) treatment is known to reduce Cd and As toxicity in rice plants. To better understand the shared mechanisms by which Si alleviates Cd and As stress, rice seedlings were hydroponically exposed to Cd or As, then treated with Si. The addition of Si significantly ameliorated the inhibitory effects of Cd and As on rice seedling growth. Si supplementation decreased Cd and As translocation from roots to shoots, and significantly reduced Cd- and As-induced reactive oxygen species generation in rice seedlings. Transcriptomics analyses were conducted to elucidate molecular mechanisms underlying the Si-mediated response to Cd or As stress in rice. The expression patterns of the differentially expressed genes in Cd- or As-stressed rice roots with and without Si application were compared. The transcriptomes of the Cd- and As-stressed rice roots were similarly and profoundly reshaped by Si application, suggesting that Si may play a fundamental, active role in plant defense against heavy metal/loid stresses by modulating whole genome expression. We also identified two novel genes, Os01g0524500 and Os06g0514800 , encoding a myeloblastosis (MYB) transcription factor and a thionin, respectively, which may be candidate targets for Si to alleviate Cd and As stress in rice, as well as for the generation of Cd- and/or As-resistant plants. This study provides valuable resources for further clarification of the shared molecular mechanisms underlying the Si-mediated alleviation of Cd and As toxicity in rice. [Display omitted] [ABSTRACT FROM AUTHOR]

Bluefin tuna (BFT), highly prized among consumers, accumulate high levels of mercury (Hg) as neurotoxic methylmercury (MeHg). However, how Hg bioaccumulation varies among globally distributed BFT populations is not understood. Here, we show mercury accumulation rates (MARs) in BFT are highest in the Mediterranean Sea and decrease as North Pacific Ocean > Indian Ocean > North Atlantic Ocean. Moreover, MARs increase in proportion to the concentrations of MeHg in regional seawater and zooplankton, linking MeHg accumulation in BFT to MeHg bioavailability at the base of each subbasin's food web. Observed global patterns correspond to levels of Hg in each ocean subbasin; the Mediterranean, North Pacific, and Indian Oceans are subject to geogenic enrichment and anthropogenic contamination, while the North Atlantic Ocean is less so. MAR in BFT as a global pollution index reflects natural and human sources and global thermohaline circulation. [ABSTRACT FROM AUTHOR]

Anaerobic bacteria are known to produce neurotoxic methylmercury [MeHg] when elemental mercury [Hg(0)] is provided as the sole mercury source. In this study, we examined the formation of MeHg in anaerobic incubations of sediment collected from the San Jacinto River estuary (Texas, USA) amended with aqueous Hg(0) to investigate the microbial communities involved in the conversion of Hg(0) to MeHg. The results show that the addition of the methanogen inhibitor 2-bromoethanesulfonate (BES) significantly decreased MeHg production. The mercury methylation gene, hgcA , was detected in these sediments using archaeal specific primers, and 16S rRNA sequencing showed that a member of the Methanosarcinaceae family of methanogens was active. These results suggest that methanogenic archaea play an underappreciated role in the production of MeHg in estuarine sediments contaminated with Hg(0). [ABSTRACT FROM AUTHOR]

Jarosite is an iron-hydroxysulfate mineral commonly found in acid mine drainage (AMD). Given its strong adsorption capacity and its ability to co-precipitation with heavy metals, jarosite is considered a potent scavenger of contaminants in AMD-impacted environments. Sulfate-reducing bacteria (SRB) play an important role in the reductive dissolution of jarosite; however, the mechanism involved has yet to be elucidated. In this study, an indigenous SRB community enriched from the Dabaoshan mine area (Guangdong, China) was employed to explore the mechanism of the microbial reduction of jarosite. Different cultures, with or without dissolved sulfate and the physical separation of jarosite from bacteria by dialysis bags, were examined. Results indicate that the reduction of jarosite by SRB occurred via an indirect mechanism. In systems with dissolved sulfate, lactate was incompletely oxidized to acetate coupled with the reduction of SO 4 2− to S2−, which subsequently reduced the Fe3+ in jarosite, forming secondary minerals including vivianite, mackinawite and pyrite. In systems without dissolved sulfate, jarosite dissolution occurred prior to reduction, and similar secondary minerals formed as well. Extracellular polymeric substances secreted by SRB appeared to facilitate the release of sulfate from jarosite. Structural sulfate in the solid phase of jarosite may not be available for SRB respiration. Although direct contact between SRB and jarosite is not necessary for mineral reduction, wrapping jarosite into dialysis bags suppressed the reduction to a certain extent. Microbial community composition differed in direct contact treatments and physical separation treatments. Physical separation of the SRB community from jarosite mineral supported the growth of Citrobacter , while Desulfosporosinus dominated in direct contact treatments. Unlabelled Image • An indigenous SRB community was employed to explore the mechanism of the microbial reduction of jarosite. • Dissolution is a prerequisite for jarosite reduction. • Extracellular polymeric substances secreted by SRB appeared to facilitate the release of sulfate from jarosite. • Physical separation of the SRB community from jarosite favored the growth of Citrobacter. [ABSTRACT FROM AUTHOR]

Plants typically take up Fe through either strategy I or strategy II, whereas rice uses both. Stable Fe isotopes potentially reveal pathways of Fe uptake in rice plants. In this study we measured Fe isotopic compositions of rice grown under different conditions, i.e. paddy soil with deficient Fe supply and Fe3+-EDTA aqueous solution with sufficient Fe supply, to investigate whether Fe isotope fractionation is distinct under Fe-deficient and Fe-sufficient conditions as well as their possible controlling mechanisms. Our results show that rice grown in the Fe3+-EDTA aqueous solutions with sufficient Fe supply preferentially takes up light Fe isotopes (Δ56Fe bulk plant-nutrient = −1.36‰) and accumulates Fe in different parts of plant (roots, stems, leaves, husks, and grains) with large Fe isotope fractionation. Under such a growing condition, rice takes up Fe through strategy I and the reduction of Fe3+ to Fe2+ results in plants enriching isotopically light Fe. Within the plant, the transportation of Fe is accompanied with changes in redox state, which thus causes significant Fe isotope fractionation among different plant tissues. In contrast, rice plants grown in soils with deficient Fe supply are slightly enriched in heavy Fe isotopes (Δ56Fe bulk plant-soil solution = 0.27‰) and accumulate Fe in different plant tissues with little isotope fractionation. Under this growing condition, the rice plant takes up Fe through strategy II. Plants take up Fe from soils as Fe3+-phytosiderophores (Fe3+-PS) complex and transport Fe as Fe3+-nicotianamine (Fe3+-NA) complex throughout the plant, which does not involve changes in redox state and thus results in very limited isotope fractionation. The observed difference in Fe isotope fractionation indicates two distinct Fe uptake and translocation strategies for rice grown under the two different conditions: strategy I under Fe-sufficient conditions, and strategy II under Fe-deficient conditions. Our results demonstrate that Fe isotope ratios may be used to distinguish Fe-sufficient versus Fe-deficient conditions and to elucidate Fe biogeochemical processes during rice growth. Unlabelled Image • Rice grown with sufficient Fe supply takes up Fe through strategy I and significantly fractionates Fe isotopes. • Rice grown with deficient Fe supply takes up Fe through strategy II and is coupled with limited Fe isotope fractionation. • Stable Fe isotopes reveal distinct strategies of Fe uptake and translocation in rice plants. [ABSTRACT FROM AUTHOR]

Abstract Schwertmannite is an amorphous iron(III)-oxyhydroxysulfate that forms in acid mine drainage (AMD) environments. The characteristic of high heavy metal adsorption capability makes schwertmannite a potentially useful, environmentally friendly material in wastewater treatment. Unstable schwertmannite is prone to recrystallization. Understanding the mechanisms that induce schwertmannite labilization and affect its capacity to remove heavy metals are of great environmental and geochemical significance. Thiocyanate (SCN¯) is a hazardous pseudohalide that is also normally found in AMD. However, little is known about the impact of Fe(III)-binding ligand SCN¯ on schwertmannite stability and its subsequent capacity to bind trace elements. Here, we investigated the adsorption of SCN¯ on schwertmannite and subsequent mineral transformation to characterize this little-known process. The appearance of Fe2 + indicated that the interactions between schwertmannite and SCN¯ may involve complexation and reduction reactions. Results showed that the majority of the adsorbed-SCN¯ was immobilized on schwertmannite during the 60-days transformation. The transformation rates of schwertmannite increased with increasing concentrations of SCN¯. Goethite was detected as the dominant transformation product with or without SCN¯. The mechanisms of SCN¯-promoted dissolution of schwertmannite can be described as follows: (1) formation of Fe(III)–NCS complexes on the schwertmannite surface and in solution, a process which increases the reactivity of solid phase Fe(III); (2) the extraction of Fe(III) from schwertmannite by SCN¯ and subsequent schwertmannite dissolution; and (3) the formation of secondary minerals from extracted Fe(III). These findings may improve AMD treatment strategies and provide insight into the use and potential reuse of schwertmannite as a trace element sorbent. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Schwertmannite is a ferric oxyhydroxy-sulfate mineral, which is commonly found in acid sulfate systems. In this study, the liberation of chromium from Cr(VI)-substituted schwertmannite in the presence of the siderophore desferrioxamine B was studied. In addition, mineral transformation was examined using X-ray diffraction, scanning electron microscopy, and X-ray absorption spectroscopy. Based on solid phase analyses, the transformation of schwertmannite incubated at pH 6.5 in the presence of 100 mg/L desferrioxamine B proceeded through a ligand-reductive induced pathway that released dissolved sulfate, Fe(III), and Cr(III), and generated goethite. Results of XAFS showed that CrO 4 2− substituted for SO 4 2− in the schwertmannite framework. Kinetic analysis using the Kabai and shrinking core models showed that Cr suppressed the transformation of schwertmannite into goethite and the liberation of Cr was controlled by diffusion through the secondary mineral's layer of dissolution. The information provided in this study will be useful in predicting the effects of the interaction between dissolved organic matter and minerals on the mobilization of Cr in acid mine drainage systems. Unlabelled Image • DFOB could affect the stability of schwertmannite in nature environment. • The limiting factors in Cr leaching from schwertmannite were established. • The newly formed mineral was identify and the dissolution mechanism was proposed. [ABSTRACT FROM AUTHOR]

Abstract Schwertmannites are metastable and often contaminated by chromium and arsenic. However, when schwertmannite is subjected to reducing conditions, the effect of reductive dissolution of schwertmannite coupled to the potential reduction of Cr(VI) or As(V) on the behavior of chromium and arsenic are less known. The present study systematically explored Fe(II)-induced transformation of schwertmannite with adsorbed CrO2-4 or AsO3-4 at pH 6.5, and the consequent redistribution of chromium and arsenic. The results show that adsorption of oxyanions obviously facilitated the release of schwertmannite-bound SO 4 2− from both the mineral surface and the lattice structure via SO 4 2--exchange. Adsorbed chromate and arsenate both inhibited the Fe(II)-induced transformation of schwertmannite. CrO2-4 -schwertmannite persisted as the dominant mineral phase for up to 30 d as a consequence of Fe(II) consumption and coverage of Cr(III)-Fe(III) hydroxide. In contrast, AsO3-4-schwertmannite transformed to poorly crystalline goethite via an intermediate lepidocrocite in 4 mM Fe(II) treatment. Both sorption and redox processes of Cr(VI) imprisoned chromium on schwertmannite. Transformation of AsO3-4-schwertmannite caused no re-mobilization of arsenic into solution, indicating the repartition to secondary minerals. Reduction of Cr(VI) to Cr(III) by Fe(II) would greatly lower the environmental hazard of chromium, and the persistence of As(V) would limit the toxicity of arsenic. These findings will help to understand the geochemical behavior of the important toxic Cr(VI) and As(V) specifically in the environmental systems with cyclic redox conditions. Graphical abstract Image 1 Highlights • Adsorbed CrO2-4 and AsO3-4 both inhibited the abiotic Fe(II)-induced transformation of schwertmannite. • Strong reduction of Cr(VI) to Cr(III) occurred, but As(V) did not convert to As(III). • CrO2-4 -schwertmannite persisted for up to 30 d, AsO3-4-schwertmannite transformed to goethite via an intermediate lepidocrocite. • Both sorption and redox of Cr(VI) imprisoned chromium; arsenic was persistently locked up in schwertmannite and its transformation products. [ABSTRACT FROM AUTHOR]

Lacking sufficient clean water, the paddy soils along the Hengshi River have suffered from long-term acid mine drainage (AMD) contamination. The impacted cropland is too heavily contaminated to grow food safely. The microbial communities inhabiting the environment play pivotal roles in the crop growth, health, and ecological services. In this study, the bacterial, archaeal, and fungal communities in the impacted paddy soil were examined using high-throughput Illumina MiSeq sequencing. The results showed that AMD irrigation considerably enriched the bacterial phylum Acidobacteria and the archaeal phylum Crenarchaeota , while the fungal community was more stable. The abundances of Acidobacteria and Crenarchaeota were significantly positively correlated with the AMD-related environmental factors of pH and heavy metals (Cu, Pb, and Zn). In the most contaminated samples, communities were dominated by the bacteria Candidatus Solibacter and Candidatus Koribacter from the Acidobacteria family. Functional gene profile analysis demonstrated that the energy metabolic processes of the microbial communities, especially C/N related pathways, have adjusted and are well-adapted to tolerating AMD contamination. The present study described the structural and functional differentiation of microbial communities in the rice paddy soil under AMD irrigation. The results are useful for the development of bioremediation strategies using native microbes in the cleanup and biorestoration of AMD-contaminated agriculture soil. [ABSTRACT FROM AUTHOR]

The oxidation of pyrite under acidic conditions, an important process leading to the formation of acid mine drainage, has been the subject of intense research yet remains incompletely understood. In this study, the mechanism of the electrochemical oxidation of pyrite in a pH 2 electrolyte was investigated using electrochemical techniques. The morphological changes and oxidation products of pyrite were studied using atomic force microscopy (AFM), Raman spectroscopy (RS), and X-ray photoelectron spectroscopy (XPS). At low potential of 0.50 V, electrochemical oxidation of pyrite was diffusion-limited due to a sulfur-rich layer (S 0 ) that formed and covered the pyrite surface, resulting in surface passivation. As the potential increased to 0.60 V, diffusion-limitation and surface passivation of pyrite oxidation ceased due to the conversion of amorphous elemental sulfur (S 8 ) to crystalline S 8 , resulting in the previously covered active sites being re-exposed which allowed continued oxidation of pyrite. At higher potentials of 0.70 and 0.80 V, more S 8 and polysulfides (S n 2− ), together with an iron-rich layer composed of Fe(OH) 3 , FeO and Fe 2 O 3 , formed and accumulated on the pyrite surface. These products led to a decreased rate of oxidation rather than a complete passivation of the surface. AFM imaging revealed that surface roughness increased with oxidation potential and that the oxidation of the pyrite surface was inhomogeneous. These findings provide further insight into the physical and chemical changes that pyrite undergo during electrochemical oxidation, which deepens our understanding of this important process. [ABSTRACT FROM AUTHOR]

The biological production of monomethylmercury (MeHg) in soils and sediments is an important factor controlling mercury (Hg) accumulation in aquatic and terrestrial food webs. In this study we examined the fractionation of Hg stable isotopes during Hg methylation in nongrowing cultures of the anaerobic bacteria Geobacter sulfurreducens PCA and Desulfovibrio desulfuricans ND132. Both organisms showed mass-dependent, but no mass-independent fractionation of Hg stable isotopes during Hg methylation. Despite differences in methylation rates, the two bacteria had similar Hg fractionation factors (αr/p = 1.0009 and 1.0011, respectively). Unexpectedly, δ202Hg values of MeHg for both organisms were 0.4‰ higher than the value of initial inorganic Hg after about 35% of inorganic Hg had been methylated. These results indicate that a 202Hg-enriched pool of inorganic Hg was preferentially utilized as a substrate for methylation by these organisms, but that multiple intra- and/or extracellular pools supplied inorganic Hg for biological methylation. Understanding the controls of the Hg stable isotopic composition of microbially produced MeHg is important to identifying bioavailable Hg in natural systems and the interpretation of Hg stable isotopes in aquatic food webs. [ABSTRACT FROM AUTHOR]

As mercury (Hg) biosensors are sensitive to only intracellular Hg, they are useful in the investigation of Hg uptake mechanisms and the effects of speciation on Hg bioavailability to microbes. In this study, bacterial biosensors were used to evaluate the roles that several transporters such as the glutathione, cystine/cysteine, and Mer transporters play in the uptake of Hg from Hg-thiol complexes by comparing uptake rates in strains with functioning transport systems to strains where these transporters had been knocked out by deletion of key genes. The Hg uptake into the biosensors was quantified based on the intracellular conversion of inorganic mercury (Hg(II)) to elemental mercury (Hg(0)) by the enzyme MerA. It was found that uptake of Hg from Hg-cysteine (Hg(CYS)2) and Hg-glutathione (Hg(GSH)2) complexes occurred at the same rate as that of inorganic complexes of Hg(II) into Escherichia coli strains with and without intact Mer transport systems. However, higher rates of Hg uptake were observed in the strain with a functioning Mer transport system. These results demonstrate that thiol-bound Hg is bioavailable to E. coli and that this bioavailability is higher in Hg-resistant bacteria with a complete Mer system than in non-resistant strains. No difference in the uptake rate of Hg from Hg(GSH)2 was observed in E. coli strains with or without functioning glutathione transport systems. There was also no difference in uptake rates between a wildtype Bacillus subtilis strain with a functioning cystine/cysteine transport system, and a mutant strain where this transport system had been knocked out. These results cast doubt on the viability of the hypothesis that the entire Hg-thiol complex is taken up into the cell by a thiol transporter. It is more likely that the Hg in the Hg-thiol complex is transferred to a transport protein on the cell membrane and is subsequently internalized. [ABSTRACT FROM AUTHOR]

Estuarine sediments support the production of monomethylmercury (MeHg) which accumulates in aquatic organisms. While natural variation in mercury stable isotope ratios can potentially be used to track sources and transformations of mercury in the environment, the isotopic signature of MeHg in sediments has not been measured directly. The isotopic composition of MeHg has been studied in laboratory experiments and fish using tandem gas chromatography-multicollector inductively coupled plasma mass spectrometry (MC–ICP-MS) systems; however, the precision and sensitivity of this method may be too low for the analysis of many environmental samples including sediments in which MeHg constitutes 1% or less of the total mercury. In this study, we developed an offline separation method for the precise measurement of the Hg isotopic composition of MeHg in estuarine sediments. Separation of MeHg from inorganic species was accomplished by distillation and chemical ethylation-GC, and was followed by gold amalgam trapping to collect and preconcentrate pyrolyzed MeHg, which was then released into an oxidizing solution. MeHg standards processed in this way were collected with an average yield of 97.5%. External precision for all replicate isotope analyses of MeHg process standards was ± 0.14‰ (2 SD, n = 8) for δ 202 Hg and no detectable fractionation of Hg stable isotopes occurred during the separation. δ 202 Hg values for MeHg separated from estuarine sediments using our approach varied from − 0.41 to + 0.41‰ and were generally higher, and spatially and temporally more variable, than those for total Hg (− 0.21 to − 0.48‰). [ABSTRACT FROM AUTHOR]

The mechanisms of carbon concentration in marine diatoms are controversial. At low CO2, decreases in O2 evolution after inhibition of phosphoenolpyruvate carboxylases ( PEPCs), and increases in PEPC transcript abundances, have been interpreted as evidence for a C4 mechanism in Thalassiosira pseudonana, but the ascertainment of which proteins are responsible for the subsequent decarboxylation and PEP regeneration steps has been elusive., We evaluated the responses of T. pseudonana to steady-state differences in CO2 availability, as well as to transient shifts to low CO2, by integrated measurements of photosynthetic parameters, transcript abundances and quantitative proteomics., On shifts to low CO2, two PEPC transcript abundances increased and then declined on timescales consistent with recoveries of Fv/ Fm, non-photochemical quenching ( NPQ) and maximum chlorophyll a-specific carbon fixation ( Pmax), but transcripts for archetypical decarboxylation enzymes phosphoenolpyruvate carboxykinase ( PEPCK) and malic enzyme ( ME) did not change. Of 3688 protein abundances measured, 39 were up-regulated under low CO2, including both PEPCs and pyruvate carboxylase ( PYC), whereas ME abundance did not change and PEPCK abundance declined., We propose a closed-loop biochemical model, whereby T. pseudonana produces and subsequently decarboxylates a C4 acid via PEPC2 and PYC, respectively, regenerates phosphoenolpyruvate ( PEP) from pyruvate in a pyruvate phosphate dikinase-independent (but glycine decarboxylase ( GDC)-dependent) manner, and recuperates photorespiratory CO2 as oxaloacetate ( OAA). [ABSTRACT FROM AUTHOR]

Abstract: We examined the hypothesis that sulfide drives arsenic mobilization from pyritic black shale by a sulfide–arsenide exchange and oxidation reaction in which sulfide replaces arsenic in arsenopyrite forming pyrite, and arsenide (As−1) is concurrently oxidized to soluble arsenite (As+3). This hypothesis was tested in a series of sulfide–arsenide exchange experiments with arsenopyrite (FeAsS), homogenized black shale from the Newark Basin (Lockatong formation), and pyrite isolated from Newark Basin black shale incubated under oxic (21% O2), hypoxic (2% O2, 98% N2), and anoxic (5% H2, 95% N2) conditions. The oxidation state of arsenic in Newark Basin black shale pyrite was determined using X-ray absorption-near edge structure spectroscopy (XANES). Incubation results show that sulfide (1mM initial concentration) increases arsenic mobilization to the dissolved phase from all three solids under oxic and hypoxic, but not anoxic conditions. Indeed under oxic and hypoxic conditions, the presence of sulfide resulted in the mobilization in 48h of 13–16 times more arsenic from arsenopyrite and 6–11 times more arsenic from isolated black shale pyrite than in sulfide-free controls. XANES results show that arsenic in Newark Basin black shale pyrite has the same oxidation state as that in FeAsS (−1) and thus extend the sulfide–arsenide exchange mechanism of arsenic mobilization to sedimentary rock, black shale pyrite. Biologically active incubations of whole black shale and its resident microorganisms under sulfate reducing conditions resulted in sevenfold higher mobilization of soluble arsenic than sterile controls. Taken together, our results indicate that sulfide-driven arsenic mobilization would be most important under conditions of redox disequilibrium, such as when sulfate-reducing bacteria release sulfide into oxic groundwater, and that microbial sulfide production is expected to enhance arsenic mobilization in sedimentary rock aquifers with major pyrite-bearing, black shale formations. [Copyright &y& Elsevier]

Analysis of arsenic concentrations in New Jersey well water from the Newark Basin showed up to 15% of the wells exceed 10 μg L-1, with a maximum of 215 μg L-1. In some geologic settings in the basin, this mobile arsenic could be from the weathering of pyrite (FeS2) found in black shale that contains up to 4% arsenic by weight We hypothesized that under oxic conditions at circumneutral pH, the microbially mediated oxidation of sulfide in the pyrite lattice would lead to the release of pyrite-bound arsenic. Moreover, the oxidation of aqueous As(II) to As( V) by aerobic microorganisms could further enhance arsenic mobilization from the solid phase. Enrichment cultures under aerobic. As(III)-oxidizing conditions were established under circumneutral pH with weathered black shale from the Newark Basin as the inoculum source. Strain WAO, an autotrophic inorganic-sulfur and As(III)-oxidizer, was isolated and phylogenetically and physiologically characterized. Arsenic mobilization studies from arsenopyrite (FeAsS) mineral, conducted with strain WAO at circumneutral pH, showed microbially enhanced mobilization of arsenic and complete oxidation of released arsenic and sulfur to stoichiometric amounts of arsenate and sulfate. In addition, WAO preferentially colonized pyrite on the surface of arsenic-bearing, black shale thick sections. These findings support the hypothesis that microorganisms can directly mobilize and transform arsenic bound in mineral form at circumneutral pH and suggest that the microbial mobilization of arsenic into groundwater may be important in other arsenic-impacted aquifers. [ABSTRACT FROM AUTHOR]

Speciation and reactivity of mercury were examined in Berry's Creek estuary downstream of a highly mercury-contaminated U.S. EPA Superfund site during the summers of 2002 and 2003. Surface water samples from Berry's Creek estuary, its confluence with the Hackensack River, and upstream of that confluence were analyzed for total (THg), particulate (PHgT), and dissolved (DHg) mercury, total and particulate monomethylmercury (MeHg), dissolved gaseous mercury (DGM), and bacterial merA gene and transcript abundances. Surface water concentrations of THg in Berry's Creek estuary (210-6800 pM) are among the highest in North America. A downstream gradient of Hg contamination is a permanent feature of Berry's Creek estuary, and the upper estuary appears to be a perennial source of Hg to the lower estuary and the Hackensack River. MeHg concentrations in Berry's Creek surface waters ranged from 2 to 14 pM, with the highest concentrations occurring at a midestuary site 2 km downstream of the tide gate. The suspended particle phase dominated Hg and MeHg speciation throughout this system, accounting for >90% of THg in Berry's Creek estuary and 35-94% of THg in the Hackensack River. Concentrations of D6M in Berry's Creek estuary (0.1-1.0 pM) are similar to levels of DI3M in other much less contaminated estuaries (0.04-0.75 pM). In addition, expression levels of the bacterial mercuric reductase gene, merA, a gene of the inorganic Hg(II)-regulated, mercury resistance (mer) operon, were low throughout Berry's Creek estuary. Thus, despite very high concentrations of mercury in Berry's Creek estuary, relatively low concentrations of DGM and merA gene expression levels indicate limited bioavailability of inorganic Hg in the estuary's surface waters. A system-wide limitation on the bioavailability of inorganic Hg, together with bacterial demethylation activity, may account for observed MeHg concentrations that, although elevated, are lower than expected given the concentrations of THg in this estuary. [ABSTRACT FROM AUTHOR]

Upland placement of dredged materials from navigation channels in the New York/New Jersey Harbor is currently being used to manage sediments deemed inappropriate for open water disposal. Although upland placement sites are equipped with engineering controls (leachate collection and/or barrier walls), little is known of the potential impacts of this approach to air quality. The aim of this study was to estimate the flux of mercury to the atmosphere from New York/New Jersey Harbor stabilized dredged material (SDM) that was used for land reclamation at a site in northeastern New Jersey. Total gaseous mercury (TGM) was measured at a site receiving SDM in August and October 2001 and May and November 2002. TGM was also monitored at an urban reference site 3.5 km west of the SDM site in September 2001 and from February 2002 to July 2002 and from October 2002 to February 2003. The concentration of TGM at the urban reference site averaged 2.2 ± 1.1 ng m-3, indicating some local contribution to the Northern Hemisphere background. TGM concentrations exhibited seasonality with the highest values in summer (3.3 ± 2.1 ng m-3 in June 2002) and the lowest in winter (1.7 ± 0.6 ng m-3 in January 2003). 1GM concentrations at the SDM placement site ranged from 2 to 7 ng m-3 and were significantly higher (p < 0.001) than those at the urban reference site. Sediment–air fluxes of Hg at the SDM placement site estimated by the micrometeorological technique ranged from -13 to 1040 ng m-2 h-1 (sediment to air fluxes being positive) and were significantly correlated to solar radiation (r² = 0.81). The estimated contribution of Hg emissions from land-applied SDM to local TGM concentrations was found to be negligible (<4%). However, the estimated annual volatilization rate of TGM at the SDM site (130 kg y-1) was comparable to those of other industrial sources in New Jersey (140-450 kg y-1). [ABSTRACT FROM AUTHOR]

The first estimates of atmospheric deposition fluxes of polychlorinated biphenyls (PCBs) to the Hudson River Estuary are presented. Concentrations of PCBs were measured in air, aerosol, and precipitation at nine sites representing a variety of land-use regimes at regular intervals from October 1997 through May 2001. Highest concentrations in the gas phase were observed at urban sites such as Camden and Jersey City (ΣPCB concentrations averaged 3250 and 1260 pg m-3, respectively). In great portions of the state encompassing forested, coastal, and suburban environments, gas-phase EPCB concentrations were essentially the same (averaging 150-220 pg m-3). This spatial trend suggests that atmospheric PCBs arise from highly localized, urban sources which influence atmospheric concentrations and deposition fluxes over a distance of a few tens of kilometers. Atmospheric EPCB deposition fluxes (gas absorption + dry particle deposition + wet deposition) ranged from 7.3 to 340 μg m-2 yr-1 and increased with proximity to urban areas. While the magnitude of the fluxes increased with urbanization, the relative proportions of wet, dry, and gaseous deposition remained largely constant Because the Hudson River Estuary is adjacent to urban areas such as Jersey City, it is subject to higher depositional fluxes of PCBs. These depositional fluxes are at least 2-10 times those estimated for the Chesapeake Bay and Lake Michigan. Inputs of PCBs to the Hudson River Estuary from the upper Hudson River and from wastewater treatment plants are 8-18 times atmospheric inputs, and volatilization of PCBs from the estuary exceeds atmospheric deposition of low molecular weight PCBs. [ABSTRACT FROM AUTHOR]

Phytoplankton is a nineteenth century ecological construct for a biologically diverse group of pelagic photoautotrophs that share common metabolic functions but not evolutionary histories. In contrast to terrestrial plants, a major schism occurred in the evolution of the eukaryotic phytoplankton that gave rise to two major plastid superfamilies. The green superfamily appropriated chlorophyll b, whereas the red superfamily uses chlorophyll c as an accessory photosynthetic pigment. Fossil evidence suggests that the green superfamily dominated Palaeozoic oceans. However, after the end-Permian extinction, members of the red superfamily rose to ecological prominence. The processes responsible for this shift are obscure. Here we present an analysis of major nutrients and trace elements in 15 species of marine phytoplankton from the two superfamilies. Our results indicate that there are systematic phylogenetic differences in the two plastid types where macronutrient (carbon:nitrogen:phosphorus) stoichiometries primarily reflect ancestral pre-symbiotic host cell phenotypes, but trace element composition reflects differences in the acquired plastids. The compositional differences between the two plastid superfamilies suggest that changes in ocean redox state strongly influenced the evolution and selection of eukaryotic phytoplankton since the Proterozoic era. [ABSTRACT FROM AUTHOR]

Arsenic–rich schwertmannite may cause arsenic (As) release during phase transition. In this study, microbial sulfidogenesis on As(V)–loaded schwertmannite (As-Sch) and associated As mobility at different SO 4 2− concentrations were investigated under anaerobic conditions by Desulfosporosinus meridiei (D. meridiei). For biotic treatments, the more SO 4 2− was added, the more Fe3+ was reduced to Fe2+, and the more As(V) was released during the reductive dissolution of As-Sch. The reduction of As(V) to As(III) by D. meridiei resulted in a higher concentration, toxicity, solubility and mobility of As than the corresponding abiotic treatments. However, compared with the abiotic treatments, a variety of new minerals (such as mackinawite, vivianite, sulfur, As 2 S 3 , and parasymplesite) were generated in the biotic treatments, and the As concentration in aqueous solution was less than 1 μM at the end of the incubation period regardless of the presence of SO 4 2−. The results of continuous extraction of different species of As from secondary minerals showed that the effect of microorganisms decreased As content of amorphous iron oxide-bound phase, while increasing that bound on the surface of iron oxide surface-bound phase, thus increasing As fluidity. Our findings indicated that under anaerobic conditions, D. meridiei sulfidogenesis can trigger significant As mobilization in the early stage and remove As from the aqueous solutions when new minerals are formed at a later stage. Unlabelled Image • As(V) was released during the reductive dissolution of schwertmannite by D. meridiei. • The released As(V) was reduced to As(III) by D. meridiei under anaerobic condition. • Fe(III) and SO 4 2− were reduced during the schwertmannite dissolution by D. meridiei. • Aqueous As re-precipitated or re-adsorbed to the newly formed mineral. [ABSTRACT FROM AUTHOR]