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A surface-promoted sulfate-reducing ammonium oxidation reaction was discovered to spontaneously take place on common inorganic aerosol surfaces undergoing solvation. Several key intermediate species—including elemental sulfur (S0), bisulfide (HS−), nitrous acid (HONO), and aqueous ammonia [NH3(aq)]—were identified as reaction components associated with the solvation process. Depth profiles of relative species abundance showed the surface propensity of key species. The species assignments and depth profile features were supported by classical and first-principles molecular dynamics calculations, and a detailed mechanism was proposed to describe the processes that led to unexpected products during salt solvation. This discovery revealed chemistry that is distinctly linked to a solvating surface and has great potential to illuminate current puzzles within heterogeneous chemistry. [ABSTRACT FROM AUTHOR]

Climate change is driving an expansion of marine oxygen-deficient zones, which may alter the global cycles of carbon, sulfur, nitrogen, and trace metals. Currently, however, we lack a full mechanistic understanding of how oxygen deficiency affects organic carbon cycling and burial. Here, we show that cryptic microbial sulfate reduction occurs in sinking particles from the eastern tropical North Pacific oxygen-deficient zone and that some microbially produced sulfide reacts rapidly to form organic sulfur that is resistant to acid hydrolysis. Particle-hosted sulfurization could enhance carbon preservation in sediments underlying oxygen-deficient water columns and serve as a stabilizing feedback between expanding anoxic zones and atmospheric carbon dioxide. A similar mechanism may help explain more-extreme instances of organic carbon preservation associated with marine anoxia in Earth history. [ABSTRACT FROM AUTHOR]

Microbial sulfate reduction has governed Earth's biogeochemical sulfur cycle for at least 2.5 billion years. However, the enzymatic mechanisms behind this pathway are incompletely understood, particularly for the reduction of sulfite--a key intermediate in the pathway. This critical reaction is performed by DsrAB, a widespread enzyme also involved in other dissimilatory sulfur metabolisms. Using in vitro assays with an archaeal DsrAB, supported with genetic experiments in a bacterial system, we show that the product of sulfite reduction by DsrAB is a protein-based trisulfide, in which a sulfite-derived sulfur is bridging two conserved cysteines of DsrC. Physiological studies also reveal that sulfate reduction rates are determined by cellular levels of DsrC. Dissimilatory sulfate reduction couples the four-electron reduction of the DsrC trisulfide to energy conservation. [ABSTRACT FROM AUTHOR]

The sulfur cycle influences the respiration of sedimentary organic matter, the oxidation state of the atmosphere and oceans, and the composition of seawater. However, the factors governing the major sulfur fluxes between seawater and sedimentary reservoirs remain incompletely understood. Using macrostratigraphic data, we quantified sulfate evaporite burial fluxes through Phanerozoic time. Approximately half of the modern riverine sulfate flux comes from weathering of recently deposited evaporites. Rates of sulfate burial are unsteady and linked to changes in the area of marine environments suitable for evaporite formation and preservation. By contrast, rates of pyrite burial and weathering are higher, less variable, and largely balanced, highlighting a greater role of the sulfur cycle in regulating atmospheric oxygen. [ABSTRACT FROM AUTHOR]

The iron isotope composition of sedimentary pyrite has been proposed as a potential proxy to trace microbial metabolism and the redox evolution of the oceans. We demonstrate that Fe isotope fractionation accompanies abiotic pyrite formation in the absence of Fe(II) redox change. Combined fractionation factors between Fe(II)aq, mackinawite, and pyrite permit the generation of pyrite with Fe isotope signatures that nearly encapsulate the full range of sedimentary δ56Fepyrite recorded in Archean to modern sediments. We propose that Archean negative Fe isotope excursions reflect partial Fe(II)aq utilization during abiotic pyrite formation rather than microbial dissimilatory Fe(III) reduction. Late Proterozoic to modern sediments may reflect greater Fe(II)aq utilization and variations in source composition. [ABSTRACT FROM AUTHOR]

The Mars rover Opportunity has explored Victoria crater, a -750-meter eroded impact crater formed in sulfate-rich sedimentary rocks. Impact-related stratigraphy is preserved in the crater walls, and meteoritic debris is present near the crater rim. The size of hematite-rich concretions decreases up-section, documenting variation in the intensity of groundwater processes. Layering in the crater walls preserves evidence of ancient wind-blown dunes. Compositional variations with depth mimic those -6 kilometers to the north and demonstrate that water-induced alteration at Meridiani Planum was regional in scope. [ABSTRACT FROM AUTHOR]

An active microbial assemblage cycles sulfur in a sulfate-rich, ancient marine brine beneath Taylor Glacier, an outlet glacier of the East Antarctic Ice Sheet, with Fe(III) serving as the terminal electron acceptor. Isotopic measurements of sulfate, water, carbonate, and ferrous iron and functional gene analyses of adenosine 5′-phosphosulfate reductase imply that a microbial consortium facilitates a catalytic sulfur cycle. These metabolic pathways result from a limited organic carbon supply because of the absence of contemporary photosynthesis, yielding a subglacial ferrous brine that is anoxic but not sulfidic. Coupled biogeochemical processes below the glacier enable subglacial microbes to grow in extended isolation, demonstrating how analogous organic-starved systems, such as Neoproterozoic oceans, accumulated Fe(II) despite the presence of an active sulfur cycle. [ABSTRACT FROM AUTHOR]

Anomalously fractionated sulfur isotopes in many sedimentary rocks older than 2.4 billion years have been widely believed to be the products of ultraviolet photolysis of volcanic sulfur dioxide in an anoxic atmosphere. Our laboratory experiments have revealed that reduced-sulfur species produced by reactions between powders of amino acids and sulfate at 150° to 200°C possess anomalously fractionated sulfur isotopes: Δ33S = +0.1 to +2.1 per mil and Δ 36S = -1.1 to +1.1 per mil. These results suggest that reactions between organic matter in sediments and sulfate-rich hydrothermal solutions may have produced anomalous sulfur isotope signatures in some sedimentary rocks. If so, the sulfur isotope record of sedimentary rocks may be linked to the biological and thermal evolution of Earth in ways different than previously thought. [ABSTRACT FROM AUTHOR]

The Mars Exploration Rover (MER), Opportunity, showed that Layered sulfate deposits in Meridiani Planum formed during a period of rising acidic ground water. Crystalline hematite spherules formed in the deposits as a consequence of aqueous alteration and were concentrated on the surface as a lag deposit as wind eroded the softer sulfate rocks. On the basis of Mars Express Observatoire pour La Minéralogie, L'Eau, les Glaces et l'Activité (OMEGA) orbital data, we demonstrate that crystalline hematite deposits are associated with layered sulfates in other areas on Mars, implying that Meridiani-like ground water systems were indeed widespread and representative of an extensive acid sulfate aqueous system. [ABSTRACT FROM AUTHOR]

The OMECA/Mars Express hyperspectral imager identified hydratedsulfates on light-toned layered terrains on Mars. Outcrops in VallesMarineris, Margaritifer Sinus, and Terra Meridiani show evidence forkieserite, gypsum, and polyhydrated sulfates. This identification hasits basis in vibrational absorptions between 1.3 and 2.5 micrometers.These minerals constitute direct records of the past aqueous activity onMars. [ABSTRACT FROM AUTHOR]

The Observatoire pour la Minéralogie, l'Eau, les Glaces,et l'Activité (OMEGA) imaging spectrometer observed thenorthern circumpolar regions of Mars at a resolution of a fewkilometers. An extended region at 240°E, 85°N, with an areaof 60 kilometers by 200 kilometers, exhibits absorptions at wavelengthsof 1.45, 1.75, 1.94, 2.22, 2.26, and 2.48 micrometers. These signaturescan be unambiguously attributed to calcium-rich sulfates, most likelygypsum. This region corresponds to the dark longitudinal dunes ofOlympia Planitia. These observations reveal that water alteration playeda major role in the formation of the constituting minerals of northerncircumpolar terrains. [ABSTRACT FROM AUTHOR]

Fluorescence has been observed directly across the band gap of semiconducting carbon nanotubes. We obtained individual nanotubes, each encased in a cylindrical micelle, by ultrasonically agitating an aqueous dispersion of raw single-walled carbon nanotubes in sodium dodecyl sulfate and then centrifuging to remove tube bundles, ropes, and residual catalyst. Aggregation of nanotubes into bundles otherwise quenches the fluorescence through interactions with metallic tubes and substantially broadens the absorption spectra. At pH less than 5, the absorption and emission spectra of individual nanotubes show evidence of band gap-selective protonation of the side walls of the tube. This protonation is readily reversed by treatment with base or ultraviolet light. [ABSTRACT FROM AUTHOR]

Examines the presence of sphalerite in natural biofilms dominated by aerotolerant sulphate-reducing bacteria. Monomineralic product results from buffering of sulfide concentrations at tow values by sphalerite precipitation; Measurement of microbial reduction.

The minor extent of sulfur isotope fractionation preserved in many Neoarchean sedimentary successions suggests that sulfate-reducing microorganisms played an insignificant role in ancient marine environments, despite evidence that these organisms evolved much earlier. We present bulk, microdrilled, and ion probe sulfur isotope data from carbonate-associated pyrite in the ~2.5-billion-year-old Batatal Formation of Brazil, revealing large mass-dependent fractionations (approaching 50 per mil) associated with microbial sulfate reduction, as well as consistently negative Δ33S values (~ -2 per mil) indicative of atmospheric photochemical reactions. Persistent 33S depletion through ~60 meters of shallow marine carbonate implies long-term stability of seawater sulfate abundance and isotope composition. In contrast, a negative Δ33S excursion in lower Batatal strata indicates a response time of ~40,000 to 150,000 years, suggesting Neoarchean sulfate concentrations between ~1 and 10 µM. [ABSTRACT FROM AUTHOR]

Sewer systems are among the most critical infrastructure assets for modern urban societies and provide essential human health protection. Sulfide-induced concrete sewer corrosion costs billions of dollars annually and has been identified as a main cause of global sewer deterioration. We performed a 2-year sampling campaign in South East Queensland (Australia), an extensive industry survey across Australia, and a comprehensive model-based scenario analysis of the various sources of sulfide. Aluminum sulfate addition during drinking water production contributes substantially to the sulfate load in sewage and indirectly serves as the primary source of sulfide. This unintended consequence of urban water management structures could be avoided by switching to sulfate-free coagulants, with no or only marginal additional expenses compared with the large potential savings in sewer corrosion costs. [ABSTRACT FROM AUTHOR]

Fluid inclusion data suggest that the composition of major elements in seawater changes slowly over geological time scales. This view contrasts with high-resolution isotope data that imply more rapid fluctuations of seawater chemistry. We used a non-steady-state box model of the global sulfur cycle to show that the global γ34S record can be explained by variable marine sulfate concentrations triggered by basin-scale evaporite precipitation and dissolution. The record is characterized by long phases of stasis, punctuated by short intervals of rapid change. Sulfate concentrations affect several important biological processes, including carbonate mineralogy, microbially mediated organic matter remineralization, sedimentary phosphorous regeneration, nitrogen fixation, and sulfate aerosol formation. These changes are likely to affect ocean productivity, the global carbon cycle, and climate. [ABSTRACT FROM AUTHOR]

The environmental expression of sulfur compound disproportionation has been placed between 640 and 1050 million years ago (Ma) and linked to increases in atmospheric oxygen. These arguments have their basis in temporal changes in the magnitude of [sup 34]S/[sup 32]S fractionations between sulfate and sulfide. Here, we present a Proterozoic seawater sulfate isotope record that includes the less abundant sulfur isotope [sup 33]S. These measurements imply that sulfur compound disproportionation was an active part of the sulfur cycle by 1300 Ma and that progressive Earth surface oxygenation may have characterized the Mesoproterozoic. [ABSTRACT FROM AUTHOR]

Heparan sulfate (HS) is required for morphogen signaling during Drosophila pattern formation, but little is known about its physiological importance in mammalian development. To define the developmental role of HS in mammalian species, we conditionally disrupted the HS-polymerizing enzyme EXT1 in the embryonic mouse brain. The EXT1-null brain exhibited patterning defects that are composites of those caused by mutations of multiple HS-binding morphogens. Furthermore, the EXT1-null brain displayed severe guidance errors in major commissural tracts, revealing a pivotal role of HS in midline axon guidance. These findings demonstrate that HS is essential for mammalian brain development. [ABSTRACT FROM AUTHOR]

The author discusses a report within the issue by Zhelezinskaia et al. reporting a large sulfur depletion and widely-varying sulfur isotope ratios in pyrites in 2.5-billion-year-old carbonates from Brazil. Topics include the use of the ratio of two stable sulfur isotopes, 34S and 32S, to trace sulfate-reducing prokaryotes (SRPs) activity in Archean sedimentary rocks, Archean sulfate (SO42-) levels, and the production of pyrites from seawater sulfate.

The article discusses the negative effects of sulfate content of wastewater in urban areas and presents information on substitutes that can be used for sulfate to improve sewer infrastructure. Topics include a graph of network-based water systems, sources of sulfate in water such as waste products, and the role of hydrogen sulfide emission in sewers.

The article discusses geochemistry studies by U. G. Wortmann and A. Paytan and a team led by I. Halevy within the issue. Both teams showed that on a time scales of millions of years, the sulfur cycle played a much greater role in regulating atmospheric oxygen levels than previously thought. Topics include the correlation between the sulfate concentration of the ocean and the oxidation history of planet Earth's surface, previous studies showing the variation of Phanerozoic sulfate concentrations, and the dynamic nature of the Phanerozoic sulfur cycle, including its role in regulating ocean-atmosphere chemistry.

Focuses on study findings indicating the important role played by sulphate-reducing bacteria in global geochemical cycles. Description of the sulfur cycle; Description of the role played by sulfate-reducing bacteria in natural processes.

The article reports on the efforts of Ronald Peterson, a mineralogist at Queen's University in Kingston, Ontario, in pursuing a new mineral that may be more at home on Mars. Peterson first suspected the existence of the exotic substance in 2005 when the Mars rover Opportunity kicked up magnesium sulfate dust and photographed lens-shaped holes in sedimentary rocks on the cratered plain of Meridiani Planum. Moreover, Peterson and his colleague Ruiyao Wang posited that the rover had spotted evidence of a novel platelike form of magnesium sulfate.

The article presents response to comments on an article "Reactions at Interfaces as a Source of Sulfate Formation in Sea-Salt Particles," that was published in the journal "Science."

The article presents comments on an abstract of an article "Reactions at Interfaces as a Source of Sulfate Formation in Sea-Salt Particles" published in the journal "Science," on surface reactions.

The article presents an abstract of the research article "Reactions at Interfaces As a Source of Sulfate Formation in Sea-Salt Particles," published in the journal "Science," on oxidation in sea-salt aerosols.