Biogeochemical Importance of the Bacterial Community in Uranium Waste Deposited at Key Lake,Northern Saskatchewan

The long-term stability of immobilized elements of concern in uranium tailings deposited in the Deilmann Tailings Management Facility (DTMF), northern Saskatchewan, is dependent upon maintenance of highly oxic conditions within the tailings mass. The main objective of this study was to investigate the effect of stimulating microbial activity on the redox potential and state of ferrihydrite, which are considered to be the primary controlling condition and mineral phase, respectively, within the tailings. To determine the potential for biologically mediated decreases in redox potential and ferrihydrite reduction, a series of microcosm assays were performed. Non-sterile material from the tailings–water interface of the DTMF site was inoculated with indigenous flora previously isolated from the tailings material and enriched with a carbon source (50 ppm trypticase soy broth) and incubated under continuous-flow or intermittent-flow conditions, and compared with an uninoculated, no-carbon control that received continuous flow. Highly reducing conditions with redox potentials of less than ?300 mV were detected after 2 days of incubation within the carbon-enriched tailings of microcosms receiving continuous flow, and less than ?280 mV after 11 days of incubation within carbon-enriched tailings in microcosms receiving intermittent flow. The lowest recorded Eh value (?545 mV) was recorded after 14 days in a carbon-enriched microcosm receiving intermittent flow. In contrast, the redox conditions in the control microcosm never dropped below ?93 mV; thus, it was clear that microbial activity and available carbon drove the Eh conditions to become highly reducing. The occurrence of low redox conditions was concomitant with the bulk chemical detection of Fe (II) in the effluent of treated microcosms. Sites of microbial ferrihydrite reduction were also detected using scanning transmission X-ray microscopy where Fe (II) species were observed in close proximity with bacterial cells. Analysis of the microbial diversity present within the microcosms confirmed that microbes indigenous to the DTMF system have the potential to generate conditions suitable for the proliferation of sulfate and iron reducing bacteria, such as Desulfosporosinus, which was detected by high-throughput 16S rRNA gene sequencing.     

Microbial Processes of the Carbon and Sulfur Cycles in Lake Shira (Khakasia)

Microbiological and biogeochemical studies of the meromictic saline Lake Shira (Khakasia) were conducted. In the upper part of the hydrogen-sulfide zone, at a depth of 13.5–14 m, there was a pale pink layer of water due to the development of purple bacteria (6 × 10⁵ cells/ml), which were assigned by their morphological and spectral characteristics toLamprocystis purpurea (formerly Amoebobacter purpureus). In August, the production of organic matter (OM) in Lake Shira was estimated to be 943 mg C/(m²day). The contribution of anoxygenic photosynthesis was insignificant (about 7% of the total OM production). The share of bacterial chemosynthesis was still less (no more than 2%). In the anaerobic zone, the community of sulfate-reducing bacteria played a decisive role in the terminal decomposition of OM. The maximal rates of sulfate reduction were observed in the near-bottom water (114 g S/(l day)) and in the surface layer of bottom sediments (901 g S/(dm³ day)). The daily expenditure of C_org for sulfate reduction was 73% of C_org formed daily in the processes of oxygenic and anoxygenic photosynthesis and bacterial chemosynthesis. The profile of methane distribution in the water column and bottom sediments was typical of meromictic reservoirs. The methane content in the water column increased beginning with the thermocline (7–8 m) and reached maximum values in the near-bottom water (17 l/l). In bottom sediments, the greatest methane concentrations (57 l/l) were observed in the surface layer (0–3 cm). The integral rate of methane formation in the water column and bottom sediments was almost an order of magnitude higher than the rate of its oxidation by aerobic and anaerobic methanotrophic microorganisms.     

Microbiological Processes of the Carbon and Sulfur Cycles at Cold Methane Seeps of the North Atlantic

Functioning of microbial communities in surface sediments of the Haakon Mosby underwater mud volcano (lat. 72°N) and in gas seepage fields of the Vestnesa Ridge was investigated using Mir-1 and Mir-2 deep-sea submersibles during the 40th voyage of the research vessel Academician Mstislav Keldysh. Large areas of sedimentary deposits of the Haakon Mosby mud volcano (HMMV) and pockmarks of the Vestnesa Ridge (VR) are covered with bacterial mats 0.1 to 0.5 cm thick. The microbial community making up bacterial mats of the HMMV was dominated by large filamentous bacteria with filaments measuring up to 100 m in length and 2 to 8 m in width. The occurrence of rosettes allowed the observed filamentous bacteria to be referred to the morphologically similar genera Leucothrix or Thiothrix. Three morphological types of filamentous bacteria were identified in bacterial mats covering VR pockmarks. Filaments of type one are morphologically similar with representatives of the genera Thioploca or Desmanthos. Type two filaments had numerous inclusions of sulfur and resembled representatives of the genus Thiothrix. The third morphological type was constituted by single filaments made up of tightly connected disk-like cells and can be assigned to the genus Beggiatoa. The rates of methane oxidation (up to 1570 l C/(dm³ day)) and sulfate reduction (up to 17 mg S/(dm³day)) measured in the surface sediments of HMMV and VR were close to the maximum rates of these processes observed in heavily polluted regions of the northwestern shelf of the Black Sea. High rates of microbiological processes correlated with the high number of bacteria. The rate of methane production in sediments studied was notably lower and ranged from 0.1 to 3.5 CH₄/(dm³ day). Large areas of the HMMV caldera were populated by pogonophoras, represented by the two species Sclerolinum sp. and Oligobrachia sp. The mass development of Sclerolinum sp. in the HMMV caldera was by the activity of aerobic methane-oxidizing bacteria localized inside the cells of these animals. Bacterial cells were also found in the trophosome tissue of Oligobrachia sp., but in cells of these bacteria, we did not observe the membrane structures typical of methanotrophs. The localization pattern of pogonophoras on the surface of reduced sediments suggests that the predominant bacteria in Oligobrachia tissues are sulfur-oxidizing endosymbionts.     

Evidence of the activity of dissimilatory sulfate-reducing prokaryotes in nonsulfidogenic tropical mobile muds

In spite of the nonsulfidic conditions and abundant reactive iron(III) commonly found in mobile tropical deltaic muds, genes encoding dissimilatory sulfite reductase (dsr) were successfully amplified from the upper approximately 1 m of coastal deposits sampled along French Guiana and in the Gulf of Papua. The dsr sequences retrieved were highly diverse, were generally represented in both study regions and fell into six large phylogenetic groupings: Deltaproteobacteria, Thermodesulfovibrio groups, Firmicutes and three groups without known cultured representatives. The spatial and temporal distribution of dsr sequences strongly supports the contention that the sulfate-reducing prokaryote communities in mobile mud environments are cosmopolitan and stable over a period of years. The decrease in the (35)SO(4) (2-) tracer demonstrates that, despite abundant reactive sedimentary iron(III) ( approximately 350-400 mumol g(-1)), the sulfate-reducing prokaryotes present are active, with the highest levels of sulfide being generated in the upper zones of the cores (0-30 cm). Both the time course of the (35)S-sulfide tracer activity and the lack of reduced sulfur in sediments demonstrate virtually complete anaerobic loss of solid phase sulfides. We propose a pathway of organic matter oxidation involving at least 5-25% of the remineralized carbon, wherein sulfide produced by sulfate-reducing prokaryotes is cyclically oxidized biotically or abiotically by metal oxides.     

Microbial Processes of the Carbon and Sulfur Cycles in Lake Mogil'noe

In the beginning of the summer of 1999, complex microbiological and biogeochemical investigations of meromictic Lake Mogil'noe (Kil'din Island, Barents Sea) were carried out. The analysis of the results shows a clearly pronounced vertical zonality of the microbial processes occurring in the water column of the lake. To a depth of 8 m, the total number and activity of microorganisms was limited by the relatively low content of organic matter (OM). In the upper part of the hydrogen-sulfide zone of the lake (beginning at a depth of 8.25 m), the content of particulate OM and the microbial number sharply increased. In this zone, the daily production of OM during anaerobic photosynthesis at the expense of massive development of colored sulfur bacteria reached 620 mg C/m², which was twofold greater than the daily production of phytoplankton photosynthesis and led to a considerable change in the isotopic composition (¹³C) of the particulate OM. In the same intermediate layer, the highest rates of sulfate reduction were recorded, and fractionation of stable sulfur isotopes occurred. Below 10 m was the third hydrochemical zone, characterized by maximum concentrations of H₂S and CH₄and by a relatively high rate of autotrophic methanogenesis. The comparison of the results obtained with the results of investigations of previous years, performed in the end of summer, shows a decrease in the intensity of all microbial processes inspected. An exception was anoxygenic photosynthesis, which can utilize not only the de novo formed H₂S but also the H₂S accumulated in the lake during the winter period.     

Biogeochemical cycling of sulfur and iron in sediments of a south-east Asian mangrove,Phuket Island,Thailand

Benthic sulfate reduction and sediment pools of sulfur and iron were examined during January 1992 at 3 stations in the Ao Nam Bor mangrove, Phuket, Thailand. Patterns of sulfate reduction rates (0–53 cm) reflected differences in physical and biological conditions at the 3 stations, and highest rates were found at the vegetated site within the mangrove (Rhizophora apiculata) forest. Due to extended oxidation of mangrove sediments, a large portion of the added³⁵S-label was recovered in the chromium reducible pools (FeS₂ and S⁰) (41–91% of the reduced sulfur). Pyrite was the most important inorganic sulfur component, attaining pool sizes 50–100 times higher than acid volatile pools (FeS). HCl-extractable (0.5 M HCl) iron pools, including Fe(II)_HCl and Fe(III)_HCl, were generally low and Fe(III)_HCl was only present in the upper surface layers (0–5 cm). Maximum concentrations of dissolved Fe²⁺ (35–285 M) occurred just about the depth where dissolved H₂S accumulated. Furthermore Fe²⁺ and H₂S coexisted only where concentrations of both were low. There was an accumulation of organic sulfur in the deep sediment at 2 stations in the inner part of the mangrove. The reoxidation of reduced sulfides was rapid, and storage of sulfur was minor in the upper sediment layers, where factors like bioturbation, the presence of roots, or tidal mixing enhance oxidation processes.Author of correspondence.     

用硫酸盐还原菌处理重金属废水的研究

介绍了用硫酸盐还原菌处理重金属废水的几种主要方法和原理。硫酸盐还原菌处理含重金属废水主要是通过将可溶性的重金属离子转化成不溶性的金属硫化物、氢氧化物、碳酸盐的方式 ,或直接通过以菌体对重金属离子的吸附完成的。目前研究用硫酸盐还原菌处理重金属废水的主要方法有分批沉淀工艺、吸附处理工艺、化学法和硫酸盐还原菌的混合工艺、全混合处理工艺及硫酸盐还原菌的厌氧上流式污泥床和流化床工艺 ,并对其主要的工艺指标进行了比较。     

Effects of Metabolism and Physiology on the Production of Okenone and Bacteriochlorophyll a in Purple Sulfur Bacteria

Purple sulfur bacteria (PSB) are important photoautotrophs inhabiting chemoclines in euxinic and meromictic lakes. These organisms are the only producers of the carotenoid, okenone, a compound that has been targeted as a biomarker for photic zone euxinia, particularly in ancient sedimentary environments. Although the natural occurrence and geochemistry of this compound has been studied previously, this is the first systematic and comprehensive report on the microbial physiology of okenone production in pure cultures. Four strains/species: Marichromatium purpuratum DSMZ 1591, Marichromatium purpuratum DSMZ 1711, Thiocapsa marina DSMZ 5653, and FGL21 (isolated from Fayetteville Green Lake, New York) were chosen because they produce okenone and Bacteriochlorophyll a (Bchl a). We developed a new, in vivo technique for the quantification of okenone allowing for more rapid and accurate quantification. The ratio of okenone to Bchl a differs among species and strains of PSB, varying from 0.463 ± 0.002 to 0.864 ± 0.002. Photoheterotrophically grown PSB have statistically significant, lowered okenone:Bchl a ratios, decreasing from 0.784 ± 0.009 under autotrophic metabolism to 0.681 ± 0.002, which we interpret to indicate a decreased requirement for okenone when PSB are provided with a complex (> C1) carbon source. The variation in okenone production raises the question on whether okenone expression is constitutive or inducible. The broader implication is that concentrations of okenone in sediments are dependent on metabolism and species composition, and not solely on PSB cell density.     

Potentially Active Iron,Sulfur, and Sulfate Reducing Bacteria in Skagerrak and Bothnian Bay Sediments

In many marine surface sediments, the reduction of manganese (Mn) and iron (Fe) oxides is obscured by sulfate reduction, which is regarded as the predominant anaerobic microbial respiration process. However, many dissimilatory sulfate and sulfur reducing microorganisms are known to utilize alternative electron acceptors such as metal oxides. In this study, we tested whether sulfate and sulfur reducing bacteria are linked to metal oxide reduction based on biogeochemical modeling of porewater concentration profiles of Mn²⁺ and Fe²⁺ in Bothnian Bay (BB) and Skagerrak (SK) sediments. Steady-state modeling of Fe²⁺ and Mn²⁺ porewater profiles revealed zones of net Fe (0–9 cm BB; ～10 and 20 cm SK) and Mn (0–5 cm BB; 2–8 cm SK) species transformations. 16S rRNA pyrosequencing analysis of the in-situ community showed that Desulfobacteraceae, Desulfuromonadaceae and Desulfobulbaceae were present in the zone of Fe-reduction of both sediments. Rhodobacteraceae were also detected at high relative abundance in both sediments. BB sediments appeared to harbor a greater diversity of potential Fe-reducers compared to SK. Additionally, when the upper 10 cm of sediment from the SK was incubated with lepidocrocite and acetate, Desulfuromonas was the dominant bacteria. Real-time quantitative polymerase chain reaction (qPCR) results showed decreasing dsrA gene copy numbers with depth coincided with decreased Fe-reduction activity. Our results support the idea that sulfur and sulfate reducing bacteria contribute to Fe-reduction in the upper centimeters of both sediments.     

Species and Biogeochemical Cycles of Organic Phosphorus in Sediments From a River With Different Aquatic Plants Located in Huaihe River Watershed,China

The results of phosphorus fractionation in the sediments from a contaminated river containing different aquatic plants, analyzed by solution ³¹P-NMR for Organic Phosphorus, showed that the concentration of Inorganic Phosphorus dominated in all species and Organic Phosphorus accounted for over 20% of Total Phosphorus. In general, orthophosphate was dominant in all the sampling sites. The proportion of Organic Phosphorus accounting for the Total Phosphorus in the sediments with different plant decreased in the following order: Paspalum distichum > Typha orientalis > Hydrilla verticillata. Phosphorus-accumulation ability of Paspalum distichum was obviously stronger than Typha orientalis and Hydrilla verticillata. The Organic Phosphorus was in aquatic plants dominated by humic-associated P (Hu-P), which converted to Inorganic Ohosphorus more significantly in submerged plants than in emerged plants. The sediment dominated by Paspalum distichum abundantly accumulated Organic Phosphorus in the orthophosphate monoester fraction. The degradation and mineralization of orthophosphate monoester was the important source of high Inorganic Phosphorus concentration and net primary productivity in Suoxu River. The Organic Phosphorus derived from Typha orientalis and Hydrilla verticillata was dramatically converted to Inorganic Phosphorus when the environmental factors varied.     

Microbial Nitrogen and Sulfur Cycles at the Gypsum Dunes of White Sands National Monument,New Mexico

The White Sands National Monument from New Mexico (U.S.A) contains one of the largest known gypsum dune fields with unique, rapidly migrating, arid, evaporitic habitats. Deposits from dune sides and interdune areas were collected in order to determine the characteristics of microbial habitat and communities through mineral assemblages, microbial pigments along with investigations of nitrogen and sulfur cycles. The most abundant pigments, scytonemin and carotenoids, were common UV protective pigments. Predominance of nitrite and nitrate over ammonium nitrogen (2.16: 1) implies that nitrification processes might be important in this ecosystem. Ammonium oxidizers from groups of β-, γ-proteobacteria and archaea were detected in all deposits, thereby indicating microbial involvement in nitrification. Additionally, denitrifying organisms with nirS and nirK genes were also present in most of the analyzed samples. The presence of trace carbonate mineral phases in association with biofilm implies possible microbial sulfate reduction. Microbes with metabolic abilities for sulfur cycling (i.e., dissimilatory sulfite reducers, purple sulfur bacteria, green sulfur and non-sulfur bacteria, and organisms with the APS enzyme) were identified in all samples. These particular organisms have the ability to reduce sulfate and to re-oxidize reduced sulfur compounds back to sulfate.     

Relating Microbial Community Structure and Geochemistry in Deep Regolith Developed on Volcaniclastic Rock in the Luquillo Mountains,Puerto Rico

Fe oxidation is often the first chemical reaction that initiates weathering and disaggregation of intact bedrock into regolith. Here we explore the use of pyrosequencing tools to test for evidence that bacteria participate in these reactions in deep regolith. We analyze regolith developed on volcaniclastic rocks of the Fajardo formation in a ridgetop within the rainforest of the Luquillo Mountains of Puerto Rico. In the 9-m-deep regolith profile, the primary minerals chlorite, feldspar, and pyroxene are detected near 8.3 m but weather to kaolinite and Fe oxides found at shallower depths. Over the regolith profile, both total and heterotrophic bacterial cell counts generally increase from the bedrock to the surface. Like other soil microbial studies, the dominant phyla detected are Proteobacteria, Acidobacteria, Planctomycetes, and Actinobacteria. Proteobacteria (α, β, γ and δ) were the most abundant at depth (6.8–9 m, 41–44%), while Acidobacteria were the most abundant at the surface (1.4–4.4 m, 37–43%). Despite the fact that Acidobacteria dominated surficial communities while Proteobacteria dominated near bedrock, the near-surface and near-bedrock communities were not statistically different in structure but were statistically different from mid-depth communities. Approximately 21% of all sequences analyzed did not match known sequences: the highest fraction of unmatched sequences was greatest at mid-depth (45% at 4.4 m). At the regolith-bedrock interface where weathering begins, several lines of evidence are consistent with biotic Fe oxidation. At that interface, iron-related bacterial activity tests and culturing indicate the presence of iron-related bacteria, and phylogenetic analyses identified sub-phyla containing known iron-oxidizing microorganisms. Cell densities of iron-oxidizers in the deep saprolite were estimated to be on the order of 10⁵ cells g^?1. Overall Fe loss was also observed at the regolith-bedrock interface, consistent with bacterial production of organic acids and leaching of Fe-organic complexes. Fe-organic species were also detected to be enriched near the bedrock-regolith interface. In this and other deep weathering profiles, chemolithoautotrophic bacteria that use Fe for energy and nitrate or oxygen as an electron acceptor may play an important role in initiating disaggregation of bedrock.     

Organic Carbon Degradation in Arctic Marine Sediments,Svalbard: A Comparison of Initial and Terminal Steps

Degradation of marine organic matter under anoxic conditions involves microbial communities working in concert to remineralize complex substrates to CO ₂ . In order to investigate the coupling between the initial and terminal steps of this sequence in permanently cold sediments, rates of extracellular enzymatic hydrolysis and sulfate reduction were measured in parallel cores collected from 5 fjords on the west and northwest coast of Svalbard, in the high Arctic. Inventories of total dissolved carbohydrates were also measured in order to evaluate their potential role in carbon turnover. Polysaccharide hydrolysis rates exhibited substrate-related and, to a lesser extent, depth-related differences (p < 0.0001); laminarin hydrolysis was consistently most rapid at nearly all depths and sites, and fucoidan hydrolysis was least rapid. Although there was a high degree of variability in parallel cores, sulfate reduction rates also exhibited statistically significant depth-and station-related differences. A comparison with data from previous investigations in Svalbard sediments suggests that this variability is linked to substrate availability rather than to organism distribution. Total dissolved carbohydrate concentrations were comparable to those measured in more temperate sediments, and likely comprise a considerable fraction of porewater dissolved organic carbon. A comparison of dissolved carbohydrate inventories with hydrolysis and sulfate reduction rates suggests that the turnover of carbon through the dissolved pool occurs quite rapidly, on the order of a few days to weeks. The transformation of particulate to dissolved organic matter must also be sufficiently rapid to maintain the measured rates of terminal remineralization.     

溶微囊藻细菌的富集筛选及其菌群结构特征

利用铜绿微囊藻(Microcystis aeruginosa)作为溶藻对象富集、筛选, 获得一个稳定的溶藻菌群。采用叶绿素、PCR和变性梯度凝胶电泳(DGGE)方法研究溶藻过程及其细菌种群结构的变化。结果显示, 富集的溶藻菌经1×10-5稀释后仍有显著溶藻效果。Rubritepida菌C1、假单胞菌C2和鞘氨醇单胞菌C3是存在于铜绿微囊藻中的3种伴生细菌。加入富集的溶藻菌群后, 菌群结构发生明显的变化, Rubritepida菌C1、假单胞菌C2消失, 混合菌群包含未培养黄杆菌A2、鞘氨醇单胞菌C3和噬氢     

Sedimentary anaerobic microbial biogeochemistry in the Gulf of Trieste, northern Adriatic Sea: Influences of bottom water oxygen depletion

Sediment samples from two locationsin the Gulf of Trieste (northern Adriatic Sea) werecollected during periods of maximum and minimumtemperatures for two years. Both sites were rich incarbonate material and inhabited by a diverse benthicinfaunal community. However, Site F exhibited adeeper dwelling faunal community, higher content ofcarbonate minerals, and larger grained sediments thanat site MA, which was closer to shore. Depth profilesof sulfate reduction and potential rates of iron andmanganese reduction were determined together withmeasurements of pore water and solid phase chemistry. Bottom waters at all sites were nearly saturated withoxygen for all of the dates sampled except forSeptember 1993 when bottom waters at site F were lessthan 50% saturated. Sulfate reduction rates were ashigh as 400 nmol ml^-1 day^-1 during latesummer and fall when temperatures were >20 °C,while rates during March (8 °C) were <30 nmolml^-1 day^-1. Potential rates of ironreduction, as determined by the accumulation of bothdissolved and acid-soluble reduced iron, were high insurficial sediments at each site except at site F whenbottom waters were partially depleted in oxygen. In the latter instance, sulfate reduction overwhelmedmetal reduction. Although the portion of metalreduction due directly to enzymatic use by bacteriawas not determined, the potential rate data suggestedthat Fe and perhaps Mn reduction were significantcomponents of anaerobic carbon degradation in thesesediments during much of the year. Both sitesappeared to support active metal-reducing bacterialcommunities. However, occasional depletion of oxygenin bottom waters appeared to cause a decrease inirrigation/reworking activity by infauna whichdepressed redox cycling of elements enhancing theimportance of sulfate reduction. A shift from metalreduction to sulfate reduction potentially exacerbatestoxic effects of oxygen depletion on fauna byincreasing the accumulation of toxic sulfide.     

Role of Organic Carbon Sources and Sulfate in Controlling Net Methylmercury Production in Riverbank Sediments of the South River,VA (USA)

Mercury (Hg) transport and methylmercury (MeHg) production in riverbank sediments are complex processes influenced by site-specific physical and biogeochemical conditions. The South River watershed in VA, USA, contains elevated concentrations of Hg in riverbank and floodplain sediments, which has the potential to methylate. The role of specific organic carbon sources in promoting methylation reactions in natural sediments under dynamic flow conditions is not well understood. Four saturated column experiments were conducted, including a control column, which received South River water as an influent solution, and three columns that received South River water amended with: acetate (5.8 mM); lactate (5.7 mM); and lactate (5.7 mM) with SO₄^2? (10.1 mM). The amendments were selected to promote growth of different microorganisms to gain an understanding of the microbial processes, controlling rates of methylation. The column receiving lactate and SO₄^2? had the highest MeHg concentrations in the effluent and in the pore water near the effluent at 1.8 and 4.9 μg L^?1, respectively. At the cessation of the column experiments, the lactate–sulfate column sediments contained the highest populations of enumerable sulfur-reducing bacteria and the highest solid-phase MeHg at 530 ± 100 ng g^?1 dry wt. from the interval closest to the influent. The results suggest that the form and availability of electron donors and acceptors are primary factors controlling rates of methylation in the South River sediment.     

The Origin and Age of Biogeochemical Trends in Deep Fracture Water of the Witwatersrand Basin,South Africa

Water residing within crustal fractures encountered during mining at depths greater than 500 meters in the Witwatersrand basin of South Africa represents a mixture of paleo-meteoric water and 2.0–2.3 Ga hydrothermal fluid. The hydrothermal fluid is highly saline, contains abiogenic CH ₄ and hydrocarbon, occasionally N ₂ , originally formed at ～ 250–300°C and during cooling isotopically exchanged O and H with minerals and accrued H ₂ , ⁴ He and other radiogenic gases. The paleo-meteoric water ranges in age from ～ 10 Ka to > 1.5 Ma, is of low salinity, falls along the global meteoric water line (GMWL) and is CO ₂ and atmospheric noble gas-rich. The hydrothermal fluid, which should be completely sterile, has probably been mixing with paleo-meteoric water for at least the past ～100 Myr, a process which inoculates previously sterile environments at depths > 2.0 to 2.5 km. Free energy flux calculations suggest that sulfate reduction is the dominant electron acceptor microbial process for the high salinity fracture water and that it is 10 ⁷ times that normally required for cell maintenance in lab cultures. Flux calculations also indicate that the potential bioavailable chemical energy increases with salinity, but because the fluence of bioavailable C, N and P also increase with salinity, the environment remains energy-limited. The ⁴ He concentrations and theoretical calculations indicate that the H ₂ that is sustaining the subsurface microbial communities (e.g. H ₂ -utilizing SRB and methanogens) is produced by water radiolysis at a rate of ～1 nM yr ^?1 . Microbial CH ₄ mixes with abiogenic CH ₄ to produce the observed isotopic signatures and indicates that the rate of methanogenesis diminishes with depth from ～ 100 at < 1 kmbls, to < 0.01 nM yr ^?1 at > 3 kmbls. Microbial Fe(III) reduction is limited due to the elevated pH. The δ¹³C of dissolved inorganic carbon is consistent with heterotrophy rather than autotrophy dominating the deeper, more saline environments. One potential source of the organic carbon may be microfilms present on the mineral surfaces.     

Bacterial biomass and productivity in sediments,stromatolites, and water of hamelin pool,shark bay,Western Australia

Heterotrophic bacterial biomass and growth rates were examined in stromatolites formed from four different types of benthic cyanobacterial mats. Bacteria in algal mats were counted using direct microscopy and biomass was estimated from the numbers of bacteria. Heterotrophic bacterial growth rates were estimated from the rate of incorporation of tritiated thy‐midine into DNA. Pustular mat, which occurs in the upper in‐tertidal zone, contained relatively few bacteria in the surface layers (0–5 mm), having about 0.2 x 10⁶ cells mm^‐3, or 20 mgC m^‐2 per millimetre depth. Other mats in the lower intertidal and subtidal zones had from 1 x 10⁶ cells mm^‐3 to 8 x 10⁶ cells mm^‐3. Heterotrophic bacterial productivities were 2.1 to 5.0 mgC m^‐2 h^‐1. Turnover times were an average of 1 day in the sandy sediment and 5 days in the colloform mat. Although these results are minimum estimates, they indicate that heterotrophic bacteria contribute substantially to the carbon cycle in stromatolites, by utilizing about 20 to 30% of primary production.     

Quantitative Proteomic Analysis of Biological Processes and Responses of the Bacterium Desulfovibrio desulfuricans ND132 upon Deletion of Its Mercury Methylation Genes

Recent studies of microbial mercury (Hg) methylation revealed a key gene pair, hgcAB, which is essential for methylmercury (MeHg) production in the environment. However, many aspects of the mechanism and biological processes underlying Hg methylation, as well as any additional physiological functions of the hgcAB genes, remain unknown. Here, quantitative proteomics are used to identify changes in potential functional processes related to hgcAB gene deletion in the Hg‐methylating bacterium Desulfovibrio desulfuricans ND132. Global proteomics analyses indicate that the wild type and ΔhgcAB strains are similar with respect to the whole proteome and the identified number of proteins, but differ significantly in the abundance of specific proteins. The authors observe changes in the abundance of proteins related to the glycolysis pathway and one‐carbon metabolism, suggesting that the hgcAB gene pair is linked to carbon metabolism. Unexpectedly, the authors find that the deletion of hgcAB significantly impacts a range of metal transport proteins, specifically membrane efflux pumps such as those associated with heavy metal copper (Cu) export, leading to decreased Cu uptake in the ΔhgcAB mutant. This observation indicates possible linkages between this set of proteins and metal homeostasis in the cell. However, hgcAB gene expression is not induced by Hg, as evidenced by similarly low abundance of HgcA and HgcB proteins in the absence or presence of Hg (500 nm ). Taken together, these results suggest an apparent link between HgcAB, one‐carbon metabolism, and metal homeostasis, thereby providing insights for further exploration of biochemical mechanisms and biological functions of microbial Hg methylation.     

Stable sulfur isotopic distributions and sulfate reduction in lake sediments of the Adirondack Mountains,New York

Cores from five lakes of the Adirondack Mountains, New York, were analyzed for sedimentary sulfur concentrations and stable sulfur isotopic compositions. Isotopic values of total sedimentary sulfur were as much as 6 to 8 lower than isotopic values of sulfur sources (soils, tree leaves and lake water sulfate) which showed little isotopic variation in the Adirondacks. The low isotopic values of recent sediments indicate increased sulfate reduction, probably in response to increased sulfate loading and acid deposition. Detailed historical reconstruction of sulfate loading histories from sedimentary sulfur profiles is premature, however, since model calculations indicate that sulfur can be added to deeper older sediments by ongoing, contemporary sulfate reduction.