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.     

Bacterial Associations with Weathering Minerals at the Regolith-Bedrock Interface,Luquillo Experimental Forest,Puerto Rico

Microbe-mineral associations in regolith overlying granodiorite bedrock (4.6–4.9 m depth) from the Luquillo Experimental Forest, Puerto Rico, were imaged with confocal scanning laser microscopy at a novel scale of 400X magnification. After adding BacLight? stain, proportionally more surface area of minerals (quartz, biotite, and mixed opaque kaolinite/goethite) emitted fluorescence from cell-impermeant propidium iodide than from cell-permeant SYTO 9, which suggested greater coverage of minerals by extracellular DNA or DNA in non-intact cells than by intact cells. Microscopic observations of predominantly non-intact cell material in deep saprolite were consistent with the abundance of rRNA sequences related to heterotrophic bacteria in clone libraries prepared from community DNA. A few sequences were affiliated with bacteria recognized to produce siderophores, oxidize Fe(II), or fix N₂. Bacterial DNA in deep regolith from two boreholes 1.5 m apart yielded libraries with high diversity and taxa specific for each borehole. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the free supplemental files.     

Preliminary characterization and biological reduction of putative biogenic iron oxides (BIOS) from the Tonga-Kermadec Arc, southwest Pacific Ocean

Sediment samples were obtained from areas of diffuse hydrothermal venting along the seabed in the Tonga sector of the Tonga‐Kermadec Arc, southwest Pacific Ocean. Sediments from Volcano 1 and Volcano 19 were analyzed by X‐ray diffraction (XRD) and found to be composed primarily of the iron oxyhydroxide mineral, two‐line ferrihydrite. XRD also suggested the possible presence of minor amounts of more ordered iron (hydr)oxides (including six‐line ferrihydrite, goethite/lepidocrocite and magnetite) in the biogenic iron oxides (BIOS) from Volcano 1; however, Mössbauer spectroscopy failed to detect any mineral phases more crystalline than two‐line ferrihydrite. The minerals were precipitated on the surfaces of abundant filamentous microbial structures. Morphologically, some of these structures were similar in appearance to the known iron‐oxidizing genus Mariprofundus spp., suggesting that the sediments are composed of biogenic iron oxides. At Volcano 19, an areally extensive, active vent field, the microbial cells appeared to be responsible for the formation of cohesive chimney‐like structures of iron oxyhydroxide, 2–3 m in height, whereas at Volcano 1, an older vent field, no chimney‐like structures were apparent. Iron reduction of the sediment material (i.e. BIOS) by Shewanella putrefaciens CN32 was measured, in vitro, as the ratio of [total Fe(II)]:[total Fe]. From this parameter, reduction rates were calculated for Volcano 1 BIOS (0.0521 day^?1), Volcano 19 BIOS (0.0473 day^?1), and hydrous ferric oxide, a synthetic two‐line ferrihydrite (0.0224 day^?1). Sediments from both BIOS sites were more easily reduced than synthetic ferrihydrite, which suggests that the decrease in effective surface area of the minerals within the sediments (due to the presence of the organic component) does not inhibit subsequent microbial reduction. These results indicate that natural, marine BIOS are easily reduced in the presence of dissimilatory iron‐reducing bacteria, and that the use of common synthetic iron minerals to model their reduction may lead to a significant underestimation of their biological reactivity.     

Mapping the spatial distribution of the biomass and filter‐feeding effect of invasive dreissenid mussels on the winter‐spring phytoplankton bloom in Lake Michigan

相似文献   

Culturable Rhodobacter and Shewanella species are abundant in estuarine turbidity maxima of the Columbia River

Measurements of dissolved, ascorbate‐reducible and total Mn by ICP‐OES revealed significantly higher concentrations during estuarine turbidity maxima (ETM) events, compared with non‐events in the Columbia River. Most probable number (MPN) counts of Mn‐oxidizing or Mn‐reducing heterotrophs were not statistically different from that of other heterotrophs (10³–10⁴ cells ml^?1) when grown in defined media, but counts of Mn oxidizers were significantly lower in nutrient‐rich medium (13 cells ml^?1). MPN counts of Mn oxidizers were also significantly lower on Mn(III)‐pyrophosphate and glycerol (21 cells ml^?1). Large numbers of Rhodobacter spp. were cultured from dilutions of 10^?2 to 10^?5, and many of these were capable of Mn(III) oxidation. Up to c. 30% of the colonies tested LBB positive, and all 77 of the successfully sequenced LBB positive colonies (of varying morphology) yielded sequences related to Rhodobacter spp. qPCR indicated that a cluster of Rhodobacter isolates and closely related strains (95–99% identity) represented approximately 1–3% of the total Bacteria, consistent with clone library results. Copy numbers of SSU rRNA genes for either Rhodobacter spp. or Bacteria were four to eightfold greater during ETM events compared with non‐events. Strains of a Shewanella sp. were retrieved from the highest dilutions (10^?5) of Mn reducers, and were also capable of Mn oxidation. The SSU rRNA gene sequences from these strains shared a high identity score (98%) with sequences obtained in clone libraries. Our results support previous findings that ETMs are zones with high microbial activity. Results indicated that Shewanella and Rhodobacter species were present in environmentally relevant concentrations, and further demonstrated that a large proportion of culturable bacteria, including Shewanella and Rhodobacter spp., were capable of Mn cycling in vitro.     

Growth,Grazing, and Starvation Survival in Three Heterotrophic Dinoflagellate Species

To assess the effects of fluctuating prey availability on predator population dynamics and grazing impact on phytoplankton, we measured growth and grazing rates of three heterotrophic dinoflagellate species—Oxyrrhis marina, Gyrodinium dominans and Gyrodinium spirale—before and after depriving them of phytoplankton prey. All three dinoflagellate species survived long periods (> 10 d) without algal prey, coincident with decreases in predator abundance and cell size. After 1–3 wks, starvation led to a 17–57% decrease in predator cell volume and some cells became deformed and transparent. When re‐exposed to phytoplankton prey, heterotrophs ingested prey within minutes and increased cell volumes by 4–17%. At an equivalent prey concentration, continuously fed predators had ~2‐fold higher specific growth rates (0.18 to 0.55 d^?1) than after starvation (?0.16 to 0.25 d^?1). Maximum specific predator growth rates would be achievable only after a time lag of at least 3 d. A delay in predator growth poststarvation delays predator‐induced phytoplankton mortality when prey re‐emerges at the onset of a bloom event or in patchy prey distributions. These altered predator‐prey population dynamics have implications for the formation of phytoplankton blooms, trophic transfer rates, and potential export of carbon.     

Soil carbon stocks and carbon sequestration rates in seminatural grassland in Aso region,Kumamoto, Southern Japan

Global soil carbon (C) stocks account for approximately three times that found in the atmosphere. In the Aso mountain region of Southern Japan, seminatural grasslands have been maintained by annual harvests and/or burning for more than 1000 years. Quantification of soil C stocks and C sequestration rates in Aso mountain ecosystem is needed to make well‐informed, land‐use decisions to maximize C sinks while minimizing C emissions. Soil cores were collected from six sites within 200 km² (767–937 m asl.) from the surface down to the k‐Ah layer established 7300 years ago by a volcanic eruption. The biological sources of the C stored in the Aso mountain ecosystem were investigated by combining C content at a number of sampling depths with age (using ¹⁴C dating) and δ¹³C isotopic fractionation. Quantification of plant phytoliths at several depths was used to make basic reconstructions of past vegetation and was linked with C‐sequestration rates. The mean total C stock of all six sites was 232 Mg C ha^?1 (28–417 Mg C ha^?1), which equates to a soil C sequestration rate of 32 kg C ha^?1 yr^?1 over 7300 years. Mean soil C sequestration rates over 34, 50 and 100 years were estimated by an equation regressing soil C sequestration rate against soil C accumulation interval, which was modeled to be 618, 483 and 332 kg C ha^?1 yr^?1, respectively. Such data allows for a deeper understanding in how much C could be sequestered in Miscanthus grasslands at different time scales. In Aso, tribe Andropogoneae (especially Miscanthus and Schizoachyrium genera) and tribe Paniceae contributed between 64% and 100% of soil C based on δ¹³C abundance. We conclude that the seminatural, C₄‐dominated grassland system serves as an important C sink, and worthy of future conservation.     

Total phosphorus thresholds for regime shifts are nearly equal in subtropical and temperate shallow lakes with moderate depths and areas

相似文献   

In situ analysis of oxygen consumption and diffusive transport in high‐temperature acidic iron‐oxide microbial mats

The role of dissolved oxygen as a principal electron acceptor for microbial metabolism was investigated within Fe(III)‐oxide microbial mats that form in acidic geothermal springs of Yellowstone National Park (USA). Specific goals of the study were to measure and model dissolved oxygen profiles within high‐temperature (65–75°C) acidic (pH = 2.7–3.8) Fe(III)‐oxide microbial mats, and correlate the abundance of aerobic, iron‐oxidizing Metallosphaera yellowstonensis organisms and mRNA gene expression levels to Fe(II)‐oxidizing habitats shown to consume oxygen. In situ oxygen microprofiles were obtained perpendicular to the direction of convective flow across the aqueous phase/Fe(III)‐oxide microbial mat interface using oxygen microsensors. Dissolved oxygen concentrations dropped from ～ 50–60 μM in the bulk‐fluid/mat surface to below detection (< 0.3 μM) at a depth of ～ 700 μm (～ 10% of the total mat depth). Net areal oxygen fluxes into the microbial mats were estimated to range from 1.4–1.6 × 10^?4 μmol cm^?2 s^?1. Dimensionless parameters were used to model dissolved oxygen profiles and establish that mass transfer rates limit the oxygen consumption. A zone of higher dissolved oxygen at the mat surface promotes Fe(III)‐oxide biomineralization, which was supported using molecular analysis of Metallosphaera yellowstonensis 16S rRNA gene copy numbers and mRNA expression of haem Cu oxidases (FoxA) associated with Fe(II)‐oxidation.     

In situ growth of Gallionella biofilms and partitioning of lanthanides and actinides between biological material and ferric oxyhydroxides

Gallionella ferruginea is an iron‐oxidizing chemolithotrophic micro‐organism that lives in low‐oxygen conditions (0.1–1.5 mg L^?1 saturation). It produces a stalk structure from the concave side of the cell depending on population development, pH and redox conditions. After Gallionella oxidizes ferrous iron, bacteriogenic iron oxides (BIOS) precipitate on the stalk material and over time the stalks and/or the precipitated BIOS attenuate trace metals from surrounding groundwater. Gallionella ferruginea biofilms were cultured in situ in an artificial channel (2000 × 300 × 250 mm) using groundwater sourced from a borehole 297 m below sea level in the Äspö Hard Rock Laboratory in southern Sweden. The pH of the groundwater in the channels was always between 7.4 and 7.7 with oxygen saturation below 1.5 mg L^?1 and Eh between 100 and 200 mV. Oxygen eventually declined to <0.3 mg L^?1, terminating prolific biofilm growth. Biofilms formed within 2 weeks and were sampled every 2 weeks over 3 months. Cell number, stalk length and ferric iron concentration were measured for each sample and trace metal concentration was measured by inductively coupled plasma mass spectrometry. Results from well‐developed in situ biofilms suggest that Gallionella could concentrate metals at levels up to 1 × 10³‐fold higher than found within the host rock and more than 1 × 10⁶ times the levels found in the groundwater. These new experiments were used to support the results from the well‐developed biofilms and to relate biofilm development and population characteristics to metal attenuation. After 3 months, rare earth element (REE) plots indicated that BIOS can accumulate metals at levels up to 1 × 10⁴‐fold higher than found in the groundwater and fractionate heavy rare earth elements over light rare earth elements. Generally the presence of the organic phase promotes the adsorption of all lanthanides and actinides that are not adsorbed by the inorganic phase. The iron oxides are directly correlated with stalk length (R = 0.96), indicating that rapid REE and actinide adsorption requires both iron oxides and a nucleating biological structure for the iron oxides.     

Bacterial abundance and composition in marine sediments beneath the Ross Ice Shelf,Antarctica

Marine sediments of the Ross Sea, Antarctica, harbor microbial communities that play a significant role in the decomposition, mineralization, and recycling of organic carbon (OC). In this study, the cell densities within a 153‐cm sediment core from the Ross Sea were estimated based on microbial phospholipid fatty acid (PLFA) concentrations and acridine orange direct cell counts. The resulting densities were as high as 1.7 × 10⁷ cells mL^?1 in the top ten centimeters of sediments. These densities are lower than those calculated for most near‐shore sites but consistent with deep‐sea locations with comparable sedimentation rates. The δ¹³C measurements of PLFAs and sedimentary and dissolved carbon sources, in combination with ribosomal RNA (SSU rRNA) gene pyrosequencing, were used to infer microbial metabolic pathways. The δ¹³C values of dissolved inorganic carbon (DIC) in porewaters ranged downcore from ?2.5‰ to ?3.7‰, while δ¹³C values for the corresponding sedimentary particulate OC (POC) varied from ?26.2‰ to ?23.1‰. The δ¹³C values of PLFAs ranged between ?29‰ and ?35‰ throughout the sediment core, consistent with a microbial community dominated by heterotrophs. The SSU rRNA gene pyrosequencing revealed that members of this microbial community were dominated by β‐, δ‐, and γ‐Proteobacteria, Actinobacteria, Chloroflexi and Bacteroidetes. Among the sequenced organisms, many appear to be related to known heterotrophs that utilize OC sources such as amino acids, oligosaccharides, and lactose, consistent with our interpretation from δ¹³C_PLFA analysis. Integrating phospholipids analyses with porewater chemistry, δ¹³C_DIC and δ¹³C_POC values and SSU rRNA gene sequences provides a more comprehensive understanding of microbial communities and carbon cycling in marine sediments, including those of this unique ice shelf environment.     

Climate change-predicted shifts in the temperature regime of shallow groundwater produce rapid responses in ciliate communities

The ciliates living in a shallow groundwater system in southern Ontario, Canada were subjected to an in situ temperature manipulation over 14 months. Ciliates were collected from the bed surface of a small springbrook and from interstitial water collected at five depths beneath its surface. Mean temperature elevations established at each depth (?20, ?40, ?60, ?80, and ?100 cm) between the experiment's control and treatment blocks were 1.9, 3.5, 3.9, 3.8, and 3.6 °C, respectively, and were based on global warming projections for the region. In total, 160 species of ciliate belonging to 85 genera were identified. Overall, the treatment block had a higher density (6510±342 cells L^?1; ±1 SE) than the control (5797±237 cells L^?1), but densities were both vertically and longitudinally variable. Control densities decreased with depth, whereas treatment densities were more equal among depths. Total species richness showed no significant difference between blocks when combining all sampling dates and depths, although species composition changed. The ciliate community was dominated by small (15–50 μm), followed by medium (50–200 μm), and only a few large‐sized (>200 μm) species. Small ciliates contributed 82–97% of the total density. Small ciliates also contributed more to the treatment (94%) than the control block (88%). The most common ciliate feeding groups were bacterivores, omnivores, predators, and algae‐diatom feeders, with bacterivores being most dominant (83–99% of the total numbers collected). Ordination analyses revealed that ciliate distribution was strongly correlated with groundwater temperature, although dissolved oxygen level, concentrations of ammonia and nitrate, and depth also appeared to be influential. Peak densities of many species occurred in either the control or treatment blocks, but not in both. The benefits of using ciliates as a proxy for higher, much longer‐lived, eukaryotes in climate change studies are discussed.     

Mark–recapture of Cerambyx welensii in dehesa woodlands: dispersal behaviour,population density,and mass trapping efficiency with low trap densities

The longhorn beetle, Cerambyx welensii Küster (Coleoptera: Cerambycidae), is an emerging pest involved in oak decline episodes in dehesa open woodlands. Larvae are xylophagous and cause considerable physiological, mechanical, and structural damages to trees. Chemical and biological control are currently unsatisfactory. Recent research has shown that mass trapping with a high density of baited traps (40 traps ha^?1) could be useful to manage C. welensii populations, although such a trap density was too high to be cost‐effective. In this 2‐year study (2010–2011) we investigated with mark–recapture methods in a large plot (1) the flight dispersal behaviour, (2) the adult population density, and (3) the efficiency of mass trapping at two low trap densities (one or four traps ha^?1). Results indicated that many adults were sedentary (60%) but flying adults displayed a strong propensity to move, both sexes dispersing on average more than 200 m and one male and one female flying at least 540 and 349 m, respectively. Recapture rates were high (0.26–0.35) and population density was estimated to be 6–22 adults ha^?1 with maximum likelihood models. Trapping efficiency ranged 48–61% with no significant effect of trap density or year. We conclude that results were not satisfactory enough to recommend mass trapping with low trap densities as control method for C. welensii and that more research is still required on the technical, ecological, and behavioural factors affecting control efficiency.     

Inoculum effects on community composition and nitritation performance of autotrophic nitrifying biofilm reactors with counter‐diffusion geometry

The link between nitritation success in a membrane‐aerated biofilm reactor (MABR) and the composition of the initial ammonia‐ and nitrite‐oxidizing bacterial (AOB and NOB) population was investigated. Four identically operated flat‐sheet type MABRs were initiated with two different inocula: from an autotrophic nitrifying bioreactor (Inoculum A) or from a municipal wastewater treatment plant (Inoculum B). Higher nitritation efficiencies (NO₂^‐‐N/NH₄⁺‐N) were obtained in the Inoculum B‐ (55.2–56.4%) versus the Inoculum A‐ (20.2–22.1%) initiated reactors. The biofilms had similar oxygen penetration depths (100–150 µm), but the AOB profiles [based on 16S rRNA gene targeted real‐time quantitative PCR (qPCR)] revealed different peak densities at or distant from the membrane surface in the Inoculum B‐ versus A‐initiated reactors, respectively. Quantitative fluorescence in situ hybridization (FISH) revealed that the predominant AOB in the Inoculum A‐ and B‐initiated reactors were Nitrosospira spp. (48.9–61.2%) versus halophilic and halotolerant Nitrosomonas spp. (54.8–63.7%), respectively. The latter biofilm displayed a higher specific AOB activity than the former biofilm (1.65 fmol cell^?1 h^?1 versus 0.79 fmol cell^?1 h^?1). These observations suggest that the AOB and NOB population compositions of the inoculum may determine dominant AOB in the MABR biofilm, which in turn affects the degree of attainable nitritation in an MABR.     

Halophilic Archaea cultured from ancient halite,Death Valley,California

Halophilic Archaea cultured from ancient fluid inclusions in a 90‐m‐long (0‐ to 100 000‐year‐old) salt core from Death Valley, California, demonstrate survival of bacterial cells in subsurface halite for up to 34 000 years. Five enrichment cultures, representing three genera of halophilic Archaea (Halorubrum, Natronomonas and Haloterrigena), were obtained from five surface‐sterilized halite crystals exclusively in one section of the core (13.0–17.8 m; 22 000–34 000 years old) containing perennial saline lake deposits. Prokaryote cells were observed microscopically in situ within fluid inclusions from every layer that produced culturable cells. Another 876 crystals analysed from depths of 8.1–86.7 m (10 000–100 000 years old) failed to yield live halophilic Archaea. Considering the number of halite crystals tested (culturing success of 0.6%), microbial survival in fluid inclusions in halite is rare and related to the paleoenvironment, which controls the distribution and abundance of trapped microorganisms. Two cultures from two crystals at 17.8 m that yielded identical 16S rRNA sequences (genus: Haloterrigena) demonstrate intra‐laboratory reproducibility. Inter‐laboratory reproducibility is shown by two halophilic Archaea (genus: Natronomonas), with 99.3% similarity of 16S rRNA sequences, cultured from the same core interval, but at separate laboratories.     

Rates of methanogenesis and methanotrophy in deep-sea sediments

We use the carbon isotopic composition (δ¹³C) of the dissolved inorganic carbon (DIC) of pore fluids from Leg 175 of the Ocean Drilling Program (ODP) along the West African Margin to quantify rates of methane production (methanogenesis) and destruction via oxidation (methanotrophy) in deep‐sea sediments. Results from a model of diffusion and reaction in the sedimentary column show that anaerobic methane oxidation (AOM) occurs in the transition zone between the presence of sulfate and methane, and methanogenesis occurs below these depths in a narrow confined zone that ends at about 250 m below the sea‐sediments surface in all sediment profiles. Our model suggests that the rates of methanogenesis and AOM range between 6 · 10⁻⁸ and 1 · 10⁻¹⁰ mol cm⁻³ year⁻¹ at all sites, with higher rates at sites where sulfate is depleted in shallower depths. Our AOM rates agree with those based solely on sulfate concentration profiles, but are much lower than those calculated from experiments of sulfate reduction through AOM done under laboratory conditions. At sites where the total organic carbon (TOC) is less than 5% of the total sediment, we calculate that AOM is the main pathway for sulfate reduction. We calculate that higher rates of AOM are associated with increased recrystallization rates of carbonate minerals. We do not find a correlation between methanogenesis rates and the content of carbonate or TOC in the sediments, porosity, sedimentation rate, or the C:N ratio, and the cause of lack of methanogenesis below a certain depth is not clear. There does, however, appear to be an association between the rates of methanogenesis and the location of the site in the upwelling system, suggesting that some variable such as the type of the organic matter or the nature of the microbiological community may be important.     

Microbially enhanced dissolution of HgS in an acid mine drainage system in the California Coast Range

Mercury sulfides (cinnabar and metacinnabar) are the main ores of Hg and are relatively stable under oxic conditions (K_sp = 10^?54 and 10^?52, respectively). However, until now their stability in the presence of micro‐organisms inhabiting acid mine drainage (AMD) systems was unknown. We tested the effects of the AMD microbial community from the inoperative Hg mine at New Idria, CA, present in sediments of an AMD settling pond adjacent to the main waste pile and in a microbial biofilm on the surface of this pond, on the solubility of crystalline HgS. A 16S rRNA gene clone library revealed that the AMD microbial community was dominated by Fe‐oxidizing (orders Ferritrophicales and Gallionellas) and S‐oxidizing bacteria (Thiomonas sp.), with smaller amounts (≤6%) being comprised of the orders Xanthomondales and Rhodospirillales. Though the order Ferritrophicales dominate the 16S rRNA clones (>60%), qPCR results of the microbial community indicate that the Thiomonas sp. represents ~55% of the total micro‐organisms in the top 1 cm of the AMD microbial community. Although supersaturated with respect to cinnabar and metacinnabar, microcosms inoculated with the AMD microbial community were capable of releasing significantly more Hg into solution compared to inactivated or abiotic controls. Four different Hg‐containing materials were tested for bacterially enhanced HgS dissolution: pure cinnabar, pure metacinnabar, mine tailings, and calcine material (processed ore). In the microcosm with metacinnabar, the presence of the AMD microbial community resulted in an increase of dissolved Hg concentrations up to 500 μg L^‐1 during the first 30 days of incubation. In abiotic control microcosms, dissolved Hg concentrations did not increase above 100 ng L^?1. When Hg concentrations were below 50 μg L^‐1, the Fe‐oxidizing bacteria in the AMD microbial community were still capable of oxidizing Fe(II) to Fe(III) in the AMD solution, whereas concentrations above 50 μg L^?1 resulted in inhibition of microbial iron oxidation. Our experiments show that the AMD microbial community contributes to the dissolution of mercury sulfide minerals. These findings have major implications for risk assessment and future management of inoperative Hg mines worldwide.     

Population pattern and dynamics of the Bluemouth Helicolenus dactylopterus (Delaroche, 1809) in the eastern Mediterranean Sea

Present study evaluated the population status of the Bluemouth (Helicolenus dactylopterus) population distributed in the Antalya Bay for the first time, within the scope of two different surveys carried out in monthly basis, between September 2009 and June 2011 (200–900 m). In accordance with the major availability of the food, 80.9% of the total catch (in number) of the species at the upper slope (200–499 m). The 80.8% of all recruits’ specimens inhabits between 200 and 399 m while 72% of the total spawner specimens (TL ≥ 20 cm) inhabits at depths of between 600 and 799 m. Highest average abundance of the species was estimated 1,060 n/km² (400 m), while the highest average biomass was 93 kg/km² (600 m). Lengths of individuals ranged from 4 to 36 cm, and estimated ages from 0 to 27 years. Parameters of the von Bertalanffy growth curves were L _∞   = 34.14 cm, K = 0.09 year^?1, and t₀ = ?1.28 years. Margin band analysis confirmed the formation of a single growth annulus per year. In the central part of the otolith, close to the nucleus, a strongly marked check ring is formed which presenting first time for this species in the literature. The duration of the spawning stage for the females was observed between December and February. Selectivity rate of the commercially used 44 mm diamond codend mesh, with a 7.4 cm catch size, found to be very low for the species (a first spawning size of 17–20 cm). The stock of Bluemouth in the Antalya Bay was considered in above reference levels and in high abundance status due to estimated low fishing mortality (0.067^?1), exploitation rate status below reference level (0.207^?1) and F_curr is very low than reference point (0.219^?1).     

Nematode Community Structure along the Continental Slope off the Kenyan Coast,Western Indian Ocean

Metazoan meiofauna and in particular nematode densities, diversity, community structure were studied in relation to water depth (20 m, 50 m, 500 m, 1000 m and 2000 m) along four bathymetric transects in the Western Indian Ocean off the Kenyan coast. Nematode densities ranged between 276–944 ind./10 cm², which is comparable to values from other oligotrophic areas in the world. Densities was correlated with oxygen concentrations in the overlying water, since they were lowest at mid‐depth (500–1000 m) coinciding with the minimum oxygen level. Nematode community structure (at genus level) resembles communities found in temperate slope regions, which are also characterized by a low productivity. The community structure showed correlations with sediment composition, water depth and oxygen levels in the overlying water. Sediment composition was mainly important at the shelf where nematodes separated into a silty sediment‐dwelling community with high abundances of Daptonema, Dorylaimopsis, Terschellingia and Halalaimus, and a sandy sediment‐dwelling community characterised by high abundances of Microlaimus and Halalaimus. The genera Monhystera, Acantholaimus, Sabatieria, Molgolaimus and Halalaimus dominated the slope communities. The characteristic deep‐sea taxa, the monhysterids and Acantholaimus increased in relative abundance with increasing depth, to become dominant at the lower slope (2000 m). The upper (500 m) and mid‐slope (1000 m), which coincided with the lowest oxygen concentrations, were colonised by Sabatieria, a genus that is known to inhabit suboxic sediments. Diversity at the level of the genera showed an unimodal trend along the sampled gradient, with highest values at mid‐depth (500 m). Although the oxygen minimum at mid depths is much less pronounced than in adjacent areas, the results of this study suggest an impact on the present communities.     

Biogeochemical probing of microbial communities in a basalt‐hosted hot spring at Kverkfjöll volcano,Iceland

We investigated bacterial and archaeal communities along an ice‐fed surficial hot spring at Kverkfjöll volcano—a partially ice‐covered basaltic volcano at Vatnajökull glacier, Iceland, using biomolecular (16S rRNA, apsA, mcrA, amoA, nifH genes) and stable isotope techniques. The hot spring environment is characterized by high temperatures and low dissolved oxygen concentrations at the source (68°C and <1 mg/L (±0.1%)) changing to lower temperatures and higher dissolved oxygen downstream (34.7°C and 5.9 mg/L), with sulfate the dominant anion (225 mg/L at the source). Sediments are comprised of detrital basalt, low‐temperature alteration phases and pyrite, with <0.4 wt. % total organic carbon (TOC). 16S rRNA gene profiles reveal that organisms affiliated with Hydrogenobaculum (54%–87% bacterial population) and Thermoproteales (35%–63% archaeal population) dominate the micro‐oxic hot spring source, while sulfur‐oxidizing archaea (Sulfolobales, 57%–82%), and putative sulfur‐oxidizing and heterotrophic bacterial groups dominate oxic downstream environments. The δ¹³C_org (‰ V‐PDB) values for sediment TOC and microbial biomass range from ?9.4‰ at the spring's source decreasing to ?12.6‰ downstream. A reverse effect isotope fractionation of ~3‰ between sediment sulfide (δ³⁴S ~0‰) and dissolved water sulfate (δ³⁴S +3.2‰), and δ¹⁸O values of ~ ?5.3‰ suggest pyrite forms abiogenically from volcanic sulfide, followed by abiogenic and microbial oxidation. These environments represent an unexplored surficial geothermal environment analogous to transient volcanogenic habitats during putative “snowball Earth” scenarios and volcano–ice geothermal environments on Mars.