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  • 1
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Fine-scale physical and chemical gradients and deep photosynthetic microbial populations were assessed to provide an initial characterisation of a small, thermally stratified reservoir (Cross Reservoir, Kansas, U.S.A.) and its deep chlorophyll maxima (DCM). Factors were identified that may affect vertical positioning of subepilimnetic photosynthetic sulphur bacteria (PSB) in lakes.2. Results indicate that Cross Reservoir is a mesotrophic, dimictic lake with large subepilimnetic chlorophyll maxima containing dense layers of PSB. Characteristics of the deep PSB community of Cross Reservoir strongly correlate with both light and nutrient gradients.3. The deep bacterial community mostly contained single-celled and aggregating green sulphur bacteria, specifically free-living Chlorobium limicola and the conspicuous motile ectosymbiotic consortium known as ‘Chlorochromatium aggregatum’. The bacteria were within the anaerobic hypolimnion, beneath a metalimnetic plate of Cryptomonas spp. and within very low sulphide and light conditions [mean of 67 μgS L−1 and 0.05% photosynthetically active radiation (PAR)]. Pigment concentrations and fluorescence trends indicate that the bacteria made up a larger proportion of the DCM biomass than did phytoplankton in 1996.4. Cross Reservoir shares characteristics with natural lakes world-wide that also include a deep PSB community containing dense layers of ‘C. aggregatum’. Correlation analyses indicate that PSB community positioning and density are related to light, sulphide supply, redox potentials and pH. A 2-factor principal components analysis (PCA) and other data trends supported these interpretations and indicated that PSB are sensitive to the thermal stability of the water column, are nitrogen limited and regulated more by sulphide or sulphide to light ratios than local levels of light. The sensitivity of these deep photosynthetic bacteria to environmental gradients, and their significance to some aquatic systems, demonstrate their potential as indicators of environmental disturbance.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 326 (1987), S. 384-386 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A suite of basaltic glasses from small seamounts near the East Pacific Rise at 10-14° N has been analysed. This seamount field erupts chemically diverse lavas ranging from tholeiite (with mid-ocean-ridge basalt (MORE) chemistry) to alkali basalt (from a source with time-integrated higher Rb/Sr, ...
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 433 (2005), S. 25-26 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] A record of Earth's formation and its evolutionary history during the past 4,500 million years is preserved within the chemical and isotopic composition of the mantle. Fluids and the magmas expelled at the Earth's surface as basalt rocks provide samples for deciphering this record. In particular, ...
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Soluble methane monooxygenase (sMMO) expression and activity were monitored under conditions that either promoted or suppressed the expression of nitrogenase in Methylosinus trichosporium OB3b wild-type (WT) and in its sMMO-constitutive mutant, PP319. Both WT and mutant cultures had reduced sMMO activity and protein levels under elevated O2 conditions (188 μM) compared with low O2 conditions (24 μM). Simultaneous N2 fixation also reduced sMMO activity in both cultures when O2 was low. However, when O2 levels were increased, nitrogenase expression ceased and sMMO activity was reduced by ∼77% in the WT, whereas sMMO and nitrogenase expression and activity in PP319 were relatively unaffected by the higher O2 levels. Western immunoblot analysis showed that the nitrogenase Fe protein resolved as two components (apparent molecular mass of 30.5 and 32 kDa) in both the WT and PP319 when O2 levels were low. When O2 levels were high, only the 32-kDa form of the Fe protein was present in PP319, whereas neither form was detectable in the WT. Aerotolerant N2 fixation appears to be associated with the 32-kDa Fe protein in M. trichosporium OB3b.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Sudden exposure of an aquatic system to an insecticide can have significant effects on populations other than susceptible organisms. Although this is intuitively obvious, little is actually known about how such exposure might affect bacterial communities and their relative metabolic activity in ecosystems. Here, we assessed small sub-unit (ssu)-RNA levels in open and shaded 9 m3 aquatic mesocosms (16 units – 2 × 2 factorial design in quadruplicate) to examine the effects of sudden addition of deltamethrin to the units. When deltamethrin was added, a cascade of bacterial then phytoplankton “blooms” occurred over time. The bacterial bloom, which most likely included organisms from the plastid/cyanobacterial phylogenetic guild, was almost immediate (within hours), whereas the phytoplankton (algal) bloom lagged by about 4 days. This sequential response can be explained by an apparent sudden release of nutrients consequent to arthropod death that triggered a series of responses in the microbial loop. Interestingly, bacterial blooms were noted in both open and shaded mesocosms, whereas the algal bloom was only seen in open units, suggesting that both deltamethrin addition (and presumptive nutrient release) and an adequate light supply was required for the phytoplankton response. Overall, this work shows that microbial activities as reflected by ssu-rRNA levels can respond dramatically via apparently indirect effects following insecticide application.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Pb, Sr and Nd isotope variations are correlated in diverse lavas erupted at small seamounts near the East Pacific Rise. Tholeiites are isotopically indistinguishable from MORB (206Pb/204Pb=18.1–18.5; 87Sr/86Sr=0.7023–0.7028; 143Nd/144Nd=0.51326-0.51308); associated alkali basalts always show more radiogenic Pb and Sr signatures (206Pb/204Pb=18.8–19.2; 87Sr/86Sr=0.7029–0.7031) and less radiogenic Nd (143Nd/144Nd=0.51289–0.51301). The isotopic variability covers ∼80% of the variability for Pacific MORB, due to the presence of small-scale heterogeneity in the underlying mantle. Isotope compositions also correlate with trace element ratios such as La/Sm. Tholeiites at these seamounts have 3He/4He between 7.8–8.7 R A(R A= atmospheric ratio), also indistinguishable from MORB. He trapped in vesicles of alkali basalts, released by crushing in vacuo, has low 3He/4He (1.2–2.6 R)Ain conjunction with low helium concentrations ([He]〈5×10−8 ccSTP/g). In many cases post-eruptive radiogenic ingrowth has produced He isotope disequilibrium between vesicles and glass in the alkali basalts; subatmospheric 3He/4He ratios characterize the He dissolved in the glass which is released by melting the crushed powders. The narrow range of 3He/4He in the vesicles of the alkali basalts suggests that low 3He/4He is a source characteristic, but given their low [He] and high (U + Th), pre-eruptive radiogenic ingrowth cannot be excluded as a cause for low inherited 3He/4He ratios. Pb, Sr and Nd isotope compositions in lavas erupted at Shimada Seamount, an isolated volcano on 20 m.y. old seafloor at 17°N, are distinctly different from other seamounts in the East Pacific (206Pb/204Pb=18.8–19.0, 87Sr/ 86Sr≅0.7048 and 143Nd/144Nd≅0.51266). Relatively high 207Pb/204Pb (15.6–15.7) indicates ancient (〉2 Ga) isolation of the source from the depleted upper mantle, similar to Dupal components which are more prevalent in the southern hemisphere mantle. 3He/4He at Shimada Seamount is between 3.9–4.8 R A. Because the helium concentrations range up to 1.5×10−6, the low 3He/4He can not be due to radiogenic accumulation of 4He in the magma for reasonable volcanic evolution times. The low 3He/4He may be due to the presence of “enriched” domains within the lithosphere with high (U + Th)/He ratios, possibly formed during its accretion near the ridge. Alternatively, the low 3He/4He may be an inherent characteristic of an enriched component in the mantle beneath the East Pacific. Collectively, the He-Pb-Sr-Nd isotope systematics at East Pacific seamounts suggest that the range of isotope compositions present in the mantle is more readily sampled by seamount and island volcanism than by axial volcanism. Beneath thicker lithosphere away from the ridge axis, smaller degrees of melting in the source regions are less efficient in averaging the chemical characteristics of small-scale heterogeneities.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1432-0819
    Keywords: Key words Hawaii ; Loihi ; Magmatic processes ; Submarine volcanism ; Petrology ; Geochronology ; Lava geochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Samples of basalt were collected during the Rapid Response cruise to Loihi seamount from a breccia that was probably created by the July to August 1996 Loihi earthquake swarm, the largest swarm ever recorded from a Hawaiian volcano. 210Po–210Pb dating of two fresh lava blocks from this breccia indicates that they were erupted during the first half of 1996, making this the first documented historical eruption of Loihi. Sonobuoys deployed during the August 1996 cruise recorded popping noises north of the breccia site, indicating that the eruption may have been continuing during the swarm. All of the breccia lava fragments are tholeiitic, like the vast majority of Loihi's most recent lavas. Reverse zoning at the rim of clinopyroxene phenocrysts, and the presence of two chemically distinct olivine phenocryst populations, indicate that the magma for the lavas was mixed just prior to eruption. The trace element geochemistry of these lavas indicates there has been a reversal in Loihi's temporal geochemical trend. Although the new Loihi lavas are similar isotopically and geochemically to recent Kilauea lavas and the mantle conduits for these two volcanoes appear to converge at depth, distinct trace element ratios for their recent lavas preclude common parental magmas for these two active volcanoes. The mineralogy of Loihi's recent tholeiitic lavas signify that they crystallized at moderate depths (∼8–9 km) within the volcano, which is approximately 1 km below the hypocenters for earthquakes from the 1996 swarm. Taken together, the petrological and seismic evidence indicates that Loihi's current magma chamber is considerably deeper than the shallow magma chamber (∼3–4 km) in the adjoining active shield volcanoes.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1432-184X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Competition experiments were performed in a continuous-flow reactor using Methylosinus trichosporium OB3b, a type II methanotroph, and Methylomonas albus BG8, a type I methanotroph. The experiments were designed to establish conditions under which type II methanotrophs, which have significant cometabolic potential, prevail over type I strains. The primary determinants of species selection were dissolved methane, copper, and nitrate concentrations. Dissolved oxygen and methanol concentrations played secondary roles. M. trichosporium OB3b proved dominant under copper and nitratelimited conditions. The ratio of M. trichosporium to M. albus in the reactor increased ten-fold in less than 100 hours following the removal of copper from the reactor feed. Numbers of M. albus declined to levels that were below detection limits (〈106/ml) under nitrogen-limited conditions. In the latter experiment, the competitive success of M. trichosporiumdepended on the maintenance of an ambient dissolved oxygen level below about 7.5 × 10−5 M, or 30% of saturation with air. The ability of M. trichosporium to express soluble methane monooxygenase under copper limitation and nitrogenase under nitrate limitation was very significant. M. albus predominated under methane-limited conditions, especially when low levels of methanol were simultaneously added with methane to the reactor. The results imply that nitrogen limitation can be used to select for type II strains such as M. trichosporium OB3b.
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