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  • 1
    ISSN: 1745-6592
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Benzene, toluene, ethylbenzene, and xylene (BTEX) hydrocarbons are typically the most abundant carbon source for bacteria in gasoline-contaminated ground water. In situ bioremediation strategies often involve stimulating bacterial heterotrophic production in an attempt to increase carbon demand of the assemblage. This may, in turn, stimulate biodegradation of contaminant hydrocarbons. In this study, ground water circulation wells (GCWs) were used as an in situ treatment for a fuel-contaminated aquifer to stimulate bacterial production, purportedly by increasing oxygen transfer to the subsurface, circulating limiting nutrients, enhancing bioavailability of hydrocarbons, or by removing metabolically inhibitory volatile organics. Bacterial production, as measured by rates of bacterial protein synthesis, was stimulated across the zone of influence (ZOI) of a series of GCWs. Productivity increased from ∼102 to 〉105 ng C/L hour across the ZOI, suggesting that treatment stimulated overall biodegradation of carbon sources present in the ground water. However, even if BTEX carbon met all bacterial carbon demand, biodegradation would account for 〈4.3% of the total estimated BTEX removed from the ground water. Although bacterial productivity measurements alone cannot prove the effectiveness of in situ bioremediation, they can estimate the maximum amount of contaminant that may be biodegraded by a treatment system.
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  • 2
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Natural gas hydrates are a potential source of energy and may play a role in climate change and geological hazards. Most natural gas hydrate appears to be in the form of ‘structure I’, with methane as the trapped guest molecule, although ‘structure II’ hydrate has also ...
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  • 3
    ISSN: 1574-6941
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Stable isotope analysis of bacterial nucleic acids can be used to trace carbon that is assimilated and respired by the bacterioplankton in aquatic ecosystems. However, in sediment and soil environments humic acids co-extract with the nucleic acids, resulting in inaccurate isotope analysis. In this study we have examined the use of amino acids found in bacterial cell walls as biomarkers to trace carbon sources that support growth. In the development of the method, peptidoglycan from laboratory grown Pseudomonas sp. was hydrolyzed to amino acids. Stable carbon isotope ratios (δ13C) were analyzed with a dual mass spectrometer, ion trap and isotope ratio, equipped with a gas chromatograph sample inlet (GC/ITMS/IRMS). Comparisons of δ13C values of whole cells, cell wall peptidoglycan and the amino acids d-alanine and diaminopimelic acid from the cell wall were made using different carbon substrates and through different stages of growth to determine isotopic fractionation of these compounds. The δ13C values of whole cells, peptidoglycan and d-alanine and the substrate sources (glucose, glutamic acid, isoleucine, lysine, phenylalanine) were similar. The δ13C values of the d-alanine were within 0.5‰ of the substrate. In comparison, diaminopimelic acid was enriched in 13C by 10.3‰ relative to the whole cells, peptidoglycan and substrate. Additional laboratory experiments also demonstrated that the δ13C of d-alanine did not vary significantly relative to the whole cell and substrate through different growth stages. Stable carbon isotope analysis of the bacterial amino acids was determined at two field locations, water from Santa Rosa Sound, Florida, a humic rich estuarine ecosystem, and jet-fuel contaminated soils of Tyndall Air Force Base, Florida. d-alanine and diaminopimelic acid were isolated from these water and soil samples and the amino acids were analyzed for purity after extraction and for their δ13C values relative to organic matter in the environments. In the Santa Rosa Sound the δ13C value of d-alanine was −27.6±0.6‰. This value is in the range of δ13C values of bacteria and organic matter previously measured in the system, −24.0 to −27.0‰. The δ13C value of d-alanine in soil samples from Tyndall Air Force Base was −20.5±1.7‰ (n= 4) similar to ranges of values measured for spilled jet-fuel and CO2 respired from the soil at this site. Results from this study demonstrate that d-alanine can be used as a biomarker for analysis of carbon sources that are assimilated by bacteria in soils and sediments.
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  • 4
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR á€" Recent investigations of the ocean's iron cycle have focused primarily on the response of phytoplankton to iron enrichment1. Bacteria, however, are important in the trophodynamics and elemental cycles of marine ecosystems2'3. With the exception of phototrophic ...
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Microbial ecology 10 (1984), S. 137-149 
    ISSN: 1432-184X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Grazing on planktonic bacteria by microzooplankton was estimated by separating bacteria from the larger plankton with 1μm pore Nuclepore filtration and measuring changes in bacteria in filtered and unfiltered samples over 24 hours. In the absence of grazers, bacteria increased linearly. The regression coefficient of linear increase was used to estimatein situ bacterial production. When grazers were present, the changes in bacteria concentration usually took the form of a linear decline, and grazing was estimated by subtracting the regression coefficient of the unfiltered sample from that of the 1μm filtrate. Results from the Essex estuary-coastal system of northern Massachusetts show grazing and production at rates that indicate a daily turnover of the standing crop of bacteria, with highest values in mid-estuarine waters. Experiments on the size distribution of grazing showed that microzooplankton from 1–3μm were responsible for most of the observed decrease in bacteria. It was suggested that the basic pattern of linear increase of the bacteria in the absence of grazing reflects density-dependent limitation by substrate present at the outset of the incubation and is indicative of a population that has been maintained around the mid-point of the logistic growth curve by grazing.
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  • 6
    ISSN: 1432-184X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Microcosms may potentially be used as tools for evaluating the fate and effects of genetically engineered microorganisms released into the environment. Extrapolation of data to the field, however, requires that the correspondence between microcosm and field is known. Microbial trophic interactions within the microbial loop were compared quantitatively and qualitatively between field and microcosms containing estuarine water with and without intact sediment cores. The comparison showed that whereas proportions between trophic levels in microcosms were qualitatively similar to those in the field, rates of microbial processes were from 25 to 40% lower in microcosms. Nitrogen cycling was disrupted in microcosms incubated in the dark to eliminate primary production. Examination of the microbial parameters further suggests that sediment in microcosms may be an important factor regulating the bacterial trophic level. These results demonstrate that analysis of microbial trophic interactions is a sensitive method for the field comparison of aquatic microcosms and a potentially useful tool in the risk assessment of genetically engineered microorganisms.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 353 (1997), S. 53-61 
    ISSN: 1573-5117
    Keywords: bacteria ; heterotrophic microflagellates ; production ; grazing ; carbon ; estuary
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Bacterial and microflagellate biomass and production and grazing onbacteria were compared weekly at a fixed station in Santa Rosa Sound,Florida, starting in February and ending in October. For bothpopulations the weekly variation in biomass and production was aslarge as the seasonal variation. Cycles for biomass and production ofthese organisms were generally out of phase, rendering it difficultto estimate the net grazing of bacteria by microflagellates atindividual time points. For evaluation of factors that control thefate of carbon cycled by bacterial, experiments were conducted toexamine bacterial growth rates in the absence of predators. Thisexamination resulted in low bacterial growth rates when biomass washigh, and rapid growth rates typically occurred near minimumpopulations. Further analysis suggested that microflagellatepredation was greater than bacterial production during minimumbacterial growth rates. With integration of production and grazingrates over the study period, factors controlling bacterial growthwere examined. Using this approach, 71% of the bacterial productionwas grazed by 〈 8.0µm predators. The microflagellate biomassproduction was 41% of the grazing rate on bacteria. The total amountof bacterial production assimilated into microflagellate biomass was29%. However, based on the variations in biomass and activity of themicrobial assemblages, it appears that substrate and predation exertalternating control on bacterial abundance and production.
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  • 8
    Publication Date: 2022-05-25
    Description: This paper is not subject to U.S. copyright. The definitive version was published in Geochimica et Cosmochimica Acta 108 (2013): 184–201, doi:10.1016/j.gca.2013.01.022.
    Description: Sulfate-dependent anaerobic oxidation of methane (AOM) is the key sedimentary microbial process limiting methane emissions from marine sediments and methane seeps. In this study, we investigate how the presence of low-organic content sediment influences the capacity and efficiency of AOM at Bullseye vent, a gas hydrate-bearing cold seep offshore of Vancouver Island, Canada. The upper 8 m of sediment contains 〈0.4 wt.% total organic carbon (OC) and primarily consists of glacially-derived material that was deposited 14,900–15,900 yrs BP during the retreat of the late Quaternary Cordilleran Ice Sheet. We hypothesize this aged and exceptionally low-OC content sedimentary OM is biologically refractory, thereby limiting degradation of non-methane OM by sulfate reduction and maximizing methane consumption by sulfate-dependent AOM. A radiocarbon-based dissolved inorganic carbon (DIC) isotope mass balance model demonstrates that respired DIC in sediment pore fluids is derived from a fossil carbon source that is devoid of 14C. A fossil origin for the DIC precludes remineralization of non-fossil OM present within the sulfate zone as a significant contributor to pore water DIC, suggesting that nearly all sulfate is available for anaerobic oxidation of fossil seep methane. Methane flux from the SMT to the sediment water interface in a diffusion-dominated flux region of Bullseye vent was, on average, 96% less than at an OM-rich seep in the Gulf of Mexico with a similar methane flux regime. Evidence for enhanced methane oxidation capacity within OM-poor sediments has implications for assessing how climate-sensitive reservoirs of sedimentary methane (e.g., gas hydrate) will respond to ocean warming, particularly along glacially-influenced mid and high latitude continental margins.
    Description: Partial support for this research was provided by Interagency Agreements DE-FE0002911 and DE-NT0006147 between the US Geological Survey Gas Hydrates Project and the US Department of Energy’s Methane Hydrates Research and Development Program.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 9
    Publication Date: 2022-05-25
    Description: This paper is not subject to U.S. copyright. The definitive version was published in Marine and Petroleum Geology 25 (2008): 952-959, doi:10.1016/j.marpetgeo.2008.01.015.
    Description: To determine the impact of seeps and focused flow on the occurrence of shallow gas hydrates, several seafloor mounds in the Atwater Valley lease area of the Gulf of Mexico were surveyed with a wide range of seismic frequencies. Seismic data were acquired with a deep-towed, Helmholz resonator source (220–820 Hz); a high-resolution, Generator-Injector air-gun (30–300 Hz); and an industrial air-gun array (10–130 Hz). Each showed a significantly different response in this weakly reflective, highly faulted area. Seismic modeling and observations of reversed-polarity reflections and small scale diffractions are consistent with a model of methane transport dominated regionally by diffusion but punctuated by intense upward advection responsible for the bathymetric mounds, as well as likely advection along pervasive filamentous fractures away from the mounds.
    Description: This work was funded through ONR program element 61153N, and U.S. Department of Energy Grant DE-A126-97FT3423.
    Keywords: Methane hydrate ; Seafloor seep
    Repository Name: Woods Hole Open Access Server
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  • 10
    Publication Date: 2022-05-25
    Description: This paper is not subject to U.S. copyright. The definitive version was published in Marine and Petroleum Geology 25 (2008): 942-951, doi:10.1016/j.marpetgeo.2008.01.016.
    Description: Pore waters extracted from 18 piston cores obtained on and near a salt-cored bathymetric high in Keathley Canyon lease block 151 in the northern Gulf of Mexico contain elevated concentrations of chloride (up to 838 mM) and have pore water chemical concentration profiles that exhibit extensive departures (concavity) from steady-state (linear) diffusive equilibrium with depth. Minimum δ13C dissolved inorganic carbon (DIC) values of −55.9‰ to −64.8‰ at the sulfate–methane transition (SMT) strongly suggest active anaerobic oxidation of methane (AOM) throughout the study region. However, the nonlinear pore water chemistry-depth profiles make it impossible to determine the vertical extent of active AOM or the potential role of alternate sulfate reduction pathways. Here we utilize the conservative (non-reactive) nature of dissolved chloride to differentiate the effects of biogeochemical activity (e.g., AOM and/or organoclastic sulfate reduction) relative to physical mixing in high salinity Keathley Canyon sediments. In most cases, the DIC and sulfate concentrations in pore waters are consistent with a conservative mixing model that uses chloride concentrations at the seafloor and the SMT as endmembers. Conservative mixing of pore water constituents implies that an undetermined physical process is primarily responsible for the nonlinearity of the pore water-depth profiles. In limited cases where the sulfate and DIC concentrations deviated from conservative mixing between the seafloor and SMT, the δ13C-DIC mixing diagrams suggest that the excess DIC is produced from a 13C-depleted source that could only be accounted for by microbial methane, the dominant form of methane identified during this study. We conclude that AOM is the most prevalent sink for sulfate and that it occurs primarily at the SMT at this Keathley Canyon site.
    Description: This work was supported by DOE’s National Energy Technology Laboratory, the Office of Naval Research, and the Naval Research Laboratory. J.W.P was supported by a USGS Mendenhall Postdoctoral Research Fellowship Program during preparation of this manuscript.
    Keywords: Gas hydrate ; Methane ; Anaerobic methane oxidation ; Sulfate ; Brine ; Gulf of Mexico
    Repository Name: Woods Hole Open Access Server
    Type: Article
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