Publications by authors named "Markus Maisch"

Rhodopseudomonas palustris TIE-1 grows photoautotrophically with Fe(II) as an electron donor and photoheterotrophically with a variety of organic substrates. However, it is unclear whether R. palustris TIE-1 conducts Fe(II) oxidation in conditions where organic substrates and Fe(II) are available simultaneously.

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Phototrophic Fe(II)-oxidizers use Fe(II) as electron donor for CO fixation thus linking Fe(II) oxidation, ATP formation, and growth directly to the availability of sunlight. We compared the effect of short (10 h light/14 h dark) and long (2-3 days light/2-3 days dark) light/dark cycles to constant light conditions for the phototrophic Fe(II)-oxidizer Chlorobium ferrooxidans KoFox. Fe(II) oxidation was completed first in the setup with constant light (9 mM Fe(II) oxidised within 8.

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Ice-rich Pleistocene-age permafrost is particularly vulnerable to rapid thaw, which may quickly expose a large pool of sedimentary organic matter (OM) to microbial degradation and lead to emissions of climate-sensitive greenhouse gases. Protective physico-chemical mechanisms may, however, restrict microbial accessibility and reduce OM decomposition; mechanisms that may be influenced by changing environmental conditions during sediment deposition. Here we study different OM fractions in Siberian permafrost deposited during colder and warmer periods of the past 55,000 years.

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Iron(II) (Fe(II)) can be formed by abiotic Fe(III) photoreduction, particularly when Fe(III) is organically complexed. Light-influenced environments often overlap or even coincide with oxic or microoxic geochemical conditions, for example, in sediments. So far, it is unknown whether microaerophilic Fe(II)-oxidizing bacteria are able to use the Fe(II) produced by Fe(III) photoreduction as electron donor.

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Iron(III) photoreduction is an important source of Fe(II) in illuminated aquatic and sedimentary environments. Under oxic conditions, the Fe(II) can be re-oxidized by oxygen (O) forming reactive O-species such as hydrogen peroxide (HO) which further react with Fe(II) thus enhancing Fe(II) oxidation rates. However, it is unknown by aquatic sediments how the parameters wavelength of radiation, photon flux, origin of Fe(III) source and presence or absence of O influence the extent of Fe(II) and HO turnover.

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Microbial reduction of Fe(III) minerals is a prominent process in redoximorphic soils and is strongly affected by organic matter (OM). We herein determined the rate and extent of microbial reduction of ferrihydrite (Fh) with either adsorbed or coprecipitated OM by . We focused on OM-mediated effects on electron uptake and alterations in Fh crystallinity.

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Neutrophilic microbial pyrite (FeS) oxidation coupled to denitrification is thought to be an important natural nitrate attenuation pathway in nitrate-contaminated aquifers. However, the poor solubility of pyrite raises questions about its bioavailability and the mechanisms underlying its oxidation. Here, we investigated direct microbial pyrite oxidation by a neutrophilic chemolithoautotrophic nitrate-reducing Fe(II)-oxidizing culture enriched from a pyrite-rich aquifer.

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Magnetite nanoparticles are promising materials for treating toxic Cr(VI), but safe handling is challenging due to their small size. We prepared flow-through columns containing 10% or 100% (v/v) magnetite-coated sand. Cr(VI) removal efficiency was determined for different Cr(VI) concentrations (0.

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Article Synopsis
  • * Glaciers contribute essential iron to marine ecosystems, mainly benefiting phytoplankton, but most of this iron (up to 95%) ends up settling near the glaciers instead of being available for use.
  • * Research indicates that even though only a small percentage of glacial iron is initially bioavailable, processes in fjord sediments can increase its availability significantly; however, as glaciers retreat, the supply of iron to these sediments may decrease, impacting coastal marine health.
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Iron (Fe) biogeochemistry in marine sediments is driven by redox transformations creating Fe(II) and Fe(III) gradients. As sediments are physically mixed by wave action or bioturbation, Fe gradients re-establish regularly. In order to identify the response of dissolved Fe(II) (Fe) and Fe mineral phases toward mixing processes, we performed voltammetric microsensor measurements, sequential Fe extractions, and Mössbauer spectroscopy of 12 h light-dark cycle incubated marine coastal sediment.

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Microbial Fe(III) reduction plays an important role for biogeochemical carbon and iron cycling in sediments and soils. Biochar is used as a soil amendment to increase fertility and lower NO/CO emissions. It is redox-active and can stimulate microbial Fe(III) mineral reduction.

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Neutrophilic microbial aerobic oxidation of ferrous iron (Fe(II)) is restricted to pH-circumneutral environments characterized by low oxygen where microaerophilic Fe(II)-oxidizing microorganisms successfully compete with abiotic Fe(II) oxidation. However, accumulation of ferric (bio)minerals increases competition by stimulating abiotic surface-catalyzed heterogeneous Fe(II) oxidation. Here, we present an experimental approach that allows quantification of microbial and abiotic contribution to Fe(II) oxidation in the presence or initial absence of ferric (bio)minerals.

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To distinguish between biotic and abiotic processes in laboratory experiments with environmental samples, an effective sterilization method is required that prevents biological activity but does not change physico-geochemical properties of samples. We compared standard sterilization methods with respect to their impact on microbial abundance and activity. We exposed marine sediment to (i) autoclaving, (ii) gamma-radiation or (iii) sodium azide (NaN3) and determined how nucleic acids, microbial productivity, colony forming units (CFUs) and community composition of microorganisms, fungi, unicellular protists and protozoa were affected.

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Many marine Precambrian iron formations (IF) record deep anoxic seawater enriched in Fe(II) (i.e. ferruginous) overlain by mildly oxygenated surface water.

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A conventional concept for the deposition of some Precambrian Banded Iron Formations (BIF) proceeds on the assumption that ferrous iron [Fe(II)] upwelling from hydrothermal sources in the Precambrian ocean was oxidized by molecular oxygen [O2] produced by cyanobacteria. The oldest BIFs, deposited prior to the Great Oxidation Event (GOE) at about 2.4 billion years (Gy) ago, could have formed by direct oxidation of Fe(II) by anoxygenic photoferrotrophs under anoxic conditions.

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