Yeala Shaked | The Hebrew University of Jerusalem (original) (raw)

Papers by Yeala Shaked

Research paper thumbnail of Enhanced ferrihydrite dissolution by a unicellular, planktonic cyanobacterium: a biological contribution to particulate iron bioavailability

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Research paper thumbnail of Rapid Hydrogen Peroxide Release during Coral-Bacteria Interactions

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Research paper thumbnail of Iron-Nutrient Interactions within Phytoplankton

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Research paper thumbnail of Chemical characterization of atmospheric dust from a weekly time series in the

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Research paper thumbnail of Mineral iron utilization by natural and cultured Trichodesmium and associated bacteria

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Research paper thumbnail of Mineral iron dissolution in Trichodesmium colonies: The role of O 2 and pH microenvironments

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Research paper thumbnail of Metallophores associated with Trichodesmium erythraeum colonies from the Gulf of Aqaba

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Research paper thumbnail of Insights into the bioavailability of oceanic dissolved Fe from phytoplankton uptake kinetics

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Research paper thumbnail of Investigation of Siderophore-Promoted and Reductive Dissolution of Dust in Marine Microenvironments Such as Trichodesmium Colonies

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Research paper thumbnail of Sulfur isotope homogeneity of oceanic DMSP and DMS

PNAS, 2013

Oceanic emissions of volatile dimethyl sulfide (DMS) represent the largest natural source of bio... more Oceanic emissions of volatile dimethyl sulfide (DMS) represent the
largest natural source of biogenic sulfur to the global atmosphere,
where it mediates aerosol dynamics. To constrain the contribution
of oceanic DMS to aerosols we established the sulfur isotope ratios
(34S/32S ratio, δ34S) of DMS and its precursor, dimethylsulfoniopropionate
(DMSP), in a range of marine environments. In view of the
low oceanic concentrations of DMS/P, we applied a unique method
for the analysis of δ34S at the picomole level in individual compounds.
Surface water DMSP collected from six different ocean
provinces revealed a remarkable consistency in δ34S values ranging
between +18.9 and +20.3‰. Sulfur isotope composition of DMS
analyzed in freshly collected seawater was similar to δ34S of DMSP,
showing that the in situ fractionation between these species is
small (<+1‰). Based on volatilization experiments, emission of
DMS to the atmosphere results in a relatively small fractionation
(−0.5 ± 0.2‰) compared with the seawater DMS pool. Because
δ34S values of oceanic DMS closely reflect that of DMSP, we conclude
that the homogenous δ34S of DMSP at the ocean surface represents
the δ34S of DMS emitted to the atmosphere, within +1‰.
The δ34S of oceanic DMS flux to the atmosphere is thus relatively
constant and distinct from anthropogenic sources of atmospheric
sulfate, thereby enabling estimation of the DMS contribution
to aerosols.

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Research paper thumbnail of Dynamics of hydrogen peroxide in a coral reef: Sources and sinks

JGR: Biogeosciences, 2013

The dynamics of hydrogen peroxide (H2O2) was studied in the fringing coral reef off the coast of ... more The dynamics of hydrogen peroxide (H2O2) was studied in the fringing coral reef off the coast of Eilat, Red Sea. Diurnal changes in H2O2 concentrations in the reef lagoon were typical of photochemically produced species. During the daytime H2O2 accumulated in the lagoon at low tide and exceeded open water concentrations by 100–250 nM. Elevated H2O2 decay kinetics (termed hereafter antioxidant activity) were also recorded in the lagoon at low tide. The observed antioxidant activities were high enough to moderate H2O2 accumulation in the lagoon. In pursuit of the antioxidant source, the ability of corals to release antioxidant activity to their surrounding water was examined in both natural and laboratory settings.
Water collected in situ from surfaces of individual corals and next to a coral knoll contained high antioxidant activity. Incubation experiments revealed that many Red Sea corals release
antioxidant activity to their external milieu. Besides serving a potential antioxidant source to the reef system, the antioxidant activity detected on coral surfaces enabled corals to lower
H2O2 concentrations in their vicinity. The ability of corals to offset exogenous H2O2 was validated in incubations with Stylophora pistillata in the absence of mixing. Conversely,
corals subjected to mixing in a beaker were found to release H2O2, implying that corals may act as both a sink and a source for H2O2 in the reef. This newly described ability of corals to
change H2O2 dynamics by releasing both H2O2 and antioxidants may bare important implications for coral physiology and interactions with the environment.

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Research paper thumbnail of Coordinated transporter activity shapes high-affinity iron acquisition in cyanobacteria

ISME, 2014

Iron bioavailability limits biological activity in many aquatic and terrestrial environments. Bro... more Iron bioavailability limits biological activity in many aquatic and terrestrial environments. Broad scale genomic meta-analyses indicated that within a single organism, multiple iron transporters may contribute to iron acquisition. Here, we present a functional characterization of a cyanobacterial iron transport pathway that utilizes concerted transporter activities. Cyanobacteria are significant contributors to global primary productivity with high iron demands. Certain cyanobacterial species employ a siderophore-mediated uptake strategy; however, many strains possess neither siderophore biosynthesis nor siderophore transport genes. The unicellular, planktonic, freshwater
cyanobacterium, Synechocystis sp. PCC 6803, employs an alternative to siderophore-based uptake-reduction of Fe(III) species before transport through the plasma membrane. In this study, we combine short-term radioactive iron uptake and reduction assays with a range of disruption mutants to generate a working model for iron reduction and uptake in Synechocystis sp. PCC 6803.
We found that the Fe(II) transporter, FeoB, is the major iron transporter in this organism. In addition, we uncovered a link between a respiratory terminal oxidase (Alternate Respiratory Terminal Oxidase) and iron reduction - suggesting a coupling between these two electron transfer reactions.
Furthermore, quantitative RNA transcript analysis identified a function for subunits of the Fe(III) transporter, FutABC, in modulating reductive iron uptake. Collectively, our results provide
a molecular basis for a tightly coordinated, high-affinity iron transport system.

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Research paper thumbnail of Seas of Superoxide

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Research paper thumbnail of Disassembling iron availability to phytoplankton

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Research paper thumbnail of Iron availability, cellular iron quotas, and nitrogen fixation in Trichodesmium

Limnology and Oceanography, 2001

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Research paper thumbnail of Phytoplankton-Mediated Redox Cycle of Iron in the Epilimnion of Lake Kinneret

Environmental Science & Technology, 2002

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Research paper thumbnail of The biogeochemical cycle of iron and associated elements in Lake Kinneret

Geochimica Et Cosmochimica Acta, 2004

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Research paper thumbnail of Simultaneous determination of iron reduction and uptake by phytoplankton

We have developed a new method to assess simultaneously the rates of biological reduction of Fe(I... more We have developed a new method to assess simultaneously the rates of biological reduction of Fe(III)-ligand
complexes at nanomolar concentrations and iron uptake in marine phytoplankton. Other methods for measuring
iron reduction require micromolar iron concentrations, which can saturate iron uptake in these organisms.
In the present study, high sensitivity was obtained by combining radiometric techniques, ligand competition,
and selective retention on solid phase extraction columns (C18 Sep-Pak). Following the addition of the
Fe(II) specific ligand ferrozine (FZ) to seawater spiked with nanomolar concentrations of radiolabeled iron, the
rate of iron uptake is determined by filtering aliquots of cultures, and the rate of Fe(II) binding to FZ by passing
the filtrate through a column, which retains the Fe(II)FZ3 complex. The method was calibrated using 55Fe(II)
standards in NaCl solution, yielding high recovery efficiency and linear behavior across the entire range tested
from 3 × 10–11 M to 2 × 10–6 M Fe(II). Special attention was given to possible artifacts caused by reduction of
Fe(III) in the presence of FZ and Fe(III) adsorption onto the column, which are critical when measuring picomolar
concentrations of Fe(II). The method was successfully applied to Thalassiosira weissflogii cultures and to
natural phytoplankton populations in the Bering Sea using ethylenediaminetetraacetic acid as a model ligand

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Research paper thumbnail of A general kinetic model for iron acquisition by eukaryotic phytoplankton

Limnology and Oceanography, 2005

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Research paper thumbnail of Extracellular production of superoxide by marine diatoms: Contrasting effects on iron redox chemistry and bioavailability

Limnology and Oceanography, 2005

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Research paper thumbnail of Enhanced ferrihydrite dissolution by a unicellular, planktonic cyanobacterium: a biological contribution to particulate iron bioavailability

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Rapid Hydrogen Peroxide Release during Coral-Bacteria Interactions

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Iron-Nutrient Interactions within Phytoplankton

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Chemical characterization of atmospheric dust from a weekly time series in the

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Mineral iron utilization by natural and cultured Trichodesmium and associated bacteria

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Mineral iron dissolution in Trichodesmium colonies: The role of O 2 and pH microenvironments

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Metallophores associated with Trichodesmium erythraeum colonies from the Gulf of Aqaba

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Insights into the bioavailability of oceanic dissolved Fe from phytoplankton uptake kinetics

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Investigation of Siderophore-Promoted and Reductive Dissolution of Dust in Marine Microenvironments Such as Trichodesmium Colonies

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Sulfur isotope homogeneity of oceanic DMSP and DMS

PNAS, 2013

Oceanic emissions of volatile dimethyl sulfide (DMS) represent the largest natural source of bio... more Oceanic emissions of volatile dimethyl sulfide (DMS) represent the
largest natural source of biogenic sulfur to the global atmosphere,
where it mediates aerosol dynamics. To constrain the contribution
of oceanic DMS to aerosols we established the sulfur isotope ratios
(34S/32S ratio, δ34S) of DMS and its precursor, dimethylsulfoniopropionate
(DMSP), in a range of marine environments. In view of the
low oceanic concentrations of DMS/P, we applied a unique method
for the analysis of δ34S at the picomole level in individual compounds.
Surface water DMSP collected from six different ocean
provinces revealed a remarkable consistency in δ34S values ranging
between +18.9 and +20.3‰. Sulfur isotope composition of DMS
analyzed in freshly collected seawater was similar to δ34S of DMSP,
showing that the in situ fractionation between these species is
small (<+1‰). Based on volatilization experiments, emission of
DMS to the atmosphere results in a relatively small fractionation
(−0.5 ± 0.2‰) compared with the seawater DMS pool. Because
δ34S values of oceanic DMS closely reflect that of DMSP, we conclude
that the homogenous δ34S of DMSP at the ocean surface represents
the δ34S of DMS emitted to the atmosphere, within +1‰.
The δ34S of oceanic DMS flux to the atmosphere is thus relatively
constant and distinct from anthropogenic sources of atmospheric
sulfate, thereby enabling estimation of the DMS contribution
to aerosols.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Dynamics of hydrogen peroxide in a coral reef: Sources and sinks

JGR: Biogeosciences, 2013

The dynamics of hydrogen peroxide (H2O2) was studied in the fringing coral reef off the coast of ... more The dynamics of hydrogen peroxide (H2O2) was studied in the fringing coral reef off the coast of Eilat, Red Sea. Diurnal changes in H2O2 concentrations in the reef lagoon were typical of photochemically produced species. During the daytime H2O2 accumulated in the lagoon at low tide and exceeded open water concentrations by 100–250 nM. Elevated H2O2 decay kinetics (termed hereafter antioxidant activity) were also recorded in the lagoon at low tide. The observed antioxidant activities were high enough to moderate H2O2 accumulation in the lagoon. In pursuit of the antioxidant source, the ability of corals to release antioxidant activity to their surrounding water was examined in both natural and laboratory settings.
Water collected in situ from surfaces of individual corals and next to a coral knoll contained high antioxidant activity. Incubation experiments revealed that many Red Sea corals release
antioxidant activity to their external milieu. Besides serving a potential antioxidant source to the reef system, the antioxidant activity detected on coral surfaces enabled corals to lower
H2O2 concentrations in their vicinity. The ability of corals to offset exogenous H2O2 was validated in incubations with Stylophora pistillata in the absence of mixing. Conversely,
corals subjected to mixing in a beaker were found to release H2O2, implying that corals may act as both a sink and a source for H2O2 in the reef. This newly described ability of corals to
change H2O2 dynamics by releasing both H2O2 and antioxidants may bare important implications for coral physiology and interactions with the environment.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Coordinated transporter activity shapes high-affinity iron acquisition in cyanobacteria

ISME, 2014

Iron bioavailability limits biological activity in many aquatic and terrestrial environments. Bro... more Iron bioavailability limits biological activity in many aquatic and terrestrial environments. Broad scale genomic meta-analyses indicated that within a single organism, multiple iron transporters may contribute to iron acquisition. Here, we present a functional characterization of a cyanobacterial iron transport pathway that utilizes concerted transporter activities. Cyanobacteria are significant contributors to global primary productivity with high iron demands. Certain cyanobacterial species employ a siderophore-mediated uptake strategy; however, many strains possess neither siderophore biosynthesis nor siderophore transport genes. The unicellular, planktonic, freshwater
cyanobacterium, Synechocystis sp. PCC 6803, employs an alternative to siderophore-based uptake-reduction of Fe(III) species before transport through the plasma membrane. In this study, we combine short-term radioactive iron uptake and reduction assays with a range of disruption mutants to generate a working model for iron reduction and uptake in Synechocystis sp. PCC 6803.
We found that the Fe(II) transporter, FeoB, is the major iron transporter in this organism. In addition, we uncovered a link between a respiratory terminal oxidase (Alternate Respiratory Terminal Oxidase) and iron reduction - suggesting a coupling between these two electron transfer reactions.
Furthermore, quantitative RNA transcript analysis identified a function for subunits of the Fe(III) transporter, FutABC, in modulating reductive iron uptake. Collectively, our results provide
a molecular basis for a tightly coordinated, high-affinity iron transport system.

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Seas of Superoxide

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Disassembling iron availability to phytoplankton

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Iron availability, cellular iron quotas, and nitrogen fixation in Trichodesmium

Limnology and Oceanography, 2001

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Phytoplankton-Mediated Redox Cycle of Iron in the Epilimnion of Lake Kinneret

Environmental Science & Technology, 2002

Bookmarks Related papers MentionsView impact

Research paper thumbnail of The biogeochemical cycle of iron and associated elements in Lake Kinneret

Geochimica Et Cosmochimica Acta, 2004

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Simultaneous determination of iron reduction and uptake by phytoplankton

We have developed a new method to assess simultaneously the rates of biological reduction of Fe(I... more We have developed a new method to assess simultaneously the rates of biological reduction of Fe(III)-ligand
complexes at nanomolar concentrations and iron uptake in marine phytoplankton. Other methods for measuring
iron reduction require micromolar iron concentrations, which can saturate iron uptake in these organisms.
In the present study, high sensitivity was obtained by combining radiometric techniques, ligand competition,
and selective retention on solid phase extraction columns (C18 Sep-Pak). Following the addition of the
Fe(II) specific ligand ferrozine (FZ) to seawater spiked with nanomolar concentrations of radiolabeled iron, the
rate of iron uptake is determined by filtering aliquots of cultures, and the rate of Fe(II) binding to FZ by passing
the filtrate through a column, which retains the Fe(II)FZ3 complex. The method was calibrated using 55Fe(II)
standards in NaCl solution, yielding high recovery efficiency and linear behavior across the entire range tested
from 3 × 10–11 M to 2 × 10–6 M Fe(II). Special attention was given to possible artifacts caused by reduction of
Fe(III) in the presence of FZ and Fe(III) adsorption onto the column, which are critical when measuring picomolar
concentrations of Fe(II). The method was successfully applied to Thalassiosira weissflogii cultures and to
natural phytoplankton populations in the Bering Sea using ethylenediaminetetraacetic acid as a model ligand

Bookmarks Related papers MentionsView impact

Research paper thumbnail of A general kinetic model for iron acquisition by eukaryotic phytoplankton

Limnology and Oceanography, 2005

Bookmarks Related papers MentionsView impact

Research paper thumbnail of Extracellular production of superoxide by marine diatoms: Contrasting effects on iron redox chemistry and bioavailability

Limnology and Oceanography, 2005

Bookmarks Related papers MentionsView impact