Publications by authors named "Seth G John"

17 Publications

  • Page 1 of 1

Iron colloids dominate sedimentary supply to the ocean interior.

Proc Natl Acad Sci U S A 2021 Mar;118(13)

School of Ocean and Earth Science, University of Southampton, Southampton SO17 1BJ, United Kingdom.

Dissolution of marine sediment is a key source of dissolved iron (Fe) that regulates the ocean carbon cycle. Currently, our prevailing understanding, encapsulated in ocean models, focuses on low-oxygen reductive supply mechanisms and neglects the emerging evidence from iron isotopes in seawater and sediment porewaters for additional nonreductive dissolution processes. Here, we combine measurements of Fe colloids and dissolved δFe in shallow porewaters spanning the full depth of the South Atlantic Ocean to demonstrate that it is lithogenic colloid production that fuels sedimentary iron supply away from low-oxygen systems. Iron colloids are ubiquitous in these oxic ocean sediment porewaters and account for the lithogenic isotope signature of dissolved Fe (δFe = +0.07 ± 0.07‰) within and between ocean basins. Isotope model experiments demonstrate that only lithogenic weathering in both oxic and nitrogenous zones, rather than precipitation or ligand complexation of reduced Fe species, can account for the production of these porewater Fe colloids. The broader covariance between colloidal Fe and organic carbon (OC) abundance suggests that sorption of OC may control the nanoscale stability of Fe minerals by inhibiting the loss of Fe(oxyhydr)oxides to more crystalline minerals in the sediment. Oxic ocean sediments can therefore generate a large exchangeable reservoir of organo-mineral Fe colloids at the sediment water interface (a "rusty source") that dominates the benthic supply of dissolved Fe to the ocean interior, alongside reductive supply pathways from shallower continental margins.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.2016078118DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8020654PMC
March 2021

Anthropogenic Asian aerosols provide Fe to the North Pacific Ocean.

Proc Natl Acad Sci U S A 2020 11 22;117(45):27862-27868. Epub 2020 Oct 22.

Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089.

Fossil-fuel emissions may impact phytoplankton primary productivity and carbon cycling by supplying bioavailable Fe to remote areas of the ocean via atmospheric aerosols. However, this pathway has not been confirmed by field observations of anthropogenic Fe in seawater. Here we present high-resolution trace-metal concentrations across the North Pacific Ocean (158°W from 25°to 42°N). A dissolved Fe maximum was observed around 35°N, coincident with high dissolved Pb and Pb isotope ratios matching Asian industrial sources and confirming recent aerosol deposition. Iron-stable isotopes reveal in situ evidence of anthropogenic Fe in seawater, with low δFe (-0.23‰ > δFe > -0.65‰) observed in the region that is most influenced by aerosol deposition. An isotope mass balance suggests that anthropogenic Fe contributes 21-59% of dissolved Fe measured between 35° and 40°N. Thus, anthropogenic aerosol Fe is likely to be an important Fe source to the North Pacific Ocean.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.2010315117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7668086PMC
November 2020

Independent iron and light limitation in a low-light-adapted Prochlorococcus from the deep chlorophyll maximum.

ISME J 2021 01 23;15(1):359-362. Epub 2020 Sep 23.

Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA.

Throughout the open ocean, a minimum in dissolved iron concentration (dFe) overlaps with the deep chlorophyll maximum (DCM), which marks the lower limit of the euphotic zone. Maximizing light capture in these dim waters is expected to require upregulation of Fe-bearing photosystems, further depleting dFe and possibly leading to co-limitation by both iron and light. However, this effect has not been quantified for important phytoplankton groups like Prochlorococcus, which contributes most of the productivity in the oligotrophic DCM. Here, we present culture experiments with Prochlorococcus strain MIT1214, a member of the Low Light 1 ecotype isolated from the DCM in the North Pacific subtropical gyre. Under a matrix of iron and irradiance matching those found at the DCM, the ratio of Fe to carbon in Prochlorococcus MIT1214 cells ranged from 10-40 × 10 mol Fe:mol C and increased with light intensity and growth rate. These results challenge theoretical models predicting highest Fe:C at lowest light intensity, and are best explained by a large photosynthetic Fe demand that is not downregulated at higher light. To sustain primary production in the DCM with the rigid Fe requirements of low-light-adapted Prochlorococcus, dFe must be recycled rapidly and at high efficiency.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41396-020-00776-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7852507PMC
January 2021

Metabolic and biogeochemical consequences of viral infection in aquatic ecosystems.

Nat Rev Microbiol 2020 01 5;18(1):21-34. Epub 2019 Nov 5.

Department of the Geophysical Sciences, University of Chicago, Chicago, IL, USA.

Ecosystems are controlled by 'bottom-up' (resources) and 'top-down' (predation) forces. Viral infection is now recognized as a ubiquitous top-down control of microbial growth across ecosystems but, at the same time, cell death by viral predation influences, and is influenced by, resource availability. In this Review, we discuss recent advances in understanding the biogeochemical impact of viruses, focusing on how metabolic reprogramming of host cells during lytic viral infection alters the flow of energy and nutrients in aquatic ecosystems. Our synthesis revealed several emerging themes. First, viral infection transforms host metabolism, in part through virus-encoded metabolic genes; the functions performed by these genes appear to alleviate energetic and biosynthetic bottlenecks to viral production. Second, viral infection depends on the physiological state of the host cell and on environmental conditions, which are challenging to replicate in the laboratory. Last, metabolic reprogramming of infected cells and viral lysis alter nutrient cycling and carbon export in the oceans, although the net impacts remain uncertain. This Review highlights the need for understanding viral infection dynamics in realistic physiological and environmental contexts to better predict their biogeochemical consequences.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41579-019-0270-xDOI Listing
January 2020

Tracing and constraining anthropogenic aerosol iron fluxes to the North Atlantic Ocean using iron isotopes.

Nat Commun 2019 06 14;10(1):2628. Epub 2019 Jun 14.

Department of Earth Sciences, University of Southern California, Los Angeles, CA, 90089, USA.

Atmospheric dust is an important source of the micronutrient Fe to the oceans. Although relatively insoluble mineral Fe is assumed to be the most important component of dust, a relatively small yet highly soluble anthropogenic component may also be significant. However, quantifying the importance of anthropogenic Fe to the global oceans requires a tracer which can be used to identify and constrain anthropogenic aerosols in situ. Here, we present Fe isotope (δFe) data from North Atlantic aerosol samples from the GEOTRACES GA03 section. While soluble aerosol samples collected near the Sahara have near-crustal δFe, soluble aerosols from near North America and Europe instead have remarkably fractionated δFe values (as light as -1.6‰). Here, we use these observations to fingerprint anthropogenic combustion sources, and to refine aerosol deposition modeling. We show that soluble anthropogenic aerosol Fe flux to the global surface oceans is highly likely to be underestimated, even in the dusty North Atlantic.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-019-10457-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6570766PMC
June 2019

A new anion exchange purification method for Cu stable isotopes in blood samples.

Anal Bioanal Chem 2019 Jan 22;411(3):765-776. Epub 2018 Nov 22.

Department of Earth Sciences, University of Southern California, 3651 Trousdale Pkwy, Los Angeles, CA, USA.

The isotopic composition of iron, zinc, copper, and cadmium (δFe, δZn, δCu, and δCd) are novel and promising tools to study the metabolism and homeostasis of trace metals in the human body. Serum δCu has been proposed as a potential tool for diagnosis of cancer in liquid biopsy, and other metals may have similar utility. However, accurate analysis of trace metal isotopes is challenging because of the difficulties in purifying the metals from biological samples. Here we developed a simple and rapid method for sequential purification of Cu, Fe, Zn, and Cd from a single blood plasma sample. By using a combination of 11 M acetic acid and 4 M HCl in the first steps of column chemistry on AG-MP1 resin, we dramatically improve the separation of Cu from matrix elements compared to previous methods which use concentrated HCl alone. Our new method achieves full recovery of Cu, Fe, Zn, and Cd to prevent column-induced isotope fractionation effects, and effectively separates analytes from the matrix in order to reduce polyatomic interferences during isotope analysis. Our methods were verified by the analysis of isotope standards, a whole blood reference material, and a preliminary sample set including five plasma samples from healthy individuals and five plasma samples from cancer patients. This new method simplifies preparation of blood samples for metal isotope analysis, accelerating multi-isotope approaches to medical studies and contributing to our understanding of the cycling of Fe, Zn, Cu, and Cd in the human body. Graphical abstract ᅟ.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s00216-018-1498-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7450686PMC
January 2019

Tracking the rise of eukaryotes to ecological dominance with zinc isotopes.

Geobiology 2018 07 5;16(4):341-352. Epub 2018 Jun 5.

Geology and Geophysics, Yale University, New Haven, Connecticut.

The biogeochemical cycling of zinc (Zn) is intimately coupled with organic carbon in the ocean. Based on an extensive new sedimentary Zn isotope record across Earth's history, we provide evidence for a fundamental shift in the marine Zn cycle ~800 million years ago. We discuss a wide range of potential drivers for this transition and propose that, within available constraints, a restructuring of marine ecosystems is the most parsimonious explanation for this shift. Using a global isotope mass balance approach, we show that a change in the organic Zn/C ratio is required to account for observed Zn isotope trends through time. Given the higher affinity of eukaryotes for Zn relative to prokaryotes, we suggest that a shift toward a more eukaryote-rich ecosystem could have provided a means of more efficiently sequestering organic-derived Zn. Despite the much earlier appearance of eukaryotes in the microfossil record (~1700 to 1600 million years ago), our data suggest a delayed rise to ecological prominence during the Neoproterozoic, consistent with the currently accepted organic biomarker records.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/gbi.12289DOI Listing
July 2018

Iron Chloride Flocculation of Bacteriophages from Seawater.

Methods Mol Biol 2018 ;1681:49-57

Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, 85721, USA.

Viruses influence ecosystem dynamics by modulating microbial host population dynamics, evolutionary trajectories and metabolic outputs. While they are ecologically important across diverse ecosystems, viruses are challenging to study due to minimal biomass often obtained when sampling natural communities. Here we describe a technique using chemical flocculation, filtration and resuspension to recover bacteriophages from seawater and other natural waters. The method uses iron to precipitate viruses which are recovered by filtration onto large-pore size membranes and then resuspended using a buffer containing magnesium and a reductant (ascorbic acid or oxalic acid) at slightly acid pH (6-6.5). The recovery of bacteriophages using iron flocculation is efficient (>90%), inexpensive and reliable, resulting in preparations that are amenable to downstream analysis by next generation DNA sequencing, proteomics and, in some cases, can be used to study virus-host interactions.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/978-1-4939-7343-9_4DOI Listing
June 2018

Divergent responses of Atlantic coastal and oceanic Synechococcus to iron limitation.

Proc Natl Acad Sci U S A 2015 Aug 27;112(32):9944-9. Epub 2015 Jul 27.

Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02536;

Marine Synechococcus are some of the most diverse and ubiquitous phytoplankton, and iron (Fe) is an essential micronutrient that limits productivity in many parts of the ocean. To investigate how coastal and oceanic Atlantic Synechococcus strains acclimate to Fe availability, we compared the growth, photophysiology, and quantitative proteomics of two Synechococcus strains from different Fe regimes. Synechococcus strain WH8102, from a region in the southern Sargasso Sea that receives substantial dust deposition, showed impaired growth and photophysiology as Fe declined, yet used few acclimation responses. Coastal WH8020, from the dynamic, seasonally variable New England shelf, displayed a multitiered, hierarchical cascade of acclimation responses with different Fe thresholds. The multitiered response included changes in Fe acquisition, storage, and photosynthetic proteins, substitution of flavodoxin for ferredoxin, and modified photophysiology, all while maintaining remarkably stable growth rates over a range of Fe concentrations. Modulation of two distinct ferric uptake regulator (Fur) proteins that coincided with the multitiered proteome response was found, implying the coastal strain has different regulatory threshold responses to low Fe availability. Low nitrogen (N) and phosphorus (P) availability in the open ocean may favor the loss of Fe response genes when Fe availability is consistent over time, whereas these genes are retained in dynamic environments where Fe availability fluctuates and N and P are more abundant.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.1509448112DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4538626PMC
August 2015

An inexpensive, accurate, and precise wet-mount method for enumerating aquatic viruses.

Appl Environ Microbiol 2015 May 20;81(9):2995-3000. Epub 2015 Feb 20.

Department of Earth and Ocean Sciences, University of South Carolina, Columbia, South Carolina, USA

Viruses affect biogeochemical cycling, microbial mortality, gene flow, and metabolic functions in diverse environments through infection and lysis of microorganisms. Fundamental to quantitatively investigating these roles is the determination of viral abundance in both field and laboratory samples. One current, widely used method to accomplish this with aquatic samples is the "filter mount" method, in which samples are filtered onto costly 0.02-μm-pore-size ceramic filters for enumeration of viruses by epifluorescence microscopy. Here we describe a cost-effective (ca. 500-fold-lower materials cost) alternative virus enumeration method in which fluorescently stained samples are wet mounted directly onto slides, after optional chemical flocculation of viruses in samples with viral concentrations of <5×10(7) viruses ml(-1). The concentration of viruses in the sample is then determined from the ratio of viruses to a known concentration of added microsphere beads via epifluorescence microscopy. Virus concentrations obtained by using this wet-mount method, with and without chemical flocculation, were significantly correlated with, and had precision equivalent to, those obtained by the filter mount method across concentrations ranging from 2.17×10(6) to 1.37×10(8) viruses ml(-1) when tested by using cultivated viral isolates and natural samples from marine and freshwater environments. In summary, the wet-mount method is significantly less expensive than the filter mount method and is appropriate for rapid, precise, and accurate enumeration of aquatic viruses over a wide range of viral concentrations (≥1×10(6) viruses ml(-1)) encountered in field and laboratory samples.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1128/AEM.03642-14DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4393455PMC
May 2015

Quantification of dissolved iron sources to the North Atlantic Ocean.

Nature 2014 Jul 2;511(7508):212-5. Epub 2014 Jul 2.

Department of Earth and Ocean Sciences, University of South Carolina, Columbia, South Carolina 29208, USA.

Dissolved iron is an essential micronutrient for marine phytoplankton, and its availability controls patterns of primary productivity and carbon cycling throughout the oceans. The relative importance of different sources of iron to the oceans is not well known, however, and flux estimates from atmospheric dust, hydrothermal vents and oceanic sediments vary by orders of magnitude. Here we present a high-resolution transect of dissolved stable iron isotope ratios (δ(56)Fe) and iron concentrations ([Fe]) along a section of the North Atlantic Ocean. The different iron sources can be identified by their unique δ(56)Fe signatures, which persist throughout the water column. This allows us to calculate the relative contribution from dust, hydrothermal venting and reductive and non-reductive sedimentary release to the dissolved phase. We find that Saharan dust aerosol is the dominant source of dissolved iron along the section, contributing 71-87 per cent of dissolved iron. Additional sources of iron are non-reductive release from oxygenated sediments on the North American margin (10-19 per cent), reductive sedimentary dissolution on the African margin (1-4 per cent) and hydrothermal venting at the Mid-Atlantic Ridge (2-6 per cent). Our data also indicate that hydrothermal vents in the North Atlantic are a source of isotopically light iron, which travels thousands of kilometres from vent sites, potentially influencing surface productivity. Changes in the relative importance of the different iron sources through time may affect interactions between the carbon cycle and climate.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/nature13482DOI Listing
July 2014

Undocumented water column sink for cadmium in open ocean oxygen-deficient zones.

Proc Natl Acad Sci U S A 2014 May 28;111(19):6888-93. Epub 2014 Apr 28.

School of Earth and Ocean Sciences, University of Victoria, Victoria, BC, Canada V8W 2Y2;

Cadmium (Cd) is a micronutrient and a tracer of biological productivity and circulation in the ocean. The correlation between dissolved Cd and the major algal nutrients in seawater has led to the use of Cd preserved in microfossils to constrain past ocean nutrient distributions. However, linking Cd to marine biological processes requires constraints on marine sources and sinks of Cd. Here, we show a decoupling between Cd and major nutrients within oxygen-deficient zones (ODZs) in both the Northeast Pacific and North Atlantic Oceans, which we attribute to Cd sulfide (CdS) precipitation in euxinic microenvironments around sinking biological particles. We find that dissolved Cd correlates well with dissolved phosphate in oxygenated waters, but is depleted compared with phosphate in ODZs. Additionally, suspended particles from the North Atlantic show high Cd content and light Cd stable isotope ratios within the ODZ, indicative of CdS precipitation. Globally, we calculate that CdS precipitation in ODZs is an important, and to our knowledge a previously undocumented marine sink of Cd. Our results suggest that water column oxygen depletion has a substantial impact on Cd biogeochemical cycling, impacting the global relationship between Cd and major nutrients and suggesting that Cd may be a previously unidentified tracer for water column oxygen deficiency on geological timescales. Similar depletions of copper and zinc in the Northeast Pacific indicate that sulfide precipitation in ODZs may also have an influence on the global distribution of other trace metals.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1073/pnas.1402388111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4024915PMC
May 2014

A new method for precise determination of iron, zinc and cadmium stable isotope ratios in seawater by double-spike mass spectrometry.

Anal Chim Acta 2013 Sep 15;793:44-52. Epub 2013 Jul 15.

Department of Earth and Ocean Sciences, University of South Carolina, Columbia, SC 29208, USA.

The study of Fe, Zn and Cd stable isotopes (δ(56)Fe, δ(66)Zn and δ(114)Cd) in seawater is a new field, which promises to elucidate the marine cycling of these bioactive trace metals. However, the analytical challenges posed by the low concentration of these metals in seawater has meant that previous studies have typically required large sample volumes, highly limiting data collection in the oceans. Here, we present the first simultaneous method for the determination of these three isotope systems in seawater, using Nobias PA-1 chelating resin to extract metals from seawater, purification by anion exchange chromatography, and analysis by double spike MC-ICPMS. This method is designed for use on only a single litre of seawater and has blanks of 0.3, 0.06 and <0.03 ng for Fe, Zn and Cd respectively, representing a 1-20 fold reduction in sample size and a 4-130 decrease in blank compared to previously reported methods. The procedure yields data with high precision for all three elements (typically 0.02-0.2‰; 1σ internal precision), allowing us to distinguish natural variability in the oceans, which spans 1-3‰ for all three isotope systems. Simultaneous extraction and purification of three metals makes this method ideal for high-resolution, large-scale endeavours such as the GEOTRACES program.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.aca.2013.07.025DOI Listing
September 2013

Distinct iron isotopic signatures and supply from marine sediment dissolution.

Nat Commun 2013 ;4:2143

Ocean and Earth Science, University of Southampton, National Oceanography Centre, European Way, Southampton SO14 3ZH, UK.

Oceanic iron inputs must be traced and quantified to learn how they affect primary productivity and climate. Chemical reduction of iron in continental margin sediments provides a substantial dissolved flux to the oceans, which is isotopically lighter than the crust, and so may be distinguished in seawater from other sources, such as wind-blown dust. However, heavy iron isotopes measured in seawater have recently led to the proposition of another source of dissolved iron from 'non-reductive' dissolution of continental margins. Here we present the first pore water iron isotope data from a passive-tectonic and semi-arid ocean margin (South Africa), which reveals a smaller and isotopically heavier flux of dissolved iron to seawater than active-tectonic and dysoxic continental margins. These data provide in situ evidence of non-reductive iron dissolution from a continental margin, and further show that geological and hydro-climatic factors may affect the amount and isotopic composition of iron entering the ocean.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/ncomms3143DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3759054PMC
January 2014

Does activation of the anti proton, rather than concertedness, determine the stereochemistry of base-catalyzed 1,2-elimination reactions? Anti stereospecificity in E1cB eliminations of β-3-trifluoromethylphenoxy esters, thioesters, and ketones.

J Org Chem 2012 Mar 24;77(6):2819-28. Epub 2012 Feb 24.

Department of Chemistry, Carleton College, Northfield, Minnesota 55057, USA.

As part of a comprehensive investigation on the stereochemical aspects of base-catalyzed 1,2-elimination reactions, we have studied a set of acyclic carbonyl substrates that react by an irreversible E1cB mechanism with largely anti stereospecificity. (2)H NMR data show that these reactions using KOH in EtOH/H(2)O under non-ion-pairing conditions produce a minimum of 85-89% anti elimination on stereospecifically labeled tert-butyl (2R*,3R*)- and (2R*,3S*)-3-(3-trifluoromethylphenoxy)-2,3-(2)H(2)-butanoate, S-tert-butyl (2R*,3R*)- and (2R*,3S*)-3-(3-trifluoromethylphenoxy)-2,3-(2)H(2)-butanethioate, and the related ketones, (4R*,5R*)- and (4R*,5S*)-5-(3-trifluoromethylphenoxy)-4,5-(2)H(2)-3-hexanone. With both diastereomers of each substrate available, the KIEs can be calculated and the innate stereoselectivities determined. The elimination reactions of the β-3-trifluoromethylphenoxy substrates occur by E1cB mechanisms with diffusionally equilibrated enolate-anion intermediates. Thus, it is clear that anti elimination does not depend solely upon concerted E2 mechanisms. Negative hyperconjugation provides a satisfactory explanation for the anti stereospecificity exhibited by our carbonyl substrates, where the leaving group activates the anti proton, leading to the enolate intermediate. The activation of the anti proton by negative hyperconjugation may also play a role in the concerted pathways of E2 mechanisms. We have also measured the rates of the hydroxide-catalyzed elimination reactions of butanoate, thiobutanoate, and ketone substrates in EtOH/H(2)O, with β-tosyloxy, acetoxy, and 3-trifluoromethylphenoxy nucleofuges.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jo300053wDOI Listing
March 2012

A simple and efficient method for concentration of ocean viruses by chemical flocculation.

Environ Microbiol Rep 2011 Apr;3(2):195-202

Ocean viruses alter ecosystems through host mortality, horizontal gene transfer and by facilitating remineralization of limiting nutrients. However, the study of wild viral populations is limited by inefficient and unreliable concentration techniques. Here, we develop a new technique to recover viruses from natural waters using iron-based flocculation and large-pore-size filtration, followed by resuspension of virus-containing precipitates in a pH 6 buffer. Recovered viruses are amenable to gene sequencing, and a variable proportion of phages, depending upon the phage, retain their infectivity when recovered. This Fe-based virus flocculation, filtration and resuspension method (FFR) is efficient (> 90% recovery), reliable, inexpensive and adaptable to many aspects of marine viral ecology and genomics research.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/j.1758-2229.2010.00208.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3087117PMC
April 2011

Purification and characterization of rhodobactin: a mixed ligand siderophore from Rhodococcus rhodochrous strain OFS.

Biometals 2007 Dec 2;20(6):853-67. Epub 2007 Feb 2.

Bioscience, Los Alamos National Laboratory, Mail Stop M888, Los Alamos, NM 87545, USA.

The siderophore produced by Rhodococcus rhodochrous strain OFS, rhodobactin, was isolated from iron-deficient cultures and purified by a combination of XAD-7 absorptive/partition resin column and semi-preparative HPLC. The siderophore structure was characterized using 1D and 2D (1)H, (13)C and (15)N NMR techniques (DQFCOSY, TOCSY, NOESY, HSQC and LR-HSQC) and was confirmed using ESI-MS and MS/MS experiments. The structural characterization revealed that the siderophore, rhodobactin, is a mixed ligand hexadentate siderophore with two catecholate and one hydroxamate moieties for iron chelation. We further investigated the effects of Fe concentrations on siderophore production and found that Fe limiting conditions (Fe concentrations from 0.1 microM to 2.0 microM) facilitated siderophore excretion. Our interests lie in the role that siderophores may have in binding metals at mixed contamination sites (containing metals/radionuclides and organics). Given the broad metabolic capacity of this microbe and its Fe scavenging ability, R. rhodochrous OFS may have a competitive advantage over other organisms employed in bioremediation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s10534-006-9079-yDOI Listing
December 2007