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  • 1
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    Characterization of meta-Cresol Purple for spectrophotometric pH measurements in saline and hypersaline media at sub-zero temperatures (2017)
    Nature Research
    In:  Scientific Reports, 7 (2481).
    Details
    Publication Date: 2021-04-23
    Description: Accurate pH measurements in polar waters and sea ice brines require pH indicator dyes characterized at near-zero and below-zero temperatures and high salinities. We present experimentally determined physical and chemical characteristics of purified meta-Cresol Purple (mCP) pH indicator dye suitable for pH measurements in seawater and conservative seawater-derived brines at salinities (S) between 35 and 100 and temperatures (T) between their freezing point and 298.15 K (25 °C). Within this temperature and salinity range, using purified mCP and a novel thermostated spectrophotometric device, the pH on the total scale (pHT) can be calculated from direct measurements of the absorbance ratio R of the dye in natural samples as pHT=−log(kT2e2)+log(R−e11−Re3e2) Based on the mCP characterization in these extended conditions, the temperature and salinity dependence of the molar absorptivity ratios and − log(kT2e2) of purified mCP is described by the following functions: e1 = −0.004363 + 3.598 × 10−5T, e3/e2 = −0.016224 + 2.42851 × 10−4T + 5.05663 × 10−5(S − 35), and − log(kT2e2) = −319.8369 + 0.688159 S −0.00018374 S2 + (10508.724 − 32.9599 S + 0.059082S2) T−1 + (55.54253 − 0.101639 S) ln T −0.08112151T. This work takes the characterisation of mCP beyond the currently available ranges of 278.15 K ≤ T ≤ 308.15 K and 20 ≤ S ≤ 40 in natural seawater, thereby allowing high quality pHT measurements in polar systems.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/s41598-017-02624-0
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Heme in the marine environment: from cells to the iron cycle (2014)
    Royal Society of Chemistry
    In:  Metallomics, 6 (1107).
    Details
    Publication Date: 2021-04-23
    Description: Hemes are iron containing heterocyclic molecules important in many cellular processes. In the marine environment, hemes participate as enzymatic cofactors in biogeochemically significant processes like photosynthesis, respiration, and nitrate assimilation. Further, hemoproteins, hemes, and their analogs appear to be iron sources for some marine bacterioplankton under certain conditions. Current oceanographic analytical methodologies allow for the extraction and measurement of heme b from marine material, and a handful of studies have begun to examine the distribution of heme b in ocean basins. The study of heme in the marine environment is still in its infancy, but some trends can be gleaned from the work that has been published so far. In this review, we summarize what is known or might be inferred about the roles of heme in marine microbes as well as the few studies on heme in the marine environment that have been conducted to date. We conclude by presenting some future questions and challenges for the field.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1039/c4mt00031e
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Characterization of low molecular weight dissolved organic nitrogen by liquid chromatography-electrospray ionization-mass spectrometry (2009)
    American Society of Limnology and Oceanography
    In:  Limnology and Oceanography: Methods, 7 (1). pp. 52-63.
    Details
    Publication Date: 2017-10-24
    Description: Low molecular weight (LMW; 〈1 kDa) dissolved organic nitrogen ( DON) is the dominant DON fraction in marine systems. However, existing methods for DON characterization exclude this fraction through size exclusion or destruction during sample hydrolysis. In this study, we developed a method for the extraction and analysis of LMW peptides in saline waters. The procedure involves a solid phase extraction (SPE) preconcentration step using a polystyrene-divinylbenzene sorbent, then elution and detection by liquid chromatography-electrospray ionization-mass spectrometry (LC/ESI/MS). The procedure was tested with 1-L water samples containing peptides (10 ng L(-1)) ranging from 188.2-1946.0 Da. The analytes were characterized using "top-down" sequencing to confirm their structure, and the method was then successfully applied to saline water samples extracted from a mono-algal culture of Phaeodactylum tricornutum. This enabled a number of unknown analytes to be partially sequenced (complete sequencing should be possible using additional MS(n) scans and larger sample volumes). The method allows for the detection of peptides at the ng L(-1) level and further preconcentration is possible. The SPE step allowed determination of peptides from saline water, a matrix incompatible with direct LC/MS analysis. The method can, therefore, be used in DON characterization studies.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.4319/lom.2009.7.52
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Electrospray ionisation-mass spectrometry of hydroxamate siderophores (2001)
    Royal Society of Chemistry
    In:  Analyst, 126 (8). pp. 1359-1362.
    Details
    Publication Date: 2017-05-30
    Description: Electrospray ionisation-mass spectrometry (ESI-MS) was applied to the detection of the iron complexes of the hydroxamate type siderophores ferrioxamine (FO), ferrichrome (FC) and iron(iii) rhodotoluate (FR). Mass spectra of the three siderophores produced by ESI-MS were dominated by the protonated (M + 1)(+) parent ions, except for FR at pH 4.3, which was present as the positively charged 1: 1 complex. On collision with He ions, fragmentation proceeded largely via cleavage of C-N bonds. Flow injection analysis of the siderophores with detection by ESI-MS produced detection limits of 1.9 fmol for FO, 31.1 fmol for FC and 524 fmol for FR.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1039/b101268l
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Metal ion-binding properties of phytochelatins and related ligands (2009)
    Royal Society of Chemistry
    In:  In: Metallothioneins and Related Chelators. , ed. by Sigel, A., Sigel, H. and Sigel, R. K. O. Royal Society of Chemistry, Cambridge, UK, pp. 441-482. ISBN 978-1-84755-899-2
    Details
    Publication Date: 2017-10-24
    Type: Book chapter , NonPeerReviewed
    DOI: 10.1039/9781847559531
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    OceanRep: Book chapter
  • 6
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    Heme b distributions through the Atlantic Ocean: evidence for “anemic” phytoplankton populations (2020)
    Nature Research
    Details
    Publication Date: 2023-02-08
    Description: Heme b is an iron-containing cofactor in hemoproteins that participates in the fundamental processes of photosynthesis and respiration in phytoplankton. Heme b concentrations typically decline in waters with low iron concentrations but due to lack of field data, the distribution of heme b in particulate material in the ocean is poorly constrained. Here we report particulate heme b distributions across the Atlantic Ocean (59.9°N to 34.6°S). Heme b concentrations in surface waters ranged from 0.10 to 33.7 pmol L−1 (median = 1.47 pmol L−1, n = 974) and were highest in regions with a high biomass. The ratio of heme b to particulate organic carbon (POC) exhibited a mean value of 0.44 μmol heme b mol−1 POC. We identified the ratio of 0.10 µmol heme b mol−1 POC as the cut-off between heme b replete and heme b deficient (anemic) phytoplankton. By this definition, we observed anemic phytoplankton populations in the Subtropical South Atlantic and Irminger Basin. Comparison of observed and modelled heme b suggested that heme b could account for between 0.17–9.1% of biogenic iron. Our large scale observations of heme b relative to organic matter provide further evidence of the impact of changes in iron supply on phytoplankton iron status across the Atlantic Ocean.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Colonies of marine cyanobacteria Trichodesmium interact with associated bacteria to acquire iron from dust (2019)
    Nature Research
    In:  Communications Biology, 2 (Article number: 284).
    Details
    Publication Date: 2022-01-31
    Description: Iron (Fe) bioavailability limits phytoplankton growth in vast ocean regions. Iron-rich dust uplifted from deserts is transported in the atmosphere and deposited on the ocean surface. However, this dust is a poor source of iron for most phytoplankton since dust-bound Fe is poorly soluble in seawater and dust rapidly sinks out of the photic zone. An exception is Trichodesmium, a globally important, N2 fixing, colony forming, cyanobacterium, which efficiently captures and shuffles dust to its colony core. Trichodesmium and bacteria that reside within its colonies carry out diverse metabolic interactions. Here we show evidence for mutualistic interactions between Trichodesmium and associated bacteria for utilization of iron from dust, where bacteria promote dust dissolution by producing Fe-complexing molecules (siderophores) and Trichodesmium provides dust and optimal physical settings for dissolution and uptake. Our results demonstrate how intricate relationships between producers and consumers can influence productivity in the nutrient starved open ocean.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1038/s42003-019-0534-z
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Metallophores associated with Trichodesmium erythraeum colonies from the Gulf of Aqaba (2019)
    Royal Society of Chemistry
    Details
    Publication Date: 2022-08-09
    Description: Trichodesmium is a globally important marine nitrogen fixing cyanobacteria which forms colonies and utilizes atmospherically derived dust as a source for the limiting micro-nutrient iron. Here we report the identification of metallophores isolated from incubations of natural Trichodesmium colonies collected from the Gulf of Aqaba in the Red Sea. Three of our compounds were identified as the ferrioxamine siderophores B, E, and G. The remaining fifteen metallophores had mass to charge ratios that, to our knowledge, are not common to known siderophores. Putative sum formulas suggest most of these compounds were not structurally related to each other. We also found that the novel metallophores readily formed complexes with aluminium and were less specific for Fe than the ferrioxamines. In our incubations of Trichodesmium colonies, the abundance of ten of the novel metallophores positively correlated with Trichodesmium biomass, but not with bacterial biomass, whilst ferrioxamine siderophores were more strongly associated with bacterial biomass. We identified ferrioxamines and our novel metallophores in filtered surface seawater samples from the Gulf of Aqaba. However, our novel metallophores were only observed in the surface seawater sample collected at the time of highest Trichodesmium abundance, while ferrioxamines were observed even when Trichodesmium was not present. We hypothesize that the novel metallophores were specifically associated with Trichodesmium colonies. Together with the bacterially produced ferrioxamines they likely contribute to a distinctive “ligandosphere” surrounding the Trichodesmium colonies, with potential implications for metal homeostasis within the colony environment.
    Type: Article , PeerReviewed
    Format: text
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  • 9
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    Phycosphere pH of unicellular nano- and micro- phytoplankton cells and consequences for iron speciation (2022)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: Surface ocean pH is declining due to anthropogenic atmospheric CO2 uptake with a global decline of ~0.3 possible by 2100. Extracellular pH influences a range of biological processes, including nutrient uptake, calcification and silicification. However, there are poor constraints on how pH levels in the extracellular microenvironment surrounding phytoplankton cells (the phycosphere) differ from bulk seawater. This adds uncertainty to biological impacts of environmental change. Furthermore, previous modelling work suggests that phycosphere pH of small cells is close to bulk seawater, and this has not been experimentally verified. Here we observe under 140 μmol photons·m−2·s−1 the phycosphere pH of Chlamydomonas concordia (5 µm diameter), Emiliania huxleyi (5 µm), Coscinodiscus radiatus (50 µm) and C. wailesii (100 µm) are 0.11 ± 0.07, 0.20 ± 0.09, 0.41 ± 0.04 and 0.15 ± 0.20 (mean ± SD) higher than bulk seawater (pH 8.00), respectively. Thickness of the pH boundary layer of C. wailesii increases from 18 ± 4 to 122 ± 17 µm when bulk seawater pH decreases from 8.00 to 7.78. Phycosphere pH is regulated by photosynthesis and extracellular enzymatic transformation of bicarbonate, as well as being influenced by light intensity and seawater pH and buffering capacity. The pH change alters Fe speciation in the phycosphere, and hence Fe availability to phytoplankton is likely better predicted by the phycosphere, rather than bulk seawater. Overall, the precise quantification of chemical conditions in the phycosphere is crucial for assessing the sensitivity of marine phytoplankton to ongoing ocean acidification and Fe limitation in surface oceans.
    Type: Article , PeerReviewed
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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