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      Surface-bound iron: a metal ion buffer in the marine brown alga Ectocarpus siliculosus?

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          Abstract

          Although the iron uptake and storage mechanisms of terrestrial/higher plants have been well studied, the corresponding systems in marine algae have received far less attention. Studies have shown that while some species of unicellular algae utilize unique mechanisms of iron uptake, many acquire iron through the same general mechanisms as higher plants. In contrast, the iron acquisition strategies of the multicellular macroalgae remain largely unknown. This is especially surprising since many of these organisms represent important ecological and evolutionary niches in the coastal marine environment. It has been well established in both laboratory and environmentally derived samples, that a large amount of iron can be ‘non-specifically’ adsorbed to the surface of marine algae. While this phenomenon is widely recognized and has prompted the development of experimental protocols to eliminate its contribution to iron uptake studies, its potential biological significance as a concentrated iron source for marine algae is only now being recognized. This study used an interdisciplinary array of techniques to explore the nature of the extensive and powerful iron binding on the surface of both laboratory and environmental samples of the marine brown alga Ectocarpus siliculosus and shows that some of this surface-bound iron is eventually internalized. It is proposed that the surface-binding properties of E. siliculosus allow it to function as a quasibiological metal ion ‘buffer’, allowing iron uptake under the widely varying external iron concentrations found in coastal marine environments.

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          Most cited references 15

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          ATHENA, ARTEMIS, HEPHAESTUS: data analysis for X-ray absorption spectroscopy using IFEFFIT.

           B Ravel,  M Newville (2005)
          A software package for the analysis of X-ray absorption spectroscopy (XAS) data is presented. This package is based on the IFEFFIT library of numerical and XAS algorithms and is written in the Perl programming language using the Perl/Tk graphics toolkit. The programs described here are: (i) ATHENA, a program for XAS data processing, (ii) ARTEMIS, a program for EXAFS data analysis using theoretical standards from FEFF and (iii) HEPHAESTUS, a collection of beamline utilities based on tables of atomic absorption data. These programs enable high-quality data analysis that is accessible to novices while still powerful enough to meet the demands of an expert practitioner. The programs run on all major computer platforms and are freely available under the terms of a free software license.
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            The Ectocarpus genome and the independent evolution of multicellularity in brown algae.

            Brown algae (Phaeophyceae) are complex photosynthetic organisms with a very different evolutionary history to green plants, to which they are only distantly related. These seaweeds are the dominant species in rocky coastal ecosystems and they exhibit many interesting adaptations to these, often harsh, environments. Brown algae are also one of only a small number of eukaryotic lineages that have evolved complex multicellularity (Fig. 1). We report the 214 million base pair (Mbp) genome sequence of the filamentous seaweed Ectocarpus siliculosus (Dillwyn) Lyngbye, a model organism for brown algae, closely related to the kelps (Fig. 1). Genome features such as the presence of an extended set of light-harvesting and pigment biosynthesis genes and new metabolic processes such as halide metabolism help explain the ability of this organism to cope with the highly variable tidal environment. The evolution of multicellularity in this lineage is correlated with the presence of a rich array of signal transduction genes. Of particular interest is the presence of a family of receptor kinases, as the independent evolution of related molecules has been linked with the emergence of multicellularity in both the animal and green plant lineages. The Ectocarpus genome sequence represents an important step towards developing this organism as a model species, providing the possibility to combine genomic and genetic approaches to explore these and other aspects of brown algal biology further.
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              A review of the biochemistry of heavy metal biosorption by brown algae.

              The passive removal of toxic heavy metals such as Cd(2+), Cu(2+), Zn(2+), Pb(2+), Cr(3+), and Hg(2+) by inexpensive biomaterials, termed biosorption, requires that the substrate displays high metal uptake and selectivity, as well as suitable mechanical properties for applied remediation scenarios. In recent years, many low-cost sorbents have been investigated, but the brown algae have since proven to be the most effective and promising substrates. It is their basic biochemical constitution that is responsible for this enhanced performance among biomaterials. More specifically, it is the properties of cell wall constituents, such as alginate and fucoidan, which are chiefly responsible for heavy metal chelation. In this comprehensive review, the emphasis is on outlining the biochemical properties of the brown algae that set them apart from other algal biosorbents. A detailed description of the macromolecular conformation of the alginate biopolymer is offered in order to explain the heavy metal selectivity displayed by the brown algae. The role of cellular structure, storage polysaccharides, cell wall and extracellular polysaccharides is evaluated in terms of their potential for metal sequestration. Binding mechanisms are discussed, including the key functional groups involved and the ion-exchange process. Quantification of metal-biomass interactions is fundamental to the evaluation of potential implementation strategies, hence sorption isotherms, ion-exchange constants, as well as models used to characterize algal biosorption are reviewed. The sorption behavior (i.e., capacity, affinity) of brown algae with various heavy metals is summarized and their relative performance is evaluated.
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                Author and article information

                Journal
                J Exp Bot
                J. Exp. Bot
                jexbot
                jexbot
                Journal of Experimental Botany
                Oxford University Press (UK )
                0022-0957
                1460-2431
                February 2014
                24 December 2013
                24 December 2013
                : 65
                : 2
                : 585-594
                Affiliations
                1Department of Chemistry and Biochemistry, San Diego State University , San Diego, CA 92182-1030, USA
                2Section Natural Sciences, Isotopes Laboratory, University of Lübeck , Ratzeburger Allee 160, D-23538 Lübeck, Germany
                3Department of Chemistry, Duke University , Durham, 27708-0346, NC, USA
                4European Molecular Biology Laboratory (EMBL), Hamburg Unit, c/o DESY , Notkestrasse 85, D-22607 Hamburg, Germany
                5Oceanlab, University of Aberdeen , Main Street, Newburgh AB41 6AA, Scotland, UK
                * Present address: Department of Chemistry, Stanford University , Stanford, CA 94305-5080, USA.
                Author notes
                To whom correspondence should be addressed. E-mail: carrano@ 123456sciences.sdsu.edu
                Article
                10.1093/jxb/ert406
                3904714
                © The Author 2013. Published by Oxford University Press on behalf of the Society for Experimental Biology.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/3.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

                Page count
                Pages: 10
                Categories
                Research Paper

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