Characterization of marine exopolymeric substance (EPS) responsible for binding of thorium (IV) isotopes

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Title: Characterization of marine exopolymeric substance (EPS) responsible for binding of thorium (IV) isotopes
Author: Alvarado Quiroz, Nicolas Gabriel
Abstract: The functional group composition of acid polysaccharides was determined after isolation using cross -flow ultrafiltration , radiolabeling with 234Th (IV ) and other isotopes , and separation using isoelectric focusing (IEF ) and polyacrylamide gel electrophoresis (PAGE ) . Phosphate and sulphate concentrations were determined from cultured bacterial and phytoplankton colloid , particulate and colloidal samples collected from the Gulf of M ? ?xico (GOM ) . Characterization of the 234Th (IV ) -binding biomolecule was performed using ion chromatography (IC ) , and gas chromatography -mass spectrometry (GC -MS ) . Radiotracer experiments and culture experiments were conducted in determining the binding environment of the 234Th (IV ) -binding ligand (i .e . , sorption onto suspended particles ) , as well as the origin of the ligand in seawater systems . In all samples , 234Th (IV ) isoelectric focusing profiles indicated that 49 % to 65 % of the 234Th (IV ) labeled EPS from Roseobacter gallaeciensis , Sagittula stellata , Emiliania huxleyi , Synechococcus elongatus and GOM Station 4 -72m was found at a pHIEF of 2 in the IEF spectrum . The carboxylic acid group appeared at the same pHIEF as 234Th (IV ) for EPS from Roseobacter gallaeciensis , Emiliania huxleyi , Synechococcus elongatus and GOM colloidal organic matter sample . The phosphate group appeared at the same pHIEF as 234Th (IV ) for EPS from Roseobacter gallaeciensis , and Synechococcus elongatus sample . The sulphate group was found at the same pHIEF as 234Th (IV ) for EPS from S . elongatus and GOM colloidal organic matter sample . The total polysaccharide content was only 14 % and 8 % , uronic acids were approximately 5 .4 % and 87 .1 % , and total protein content was 2 .6 % and 6 .2 % of total carbon content of Sagittula stellata and Synechococcus elongatus , respectively . Monosaccharides identified in both Sagittula stellata and Synechococcus elongatus were galactose , glucose , and xylose in common . In addition , Sagittula stellata contained mannose and Synechococcus elongatus had galactoglucuronic acid . Thus , depending on the species , the size , structural composition , and functional groups of the 234Th (IV ) -binding , acidic polysaccharides will vary . From these observations , it is concluded that the steric environment and not necessarily the exact functional group might actually be responsible for thorium -234 complexation to macromolecular organic matter . This research helped to improve our understanding of the observed variability in POC /234Th ratios in the ocean and provided insights into factors that regulate organic carbon export fluxes .
URI: http : / /hdl .handle .net /1969 .1 /2250
Date: 2005-08-29

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Characterization of marine exopolymeric substance (EPS) responsible for binding of thorium (IV) isotopes. Available electronically from http : / /hdl .handle .net /1969 .1 /2250 .

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