Characterization of phytoplankton exudates and carbohydrates in relation to their complexation of copper, cadmium and iron

Abstract

The goal of this study was to investigate if transparent exopolymer particles (TEP), carbohydrates, surface-active substances (SAS), reduced sulfur species (RSS), or thio/amino groups contribute significantly to the complexing capacity of phytoplankton exudates for Cu (L TOTCu ), Cd (L TOTCd ), or Fe (L TOTFe ). Complexing capacities and apparent stability constants (K app ) were determined electrochemically for Cu and Cd in cultures of the marine diatoms Thalassiosira weissflogii and Skeletonema costatum, and in a culture of the coccolithophore Emiliana huxleyi. Furthermore, the complexing capacity with Fe, Cu and Cd of 4 marine polysaccharides (PS) (phytagel, carrageenan, laminarin and alginic acid) was investigated. As expected, more Cu than Cd was complexed in the 3 phytoplankton cultures and in the phytagel solution. Size fractionation of the phytagel solution suggests that the binding capacity for Cu was more significant in the particulate fraction (> 0.7 µm), indicating that Cu was preferably trapped within pores and channels of large hydrogels. In contrast, Cd binding sites were predominantly found in the fraction < 0.7 µm, suggesting binding to the outer surfaces of gel particles to be of greater importance for larger ions. The K app of the Cd complexes were higher than those of Cu, indicating stronger binding of Cd ions than of Cu ions. Solutions of carrageenan, laminarin and alginic acid did not form complexes with either Cu or Cd, and Febinding properties could not be detected for any of the 4 polysaccharide solutions. Thio/amino groups of sulfur-rich 'glutathione' type ligands were found in all phytoplankton cultures and were presumably responsible for the complexation of Cu. No consistent relationship was observed between TEP, carbohydrate concentration, SAS or sulfur content, or with the complexing capacity, emphasizing the high degree of heterogeneity of substance classes responsible for metal binding.

Disassembling Iron Availability to Phytoplankton

“… dFe, dissolved iron; cFe, colloidal iron; pFe, particulate Fe . References: a. Sandy and Butler (2009), b. Vraspir and Butler (2009), c. Holmén and Casey (1996), d. Martinez et al (2000), e. Kraemer et al (2005), f. Barbeau et al (2003), g. Hassler et al (2011a), h. Hassler and Schoemann (2009), i. Steigenberger et al (2010), j. Passow (2002), k. Strmecki et al (2010), l. Berman-Frank et al (2007), m. Decho (1990) .…”

Cadmium Accumulation by Plants of Brassicaceae Family and Its Connection with Their Primary and Secondary Metabolism

“…Cadmium performs the same function as zinc in this enzyme. It seems that cadmium is involved in function of this enzyme instead zinc ions, which may be replaced by cadmium ions Strmecki et al 2010). Cadmium is one of the most important contaminants of the environment.…”

Effect of Organic Fe-Ligands, Released by Emiliania huxleyi, on Fe(II) Oxidation Rate in Seawater Under Simulated Ocean Acidification Conditions: A Modeling Approach

“…Although exudates from bacteria and phytoplankton are not well characterized, sources of these biologically-mediated weak ligands include mainly exo-polymeric substances (EPS), since they form a major biological component of the total dissolved organic carbon (DOC) pool (Pakulski and Benner, 1994). EPS are polymers of high molecular weight mostly comprised of amino acids and saccharides (Strmečki et al, 2010;Decho and Gutierrez, 2017). As a functional group of some peptides, thiol moieties play an important role in controlling the speciation of some trace metals (Vasconcelos et al, 2002).…”