Effect of Light on Iron Uptake by the Freshwater Cyanobacterium Microcystis aeruginosa

Abstract

Visible light was observed to induce reductive dissociation of organically complexed Fe and dramatically increase the short-term uptake rate of radiolabeled Fe by Microcystis aeruginosa PCC7806 in Fraquil* medium buffered by a single metal chelator, ethylenediaminetetraacetic acid (EDTA). Only wavelengths <500 nm activated Fe uptake indicating that Fe photochemistry rather than biological factors is responsible for the facilitated uptake. The measured rate of photochemical Fe(II) production combined with a significant decrease in (55)Fe uptake rate in the presence of ferrozine (a strong ferrous iron chelator) confirmed that photogenerated unchelated Fe(II) was the major form of Fe taken up by M. aeruginosa under the conditions examined. Mathematical modeling based on unchelated Fe(II) uptake by concentration gradient dependent passive diffusion of Fe(II) through nonspecific transmembrane channels (porins) could account for the magnitude of Fe uptake and a variety of other observations such as the effect of competing ligands on Fe uptake. Steady-state uptake rates indicated that M. aeruginosa acquires Fe predominantly during the light cycle. This study confirms that Fe photochemistry has a dominant impact on Fe acquisition and growth by M. aeruginosa in EDTA-buffered culture medium.

Variation of iron redox kinetics and its relation with molecular composition of standard humic substances at circumneutral pH

“…A 0.1 M ferrozine (Fz) solution was prepared by dissolving ferrozine (3-(2-pyridyl)-5,6-bis(4-phenylsulfonicacid)-1,2,4-triazine, Sigma Aldrich) in purified water followed by the pH adjustment to 7.0 ± 0.05 and 8.0 ± 0.05. Ferrozine has been employed for the measurement of photochemical and non-photochemical reduction of iron in natural waters by a number of previous studies in the last few decades [42–45]. A buffer solution containing 10 mM sodium chloride (reagent grade, Kanto Chemical) and 2 mM sodium bicarbonate (reagent grade, Kanto Chemical) was prepared at pH 7.0 ± 0.05 and 8.0 ± 0.05.…”

Importance of Iron Complexation for Fenton-Mediated Hydroxyl Radical Production at Circumneutral pH

“…[f] Taken from Fujii et al (2011). [g] Complexation not explicitly modeled as experimentally shown to be rapid.…”

The Influence of Extracellular Superoxide on Iron Redox Chemistry and Bioavailability to Aquatic Microorganisms

“…Biological production of ${\text{O}}_2^{-*}$ in the extracellular milieu has been reported from culture studies involving a wide range of environmentally occurring aquatic microorganisms, including eukaryotic microalgae from the class Raphidophyceae (Oda et al, 1997; Marshall et al, 2002, 2005; Yamasaki et al, 2004; Garg et al, 2007a); dinoflagellates and prymnesiophytes (Yamasaki et al, 2004; Marshall et al, 2005); marine diatoms from the genus Thalassiosira (Kustka et al, 2005); marine cyanobacteria from the genera Synechococcus (Rose et al, 2008b), Lyngbya (Rose et al, 2005) and Trichodesmium (Godrant et al, 2009); a marine alphaproteobacterium from the genus Roseobacter (Learman et al, 2011); the freshwater cyanobacterium Microcystis aeruginosa (Fujii et al, 2011); the unicellular protozoan coral symbiont Symbiodinium (Saragosti et al, 2010); fungi and yeasts including Aspergillus nidulans (Lara-Ortíz et al, 2003) and Saccharomyces cerevisiae (Shatwell et al, 1996), as reviewed by Aguirre et al (2005); and the heterotrophic bacteria Paracoccus denitrificans (Henry and Vignais, 1980) and Escherichia coli (Korshunov and Imlay, 2006). Rates of ESP vary enormously between these different organisms, with the maximum reported rates being from the marine Raphidophycean Chattonella marina of up to ∼5 pmol cell −1  h −1 (Oda et al, 1997; Garg et al, 2007a).…”

“… a Calculated at I  = 0.1 M, ignoring formation of any other complexes using stability constants from Farkas et al (2003) . b Calculated as log K  =  p /( p −  1)[L] T where [L] T is total ligand concentration and p is proportion complexed as reported in Table 2 of Hudson et al (1992) . c Measured value at pH 8.1 reported by Witter et al (2000) . d Calculated from complex formation and dissociation rate constants measured by Fujii et al (2011) . e Calculated from complex formation and dissociation rate constants measured by Fujii et al (2010a) . f Measured value at pH 7.98 reported by Sunda and Huntsman (2003) . g Calculated from complex formation and dissociation rate constants measured by Rose and Waite (2003b) . h Calculated from complex formation and dissociation rate constants measured by Fujii et al (2010a) for a citrate concentration of 100 μM (the apparent conditional stability constant varies with ligand concentration due to the existence of multiple complex species) .…”