Received: 07 Apr 2017 – Discussion started: 19 May 2017
Abstract. A luminol chemiluminescence method was employed to study the oxidation kinetics of Fe(II) in both the absence and the presence of organic exudates released by the marine cyanobacterium Trichodesmium erythraeum. The apparent Fe(II) oxidation rate constant was studied for batch cultures grown with varying Fe' concentrations of 0.05–0.29 and 1.44–2.03 nmol L−1 at pH ranges from 8.1–8.6, corresponding to the change in pH in the cultures during the entire growth cycle. Fe(II) oxidation was accelerated when cells were growing exponentially and gradually decreased towards the stationary phase, consistent with the presence of organic exudates. The best fit of the kinetic model to the data also demonstrated clear differences in apparent Fe(II) oxidation rate constants during different growth phases. However, no significant difference was observed in oxidation rate constants between the two Fe' treatments. These findings suggest that Trichodesmium releases organic compounds into the extracellular environment that influence Fe redox chemistry, potentially affecting Fe bioavailability, and that the nature of the Fe(II) complexes formed is not influenced by Fe limitation of the organism's growth.
How to cite. Farid, H. T., Schulz, K. G., and Rose, A. L.: Organic exudates promote Fe(II) oxidation in Fe limited cultures of Trichodesmium erythraeum, Biogeosciences Discuss. [preprint], https://doi.org/10.5194/bg-2017-129, 2017.
This study provides new insights into: (a) how organic exudates from a marine cyanobacterium may influence iron speciation and bioavailability in the extracellular milieu; and (b) approaches for evaluating rate constants for Fe(II) oxidation in the presence of unknown organic ligands. Given that microorganisms play critical roles in biochemical cycling of trace metals in water systems, the findings are expected to improve nutrient uptake models and be of interest to broad range of readers.
This study provides new insights into: (a) how organic exudates from a marine cyanobacterium may...