A comparison of Fe bioavailability and binding of a catecholate siderophore with virus-mediated lysates from the marine bacterium Vibrio alginolyticus PWH3a

We have examined the bioavailability of Fe complexed to a siderophore produced by the heterotrophic marine bacterium Vibrio alginolyticus isolate PWH3a and Fe from ligand-complexes present in virus-mediated lysates (using phage PWH3a-P1) of this same bacterium. Fe-binding functional groups, stability constants and the bioavailability of Fe associated with these two separate ligand pools were determined and contrasted to previous work. Under low-Fe growth conditions, axenic cultures of V. alginolyticus PWH3a were shown to produce catecholate siderophores, while neither catecholate nor hydroxamate-type Fe-binding moieties were detected in virus-generated cell lysates. Analysis of the overall binding strength using electrochemical techniques revealed that the siderophore-containing organic extract and the organics in the virus-mediated lysates had Fe-binding constants comparable to the weaker L 2-type ligands found throughout the water column in seawater. A further purification of the siderophore-containing extract revealed a ligand with a stability constant of logK′ FeL,Fe3+ = 22.3, typical for siderophores and L 1-type of ligands found in marine surface waters. In assimilation studies, the Fe in the lysate was found to be more bioavailable to our model heterotrophic bacterium, autotrophic cyanobacterium and eukaryotic diatom cultures than the catecholate siderophore produced by the Vibrio sp. This work demonstrates that the Fe-containing components of virus-mediated cell lysates are different than siderophores secreted by these same cells, and as such continues to build the argument supporting the importance of virus-mediated Fe regeneration in marine surface waters. ► Studies on virus-mediated cell lysates show no siderophores are present. ► A catecholate siderophore was isolated from Vibrio alginolyticus. ► Voltammetry suggests the siderophore was consistent with typical L1 Fe-binding ligands. ► Materials in cell lysates were consistent with L2 Fe-binding ligands. ► Fe in lysates was more rapidly assimilated than Fe bound to the siderophore.