Publications

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2012
Roe, KL, Barbeau K, Mann EL, Haygood MG.  2012.  Acquisition of iron by Trichodesmium and associated bacteria in culture. Environmental Microbiology. 14:1681-1695.   10.1111/j.1462-2920.2011.02653.x   AbstractWebsite

Trichodesmium colonies contain an abundant microbial consortium that is likely to play a role in nutrient cycling within the colony. This study used laboratory cultures of Trichodesmium and two genome-sequenced strains of bacteria typical of Trichodesmium-associated microbes to develop an understanding of the cycling of iron, a potentially limiting micronutrient, within Trichodesmium colonies. We found that the ferric siderophores desferrioxamine B and aerobactin were not readily bioavailable to Trichodesmium, relative to ferric chloride or citrate-associated iron. In contrast, the representative bacterial strains we studied were able to acquire iron from all of the iron sources, implying that naturally occurring Trichodesmium-associated bacteria may be capable of utilizing a more diverse array of iron sources than Trichodesmium. From the organism-specific uptake data collected in this study, a theoretical Trichodesmium colony was designed to model whole colony iron uptake. The bacteria accounted for most (> 70%) of the iron acquired by the colony, highlighting the importance of determining organism-specific uptake in a complex environment. Our findings suggest that, although they may share the same micro-environment, Trichodesmium and its colony-associated microbial cohort may differ substantially in terms of iron acquisition strategy.

2015
Semeniuk, DM, Bundy RM, Payne CD, Barbeau KA, Maldonado MT.  2015.  Acquisition of organically complexed copper by marine phytoplankton and bacteria in the northeast subarctic Pacific Ocean. Marine Chemistry. 173:222-233.   10.1016/j.marchem.2015.01.005   AbstractWebsite

Copper (Cu) is an essential micronutrient for marine phytoplankton, but can cause toxicity at elevated intracellular concentrations. The majority of Cu (>99.9%) in oceanic surface waters is bound to strong organic ligands, presumably produced by prokaryotes to detoxify Cu. Although laboratory studies have demonstrated that organically complexed Cu may be bioavailable to marine eukaryotic phytoplankton, the bioavailability of Cu organic complexes to indigenous marine phytoplankton has not been examined in detail. Using the carrier free radioisotope Cu-67 at an iron limited station in the northeast subarctic Pacific Ocean, we performed size fractionated short-term Cu uptake assays with three Cu(II)-chelates, and Cu-67 bound to the strong in situ ligands, with or without additions of weak Cu(I) ligands. Estimates of the maximum supply of inorganic Cu (Cu') to the cell surface of eukaryotic phytoplankton were unable to account for the observed Cu uptake rates from the in situ ligands and two of the three added Cu(II)-chelates. Addition of 10 nM weak organic Cu(I) ligands enhanced uptake of Cu bound to the in situ ligands. Thus, Cu within the in situ and strong artificial Cu(II) organic ligands was accessible to the phytoplankton community via various possible Cu uptake strategies, including; cell surface enzymatically mediated reduction of Cu(II) to Cu(I), the substrate of the high-affinity Cu transport system in eukaryotes; or ligand exchange between weak Cu-binding ligands and the cellular Cu transporters. During a 14-hour uptake assay, particulate Cu concentrations reached a plateau in most treatments. Losses were observed in some treatments, especially in the small size fractions (<5 mu m), corresponding with faster initial Cu uptake rates. This may indicate that Cu cycling is rapid between particulate and dissolved phases due to cellular efflux or remineralization by micrograzers. The acquisition of Cu from the strong in situ ligands puts into question the historic role attributed to Cu binding ligands in decreasing Cu bioavailability. (C) 2015 Elsevier B.V. All rights reserved.