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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.

2013
Hopkinson, BM, Seegers B, Hatta M, Measures CI, Mitchell BG, Barbeau KA.  2013.  Planktonic C:Fe ratios and carrying capacity in the southern Drake Passage. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 90:102-111.   10.1016/j.dsr2.2012.09.001   AbstractWebsite

The carbon to iron (C:Fe) ratio of planktonic biomass constrains net production in iron-limited regions of the ocean and is an important parameter for predicting biomass production from iron inputs. On a cruise to the southern Drake Passage in July-August 2006, we used two approaches to determine the C:Fe ratio of planktonic material: dual-radiotracer labeling and net biomass production in iron-limited grow-out experiments. There was variability in C:Fe ratios among experiments, but values from the two methods overlapped with average values of 1.4 x 10(5) (mol:mol) for the radiotracer method and 1.7 x 10(5) for the net biomass production method. This is notable since the net biomass production method is a new approach to determine C:Fe ratios. Although it has potential issues related to bottle effects and sensitivity to trace contamination, the method avoids some of the questions associated with iron speciation and bioavailability since ambient iron supports production. Because light intensity is known to affect C:Fe ratios in phytoplankton through photosynthetic iron demands, we tested the effect of light level on C:Fe in Antarctic assemblages. In contrast to what is seen in many phytoplankton cultures, C:Fe ratios increased at low-light, but we suspect that this is due to initial photoinhibition of the low-light adapted winter assemblages at higher light levels. (c) 2012 Elsevier Ltd. All rights reserved.