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Stuart, RK, Bundy R, Buck K, Ghassemain M, Barbeau K, Palenik B.  2017.  Copper toxicity response influences mesotrophic Synechococcus community structure. Environmental Microbiology. 19:756-769.   10.1111/1462-2920.13630   AbstractWebsite

Picocyanobacteria from the genus Synechococcus are ubiquitous in ocean waters. Their phylogenetic and genomic diversity suggests ecological niche differentiation, but the selective forces influencing this are not well defined. Marine picocyanobacteria are sensitive to Cu toxicity, so adaptations to this stress could represent a selective force within, and between, species', also known as clades. Here, we compared Cu stress responses in cultures and natural populations of marine Synechococcus from two co-occurring major mesotrophic clades (I and IV). Using custom microarrays and proteomics to characterize expression responses to Cu in the lab and field, we found evidence for a general stress regulon in marine Synechococcus. However, the two clades also exhibited distinct responses to copper. The Clade I representative induced expression of genomic island genes in cultures and Southern California Bight populations, while the Clade IV representative downregulated Fe-limitation proteins. Copper incubation experiments suggest that Clade IV populations may harbour stress-tolerant subgroups, and thus fitness tradeoffs may govern Cu-tolerant strain distributions. This work demonstrates that Synechococcus has distinct adaptive strategies to deal with Cu toxicity at both the clade and subclade level, implying that metal toxicity and stress response adaptations represent an important selective force for influencing diversity within marine Synechococcus populations.

Stukel, MR, Aluwihare LI, Barbeau KA, Chekalyuk AM, Goericke R, Miller AJ, Ohman MD, Ruacho A, Song H, Stephens BM, Landry MR.  2017.  Mesoscale ocean fronts enhance carbon export due to gravitational sinking and subduction. Proceedings of the National Academy of Sciences of the United States of America. 114:1252-1257.   10.1073/pnas.1609435114   AbstractWebsite

Enhanced vertical carbon transport (gravitational sinking and subduction) at mesoscale ocean fronts may explain the demonstrated imbalance of new production and sinking particle export in coastal upwelling ecosystems. Based on flux assessments from U-238:Th-234 disequilibrium and sediment traps, we found 2 to 3 times higher rates of gravitational particle export near a deep-water front (305 mg C.m(-2).d(-1)) compared with adjacent water or to mean (nonfrontal) regional conditions. Elevated particle flux at the front wasmechanistically linked to Fe-stressed diatoms and high-mesozooplankton fecal pellet production. Using a data assimilative regional ocean model fit to measured conditions, we estimate that an additional similar to 225 mg C.m(-2).d(-1) was exported as subduction of particle-rich water at the front, highlighting a transport mechanism that is not captured by sediment traps and is poorly quantified by most models and in situ measurements. Mesoscale fronts may be responsible for over a quarter of total organic carbon sequestration in the California Current and other coastal upwelling ecosystems.

Fitzsimmons, JN, Bundy RM, Al-Subiai SN, Barbeau KA, Boyle EA.  2015.  The composition of dissolved iron in the dusty surface ocean: An exploration using size-fractionated iron-binding ligands. Marine Chemistry. 173:125-135.   10.1016/j.marchem.2014.09.002   AbstractWebsite

The size partitioning of dissolved iron and organic iron-binding ligands into soluble and colloidal phases was investigated in the upper 150 m of two stations along the GA03 U.S. GEOTRACES North Atlantic transect. The size fractionation was completed using cross-flow filtration methods, followed by analysis by isotope dilution inductively-coupled plasma mass spectrometry (ID-ICP-MS) for iron and competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV) for iron-binding ligands. On average, 80% of the 0.1-0.65 nM dissolved iron (<0.2 mu m) was partitioned into the colloidal iron (cFe) size fraction (10 kDa < cFe <0.2 gm), as expected for areas of the ocean underlying a dust plume. The 1.3-2.0 nM strong organic iron-binding ligands, however, overwhelmingly (75-77%) fell into the soluble size fraction (<10 kDa). As a result, modeling the dissolved iron size fractionation at equilibrium using the observed ligand partitioning did not accurately predict the iron partitioning into colloidal and soluble pools. This suggests that either a portion of colloidal ligands is missed by current electrochemical methods because they react with iron more slowly than the equilibration time of our CLE-ACSV method, or part of the observed colloidal iron is actually inorganic in composition and thus cannot be predicted by our model of unbound iron-binding ligands. This potentially contradicts the prevailing view that greater than >99% of dissolved iron in the ocean is organically complexed. Disentangling the chemical form of iron in the upper ocean has important implications for surface ocean biogeochemistry and may affect iron uptake by phytoplankton. (C) 2014 Elsevier B.V. All rights reserved.

Buck, KN, Selph KE, Barbeau KA.  2010.  Iron-binding ligand production and copper speciation in an incubation experiment of Antarctic Peninsula shelf waters from the Bransfield Strait, Southern Ocean. Marine Chemistry. 122:148-159.   10.1016/j.marchem.2010.06.002   AbstractWebsite

The evolution of dissolved iron (Fe) and copper (Cu) speciation was followed through a simulated spring bloom event in a 15-day incubation experiment of natural seawater collected during austral winter from high macronutrient high Fe waters of Bransfield Strait in the Southern Ocean. The incubation experiment included unamended bottles as well as Fe additions using the stable isotope of Fe, Fe-57. as inorganic ((FeCl3)-Fe-57) and organic (Fe-57-aerobactin, Fe-57-desferrioxamine B) amendments. Exposure to summer light conditions resulted in substantial growth for all treatments, mimicking the initiation of a spring bloom. The addition of Fe resulted in a 30% increase in phytoplankton biomass over unamended controls by day 15, indicating that the unamended waters became Fe limited despite initially elevated dissolved Fe concentrations. Dissolved Cu and Cu speciation remained largely unchanged for all treatments of the incubation, with Cu speciation dominated by exceedingly strong Cu-binding ligands (log K-CuL1.Cu2+(Cond) similar to 16) and low resultant Cu2+ concentrations (10(-16.3 +/- 0.3) mol L-1). In only the unamended light bottles, strong Fe-binding ligands were produced over the course of the experiment. The observed production of strong Fe-binding ligands in the control bottles that became Fe-limited supports the important role of biologically produced siderophore-type natural ligands in the marine Fe cycle. (C) 2010 Elsevier B.V. All rights reserved.