Cu transport and complexation by the marine diatom Phaeodactylum tricornutum: Implications for trace metal complexation kinetics in the surface ocean.

Elucidating whether dissolved Cu uptake is kinetically or thermodynamically controlled, and the effects of speciation on Cu transport by phytoplankton will allow better modeling of the fate and impact of dissolved Cu in the ocean. To address these questions, we performed Cu physiological and physicochemical experiments using the model diatom, Phaeodactylum tricornutum, grown in natural North Atlantic seawater (0.44 nM Cu). Using competitive ligand equilibration-cathodic stripping voltammetry (CLE-CSV), we measured two organic ligand types released by P. tricornutum to bind Cu (L1 and L2) at concentrations of ~0.35 nM L1 and 1.3 nM L2. We also established the presence of two putative Cu-binding sites at the cell surface of P. tricornutum (S1 and S2) with log K differing by ~5 orders of magnitude (i.e., 12.9 vs. 8.1) and cell surface densities by 9-fold. Only the high-affinity binding sites, S1, exhibit reductase activity. Using voltammetric kinetic measurements and a theoretical kinetic model, we calculated the forward and dissociation rate constants of L1 and S1. Complementary 67Cu uptake experiments identified a high- and a low-affinity Cu uptake system in P. tricornutum, with half-saturation constant (Km) of 154 nM and 2.63 µM dissolved Cu, respectively. In the P. tricornutum genome, we identified a putative high-affinity Cu transporter (PtCTR49224) and a putative ZIP-like, low-affinity Cu transporter (PtZIP49400). PtCTR49224 has high homology to Homo sapiens hCTR1, which depending on the accessibility to extracellular reducing agents, the hCTR1 itself is involved in the reduction of Cu2+ to Cu+ before internalization. We combined these physiological and physicochemical data to calculate the rate constants for the internalization of Cu, and established that while the high-affinity Cu uptake system (S1) is borderline between a kinetically or thermodynamically controlled system, the low-affinity Cu transporters, S2, is thermodynamically-controlled. We revised the inverse relationship between the concentrations of inorganic complexes of essential metals (i.e., Ni, Fe, Co, Zn, Cd, Mn and Cu) in the mixed layer and the formation rate constant of metal transporters in phytoplankton, highlighting the link between the chemical properties of phytoplankton metal transporters and the availability and speciation of trace metals in the surface ocean.

Distribution, sources and dispersion of polybrominated diphenyl ethers in the water column of the Strait of Georgia, British Columbia, Canada.

Dissolved and particulate polybrominated diphenyl ether (PBDE) concentrations were measured in the water column of the Strait of Georgia (SoG), Haro Strait, Juan de Fuca Strait, Burrard Inlet, and the Fraser River to assess their sources and dispersion. Total PBDE concentrations in the water column of the southern basin of the SoG are surprisingly high (similar to the load reported for coastal zones heavily impacted by human activities). Moreover, the dissolved fraction (i.e. passing through a 2.2 µm pore size filter) accounts for >95 % of the total load, which is unlike what is more typically found in other coastal zones, where particulate PBDEs generally dominate. Decreasing concentrations away from the southern SoG, eventually reaching typical open ocean values in Juan de Fuca Strait, point to the Vancouver metropolitan area as the main proximal source of PBDEs. About half of the direct PBDE input comes from wastewater treatment plants, with atmospheric deposition and the Fraser river accounting for most of the rest. However, these direct sources alone cannot explain the high dissolved PBDE load observed in the water column of southern SoG. PBDE scavenging rates estimated from concentration gradients and water transit times imply a PBDE flux to the seafloor which largely exceeds the measured burial rates of PBDEs in sediments. To reconcile these observations and explain the dominance of the dissolved fraction in the water column of the southern SoG, we invoke and provide supporting evidence for the release of colloidal PBDE from the resuspension of PBDE-contaminated sediments by bottom currents. If confirmed, this continued PBDE exchange between sediments and the water column would maintain high levels of PBDEs, and possibly other hydrophobic and persistent organic contaminants, in the water column of the southern SoG until the contaminated sediments are buried below the sediment mixed layer.

Strong Margin Influence on the Arctic Ocean Barium Cycle Revealed by Pan-Arctic Synthesis.

Early studies revealed relationships between barium (Ba), particulate organic carbon and silicate, suggesting applications for Ba as a paleoproductivity tracer and as a tracer of modern ocean circulation. But, what controls the distribution of barium (Ba) in the oceans? Here, we investigated the Arctic Ocean Ba cycle through a one-of-a-kind data set containing dissolved (dBa), particulate (pBa), and stable isotope Ba ratio (δ138Ba) data from four Arctic GEOTRACES expeditions conducted in 2015. We hypothesized that margins would be a substantial source of Ba to the Arctic Ocean water column. The dBa, pBa, and δ138Ba distributions all suggest significant modification of inflowing Pacific seawater over the shelves, and the dBa mass balance implies that ∼50% of the dBa inventory (upper 500 m of the Arctic water column) was supplied by nonconservative inputs. Calculated areal dBa fluxes are up to 10 µmol m-2 day-1 on the margin, which is comparable to fluxes described in other regions. Applying this approach to dBa data from the 1994 Arctic Ocean Survey yields similar results. The Canadian Arctic Archipelago did not appear to have a similar margin source; rather, the dBa distribution in this section is consistent with mixing of Arctic Ocean-derived waters and Baffin Bay-derived waters. Although we lack enough information to identify the specifics of the shelf sediment Ba source, we suspect that a sedimentary remineralization and terrigenous sources (e.g., submarine groundwater discharge or fluvial particles) are contributors.

Correction: Concentrations and properties of ice nucleating substances in exudates from Antarctic sea-ice diatoms.

Correction for 'Concentrations and properties of ice nucleating substances in exudates from Antarctic sea-ice diatoms' by Yu Xi et al., Environ. Sci.: Processes Impacts, 2021, 23, 323-334, DOI: 10.1039/D0EM00398K.

Proteomic analysis of metabolic pathways supports chloroplast-mitochondria cross-talk in a Cu-limited diatom.

Diatoms are one of the most successful phytoplankton groups in our oceans, being responsible for over 20% of the Earth's photosynthetic productivity. Their chimeric genomes have genes derived from red algae, green algae, bacteria, and heterotrophs, resulting in multiple isoenzymes targeted to different cellular compartments with the potential for differential regulation under nutrient limitation. The resulting interactions between metabolic pathways are not yet fully understood. We previously showed how acclimation to Cu limitation enhanced susceptibility to overreduction of the photosynthetic electron transport chain and its reorganization to favor photoprotection over light harvesting in the oceanic diatom Thalassiosira oceanica (Hippmann et al., 2017, 10.1371/journal.pone.0181753). In order to gain a better understanding of the overall metabolic changes that help alleviate the stress of Cu limitation, we have further analyzed the comprehensive proteomic datasets generated in that study to identify differentially expressed proteins involved in carbon, nitrogen, and oxidative stress-related metabolic pathways. Metabolic pathway analysis showed integrated responses to Cu limitation. The upregulation of ferredoxin (Fdx) was correlated with upregulation of plastidial Fdx-dependent isoenzymes involved in nitrogen assimilation as well as enzymes involved in glutathione synthesis, thus suggesting an integration of nitrogen uptake and metabolism with photosynthesis and oxidative stress resistance. The differential expression of glycolytic isoenzymes located in the chloroplast and mitochondria may enable them to channel both excess electrons and/or ATP between these compartments. An additional support for chloroplast-mitochondrial cross-talk is the increased expression of chloroplast and mitochondrial proteins involved in the proposed malate shunt under Cu limitation.

Concentrations and properties of ice nucleating substances in exudates from Antarctic sea-ice diatoms.

The ocean contains ice nucleating substances (INSs), some of which can be emitted to the atmosphere where they can influence the formation and properties of clouds. A possible source of INSs in the ocean is exudates from sea-ice diatoms. Here we examine the concentrations and properties of INSs in supernatant samples from dense sea-ice diatom communities collected from Ross Sea and McMurdo Sound in the Antarctic. The median freezing temperatures of the samples ranged from approximately -17 to -22 °C. Based on our results and a comparison with results reported in the literature, the ice nucleating ability of exudates from sea-ice diatoms is likely not drastically different from the ice nucleating ability of exudates from temperate diatoms. The number of INSs per mass of DOC for the supernatant samples were lower than those reported previously for the sea surface microlayer and bulk sea water collected in the Arctic and Atlantic. The INSs in the supernatant sample collected from Ross Sea were not sensitive to temperatures up to 100 °C, were larger than 300 kDa, and were different from ice shaping and recrystallization inhibiting molecules present in the same sample. Possible candidates for these INSs include polysaccharide containing nanogels. The INSs in the supernatant sample collected from McMurdo Sound were sensitive to temperatures of 80 and 100 °C and were larger than 1000 kDa. Possible candidates for these INSs include protein containing nanogels.

Probing the Bioavailability of Dissolved Iron to Marine Eukaryotic Phytoplankton Using In Situ Single Cell Iron Quotas.

We present a new approach for quantifying the bioavailability of dissolved iron (dFe) to oceanic phytoplankton. Bioavailability is defined using an uptake rate constant (kin-app) computed by combining data on: (a) Fe content of individual in situ phytoplankton cells; (b) concurrently determined seawater dFe concentrations; and (c) growth rates estimated from the PISCES model. We examined 930 phytoplankton cells, collected between 2002 and 2016 from 45 surface stations during 11 research cruises. This approach is only valid for cells that have upregulated their high-affinity Fe uptake system, so data were screened, yielding 560 single cell k in-app values from 31 low-Fe stations. We normalized k in-app to cell surface area (S.A.) to account for cell-size differences. The resulting bioavailability proxy (k in-app/S.A.) varies among cells, but all values are within bioavailability limits predicted from defined Fe complexes. In situ dFe bioavailability is higher than model Fe-siderophore complexes and often approaches that of highly available inorganic Fe'. Station averaged k in-app/S.A. are also variable but show no systematic changes across location, temperature, dFe, and phytoplankton taxa. Given the relative consistency of k in-app/S.A. among stations (ca. five-fold variation), we computed a grand-averaged dFe availability, which upon normalization to cell carbon (C) yields k in-app/C of 42,200 ± 11,000 L mol C-1 d-1. We utilize k in-app/C to calculate dFe uptake rates and residence times in low Fe oceanic regions. Finally, we demonstrate the applicability of k in-app/C for constraining Fe uptake rates in earth system models, such as those predicting climate mediated changes in net primary production in the Fe-limited Equatorial Pacific.

Insights into the bioavailability of oceanic dissolved Fe from phytoplankton uptake kinetics.

Phytoplankton growth in large parts of the world ocean is limited by low availability of dissolved iron (dFe), restricting oceanic uptake of atmospheric CO2. The bioavailability of dFe in seawater is however difficult to appraise since it is bound by a variety of poorly characterized organic ligands. Here, we propose a new approach for evaluating seawater dFe bioavailability based on its uptake rate constant by Fe-limited cultured phytoplankton. We utilized seven phytoplankton species of diverse classes, sizes, and provenances to probe for dFe bioavailability in 12 seawater samples from several ocean basins and depths. All tested phytoplankton acquired organically bound Fe in any given sample at similar rates (after normalizing to cellular surface area), confirming that multiple, Fe-limited phytoplankton species can be used to probe dFe bioavailability in seawater. These phytoplankton-based uptake rate constants allowed us to compare water types, and obtain a grand average estimate of seawater dFe bioavailability. Among water types, dFe bioavailability varied by approximately four-fold, and did not clearly correlate with Fe concentrations or any of the measured Fe speciation parameters. Compared with well-studied Fe complexes, seawater dFe is more available than model siderophore Fe, but less available than inorganic Fe. Exposure of seawater to sunlight, however, significantly enhanced dFe bioavailability. The rate constants established in this work, not only facilitate comparison between water types, but also allow calculation of Fe uptake rates by phytoplankton in the ocean based on measured dFe concentrations. The approach established and verified in this study, opens a new way for determining dFe bioavailability in samples across the ocean, and enables modeling of in situ Fe uptake rates by phytoplankton using dFe concentrations from GEOTRACES datasets.

Divergent gene expression among phytoplankton taxa in response to upwelling.

Frequent blooms of phytoplankton occur in coastal upwelling zones creating hotspots of biological productivity in the ocean. As cold, nutrient-rich water is brought up to sunlit layers from depth, phytoplankton are also transported upwards to seed surface blooms that are often dominated by diatoms. The physiological response of phytoplankton to this process, commonly referred to as shift-up, is characterized by increases in nitrate assimilation and rapid growth rates. To examine the molecular underpinnings behind this phenomenon, metatranscriptomics was applied to a simulated upwelling experiment using natural phytoplankton communities from the California Upwelling Zone. An increase in diatom growth following 5 days of incubation was attributed to the genera Chaetoceros and Pseudo-nitzschia. Here, we show that certain bloom-forming diatoms exhibit a distinct transcriptional response that coordinates shift-up where diatoms exhibited the greatest transcriptional change following upwelling; however, comparison of co-expressed genes exposed overrepresentation of distinct sets within each of the dominant phytoplankton groups. The analysis revealed that diatoms frontload genes involved in nitrogen assimilation likely in order to outcompete other groups for available nitrogen during upwelling events. We speculate that the evolutionary success of diatoms may be due, in part, to this proactive response to frequently encountered changes in their environment.

Contrasting effects of copper limitation on the photosynthetic apparatus in two strains of the open ocean diatom Thalassiosira oceanica.

There is an intricate interaction between iron (Fe) and copper (Cu) physiology in diatoms. However, strategies to cope with low Cu are largely unknown. This study unveils the comprehensive restructuring of the photosynthetic apparatus in the diatom Thalassiosira oceanica (CCMP1003) in response to low Cu, at the physiological and proteomic level. The restructuring results in a shift from light harvesting for photochemistry-and ultimately for carbon fixation-to photoprotection, reducing carbon fixation and oxygen evolution. The observed decreases in the physiological parameters Fv/Fm, carbon fixation, and oxygen evolution, concomitant with increases in the antennae absorption cross section (σPSII), non-photochemical quenching (NPQ) and the conversion factor (φe:C/ηPSII) are in agreement with well documented cellular responses to low Fe. However, the underlying proteomic changes due to low Cu are very different from those elicited by low Fe. Low Cu induces a significant four-fold reduction in the Cu-containing photosynthetic electron carrier plastocyanin. The decrease in plastocyanin causes a bottleneck within the photosynthetic electron transport chain (ETC), ultimately leading to substantial stoichiometric changes. Namely, 2-fold reduction in both cytochrome b6f complex (cytb6f) and photosystem II (PSII), no change in the Fe-rich PSI and a 40- and 2-fold increase in proteins potentially involved in detoxification of reactive oxygen species (ferredoxin and ferredoxin:NADP+ reductase, respectively). Furthermore, we identify 48 light harvesting complex (LHC) proteins in the publicly available genome of T. oceanica and provide proteomic evidence for 33 of these. The change in the LHC composition within the antennae in response to low Cu underlines the shift from photochemistry to photoprotection in T. oceanica (CCMP1003). Interestingly, we also reveal very significant intra-specific strain differences. Another strain of T. oceanica (CCMP 1005) requires significantly higher Cu concentrations to sustain both its maximal and minimal growth rate compared to CCMP 1003. Under low Cu, CCMP 1005 decreases its growth rate, cell size, Chla and total protein per cell. We argue that the reduction in protein per cell is the main strategy to decrease its cellular Cu requirement, as none of the other parameters tested are affected. Differences between the two strains, as well as differences between the well documented responses to low Fe and those presented here in response to low Cu are discussed.

Southern Ocean biological iron cycling in the pre-whaling and present ecosystems.

This study aimed to create the first model of biological iron (Fe) cycling in the Southern Ocean food web. Two biomass mass-balanced Ecopath models were built to represent pre- and post-whaling ecosystem states (1900 and 2008). Functional group biomasses (tonnes wet weight km-2) were converted to biogenic Fe pools (kg Fe km-2) using published Fe content ranges. In both models, biogenic Fe pools and consumption in the pelagic Southern Ocean were highest for plankton and small nektonic groups. The production of plankton biomass, particularly unicellular groups, accounted for the highest annual Fe demand. Microzooplankton contributed most to biological Fe recycling, followed by carnivorous zooplankton and krill. Biological Fe recycling matched previous estimates, and, under most conditions, could entirely meet the Fe demand of bacterioplankton and phytoplankton. Iron recycling by large baleen whales was reduced 10-fold by whaling between 1900 and 2008. However, even under the 1900 scenario, the contribution of whales to biological Fe recycling was negligible compared with that of planktonic consumers. These models are a first step in examining oceanic-scale biological Fe cycling, highlighting gaps in our present knowledge and key questions for future research on the role of marine food webs in the cycling of trace elements in the sea.This article is part of the themed issue 'Biological and climatic impacts of ocean trace element chemistry'.

Interacting Effects of Light and Iron Availability on the Coupling of Photosynthetic Electron Transport and CO2-Assimilation in Marine Phytoplankton.

Iron availability directly affects photosynthesis and limits phytoplankton growth over vast oceanic regions. For this reason, the availability of iron is a crucial variable to consider in the development of active chlorophyll a fluorescence based estimates of phytoplankton primary productivity. These bio-optical approaches require a conversion factor to derive ecologically-relevant rates of CO2-assimilation from estimates of electron transport in photosystem II. The required conversion factor varies significantly across phytoplankton taxa and environmental conditions, but little information is available on its response to iron limitation. In this study, we examine the role of iron limitation, and the interacting effects of iron and light availability, on the coupling of photosynthetic electron transport and CO2-assimilation in marine phytoplankton. Our results show that excess irradiance causes increased decoupling of carbon fixation and electron transport, particularly under iron limiting conditions. We observed that reaction center II specific rates of electron transport (ETR(RCII), mol e- mol RCII(-1) s(-1)) increased under iron limitation, and we propose a simple conceptual model for this observation. We also observed a strong correlation between the derived conversion factor and the expression of non-photochemical quenching. Utilizing a dataset from in situ phytoplankton assemblages across a coastal--oceanic transect in the Northeast subarctic Pacific, this relationship was used to predict ETR(RCII): CO2-assimilation conversion factors and carbon-based primary productivity from FRRF data, without the need for any additional measurements.

Sequence analysis and gene expression of potential components of copper transport and homeostasis in Thalassiosira pseudonana.

Genes involved with many Fe functions and some Cu functions are annotated in the Thalassiosira pseudonana Hasle et Heimdal genome. Using bioinformatics, we performed a systematic Blastp search to obtain all relevant sequences and to select the most complete gene models for putative components of Cu acquisition and distribution. We identified homologs of high-affinity Cu transporters (CTR), Cu transporting P1B-type ATPases, Cu chaperones and ZIP transporters. The putative CTRs in T. pseudonana have the conserved CTR Cu-binding motifs and transmembrane domains, and their gene expression was down-regulated by a Cu addition to low Cu acclimated cultures. The sequences of some putative TpZIPs were similar to those of well-known Zn and Fe transporters. Cu addition affected the expression of some TpZIP genes, suggesting an interaction between Cu metabolism and that of Zn and/or Fe. For intracellular Cu distribution, we identified putative Cu transporting P1B-type ATPases, proposed to deliver Cu to the trans-Golgi or the secretory compartment, as well as putative Cu chaperones, proposed to deliver Cu to the mitochondrion. Their gene expression was down-regulated by a Cu addition, indicating that these putative intracellular Cu transporters and chaperones might redistribute Cu, allowing T. pseudonana to meet key metabolic needs under Cu deficiency.

Diatom proteomics reveals unique acclimation strategies to mitigate Fe limitation.

Phytoplankton growth rates are limited by the supply of iron (Fe) in approximately one third of the open ocean, with major implications for carbon dioxide sequestration and carbon (C) biogeochemistry. To date, understanding how alteration of Fe supply changes phytoplankton physiology has focused on traditional metrics such as growth rate, elemental composition, and biophysical measurements such as photosynthetic competence (Fv/Fm). Researchers have subsequently employed transcriptomics to probe relationships between changes in Fe supply and phytoplankton physiology. Recently, studies have investigated longer-term (i.e. following acclimation) responses of phytoplankton to various Fe conditions. In the present study, the coastal diatom, Thalassiosira pseudonana, was acclimated (10 generations) to either low or high Fe conditions, i.e. Fe-limiting and Fe-replete. Quantitative proteomics and a newly developed proteomic profiling technique that identifies low abundance proteins were employed to examine the full complement of expressed proteins and consequently the metabolic pathways utilized by the diatom under the two Fe conditions. A total of 1850 proteins were confidently identified, nearly tripling previous identifications made from differential expression in diatoms. Given sufficient time to acclimate to Fe limitation, T. pseudonana up-regulates proteins involved in pathways associated with intracellular protein recycling, thereby decreasing dependence on extracellular nitrogen (N), C and Fe. The relative increase in the abundance of photorespiration and pentose phosphate pathway proteins reveal novel metabolic shifts, which create substrates that could support other well-established physiological responses, such as heavily silicified frustules observed for Fe-limited diatoms. Here, we discovered that proteins and hence pathways observed to be down-regulated in short-term Fe starvation studies are constitutively expressed when T. pseudonana is acclimated (i.e., nitrate and nitrite transporters, Photosystem II and Photosystem I complexes). Acclimation of the diatom to the desired Fe conditions and the comprehensive proteomic approach provides a more robust interpretation of this dynamic proteome than previous studies.

Biogeochemistry of cadmium and its release to the environment.

Cadmium is at the end of the 4d-transition series, it is relatively mobile and acutely toxic to almost all forms of life. In this review we present a summary of information describing cadmium's physical and chemical properties, its distribution in crustal materials, and the processes, both natural and anthropogenic, that contribute to the metal's mobilization in the biosphere. The relatively high volatility of Cd metal, its large ionic radius, and its chemical speciation in aquatic systems makes Cd particularly susceptible to mobilization by anthropogenic and natural processes. The biogeochemical cycle of Cd is observed to be significantly altered by anthropogenic inputs, especially since the beginning of the industrial revolution drove increases in fossil fuel burning and non-ferrous metal extraction. Estimates of the flux of Cd to the atmosphere, its deposition and processing in soils and freshwater systems are presented. Finally, the basin scale distribution of dissolved Cd in the ocean, the ultimate receptacle of Cd, is interpreted in light of the chemical speciation and biogeochemical cycling of Cd in seawater. Paradoxically, Cd behaves as a nutrient in the ocean and its cycling and fate is intimately tied to uptake by photosynthetic microbes, their death, sinking and remineralization in the ocean interior. Proximate controls on the incorporation of Cd into biomass are discussed to explain the regional specificity of the relationship between dissolved Cd and the algal nutrient phosphate (PO[Formula: see text]) in oceanic surface waters and nutriclines. Understanding variability in the Cd/PO[Formula: see text] is of primary interest to paleoceanographers developing a proxy to probe the links between nutrient utilization in oceanic surface waters and atmospheric CO(2) levels. An ongoing international survey of trace elements and their isotopes in seawater will undoubtedly increase our understanding of the deposition, biogeochemical cycling and fate of this enigmatic, sometimes toxic, sometimes beneficial heavy metal.

THE EFFECTS OF IRON AND COPPER AVAILABILITY ON THE COPPER STOICHIOMETRY OF MARINE PHYTOPLANKTON(1).

We studied the interactive effects of iron (Fe) and copper (Cu) availability on the growth rates, Cu quotas, and steady-state Cu-uptake rates (ρss Cu) of 12 phytoplankton (from four classes and two marine environments). A mixed-effect statistical model indicated that low Fe significantly decreased phytoplankton growth rates. In contrast, lowering Cu levels only decreased the growth rates of the oceanic phytoplankton. Under Fe/Cu sufficiency, the Cu quotas ranged from 0.36 to 3.8 µmol Cu · mol(-1) C. Copper levels in the growth medium had a significant positive effect on the Cu quotas, and this effect was dependent on the algal class. Under Fe/Cu sufficiency, the highest average Cu quotas were observed for the Bacillariophyceae, followed by the Cyanophyceae, Prymnesiophyceae, and lastly the Dinophyceae. Similar taxonomic trends were observed for the ρss Cu. Although the Cu:C ratios were not significantly higher in oceanic strains, there are five independent lines of evidence supporting a more important role of Cu in the physiology of the oceanic phytoplankton. The mixed-effect model indicated a significant Cu effect on the growth rates and ρss Cu of the oceanic strains, but not the coastal strains. In addition, lowering the Cu concentration in the media decreased the Cu quotas and ρss Cu of the oceanic strains to a greater extent (5.5- and 5.4-fold, respectively) than those of the coastals (3.8- and 4.7-fold, respectively). Iron limitation only had a significant effect on the Cu quotas of the oceanic strains, and this effect was dependent on Cu level and taxonomic class. Our results highlight a complex physiological interaction between Fe and Cu in marine phytoplankton.

The role of phytoplankton in the modulation of dissolved and oyster cadmium concentrations in Deep Bay, British Columbia, Canada.

We previously identified dissolved cadmium (Cd(diss)) as the main source of this metal in cultured Pacific oysters, Crassostrea gigas, in Deep Bay, British Columbia, Canada (Lekhi et al., 2008). Total suspended particulate Cd (Cd(part)) was not found to be a significant source of oyster Cd (Cd(oys)), with Cd(part) >20 µm negatively correlated with Cd(oys) concentration. High phytoplankton abundance in spring and summer was hypothesized to reduce Cd(oys) indirectly by drawing down Cd(diss) and increasing oyster growth. In the present study we expanded on these results by examining specifically how the phytoplankton community composition modulates both Cd(diss) and Cd(oys) concentrations in Deep Bay. Based on calculations of nutrients and Cd(diss) drawdown, phytoplankton accounted for approximately 90% of the overall summer reduction in Cd(diss) in the bay. Diatoms were the dominant phytoplankton group, being correlated negatively with Cd(oys) and positively with Cd(part). This suggests that diatom growth mediates the transfer of Cd from the dissolved to the particulate phase, resulting in lower Cd(oys). Spring blooms and sporadic harmful algal blooms may mediate a large flux of Cd(part) to the sediments. Thus, phytoplankton act as a sink, rather than a source, of Cd to oysters in Deep Bay and have a crucial role in the seasonality of Cd(oys) by reducing the concentration of Cd(diss) during the summer. Based on environmental variables, two descriptive models for annual Cd(oys) concentrations were developed using multiple linear regression. The first model (R(2)=0.870) was created to explain the maximum variability in Cd(oys) concentrations throughout the year, while the second (R(2)=0.806) was based on parameters that could be measured easily under farm conditions. Oyster age heavily affected both models, with the first model being secondarily affected by temperature and the second one being more sensitive to changes in salinity.

The effects of copper on the photosynthetic response of Phaeocystis cordata.

We investigated the effects of limiting (1.96 × 10(-9) mol l(-1) total Cu, corresponding to pCu 14.8; where pCu = -log [Cu(2+)]) and toxic Cu concentrations up to 8.0 × 10(-5) mol l(-1) total Cu (equivalent to pCu 9.5) on growth rates and photosynthetic activity of exponentially grown Phaeocystis cordata, using batch and semi-continuous cultures. With pulse amplitude modulated (PAM) fluorometry, we determined the photochemical response of P. cordata to the various Cu levels, and showed contrasting results for the batch and semi-continuous cultures. Although maximum photosystem II (PSII) quantum yield (Φ(M)) was optimal and constant in the semi-continuous P. cordata, the batch cultures showed a significant decrease in Φ(M) with culture age (0-72 h). The EC50 for the batch cultures was higher (2.0 × 10(-10) mol l(-1), pCu9.7), than that for the semi-continuous cultures (6.3 × 10(-11) mol l(-1), pCu10.2). The semi-continuous cultures exhibited a systematic and linear decrease in Φ(M) as Cu levels increased (for [Cu(2+)] < 1.0 × 10(-12) mol l(-1), pCu12.0), however, no effect of high Cu was observed on their operational PSII quantum yield (Φ'(M)). Similarly, semi-continuous cultures exhibited a significant decrease in Φ(M), but not in Φ'(M), because of low-Cu levels. Thus, Cu toxicity and Cu limitation damage the PSII reaction centers, but not the processes downstream of PSII. Quenching mechanisms (NPQ and Q (n)) were lower under high Cu relative to the controls, suggesting that toxic Cu impairs photo-protective mechanisms. PAM fluorometry is a sensitive tool for detecting minor physiological variations. However, culturing techniques (batch vs. semi-continuous) and sampling time might account for literature discrepancies on the effects of Cu on PSII. Semi-continuous culturing might be the most adequate technique to investigate Cu effects on PSII photochemistry.

Estudio de niveles séricos de cobre y zinc y su posible rol como indicadores de dismenorrea primaria / Study of serum levels of copper and zinc and its possible roll like indicators of primary dysmenorrheal

En este trabajo se ha determinado el contenido de cobre y zinc en suero sanguíneo de 39 mujeres con edades comprendidas entre 17 y 21 años de edad, n = 25 con dismenorrea primaria diagnosticada clínicamente y n = 14 grupo control con diagnóstico negativo para la patología estudia-da. Las muestras de suero sanguíneo se obtuvieron antes (a) y durante (d) la menstruación. Fueron analizadas por Espectroscopia de Absorción Atómica con inyección en flujo continuo (EAA-IFC). Las concentraciones obtenidas fueron de 1,56 ± 0,43 mgL-1 de cobre y 1,28 ± 0,34 mgL-1 de zinc antes de la menstruación y 1,06 ± 0,23 mgL-1 de co bre y 1,21 ±0,4 mgL-1 de zinc durante la menstruación, para el grupo control y 1,64 ± 0,52 mgL-1 de cobre y 1,88 ± 0,61 mgL-1 de zinc antes de la menstruación y 1,21 ± 0,34 mgL-1 de cobre y 0,94 ± 0,27 mgL-1 de zinc durante la mens ruaciónt en el grupo estudio. Los elementos determinados en ambos grupos antes del periodo menstrual, no observaron diferencias significativas con p= 0,63 y 0,16 para cobre y zinc, respectivamente. Sin embargo, durante la menstruación, fue evidente una diferencia con p < 0,005. Este resultado nos hace presumir, que el aumento brusco de los niveles séricos de cobre se deba probablemente por la alteración de las prostaglandinas, siendo este bioelemento uno de los responsables de las molestias que se presentan en esta patología y otros efectos secundarios motivados por el descenso brusco del zinc. La relación cobre/zinc se calculo en ambos grupos, con valores de 1,47 y 1,06 antes y durante, respectivamente para el grupo control y para el grupo bajo estudio 1,36 y 1,97 antes y durante, respectivamente.

In this work has determined the copper content and zinc in sanguineous serum of women with primary dysmenorrheal diagnosed clinically and a group of women control with I diagnose negative for the studied pathology. The samples of sanguineous serum taken before (a) and during (d) the second day of the menstruation come from 39 women in ages between 17 and 21 years of age, n = 14 controls and n = 25 women with primary dysmenorrheal. They were processed by Spectroscopy of Atomic Absorption with injection in con-tinuous flow (EAA-IFC). The concentrations obtained of 1.56± 0.43 mgL-1 of copper and 1.28± 0.34 mgL-1 of zinc before menstruation and 1.06 ±0.23 mgL-1 of copper and 1.21 ±0.4 mgL-1 of zinc during the menstruation (second day), for the group control and 1.64 ±0.52 mgL-1 of copper and 1.88 ±0.61 mgL-1 of zinc before menstruation and 1.21± 0.34 mgL-1 of copper and 0.94± 0.27 mgL-1 of zinc during the menstruation in the group study. In relation to the serum levels it initiates to them in both groups were not significant differences (p = 0.63). The zinc, observe he himself behavior, between both groups before the menstruation was not observed significant differences with p = 0.16, nevertheless, during the menstruation I throw p = 0.0033. This result evi-dence that indeed the copper is affected by the alteration of the prostaglandins, being probably one of the people in charge of the annoyances that appear in this pa hologyt and other indirect effect motivated by the abrupt reduction of the zinc, such as alteration in the synthesis and excretion of the hormone stimulating follicle (FSH), of the luteinizante hormone (LH), abnormal development of the ovary, alterations of the menstrual cycle. The copper/zinc re ationl I calculate both groups, with values of 1.47 and 1,06 before and during res pectively for the group control and the group under study 1,36 and 1.97 before and during respectively.