Search

A small subset of marine microbial enzymes and surface transporters have a disproportionately important influence on the cycling of carbon and nutrients in the global ocean. As a result, they largely determine marine biological productivity and have been the focus of considerable research attention from microbial oceanographers. Like all biological catalysts, the activity of these keystone biomolecules is subject to control by temperature and pH, leaving the crucial ecosystem functions they support potentially vulnerable to anthropogenic environmental change. We summarize and discuss both consensus and conflicting evidence on the effects of sea surface warming and ocean acidification for five of these critical enzymes [carbonic anhydrase, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), nitrogenase, nitrate reductase, and ammonia monooxygenase] and one important transporter (proteorhodopsin). Finally, we forecast how the responses of these few but essential biocatalysts to ongoing global change processes may ultimately help to shape the microbial communities and biogeochemical cycles of the future greenhouse ocean.

Microbial rhodopsins are simple light-harvesting complexes that, unlike chlorophyll photosystems, have no iron requirements for their synthesis and phototrophic functions. Here, we report the environmental concentrations of rhodopsin along the Subtropical Frontal Zone off New Zealand, where Subtropical waters encounter the iron-limited Subantarctic High Nutrient Low Chlorophyll (HNLC) region. Rhodopsin concentrations were highest in HNLC waters where chlorophyll-a concentrations were lowest. Furthermore, while the ratio of rhodopsin to chlorophyll-a photosystems was on average 20 along the transect, this ratio increased to over 60 in HNLC waters. We further show that microbial rhodopsins are abundant in both picoplankton (0.2-3 μm) and in the larger (>3 μm) size fractions of the microbial community containing eukaryotic plankton and/or particle-attached prokaryotes. These findings suggest that rhodopsin phototrophy could be critical for microbial plankton to adapt to resource-limiting environments where photosynthesis and possibly cellular respiration are impaired., (© 2021 Society for Applied Microbiology and John Wiley & Sons Ltd.)

Halomethanes (e.g., CH 3 Cl, CH 3 Br, CH 3 I and CHBr 3 ) are ozone-depleting compounds that, in contrast to the human-made chlorofluorocarbons, marine organisms synthesize naturally. Therefore, their production cannot be totally controlled by human action. However, identifying all their natural sources and understanding their synthesis regulation can help to predict their production rates and their impact on the future recovery of the Earth's ozone layer. Here we show that the synthesis of mono-halogenated halocarbons CH 3 Cl, CH 3 Br, and CH 3 I is a generalized process in representatives of the major marine heterotrophic bacteria groups. Furthermore, halomethane production was growth rate dependent in all the strains we studied, implying uniform synthesis regulation patterns among bacterioplankton. Using these experimental observations and in situ halomethane concentrations, we further evaluated the potential production rates associated with higher bacterial growth rates in response to global warming in a coastal environment within the Southern California Bight. Our estimates show that a 3°C temperature rise would translate into a 35%-84% increase in halomethane production rate by 2100. Overall, these data suggest that marine heterotrophic bacteria are significant producers of these climate-relevant gases and that their contribution to the atmospheric halogen budget could increase in the future, impacting the ozone layer recovery., (© 2020 Society for Applied Microbiology and John Wiley & Sons Ltd.)

All known phototrophic metabolisms on Earth rely on one of three categories of energy-converting pigments: chlorophyll- a (rarely - d ), bacteriochlorophyll- a (rarely - b ), and retinal, which is the chromophore in rhodopsins. While the significance of chlorophylls in solar energy capture has been studied for decades, the contribution of retinal-based phototrophy to this process remains largely unexplored. We report the first vertical distributions of the three energy-converting pigments measured along a contrasting nutrient gradient through the Mediterranean Sea and the Atlantic Ocean. The highest rhodopsin concentrations were observed above the deep chlorophyll- a maxima, and their geographical distribution tended to be inversely related to that of chlorophyll- a . We further show that proton-pumping proteorhodopsins potentially absorb as much light energy as chlorophyll- a -based phototrophy and that this energy is sufficient to sustain bacterial basal metabolism. This suggests that proteorhodopsins are a major energy-transducing mechanism to harvest solar energy in the surface ocean.

The flavins (including flavin mononucleotide (FMN) and riboflavin (RF)) are a class of organic compounds synthesized by organisms to assist in critical redox reactions. While known to be secreted extracellularly by some species in laboratory-based cultures, flavin concentrations are largely unreported in the natural environment. Here, we present pore water and water column profiles of extracellular flavins (FMN and RF) and two degradation products (lumiflavin and lumichrome) from a coastal marine basin in the Southern California Bight alongside ancillary geochemical and 16S rRNA microbial community data. Flavins were detectable at picomolar concentrations in the water column (93-300 pM FMN, 14-40 pM RF) and low nanomolar concentrations in pore waters (250-2070 pM FMN, 11-210 pM RF). Elevated pore water flavin concentrations displayed an increasing trend with sediment depth and were significantly correlated with the total dissolved Fe (negative) and Mn (positive) concentrations. Network analysis revealed a positive relationship between flavins and the relative abundance of Dehalococcoidia and the MSBL9 clade of Planctomycetes, indicating possible secretion by members of these lineages. These results suggest that flavins are a common component of the so-called shared extracellular metabolite pool, especially in anoxic marine sediments where they exist at physiologically relevant concentrations for metal oxide reduction.

Aquatic environments contain large communities of microorganisms whose synergistic interactions mediate the cycling of major and trace nutrients, including vitamins. B-vitamins are essential coenzymes that many organisms cannot synthesize. Thus, their exchange among de novo synthesizers and auxotrophs is expected to play an important role in the microbial consortia and explain some of the temporal and spatial changes observed in diversity. In this study, we analyzed metatranscriptomes of a natural marine microbial community, diel sampled quarterly over one year to try to identify the potential major B-vitamin synthesizers and consumers. Transcriptomic data showed that the best-represented taxa dominated the expression of synthesis genes for some B-vitamins but lacked transcripts for others. For instance, Rhodobacterales dominated the expression of vitamin-B 12 synthesis, but not of vitamin-B 7 , whose synthesis transcripts were mainly represented by Flavobacteria. In contrast, bacterial groups that constituted less than 4% of the community (e.g., Verrucomicrobia) accounted for most of the vitamin-B 1 synthesis transcripts. Furthermore, ambient vitamin-B 1 concentrations were higher in samples collected during the day, and were positively correlated with chlorophyll-a concentrations. Our analysis supports the hypothesis that the mosaic of metabolic interdependencies through B-vitamin synthesis and exchange are key processes that contribute to shaping microbial communities in nature., (© 2018 Society for Applied Microbiology and John Wiley & Sons Ltd.)

Only select prokaryotes can biosynthesize vitamin B 12 (i.e., cobalamins), but these organic co-enzymes are required by all microbial life and can be vanishingly scarce across extensive ocean biomes. Although global ocean genome data suggest cyanobacteria to be a major euphotic source of cobalamins, recent studies have highlighted that >95% of cyanobacteria can only produce a cobalamin analog, pseudo-B 12 , due to the absence of the BluB protein that synthesizes the α ligand 5,6-dimethylbenzimidizole (DMB) required to biosynthesize cobalamins. Pseudo-B 12 is substantially less bioavailable to eukaryotic algae, as only certain taxa can intracellularly remodel it to one of the cobalamins. Here we present phylogenetic, metagenomic, transcriptomic, proteomic, and chemical analyses providing multiple lines of evidence that the nitrogen-fixing cyanobacterium Trichodesmium transcribes and translates the biosynthetic, cobalamin-requiring BluB enzyme. Phylogenetic evidence suggests that the Trichodesmium DMB biosynthesis gene, bluB , is of ancient origin, which could have aided in its ecological differentiation from other nitrogen-fixing cyanobacteria. Additionally, orthologue analyses reveal two genes encoding iron-dependent B 12 biosynthetic enzymes (cbiX and isiB), suggesting that iron availability may be linked not only to new nitrogen supplies from nitrogen fixation, but also to B 12 inputs by Trichodesmium . These analyses suggest that Trichodesmium contains the genus-wide genomic potential for a previously unrecognized role as a source of cobalamins, which may prove to considerably impact marine biogeochemical cycles.

Coenzymes are essential across all domains of life. B vitamins (B 1 -thiamin, B 2 -riboflavin, B 3 -niacin, B 5 -pantothenate, B 6 -pyridoxine, B 7 -biotin, and B 12 -cobalamin) represent the largest class of coenzymes, which participate in a diverse set of reactions including C 1 -rearrangements, DNA repair, electron transfer, and fatty acid synthesis. B vitamin structures range from simple to complex heterocycles, yet, despite this complexity, multiple lines of evidence exist for their ancient origins including abiotic synthesis under putative early Earth conditions and/or meteorite transport. Thus, some of these critical coenzymes likely preceded life on Earth. Some modern organisms can synthesize their own B vitamins de novo while others must either scavenge them from the environment or establish a symbiotic relationship with a B vitamin producer. B vitamin requirements are widespread in some of the most ancient metabolisms including all six carbon fixation pathways, sulfate reduction, sulfur disproportionation, methanogenesis, acetogenesis, and photosynthesis. Understanding modern metabolic B vitamin requirements is critical for understanding the evolutionary conditions of ancient metabolisms as well as the biogeochemical cycling of critical elements such as S, C, and O., (© 2016 John Wiley & Sons Ltd.)

Proteorhodopsins (PR) are light-driven proton pumps widely distributed in bacterioplankton. Although they have been thoroughly studied for more than a decade, it is still unclear how the proton motive force (pmf) generated by PR is used in most organisms. Notably, very few PR-containing bacteria show growth enhancement in the light. It has been suggested that the presence of specific functions within a genome may define the different PR-driven light responses. Thus, comparing closely related organisms that respond differently to light is an ideal setup to identify the mechanisms involved in PR light-enhanced growth. Here, we analyzed the transcriptomes of three PR-harboring Flavobacteria strains of the genus Dokdonia: Dokdonia donghaensis DSW-1(T), Dokdonia MED134 and Dokdonia PRO95, grown in identical seawater medium in light and darkness. Although only DSW-1(T) and MED134 showed light-enhanced growth, all strains expressed their PR genes at least 10 times more in the light compared with dark. According to their genomes, DSW-1(T) and MED134 are vitamin-B1 auxotrophs, and their vitamin-B1 TonB-dependent transporters (TBDT), accounted for 10-18% of all pmf-dependent transcripts. In contrast, the expression of vitamin-B1 TBDT was 10 times lower in the prototroph PRO95, whereas its vitamin-B1 synthesis genes were among the highest expressed. Our data suggest that light-enhanced growth in DSW-1(T) and MED134 derives from the use of PR-generated pmf to power the uptake of vitamin-B1, essential for central carbon metabolism, including the TCA cycle. Other pmf-generating mechanisms available in darkness are probably insufficient to power transport of enough vitamin-B1 to support maximum growth of these organisms.

Vitamin B1, or thiamin, can limit primary productivity in marine environments, however the major marine environmental sources of this essential coenzyme remain largely unknown. Vitamin B1 can only be produced by organisms that possess its complete synthesis pathway, while other organisms meet their cellular B1 quota by scavenging the coenzyme from exogenous sources. Due to high bacterial cell density and diversity, marine sediments could represent some of the highest concentrations of putative B1 producers, yet these environments have received little attention as a possible source of B1 to the overlying water column. Here we report the first dissolved pore water profiles of B1 measured in cores collected in two consecutive years from Santa Monica Basin, CA. Vitamin B1 concentrations were fairly consistent between the two years ranging from 30 pM up to 770 pM. A consistent maximum at ~5 cm sediment depth covaried with dissolved concentrations of iron. Pore water concentrations were higher than water column levels and represented some of the highest known environmental concentrations of B1 measured to date, (over two times higher than maximum water column concentrations) suggesting increased rates of cellular production and release within the sediments. A one dimensional diffusion-transport model applied to the B1 profile was used to estimate a diffusive benthic flux of ~0.7 nmol m(-2) d(-1). This is an estimated flux across the sediment-water interface in a deep sea basin; if similar magnitude B-vitamin fluxes occur in shallow coastal waters, benthic input could prove to be a significant B1-source to the water column and may play an important role in supplying this organic growth factor to auxotrophic primary producers.

Vitamin traffic, the production of organic growth factors by some microbial community members and their use by other taxa, is being scrutinized as a potential explanation for the variation and highly connected behavior observed in ocean plankton by community network analysis. Thiamin (vitamin B1), a cofactor in many essential biochemical reactions that modify carbon-carbon bonds of organic compounds, is distributed in complex patterns at subpicomolar concentrations in the marine surface layer (0-300 m). Sequenced genomes from organisms belonging to the abundant and ubiquitous SAR11 clade of marine chemoheterotrophic bacteria contain genes coding for a complete thiamin biosynthetic pathway, except for thiC, encoding the 4-amino-5-hydroxymethyl-2-methylpyrimidine (HMP) synthase, which is required for de novo synthesis of thiamin's pyrimidine moiety. Here we demonstrate that the SAR11 isolate 'Candidatus Pelagibacter ubique', strain HTCC1062, is auxotrophic for the thiamin precursor HMP, and cannot use exogenous thiamin for growth. In culture, strain HTCC1062 required 0.7 zeptomoles per cell (ca. 400 HMP molecules per cell). Measurements of dissolved HMP in the Sargasso Sea surface layer showed that HMP ranged from undetectable (detection limit: 2.4 pM) to 35.7 pM, with maximum concentrations coincident with the deep chlorophyll maximum. In culture, some marine cyanobacteria, microalgae and bacteria exuded HMP, and in the Western Sargasso Sea, HMP profiles changed between the morning and evening, suggesting a dynamic biological flux from producers to consumers.

Understanding biogeochemical cycling of trace metals in the ocean requires information about variability in metal concentrations and distribution over short, e.g., diel, time scales. Such variability and the factors that influence it are poorly characterized. To address this shortcoming, we measured trace metal concentrations in the total dissolved, colloidal, and soluble fractions every 3-4 h for several consecutive days and nights in surface waters from a coastal station. Our results show that both the concentration and the size partitioning of some biologically essential (Fe, Cu, Co, and Cd) and anthropogenic (Pb) metals are subjected to diel variations that may be related to both inorganic and biological processes (e.g., photolysis of high-molecular-weight dissolved organic matter, photoinduced reduction/oxidation of metal(hydrous)oxides, uptake by growing phytoplankton, degradation of organic matter, lysis, and grazing). The largest fluctuations were observed in the soluble and colloidal pools. Soluble Fe varied during the day-night cycle by a factor of 40, and the contribution of colloidal Pb to the total dissolved fraction increased from 6±3% during the day to as much as 70-80% during the night. Our results suggest that changes occurring over time scales of hours need to be considered when collecting and interpreting trace metal data from the surface ocean.

The soluble B vitamins (B1, B7, and B12) have long been recognized as playing a central metabolic role in marine phytoplankton and bacteria; however, the importance of these organic external metabolites in marine ecology has been largely disregarded, as most research has focused on inorganic nutrients and trace metals. Using recently available genomic data combined with culture-based surveys of vitamin auxotrophy (i.e., vitamin requirements), we show that this auxotrophy is widespread in the marine environment and occurs in both autotrophs and heterotrophs residing in oligotrophic and eutrophic environments. Our analysis shows that vitamins originate from the activities of some bacteria and algae and that taxonomic changes observed in marine phytoplankton communities could be the result of their specific vitamin requirements and/or vitamin availability. Dissolved vitamin concentration measurements show that large areas of the world ocean are devoid of B vitamins, suggesting that vitamin limitation could be important for the efficiency of carbon and nitrogen fixation in those regions.

The trace element selenium (Se) is required for the biosynthesis of selenocysteine (Sec), the 21st amino acid in the genetic code, but its role in the ecology of harmful algal blooms (HABs) is unknown. Here, we examined the role of Se in the biology and ecology of the harmful pelagophyte, Aureococcus anophagefferens, through cell culture, genomic analyses, and ecosystem studies. This organism has the largest and the most diverse selenoproteome identified to date that consists of at least 59 selenoproteins, including known eukaryotic selenoproteins, selenoproteins previously only detected in bacteria, and novel selenoproteins. The A. anophagefferens selenoproteome was dominated by the thioredoxin fold proteins and oxidoreductase functions were assigned to the majority of detected selenoproteins. Insertion of Sec in these proteins was supported by a unique Sec insertion sequence. Se was required for the growth of A. anophagefferens as cultures grew maximally at nanomolar Se concentrations. In a coastal ecosystem, dissolved Se concentrations were elevated before and after A. anophagefferens blooms, but were reduced by >95% during the peak of blooms to 0.05 nM. Consistent with this pattern, enrichment of seawater with selenite before and after a bloom did not affect the growth of A. anophagefferens, but enrichment during the peak of the bloom significantly increased population growth rates. These findings demonstrate that Se inventories, which can be anthropogenically enriched, can support proliferation of HABs, such as A. anophagefferens through its synthesis of a large arsenal of Se-dependent oxidoreductases that fine-tune cellular redox homeostasis.

Most eukaryotic phytoplankton require vitamin B12 to grow. However, the cycling of this organic growth factor has received substantially less attention than other bioactive substances such as trace metals in the marine environment. This is especially true in the Mediterranean Sea, where direct measurements of dissolved vitamins have never been reported. We report here the first direct measurements of dissolved vitamin B12 across longitudinal gradients in Mediterranean waters. The range of vitamin B12 concentrations measured over the whole transect was 0.5-6.2 pM, which is slightly higher than the range (undetectable-4 pM) of ambient concentrations measured in other open ocean basins in the Pacific and Atlantic oceans. The concentrations measured in the western basin were significantly higher (p < 0.05) than those of the eastern basin. They were positively correlated with chlorophyll concentrations in the most western part of the basin, and did not show any significant correlation with any other biological variables in other regions of the sampling transect.

The response of N2 fixation and [Formula: see text] uptake to environmental conditions and nutrient enrichment experiments in three western U.S. lake systems was studied (eutrophic Clear Lake; mesotrophic Walker Lake; oligotrophic Lake Tahoe). We tested the effect of additions of bioactive trace metals molybdenum as Mo(V) and iron (Fe) as well as phosphate (P), N2 fixation, [Formula: see text], carbon (C) fixation, chlorophyll a (Chla), and bacterial cell counts under both natural conditions and in mesocosm experiments. We found distinct background N2 fixation and [Formula: see text] uptake rates: highest at Clear Lake (N2 fixation: 44.7 ± 1.8 nmol N L(-1) h(-1)), intermediate at Walker Lake (N2 fixation: 1.7 ± 1.1 nmol N L(-1) h(-1); [Formula: see text] uptake: 113 ± 37 nmol N L(-1) h(-1)), and lowest at Lake Tahoe (N2 fixation: 0.1 ± 0.07 nmol N L(-1) h(-1); [Formula: see text] uptake: 37.2 ± 10.0 nmol N L(-1) h(-1)). N2 fixation was stimulated above control values with the addition of Fe and Pin Clear Lake (up to 50 and 63%, respectively); with Mo(V), Fe, and P in Walker Lake (up to 121, 990, and 85%, respectively); and with Mo(V) and P in Lake Tahoe (up to 475 and 21%, respectively). [Formula: see text] uptake showed the highest stimulation in Lake Tahoe during September 2010, with the addition of P and Mo(V) (∼84% for both). High responses to Mo(V) additions were also observed at some sites for C fixation (Lake Tahoe: 141%), Chla (Walker Lake: 54% and Clear Lake: 102%), and bacterial cell counts (Lake Tahoe: 61%). Overall our results suggest that co-limitation of nutrients is probably a common feature in lakes, and that some trace metals may play a crucial role in limiting N2 fixation and [Formula: see text] uptake activity, though primarily in non-eutrophic lakes.

In order to identify the biogeochemical parameters controlling pCO2, total chlorophyll a, and dimethyl sulfide (DMS) concentrations during the North East Atlantic Spring Bloom (NASB), we used previously unpublished particulate and dissolved elemental concentrations to construct several linear regression models; first by hypothesis-testing, and then with exhaustive stepwise linear regression followed by leave-one-out cross-validation. The field data was obtained along a latitudinal transect from the Azores Islands to the North Atlantic, and best-fit models (determined by lowest predictive error) of up to three variables are presented. Total chlorophyll a is predicted best by biomass (POC, PON) parameters and by pigments characteristic of picophytoplankton for the southern section of the sampling transect (from the Azores to the Rockhall-Hatton Plateau) and coccolithophores in the northern portion (from the Rockhall-Hatton Plateau to the Denmark Strait). Both the pCO2 and DMS models included variables traditionally associated with the development of the NASB such as mixed-layer depth and with Fe, Si, and P-deplete conditions (dissolved Fe, dissolved and biogenic silica, dissolved PO(3-)4). However, the regressions for pCO2 and DMS also include intracellular V and Mo concentrations, respectively. Mo is involved in DMS production as a cofactor in dimethylsulfoxide reductase. No significant biological role for V has yet been determined, although intracellular V is significantly correlated (p-value <0.05) with biogenic silica (R(2) = 0.72) and total chlorophyll a (R(2) = 0.49) while the same is not true for its biogeochemical analogue Mo, suggesting active uptake of V by phytoplankton. Our statistical analysis suggests these two lesser-studied metals may play more important roles in bloom dynamics than previously thought, and highlights a need for studies focused on determining their potential biological requirements and cell quotas.

B-vitamins are recognized as essential organic growth factors for many organisms, although little is known about their abundance and distribution in marine ecosystems. Despite their metabolic functions regulating important enzymatic reactions, the methodology to directly measure different B-vitamins in aquatic environments has only recently been developed. Here, we present the first direct measurements of two B-vitamins, thiamin (B1), and pyridoxine (B6), in the Amazon River plume-influenced western tropical North Atlantic (WTNA) Ocean, an area known to have high productivity, carbon (C) and dinitrogen (N2) fixation, and C sequestration. The vitamins B1 and B6 ranged in concentrations from undetectable to 230 and 40 pM, respectively. Significantly higher concentrations were measured in the surface plume water at some stations and variation with salinity was observed, suggesting a possible riverine influence on those B-vitamins. The influences of vitamins B1 and B6 on biogeochemical processes such as C and N2 fixation were investigated using a linear regression model that indicated the availability of those organic factors could affect these rates in the WTNA. In fact, significant increases in C fixation and N2 fixation were observed with increasing vitamin B1 concentrations at some low and mesohaline stations (stations 9.1 and 1; p value <0.017 and <0.03, respectively). N2 fixation was also found to have a significant positive correlation with B1 concentrations at station 1 (p value 0.029), as well as vitamin B6 at station 9.1 (p value <0.017). This work suggests that there can be a dynamic interplay between essential biogeochemical rates (C and N2 fixation) and B-vitamins, drawing attention to potential roles of B-vitamins in ecosystem dynamics, community structure, and global biogeochemistry.

B vitamins are some of the most commonly required biochemical cofactors in living systems. Therefore, cellular metabolism of marine vitamin-requiring (auxotrophic) phytoplankton and bacteria would likely be significantly compromised if B vitamins (thiamin B(1), riboflavin B(2), pyridoxine B(6), biotin B(7), and cobalamin B(12)) were unavailable. However, the factors controlling the synthesis, ambient concentrations, and uptake of these key organic compounds in the marine environment are still not well understood. Here, we report vertical distributions of five B vitamins (and the amino acid methionine) measured simultaneously along a latitudinal gradient through the contrasting oceanographic regimes of the southern California-Baja California coast in the Northeast Pacific margin. Although vitamin concentrations ranged from below the detection limits of our technique to 30 pM for B(2) and B(12) and to ∼500 pM for B(1), B(6), and B(7), each vitamin showed a different geographical and depth distribution. Vitamin concentrations were independent of each other and of inorganic nutrient levels, enriched primarily in the upper mesopelagic zone (depth of 100-300 m), and associated with water mass origin. Moreover, vitamin levels were below our detection limits (ranging from ≤0.18 pM for B(12) to ≤0.81 pM for B(1)) in extensive areas (100s of kilometers) of the coastal ocean, and thus may exert important constraints on the taxonomic composition of phytoplankton communities, and potentially also on rates of primary production and carbon sequestration.

In order to establish the status of metal contamination in surface waters in the coastal ocean off Los Angeles, California, we determined their dissolved and particulate pools and compared them with levels reported in the 1970s prior the implementation of the Clean Water Act. These measurements revealed a significant reduction in particulate toxic metal concentrations in the last 33 years with decreases of ∼100-fold for Pb and ∼400-fold for Cu and Cd. Despite these reductions, the source of particulate metals appears to be primarily anthropogenic as enrichment factors were orders of magnitude above what is considered background crustal levels. Overall, dissolved trace metal concentrations in the Los Angeles coastal waters were remarkably low with values in the same range as those measured in a pristine coastal environment off Mexico's Baja California peninsula. In order to estimate the impact of metal contamination on regional phytoplankton, the internalization rate of trace metals in a locally isolated phytoplankton model organism (Synechococcus sp. CC9311) was also determined showing a rapid internalization (in the order of a few hours) for many trace metals (e.g., Ag, Cd, Cu, Pb) suggesting that those metals could potentially be incorporated into the local food webs.

Phytoplankton growth can be limited by numerous inorganic nutrients and organic growth factors. Using the subarctic diatom Attheya sp. in culture studies, we examined how the availability of vitamin B(12) and carbon dioxide partial pressure (pCO(2)) influences growth rate, primary productivity, cellular iron (Fe), cobalt (Co), zinc (Zn) and cadmium (Cd) quotas, and the net use efficiencies (NUEs) of these bioactive trace metals (mol C fixed per mol cellular trace metal per day). Under B(12)-replete conditions, cells grown at high pCO(2) had lower Fe, Zn and Cd quotas, and used those trace metals more efficiently in comparison with cells grown at low pCO(2). At high pCO(2), B(12)-limited cells had ~50% lower specific growth and carbon fixation rates, and used Fe ~15-fold less efficiently, and Zn and Cd ~3-fold less efficiently, in comparison with B(12)-replete cells. The observed higher Fe, Zn and Cd NUE under high pCO(2)/B(12)-replete conditions are consistent with predicted downregulation of carbon-concentrating mechanisms. Co quotas of B(12)-replete cells were ∼5- to 14-fold higher in comparison with B(12)-limited cells, suggesting that >80% of cellular Co of B(12)-limited cells was likely from B(12). Our results demonstrate that CO(2) and vitamin B(12) interactively influence growth, carbon fixation, trace metal requirements and trace metal NUE of this diatom. This suggests the need to consider complex feedback interactions between multiple environmental factors for this biogeochemically critical group of phytoplankton in the last glacial maximum as well as the current and future changing ocean.

Fossil fuel combustion is the primary anthropogenic source of both CO2 and Hg to the atmosphere. On a global scale, most Hg that enters ecosystems is derived from atmospheric Hg that deposits onto the land surface. Increasing concentrations of atmospheric CO2 may affect Hg deposition to terrestrial systems and storage in soils through CO(2)-mediated changes in plant and soil properties. We show, using free-air CO2 enrichment (FACE) experiments, that soil Hg concentrations are almost 30% greater under elevated atmospheric CO2 in two temperate forests. There were no direct CO2 effects, however, on litterfall, throughfall or stemflow Hg inputs. Soil Hg was positively correlated with percent soil organic matter (SOM), suggesting that CO(2)-mediated changes in SOM have influenced soil Hg concentrations. Through its impacts on SOM, elevated atmospheric CO2 may increase the Hg storage capacity of soils and modulate the movement of Hg through the biosphere. Such effects of rising CO2, ones that transcend the typically studied effects on C and nutrient cycling, are an important next phase for research on global environmental change.

The fresh water discharged by large rivers such as the Amazon is transported hundreds to thousands of kilometers away from the coast by surface plumes. The nutrients delivered by these river plumes contribute to enhanced primary production in the ocean, and the sinking flux of this new production results in carbon sequestration. Here, we report that the Amazon River plume supports N(2) fixation far from the mouth and provides important pathways for sequestration of atmospheric CO(2) in the western tropical North Atlantic (WTNA). We calculate that the sinking of carbon fixed by diazotrophs in the plume sequesters 1.7 Tmol of C annually, in addition to the sequestration of 0.6 Tmol of C yr(-1) of the new production supported by NO(3) delivered by the river. These processes revise our current understanding that the tropical North Atlantic is a source of 2.5 Tmol of C to the atmosphere [Mikaloff-Fletcher SE, et al. (2007) Inverse estimates of the oceanic sources and sinks of natural CO(2) and the implied oceanic carbon transport. Global Biogeochem Cycles 21, doi:10.1029/2006GB002751]. The enhancement of N(2) fixation and consequent C sequestration by tropical rivers appears to be a global phenomenon that is likely to be influenced by anthropogenic activity and climate change.

This study examines the effectiveness of remediating a well-recognized case of heavy metal pollution at Foundry Cove (FC), Hudson River, New York. This tidal freshwater marsh was polluted with battery-factory wastes (1953-1979) and dredged in 1994-1995. Eight years after remediation, dissolved and particulate metals (Cd, Co, Cu, Pb, Ni, and Ag) were found to be lower than levels in the lower Hudson near New York City. Levels of metals (Co, Ni, Cd) on suspended particles were comparatively high. Concentrations of surface sediment Cd throughout the marsh system remain high, but have decreased both in the dredged and undredged areas: Cd was 2.4-230mg/kg dw of sediment in 2005 vs. 109-1500mg/kg in the same area in 1983. The rate of tidal export of Cd from FC has decreased by >300-fold, suggesting that dredging successfully stemmed a major source of Cd to the Hudson River.

An increasing body of evidence suggests that much of the trace metal contamination observed in coastal waters is no longer derived from point-source inputs, but instead originates from diffuse, non-point sources. Previous research has shown that water temperature and dissolved oxygen regulate non-point source processes such as sediment diagenesis; however, limited information is available regarding the effect of these variables on toxic trace metal cycling and speciation in natural waters. Here, we present data on the seasonal variation of dissolved Cu cycling in the Long Island Sound, an urban estuary adjacent to New York City. An operationally defined chemical speciation technique based on kinetic lability and organic complexation has been applied to examine the most ecologically relevant metal fraction. In contrast to the decrease from spring to summer observed in the total dissolved Cu pool (average +/- SD: 15.1 +/- 4.4 nM in spring and 11.8 +/- 3.5 nM in summer), our results revealed that in the highly impacted western LIS, levels of labile Cu reached higher levels in summer (range 3.6-7.7 nM) than in spring (range 1.5-3.9 nM). Labile Cu in surface waters of the western Sound appeared to have a wastewater source during spring high flow conditions, coinciding with elevated levels of sewage-derived Ag. Labile Cu elsewhere in the LIS during spring apparently resulted from fluvial input and mixing. During summer, labile Cu increased in bottom waters (at one site, bottom water labile Cu increased from 1.5 nM in spring to 7.7 nM in summer), and covariance with tracers of diagenetic remobilization (e.g., Mn) revealed a sedimentary source. Although total dissolved Cu showed no consistent trends with water quality parameters, labile Cu in bottom waters showed an inverse correlation with dissolved oxygen and a positive, exponential correlation with water temperature. These results suggest that future increases in coastal water temperatures may cause the benthic source of labile Cu to become proportionally more significant.

The composition of interstitial waters in Spain's Doñana National Park was assessed 4 years after a major pyrite slurry spill occurred from the Aznalcollar Mine. Metal and nutrient concentrations in pore waters from two of the most important watercourses traversing Doñana Park were measured: Guadiamar River (affected by the accident) and Partido Stream (unimpacted by the accident). Concentrations of dissolved constituents in interstitial waters varied according to land use in the two watersheds and to the effects of the mine spill. Levels of dissolved Co, Cu, Mo, Ti, and Zn were higher in pore waters from the Guadiamar River than in the Partido Stream, suggesting that concentrations of trace elements are still influenced by the spill. In contrast, concentrations of dissolved nutrients (NH4+, NO2-, NO3-, PO4(-3)) and some trace metals used in fertilizers (e.g. Al and Cr) were higher in the Partido Stream. Levels of dissolved As, Cs, DOC, Ge, Hg, Rb and V in the interstitial waters were equal in both watercourses. Metal concentrations in interstitial waters of the Guadiamar River floodplain were between 0.3 (As) and 16,000 (Zn) times lower than those previously reported in the river and groundwater a few weeks after the mine spill. Although metals in pore water appear to have reached levels characteristic of the area before the accident, concentrations are 60-150 times higher than those in pore waters from other regions. Metal:Al ratios in Doñana's pore waters suggest a transport of contaminants from the Iberian Pyrite Belt into Doñana Park.

This review summarizes some of the principal results of systematic measurements of trace metal concentrations throughout San Francisco Bay that began in 1989, and that have yielded insights on the factors controlling temporal and spatial variations of those concentrations on seasonal to decadal time scales. Pronounced seasonal variation in some metal concentrations is associated with gradients in the system's hydrology and the diagenetic remobilization of metals from benthic sediments. Additional temporal variation is associated with interannual differences in hydrologic flushing (e.g., ENSO cycles) and episodic storm events. While intra- and inter-annual variabilities complicate assessments of long-term variations in metal concentrations, recent analyses using stable lead isotopic composition distributions and time-series models have deconvoluted decadal changes in lead and silver concentrations in the estuary. Decadal variations in concentrations of other contaminant metals (e.g., mercury) are now being characterized, as well as projections of future concentrations of other metals of concern (e.g., copper). These historic assessments and projections of trace metal variations attest to the importance of long-term, systematic monitoring programs to quantify past and future impacts on water quality in San Francisco Bay and other complex estuarine systems.

Dissolved trace metal (Ag, Cd, Cu, Fe, Ni, Pb, and Zn), inorganic nutrient (NO3, NH4, PO4, H4SiO4), and DOC concentrations were measured at 43 stations during low (July 2000) and high (April 2001) river discharge conditions in surface waters of Long Island Sound (LIS). To evaluate the impact of fluvial sources to the total metal budget of the sound, samples were collected from major tributaries discharging into LIS (Thames, Quinnipiac, Housatonic, Connecticut, and East Rivers). To compare LIS with other coastal embayments, samples were also collected from five LIS coastal embayments (Manhassett Bay, Huntington Harbor, Oyster Bay, Hempstead Harbor, and Port Jefferson Harbor), which are monitored by the U.S. National Status and Trends Program. Metal and nutrient distributions identified two biogeochemical regimes within LIS: an area of relatively high nutrient and metal concentrations in the East River/Narrows region in western LIS and an area in the eastern region of the sound that had comparatively lower concentrations. Mass balance estimates indicated that, during low flow conditions, the East River was the dominant allochthonous source of most trace metals (Ag, Cd, Cu, Ni, Zn) and inorganic nutrients (NO3 and PO4); during high flow conditions, the most influential source of these constituents was the Connecticut River. Mass balance estimates also evidenced a large autochthonous source of Cu, Ni, and Zn, as their spatial distributions displayed elevated concentrations away from point sources such as the East River. Principal component analysis suggested that metal and nutrient distributions in the LIS system were influenced by different seasonal processes: remobilization from contaminated sediments, anthropogenic inputs from sewage discharges and phytoplankton scavenging during the spring freshet, and benthic remobilization during summer conditions.

The Redfield ratio of 106 carbon:16 nitrogen:1 phosphorus in marine phytoplankton is one of the foundations of ocean biogeochemistry, with applications in algal physiology, palaeoclimatology and global climate change. However, this ratio varies substantially in response to changes in algal nutrient status and taxonomic affiliation. Here we report that Redfield ratios are also strongly affected by partitioning into surface-adsorbed and intracellular phosphorus pools. The C:N:surface-adsorbed P (80-105 C:15-18 N:1 P) and total (71-80 C:13-14 N:1 P) ratios in natural populations and cultures of Trichodesmium were close to Redfield values and not significantly different from each other. In contrast, intracellular ratios consistently exceeded the Redfield ratio (316-434 C:59-83 N:1 intracellular P). These high intracellular ratios were associated with reduced N2 fixation rates, suggestive of phosphorus deficiency. Other algal species also have substantial surface-adsorbed phosphorus pools, suggesting that our Trichodesmium results are generally applicable to all phytoplankton. Measurements of the distinct phytoplankton phosphorus pools may be required to assess nutrient limitation accurately from elemental composition. Deviations from Redfield stoichiometry may be attributable to surface adsorption of phosphorus rather than to biological processes, and this scavenging could affect the interpretation of marine nutrient inventories and ecosystem models.

A suite of dissolved trace metals (Ag, Cd, Cu and Pb), inorganic nutrients (NO(3), PO(4)), and chlorophyll a was measured along a 55 mile transect from the East River into western and central Long Island Sound. The main objectives of this study were to determine the relative levels of contamination from sewage, and to assess its possible biological impact on local waters. The East River-Long Island Sound system receives large volumes of treated sewage and industrial effluent as a result of the heavy urbanization of the area. Despite these strong environmental pressures, this study is among the first to report dissolved metal levels from that region. Consistent with the locations of anthropogenic sources, a strong east-west concentration gradient was observed for Ag, Pb, NO(3) and PO(4) with the highest levels found in the East River. In contrast, dissolved Cd and Cu were relatively constant throughout the area of study, suggesting that sewage sources have a more limited influence on the levels of those metals. Remobilization from contaminated sediments may represent the primary source of Cd and Cu to the Long Island Sound under low-runoff conditions in summer. Chlorophyll a concentrations, used as an indicator of total biomass, were also low in the East River. These low chlorophyll concentrations could not be explained by nutrient or light limitation, water column stratification, or to advection of phytoplankton out of the river during tidal flushing. These preliminary results suggest a potential toxic effect of sewage on the biological communities of the East River.

The study of trace metal cycling by aquatic protists is limited by current analytical techniques. Standard "bulk" element analysis techniques that rely on physical separations to concentrate cells for analysis cannot separate cells from co-occurring detrital material or other cells of differing taxonomy or trophic function. Here we demonstrate the ability of a synchrotron-based X-ray fluorescence (SXRF) microprobe to quantify the elements Si, Mn, Fe, Ni, and Zn in individual aquatic protist cells. This technique distinguishes between different types of cells in an assemblage and between cells and other particulate matter. Under typical operating conditions, the minimum detection limits are 7.0 x 10(-16) mol microm(-2) for Si and between 5.0 x 10(-20) and 3.9 x 10(-19) mol microm(-2) for Mn, Fe, Ni, and Zn; this sensitivity is sufficient to detect these elements in cells from even the most pristine waters as demonstrated in phytoplankton cells collected from remote areas of the Southern Ocean. Replicate analyses of single cells produced variations of <5% for Si, Mn, Fe, and Zn and <10% for Ni. Comparative analyses of cultured phytoplankton cells generally show no significant differences in cellular metal concentrations measured with SXRF and standard bulk techniques (spectrophotometry and graphite furnace atomic absorption spectrometry). SXRF also produces two-dimensional maps of element distributions in cells, thereby providing information not available with other analytical approaches. This technique enables the accurate and precise measurement of trace metals in individual aquatic protists collected from natural environments.

A synthesis of the current understanding of potential iron limitation of pelagic nitrogen fixation is given, considering biochemical bases of Fe requirements and empirical observations of growth and Fe quotas of cultures and field populations of Trichodesmium. The potential for iron limitation of heterotrophic diazotrophy in the marine environment is also evaluated.

Groundwater and surface water were collected using trace metal clean techniques from the upper glacial aquifer of West Neck Bay (Shelter Island) in eastern Long Island, NY, during the late spring and summer of 1999. The collection sites on Shelter Island are located in an area that is primarily residential and believed to have uncontaminated groundwater. Ultrafiltration was used to size-fractionate the dissolved (<0.45 microm) fraction into colloidal (1 kDa - 0.45 microm) and low molecular weight (<1 kDa) size pools. These fractions were analyzed for trace metals (Al, Ag, Cd, Cu, Mn, Pb, and Zn), organic carbon, and inorganic nutrients (NH4, NO3, PO4). The levels of metals and organic carbon in the groundwater were as low as those found in the open ocean, far removed from anthropogenic inputs. These findings corroborate the need to apply trace metal clean techniques in the determination of metal levels in uncontaminated groundwater. A significant fraction of dissolved metals (22-96%) and organic carbon (approximately 40%) in the groundwater and in surface waters of the Bay was found to be associated with colloids. The significance of the metal association with the colloidal fraction decreased in the order of Al > Cu > Ag > Zn = Cd = Mn and appeared to be dependent on the affinities of these metals for humic substances. In contrast, NO3 and NH4 were found to be almost entirely (approximately 98-99%) in the low molecular weight size fraction. Metal/aluminum and metal/carbon ratios measured in the colloids were similar to those reported for humic substances and significantly different from those of soils. This suggests that colloidal particles might originate from humic materials as opposed to purely inorganic minerals. These results indicate the need to consider the colloidal fraction in the fate and mobility of metals in groundwater and that, despite the low levels of organic matter (<50 microM of DOC) measured in groundwater, some groundwater colloids appear to be organic in nature.

Marine fixation of atmospheric nitrogen is believed to be an important source of biologically useful nitrogen to ocean surface waters, stimulating productivity of phytoplankton and so influencing the global carbon cycle. The majority of nitrogen fixation in tropical waters is carried out by the marine cyanobacterium Trichodesmium, which supplies more than half of the new nitrogen used for primary production. Although the factors controlling marine nitrogen fixation remain poorly understood, it has been thought that nitrogen fixation is limited by iron availability in the ocean. This was inferred from the high iron requirement estimated for growth of nitrogen fixing organisms and the higher apparent densities of Trichodesmium where aeolian iron inputs are plentiful. Here we report that nitrogen fixation rates in the central Atlantic appear to be independent of both dissolved iron levels in sea water and iron content in Trichodesmium colonies. Nitrogen fixation was, instead, highly correlated to the phosphorus content of Trichodesmium and was enhanced at higher irradiance. Furthermore, our calculations suggest that the structural iron requirement for the growth of nitrogen-fixing organisms is much lower than previously calculated. Although iron deficiency could still potentially limit growth of nitrogen-fixing organisms in regions of low iron availability-for example, in the subtropical North Pacific Ocean-our observations suggest that marine nitrogen fixation is not solely regulated by iron supply.

Seasonal (October 1997 and May 1998) concentrations of dissolved (< 0.45 micron) trace metals (Ag, Al, Cd, Cu, Fe, Mn), inorganic nutrients (NO3, PO4, Si), DOC and DON were measured at seven wells during periods of low and high groundwater flow, in the aquifer around Flanders Bay in Eastern Long Island, New York. Similar measurements were made in surface waters of Flanders Bay, a shallow coastal embayment with restricted water flushing and river input. Dissolved constituents in the groundwater were classified according to their behavior under different flow conditions as follows: (1) peak during high flow (DOC, pH, Si, NO3, Al and Cu); (2) peak during low flow (salinity, DON, Ag, Cd, Mn); and (3) concentrations independent of flow conditions (PO4 and Fe). The primarily urban and agricultural land use on the North Fork of Long Island was reflected in higher concentrations of nutrients, Cu and Cd in groundwater, compared to samples from the South Fork which is mostly open parkland. Principal component analysis indicated that groundwater seepage could influence the chemical composition of Flanders Bay with respect to the major geochemical carriers (e.g. Fe and Mn). However, mass balance estimates for Cu indicated that, during low flow conditions, net groundwater Cu input was about 10% of the total input. In contrast, during high flow, net groundwater flow could account for up to 58% of all Cu inputs. Nevertheless, a large imbalance, which accounted for up to 70% of the outflux during low aquifer recharge, suggested that the Cu budget of the Bay was not adequately described by the inputs considered (river, net groundwater flow, atmospheric deposition, and tidal exchange). Important missing components of the Cu mass balance in Flanders Bay may include groundwater circulation driven by tides and waves as well as diffusive benthic fluxes.

Zebra mussels (Dreissena polymorpha) are widespread and abundant in major freshwater ecosystems in North America, even though the phytoplankton food resources in some of these systems seem to be too low to sustain them. Because phytoplankton biomass is greatly depleted in ecosystems with large D. polymorpha populations and bacteria do not seem to be an important food source for this species, exploitation of alternative carbon sources may explain the unexpected success of D. polymorpha in such environments. Here we examine the possibility that absorption of dissolved organic carbon (DOC) from water could provide a nutritional supplement to zebra mussels. We find that mussels absorb 14C-labelled DOC produced by cultured diatoms with an efficiency of 0.23%; this indicates that DOC in natural waters could contribute up to 50% of the carbon demand of zebra mussels. We also find that zebra mussels absorb some dissolved metals that have been complexed by the DOM; although absorption of dissolved selenium was unaffected by DOC, absorption of dissolved cadmium, silver and mercury by the mussels increased 32-, 8.7- and 3.6-fold, respectively, in the presence of high-molecular-weight DOC.