Bioactive trace metals are critical micronutrients for marine
microorganisms due to their role in mediating biological redox reactions,
and complex biogeochemical processes control their ...distributions.
Hydrothermal vents may represent an important source of metals to
microorganisms, especially those inhabiting low-iron waters, such as in the
southwest Pacific Ocean. Previous measurements of primordial 3He
indicate a significant hydrothermal source originating in the northeastern (NE)
Lau Basin, with the plume advecting into the southwest Pacific Ocean at
1500–2000 m depth (Lupton et
al., 2004). Studies investigating the long-range transport of trace metals
associated with such dispersing plumes are rare, and the biogeochemical
impacts on local microbial physiology have not yet been described. Here we
quantified dissolved metals and assessed microbial metaproteomes across a
transect spanning the tropical and equatorial Pacific with a focus on the
hydrothermally active NE Lau Basin and report elevated iron and manganese
concentrations across 441 km of the southwest Pacific. The most intense
signal was detected near the Mangatolo Triple Junction (MTJ) and Northeast
Lau Spreading Center (NELSC), in close proximity to the previously reported
3He signature. Protein content in distal-plume-influenced seawater,
which was high in metals, was overall similar to background locations,
though key prokaryotic proteins involved in metal and organic uptake,
protein degradation, and chemoautotrophy were abundant compared to deep
waters outside of the distal plume. Our results demonstrate that trace
metals derived from the NE Lau Basin are transported over appreciable
distances into the southwest Pacific Ocean and that bioactive chemical
resources released from submarine vent systems are utilized by surrounding
deep-sea microbes, influencing both their physiology and their contributions
to ocean biogeochemical cycling.
Recent studies have demonstrated regional differences in marine ecosystem C:N:P with implications for carbon and nutrient cycles. Due to strong co-variance, temperature and nutrient stress explain ...variability in C:N:P equally well. A reductionistic approach can link changes in individual environmental drivers with changes in biochemical traits and cell C:N:P. Thus, we quantified effects of temperature and nutrient stress on Synechococcus chemistry using laboratory chemostats, chemical analyses, and data-independent acquisition mass spectrometry proteomics. Nutrient supply accounted for most C:N:Pcell variability and induced tradeoffs between nutrient acquisition and ribosomal proteins. High temperature prompted heat-shock, whereas thermal effects via the "translation-compensation hypothesis" were only seen under P-stress. A Nonparametric Bayesian Local Clustering algorithm suggested that changes in lipopolysaccharides, peptidoglycans, and C-rich compatible solutes may also contribute to C:N:P regulation. Physiological responses match field-based trends in ecosystem stoichiometry and suggest a hierarchical environmental regulation of current and future ocean C:N:P.
We present evidence demonstrating the capability of "Phaeocystis antarctica "colonies to substitute cobalt (Co) and zinc (Zn) as micronutrients, in which Co limitation is alleviated by additions of ...Zn and vice versa. Maximal growth rates and biomass were determined by fluorescence and the values obtained under replete Zn and no added Co conditions were significantly higher than under replete Co and no added Zn conditions, suggesting a preference for Zn over Co. The observation of Zn-Co substitution in this high-latitude member of the Prymnesiophyceae class, coupled with similar previous observations in the coccolithophore "Emiliana huxleyi" and several centric diatoms, suggests that Zn-Co substitution could be a widespread global phenomenon in eukaryotic phytoplankton. The Zn-Co biochemical substitution seen in "Phaeocystis" might be the result of evolutionary pressure for maintaining growth rates in high export environments in which rapid depletion of Zn, Co, and carbon occur simultaneously in the upper water column.
The stoichiometry of biological components and their influence on dissolved distributions have long been of interest in the study of the oceans. Cobalt has the smallest oceanic inventory of inorganic ...micronutrients and hence is particularly vulnerable to influence by internal oceanic processes including euphotic zone uptake, remineralization, and scavenging. Here we observe not only large variations in dCo : P stoichiometry but also the acceleration of those dCo : P ratios in the upper water column in response to several environmental processes. The ecological stoichiometry of total dissolved cobalt (dCo) was examined using data from a US North Atlantic GEOTRACES transect and from a zonal South Atlantic GEOTRACES-compliant transect (GA03/3_e and GAc01) by Redfieldian analysis of its statistical relationships with the macronutrient phosphate. Trends in the dissolved cobalt to phosphate (dCo : P) stoichiometric relationships were evident in the basin-scale vertical structure of cobalt, with positive dCo : P slopes in the euphotic zone and negative slopes found in the ocean interior and in coastal environments. The euphotic positive slopes were often found to accelerate towards the surface and this was interpreted as being due to the combined influence of depleted phosphate, phosphorus-sparing (conserving) mechanisms, increased alkaline phosphatase metalloenzyme production (a zinc or perhaps cobalt enzyme), and biochemical substitution of Co for depleted Zn. Consistent with this, dissolved Zn (dZn) was found to be drawn down to only 2-fold more than dCo, despite being more than 18-fold more abundant in the ocean interior. Particulate cobalt concentrations increased in abundance from the base of the euphotic zone to become ∼ 10 % of the overall cobalt inventory in the upper euphotic zone with high stoichiometric values of ∼ 400 µmol Co mol−1 P. Metaproteomic results from the Bermuda Atlantic Time-series Study (BATS) station found cyanobacterial isoforms of the alkaline phosphatase enzyme to be prevalent in the upper water column, as well as a sulfolipid biosynthesis protein indicative of P sparing. The negative dCo : P relationships in the ocean interior became increasingly vertical with depth, and were consistent with the sum of scavenging and remineralization processes (as shown by their dCo : P vector sums). Attenuation of the remineralization with depth resulted in the increasingly vertical dCo : P relationships. Analysis of particulate Co with particulate Mn and particulate phosphate also showed positive linear relationships below the euphotic zone, consistent with the presence and increased relative influence of Mn oxide particles involved in scavenging. Visualization of dCo : P slopes across an ocean section revealed hotspots of scavenging and remineralization, such as at the hydrothermal vents and below the oxygen minimum zone (OMZ) region, respectively, while that of an estimate of Co* illustrated stoichiometrically depleted values in the mesopelagic and deep ocean due to scavenging. This study provides insights into the coupling between the dissolved and particulate phase that ultimately creates Redfield stoichiometric ratios, demonstrating that the coupling is not an instantaneous process and is influenced by the element inventory and rate of exchange between phases. Cobalt's small water column inventory and the influence of external factors on its biotic stoichiometry can erode its limited inertia and result in an acceleration of the dissolved stoichiometry towards that of the particulate phase in the upper euphotic zone. As human use of cobalt grows exponentially with widespread adoption of lithium ion batteries, there is a potential to affect the limited biogeochemical inertia of cobalt and its resultant ecology in the oceanic euphotic zone.
Recent evidence from the sulfur isotopic record indicates a transition ∼2.5 billion years ago from an ocean chemistry first dominated by iron and then by sulfide. It has been hypothesized that the ...selection of metal centers in metalloenzymes has been influenced by the availability of metals through geological time, in particular as a result of large differences in the solubility of metals-sulfides. In this study, we examine the trace metal requirements and sensitivities of marine cyanobacteria and use recent stability constants to model the abundance and chemical speciation of metals across this chemical transition ∼2.5 billion years ago. Two major results are reported here: (1) the marine cyanobacterial species studied thus far show trace metal preferences and sensitivities that are consistent with their evolution in a sulfidic marine environment, and (2) in an ancient ocean dominated by high fluxes and concentrations of iron, the relative availability of trace metals would have been similar to that of a sulfidic system—Fe>Mn, Ni, Co≫Cd, Zn, Cu—as a result of the formation of dissolved sulfide complexes. Thus, the formation of strong aqueous metal-sulfide complexes was likely as important as the precipitation of minerals in influencing the selection of metals in biology. These results suggest that marine biogeochemical cycles and marine bioinorganic chemistry have co-evolved, and that the evidence for this co-evolution has been preserved in the physiology and genomes of modern descendants of the early cyanobacteria.
The marine cyanobacterial species studied thus far show trace metal preferences consistent with evolution in a sulfidic marine environment. In an Archean ocean dominated by high fluxes and concentrations of ferrous iron, the relative availability of trace metals would have been similar to that of a sulfidic system.
Despite very low concentrations of cobalt in marine waters, cyanobacteria in the genus Prochlorococcus retain the genetic machinery for the synthesis and use of cobalt-bearing cofactors (cobalamins) ...in their genomes. We explore cobalt metabolism in a Prochlorococcus isolate from the equatorial Pacific Ocean (strain MIT9215) through a series of growth experiments under iron- and cobalt-limiting conditions. Metal uptake rates, quantitative proteomic measurements of cobalamin-dependent enzymes, and theoretical calculations all indicate that Prochlorococcus MIT9215 can sustain growth with less than 50 cobalt atoms per cell, ∼100-fold lower than minimum iron requirements for these cells (∼5,100 atoms per cell). Quantitative descriptions of Prochlorococcus cobalt limitation are used to interpret the cobalt distribution in the equatorial Pacific Ocean, where surface concentrations are among the lowest measured globally but Prochlorococcus biomass is high. A low minimum cobalt quota ensures that other nutrients, notably iron, will be exhausted before cobalt can be fully depleted, helping to explain the persistence of cobalt-dependent metabolism in marine cyanobacteria.
The fractionation of silicon (Si) stable isotopes by biological activity in the surface ocean makes the stable isotope composition of silicon (δ30Si) dissolved in seawater a sensitive tracer of the ...oceanic biogeochemical Si cycle. We present a high‐precision dataset that characterizes the δ30Si distribution in the deep Atlantic Ocean from Denmark Strait to Drake Passage, documenting strong meridional and smaller, but resolvable, vertical δ30Si gradients. We show that these gradients are related to the two sources of deep and bottom waters in the Atlantic Ocean: waters of North Atlantic and Nordic origin carry a high δ30Si signature of ≥+1.7‰ into the deep Atlantic, while Antarctic Bottom Water transports Si with a low δ30Si value of around +1.2‰. The deep Atlantic δ30Si distribution is thus governed by the quasi‐conservative mixing of Si from these two isotopically distinct sources. This disparity in Si isotope composition between the North Atlantic and Southern Ocean is in marked contrast to the homogeneity of the stable nitrogen isotope composition of deep ocean nitrate (δ15N‐NO3). We infer that the meridional δ30Si gradient derives from the transport of the high δ30Si signature of Southern Ocean intermediate/mode waters into the North Atlantic by the upper return path of the meridional overturning circulation (MOC). The basin‐scale deep Atlantic δ30Si gradient thus owes its existence to the interaction of the physical circulation with biological nutrient uptake at high southern latitudes, which fractionates Si isotopes between the abyssal and intermediate/mode waters formed in the Southern Ocean.
Key Points
Deep Atlantic Ocean displays gradient in Si isotopic composition of silicic acid
The gradient is caused by quasi‐conservative mixing of Si from NADW and AABW
Contrasting isotope signature of NADW and AABW due to interaction of biology and MOC
The distribution of dissolved iron (Fe), total organic Fe-binding ligands, and siderophores were measured between the surface and 400 m at Station ALOHA, a long term ecological study site in the ...North Pacific Subtropical Gyre. Dissolved Fe concentrations were low throughout the water column and strong organic Fe-binding ligands exceeded dissolved Fe at all depths; varying from 0.9 nmol L-1 in the surface to 1.6 nmol L-1 below 150 m. Although Fe does not appear to limit microbial production, we nevertheless found siderophores at nearly all depths, indicating some populations of microbes were responding to Fe stress. Ferrioxamine siderophores were most abundant in the upper water column, with concentrations between 0.1-2 pmol L-1, while a suite of amphibactins were found below 200 m with concentrations between 0.8-11 pmol L-1. The distinct vertical distribution of ferrioxamines and amphibactins may indicate disparate strategies for acquiring Fe from dust in the upper water column and recycled organic matter in the lower water column. Amphibactins were found to have conditional stability constants (log ) ranging from 12.0-12.5, while ferrioxamines had much stronger conditional stability constants ranging from 14.0-14.4, within the range of observed L1 ligands by voltammetry. We used our data to calculate equilibrium Fe speciation at Station ALOHA to compare the relative concentration of inorganic and siderophore complexed Fe. The results indicate that the concentration of Fe bound to siderophores was up to two orders of magnitude higher than inorganic Fe, suggesting that even if less bioavailable, siderophores were nevertheless a viable pathway for Fe acquisition by microbes at our study site. Finally, we observed rapid production of ferrioxamine E by particle-associated bacteria during incubation of freshly collected sinking organic matter. Fe-limitation may therefore be a factor in regulating carbon metabolism and nutrient regeneration in the mesopelagic.
Cobalt and marine redox evolution Swanner, Elizabeth D.; Planavsky, Noah J.; Lalonde, Stefan V. ...
Earth and planetary science letters,
03/2014, Letnik:
390
Journal Article
Recenzirano
Odprti dostop
Cobalt (Co) is a bio-essential trace element and limiting nutrient in some regions of the modern oceans. It has been proposed that Co was more abundant in poorly ventilated Precambrian oceans based ...on the greater utilization of Co by anaerobic microbes relative to plants and animals. However, there are few empirical or theoretical constraints on the history of seawater Co concentrations. Herein, we present a survey of authigenic Co in marine sediments (iron formations, authigenic pyrite and bulk euxinic shales) with the goal of tracking changes in the marine Co reservoir throughout Earth's history. We further provide an overview of the modern marine Co cycle, which we use as a platform to evaluate how changes in the redox state of Earth's surface were likely to have affected marine Co concentrations. Based on sedimentary Co contents and our understanding of marine Co sources and sinks, we propose that from ca. 2.8 to 1.8 Ga the large volume of hydrothermal fluids circulating through abundant submarine ultramafic rocks along with a predominantly anoxic ocean with a low capacity for Co burial resulted in a large dissolved marine Co reservoir. We tentatively propose that there was a decrease in marine Co concentrations after ca. 1.8 Ga resulting from waning hydrothermal Co sources and the expansion of sulfide Co burial flux. Changes in the Co reservoir due to deep-water ventilation in the Neoproterozoic, if they occurred, are not resolvable with the current dataset. Rather, Co enrichments in Phanerozoic euxinic shales deposited during ocean anoxic events (OAE) indicate Co mobilization from expanded anoxic sediments and enhanced hydrothermal sources. A new record of marine Co concentrations provides a platform from which we can reevaluate the role that environmental Co concentrations played in shaping biological Co utilization throughout Earth's history.
•Authigenic iron oxides and pyrite record marine Co concentrations.•The Precambrian marine Co reservoir was greatest from 2.8–1.84 Ga.•Sedimentary Co enhancements are linked to anoxia and hydrothermal activity.•A Neoproterozoic drop in the marine Co reservoir with ventilation is not resolvable.•The marine Co reservoir broadly corresponds to acquisition of Co-binding proteins.
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