scholarly journals Hopanoid lipids may facilitate aerobic nitrogen fixation in the ocean

2019 ◽  
Vol 116 (37) ◽  
pp. 18269-18271 ◽  
Author(s):  
Francisco M. Cornejo-Castillo ◽  
Jonathan P. Zehr
Keyword(s):  
Nitrogen Fixation ◽  
Diffusion Barrier ◽  
Open Ocean ◽  
Membrane Property ◽  
Surface Ocean ◽  
Respiration Rates ◽  
Saturated Surface

Cyanobacterial diazotrophs are considered to be the most important source of fixed N2in the open ocean. Biological N2fixation is catalyzed by the extremely O2-sensitive nitrogenase enzyme. In cyanobacteria without specialized N2-fixing cells (heterocysts), mechanisms such as decoupling photosynthesis from N2fixation in space or time are involved in protecting nitrogenase from the intracellular O2evolved by photosynthesis. However, it is not known how cyanobacterial cells limit O2diffusion across their membranes to protect nitrogenase in ambient O2-saturated surface ocean waters. Here, we explored all known genomes of the major marine cyanobacterial lineages for the presence of hopanoid synthesis genes, since hopanoids are a class of lipids that might act as an O2diffusion barrier. We found that, whereas all non−heterocyst-forming cyanobacterial diazotrophs had hopanoid synthesis genes, none of the marineSynechococcus,Prochlorococcus(non−N2-fixing), and marine heterocyst-forming (N2-fixing) cyanobacteria did. Finally, we conclude that hopanoid-enriched membranes are a conserved trait in non−heterocyst-forming cyanobacterial diazotrophs that might lower the permeability to extracellular O2. This membrane property coupled with high respiration rates to decrease intracellular O2concentration may therefore explain how non−heterocyst-forming cyanobacterial diazotrophs can fix N2in the fully oxic surface ocean.

scholarly journals Global high-resolution monthly <i>p</i>CO<sub>2</sub> climatology for the coastal ocean derived from neural network interpolation

2017 ◽  
Vol 14 (19) ◽  
pp. 4545-4561 ◽  
Author(s):  
Goulven G. Laruelle ◽  
Peter Landschützer ◽  
Nicolas Gruber ◽  
Jean-Louis Tison ◽  
Bruno Delille ◽  
...  
Keyword(s):  
Neural Network ◽  
Spatial Resolution ◽  
Seasonal Variations ◽  
Open Ocean ◽  
Global Perspective ◽  
Strong Increase ◽  
Spatial And Temporal Variability ◽  
Surface Ocean ◽  
Shelf Seas ◽  
Artificial Neural Network Method

Abstract. In spite of the recent strong increase in the number of measurements of the partial pressure of CO2 in the surface ocean (pCO2), the air–sea CO2 balance of the continental shelf seas remains poorly quantified. This is a consequence of these regions remaining strongly under-sampled in both time and space and of surface pCO2 exhibiting much higher temporal and spatial variability in these regions compared to the open ocean. Here, we use a modified version of a two-step artificial neural network method (SOM-FFN; Landschützer et al., 2013) to interpolate the pCO2 data along the continental margins with a spatial resolution of 0.25° and with monthly resolution from 1998 to 2015. The most important modifications compared to the original SOM-FFN method are (i) the much higher spatial resolution and (ii) the inclusion of sea ice and wind speed as predictors of pCO2. The SOM-FFN is first trained with pCO2 measurements extracted from the SOCATv4 database. Then, the validity of our interpolation, in both space and time, is assessed by comparing the generated pCO2 field with independent data extracted from the LDVEO2015 database. The new coastal pCO2 product confirms a previously suggested general meridional trend of the annual mean pCO2 in all the continental shelves with high values in the tropics and dropping to values beneath those of the atmosphere at higher latitudes. The monthly resolution of our data product permits us to reveal significant differences in the seasonality of pCO2 across the ocean basins. The shelves of the western and northern Pacific, as well as the shelves in the temperate northern Atlantic, display particularly pronounced seasonal variations in pCO2,  while the shelves in the southeastern Atlantic and in the southern Pacific reveal a much smaller seasonality. The calculation of temperature normalized pCO2 for several latitudes in different oceanic basins confirms that the seasonality in shelf pCO2 cannot solely be explained by temperature-induced changes in solubility but are also the result of seasonal changes in circulation, mixing and biological productivity. Our results also reveal that the amplitudes of both thermal and nonthermal seasonal variations in pCO2 are significantly larger at high latitudes. Finally, because this product's spatial extent includes parts of the open ocean as well, it can be readily merged with existing global open-ocean products to produce a true global perspective of the spatial and temporal variability of surface ocean pCO2.

scholarly journals What prevents nitrogen depletion in the oxygen minimum zone of the eastern tropical South Pacific?

2015 ◽  
Vol 12 (4) ◽  
pp. 1113-1130 ◽  
Author(s):  
B. Su ◽  
M. Pahlow ◽  
H. Wagner ◽  
A. Oschlies
Keyword(s):  
Nitrogen Fixation ◽  
Ocean Circulation ◽  
Deep Ocean ◽  
South Pacific ◽  
Open Ocean ◽  
Nitrogen Depletion ◽  
Biogeochemical Models ◽  
Model Domain ◽  
Limiting Nutrient ◽  
Oxygen Minimum

Abstract. Local coupling between nitrogen fixation and denitrification in current biogeochemical models could result in runaway feedback in open-ocean oxygen minimum zones (OMZs), eventually stripping OMZ waters of all fixed nitrogen. This feedback does not seem to operate at full strength in the ocean, as nitrate does not generally become depleted in open-ocean OMZs. To explore in detail the possible mechanisms that prevent nitrogen depletion in the OMZ of the eastern tropical South Pacific (ETSP), we develop a box model with fully prognostic cycles of carbon, nutrients and oxygen in the upwelling region and its adjacent open ocean. Ocean circulation is calibrated with Δ14C data of the ETSP. The sensitivity of the simulated nitrogen cycle to nutrient and oxygen exchange and ventilation from outside the model domain and to remineralization scales inside an OMZ is analysed. For the entire range of model configurations explored, we find that the fixed-N inventory can be stabilized at non-zero levels in the ETSP OMZ only if the remineralization rate via denitrification is slower than that via aerobic respiration. In our optimum model configuration, lateral oxygen supply into the model domain is required at rates sufficient to oxidize at least about one fifth of the export production in the model domain to prevent anoxia in the deep ocean. Under these conditions, our model is in line with the view of phosphate as the ultimate limiting nutrient for phytoplankton, and implies that for the current notion of nitrogen fixation being favoured in N-deficit waters, the water column of the ETSP could even be a small net source of nitrate.

scholarly journals Nutrient-ColimitedTrichodesmiumas a Nitrogen Source or Sink in a Future Ocean

2017 ◽  
Vol 84 (3) ◽  
Author(s):  
Nathan G. Walworth ◽  
Fei-Xue Fu ◽  
Michael D. Lee ◽  
Xiaoni Cai ◽  
Mak A. Saito ◽  
...  
Keyword(s):  
Nitrogen Fixation ◽  
Nitrogen Source ◽  
Nitrogen Metabolism ◽  
Organic Nitrogen ◽  
Open Ocean ◽  
Nitrogen Fixing ◽  
Content Type ◽  
Nitrogen Inputs ◽  
Ocean Conditions ◽  
Nitrogen Scavenging

ABSTRACTNitrogen-fixing (N2) cyanobacteria provide bioavailable nitrogen to vast ocean regions but are in turn limited by iron (Fe) and/or phosphorus (P), which may force them to employ alternative nitrogen acquisition strategies. The adaptive responses of nitrogen fixers to global-change drivers under nutrient-limited conditions could profoundly alter the current ocean nitrogen and carbon cycles. Here, we show that the globally important N2fixerTrichodesmiumfundamentally shifts nitrogen metabolism toward organic-nitrogen scavenging following long-term high-CO2adaptation under iron and/or phosphorus (co)limitation. Global shifts in transcripts and proteins under high-CO2/Fe-limited and/or P-limited conditions include decreases in the N2-fixing nitrogenase enzyme, coupled with major increases in enzymes that oxidize trimethylamine (TMA). TMA is an abundant, biogeochemically important organic nitrogen compound that supports rapidTrichodesmiumgrowth while inhibiting N2fixation. In a future high-CO2ocean, this whole-cell energetic reallocation toward organic nitrogen scavenging and away from N2fixation may reduce new-nitrogen inputs byTrichodesmiumwhile simultaneously depleting the scarce fixed-nitrogen supplies of nitrogen-limited open-ocean ecosystems.IMPORTANCETrichodesmiumis among the most biogeochemically significant microorganisms in the ocean, since it supplies up to 50% of the new nitrogen supporting open-ocean food webs. We usedTrichodesmiumcultures adapted to high-CO2conditions for 7 years, followed by additional exposure to iron and/or phosphorus (co)limitation. We show that “future ocean” conditions of high CO2and concurrent nutrient limitation(s) fundamentally shift nitrogen metabolism away from nitrogen fixation and instead toward upregulation of organic nitrogen-scavenging pathways. We show that the responses ofTrichodesmiumto projected future ocean conditions include decreases in the nitrogen-fixing nitrogenase enzymes coupled with major increases in enzymes that oxidize the abundant organic nitrogen source trimethylamine (TMA). Such a shift toward organic nitrogen uptake and away from nitrogen fixation may substantially reduce new-nitrogen inputs byTrichodesmiumto the rest of the microbial community in the future high-CO2ocean, with potential global implications for ocean carbon and nitrogen cycling.

Discovery of nondiazotrophic Trichodesmium species abundant and widespread in the open ocean

2021 ◽  
Vol 118 (46) ◽  
pp. e2112355118
Author(s):  
Tom O. Delmont
Keyword(s):  
Nitrogen Fixation ◽  
Nitrogen Assimilation ◽  
Gene Loss ◽  
Lipid Production ◽  
Open Ocean ◽  
Low Oxygen ◽  
Candidate Species ◽  
Functional Features ◽  
Low Oxygen Concentration ◽  
Cyanobacterial Genus

Filamentous and colony-forming cells within the cyanobacterial genus Trichodesmium might account for nearly half of nitrogen fixation in the sunlit ocean, a critical mechanism that sustains plankton’s primary productivity. Trichodesmium has long been portrayed as a diazotrophic genus. By means of genome-resolved metagenomics, here we reveal that nondiazotrophic Trichodesmium species not only exist but also are abundant and widespread in the open ocean, benefiting from a previously overlooked functional lifestyle to expand the biogeography of this prominent marine genus. Near-complete environmental genomes for those closely related candidate species reproducibly shared functional features including a lack of genes related to nitrogen fixation, hydrogen recycling, and hopanoid lipid production concomitant with the enrichment of nitrogen assimilation genes. Our results elucidate fieldwork observations of Trichodesmium cells fixing carbon but not nitrogen. The Black Queen hypothesis and burden of low-oxygen concentration requirements provide a rationale to explain gene loss linked to nitrogen fixation among Trichodesmium species. Disconnecting taxonomic signal for this genus from a microbial community’s ability to fix nitrogen will help refine our understanding of the marine nitrogen balance. Finally, we are reminded that established links between taxonomic lineages and functional traits do not always hold true.

Respiratory differences associated with culture aeration in Azotobacter vinelandii

1989 ◽  
Vol 35 (10) ◽  
pp. 918-924 ◽  
Author(s):  
Jay B. Peterson
Keyword(s):  
Nitrogen Fixation ◽  
Oxygen Uptake ◽  
Oxygen Concentration ◽  
Azotobacter Vinelandii ◽  
Partial Explanation ◽  
Respiration Rates ◽  
Carbon Substrates ◽  
Moderate Agitation ◽  
Different Levels ◽  
Oxygen Concentrations

Respiratory oxygen uptake of nitrogen-fixing Azotobacter vinelandii cells was altered by culturing at different levels of culture agitation (aeration). Cells were grown at low agitation or moderate agitation and with three different carbon substrates. The low-agitation cultures had much lower dissolved-oxygen concentrations than moderate-agitation cultures at the stage of growth at which they were studied. The respiration systems of cells from the moderate-agitation cultures had lower apparent affinities (higher Ks (O2) values) for oxygen than cells grown at low agitation. The higher Ks (O2)) values were dependent on the presence of Ca2+ and (or) Mg2+ in the medium. In low-agitation cultures, the oxygen concentrations were below the Ks (O2 values and the respiration rates in the cultures were therefore well below the maximal respiration (Vmax) rates. The oxygen concentrations in moderate-agitation cultures were above the Ks (O2) values and the culture respiration rates were much higher. The culture oxygen concentration relative to the Ks (O2) had a much greater effect on culture respiration rate than did the Vmax. It is proposed that changes in the respiration system resulting from culture agitation (aeration) reflect an "oxygen-sensing mechanism" that regulates respiration. This would provide at least a partial explanation for the increased respiration rates with increased culture oxygen concentration in A. vinelandii.Key words: Azotobacter, oxygen, respiration, nitrogen fixation.

scholarly journals Autonomous seawater <i>p</i>CO<sub>2</sub> and pH time series from 40 surface buoys and the emergence of anthropogenic trends

2019 ◽  
Vol 11 (1) ◽  
pp. 421-439 ◽  
Author(s):  
Adrienne J. Sutton ◽  
Richard A. Feely ◽  
Stacy Maenner-Jones ◽  
Sylvia Musielwicz ◽  
John Osborne ◽  
...  
Keyword(s):  
Time Series ◽  
Coral Reef ◽  
Decadal Variability ◽  
Fixed Time ◽  
Open Ocean ◽  
Trend Detection ◽  
Co2 Uptake ◽  
Woods Hole Oceanographic Institution ◽  
Surface Ocean ◽  
Wide Range

Abstract. Ship-based time series, some now approaching over 3 decades long, are critical climate records that have dramatically improved our ability to characterize natural and anthropogenic drivers of ocean carbon dioxide (CO2) uptake and biogeochemical processes. Advancements in autonomous marine carbon sensors and technologies over the last 2 decades have led to the expansion of observations at fixed time series sites, thereby improving the capability of characterizing sub-seasonal variability in the ocean. Here, we present a data product of 40 individual autonomous moored surface ocean pCO2 (partial pressure of CO2) time series established between 2004 and 2013, 17 also include autonomous pH measurements. These time series characterize a wide range of surface ocean carbonate conditions in different oceanic (17 sites), coastal (13 sites), and coral reef (10 sites) regimes. A time of trend emergence (ToE) methodology applied to the time series that exhibit well-constrained daily to interannual variability and an estimate of decadal variability indicates that the length of sustained observations necessary to detect statistically significant anthropogenic trends varies by marine environment. The ToE estimates for seawater pCO2 and pH range from 8 to 15 years at the open ocean sites, 16 to 41 years at the coastal sites, and 9 to 22 years at the coral reef sites. Only two open ocean pCO2 time series, Woods Hole Oceanographic Institution Hawaii Ocean Time-series Station (WHOTS) in the subtropical North Pacific and Stratus in the South Pacific gyre, have been deployed longer than the estimated trend detection time and, for these, deseasoned monthly means show estimated anthropogenic trends of 1.9±0.3 and 1.6±0.3 µatm yr−1, respectively. In the future, it is possible that updates to this product will allow for the estimation of anthropogenic trends at more sites; however, the product currently provides a valuable tool in an accessible format for evaluating climatology and natural variability of surface ocean carbonate chemistry in a variety of regions. Data are available at https://doi.org/10.7289/V5DB8043 and https://www.nodc.noaa.gov/ocads/oceans/Moorings/ndp097.html (Sutton et al., 2018).

Micronutrient export from glacier to fjord, southwest Greenland: potential impacts on open ocean primary productivity

2020 ◽  
Author(s):  
Rachael Ward ◽  
Kathrine Hendry ◽  
Jemma L. Wadham ◽  
Jon R. Hawkings ◽  
Robert M. Sherrell ◽  
...  
Keyword(s):  
Trace Metals ◽  
Surface Waters ◽  
Coastal Waters ◽  
Greenland Ice Sheet ◽  
Open Ocean ◽  
Marine Phytoplankton ◽  
Surface Ocean ◽  
Particulate Form ◽  
The Difference ◽  
Southwest Greenland

&lt;p&gt;The accelerated melting of the Greenland Ice Sheet could potentially enhance fluxes of key nutrients, to the surrounding oceans, impacting marine biogeochemical processes and ecosystems. Iron (Fe) is one key micronutrient for marine phytoplankton that may be affected by this increase in meltwater flux, with high export of dissolved and particulate Fe from glacial meltwaters into fjords and a potentially significant increase in the supply of labile and potentially bioavailable Fe to the Greenlandic shelf. However, biogeochemical processing within estuarine-like fjord systems may result in depletion of nutrients, acting as a sink of micronutrients before they can reach the coastal ocean. The extent to which glacially derived micronutrients, specifically Fe, reach coastal waters remains an unanswered question.&lt;/p&gt;&lt;p&gt;Here, we address this question by assessing the concentration of dissolved (&lt;0.45 &amp;#181;m) and labile particulate (determined using the Berger leach) bio-essential trace metals (Fe, Cd, Mn, Ni, Cu, Zn) in two contrasting glaciated fjords in southwest Greenland; one fed predominantly by marine terminating glaciers and the other by a land terminating glacier. We investigate the difference in size fractionated concentrations between fjords and the transport of these metals from stations close to glacial termini down to the fjord mouths. Our findings reveal that each micronutrient exhibits a distinctive behaviour, with some metals enhanced in meltwaters (e.g. dissolved Fe and Mn) and some depleted (e.g. dissolved Cd), relative to marine waters. The spatial variability in our dataset highlights that concentration of Fe and other trace metals (Cd, Mn, Ni, Cu, Zn) enriched in meltwaters become depleted towards the mouth of the fjords, with non-conservative loss from surface waters. Despite this depletion, the concentrations of these metals in waters that reach the coastal zone are significantly higher than typical surface ocean values, both in dissolved and labile particulate form. These data can ultimately be used in combination with a physical understanding of the fjord systems to constrain the capacity of fjords to enhance productivity downstream and deliver micronutrients into coastal and open ocean systems. Furthermore, the direct comparison of land- and marine-terminating glacial fjords could provide valuable information on the potential future impact of retreating glacial systems with enhanced melting.&lt;/p&gt;

scholarly journals Geoengineering impact of open ocean dissolution of olivine on atmospheric CO 2 , surface ocean pH and marine biology

2013 ◽  
Vol 8 (1) ◽  
pp. 014009 ◽  
Author(s):  
Peter Köhler ◽  
Jesse F Abrams ◽  
Christoph Völker ◽  
Judith Hauck ◽  
Dieter A Wolf-Gladrow
Keyword(s):  
Marine Biology ◽  
Open Ocean ◽  
Surface Ocean

scholarly journals Global high resolution monthly pCO<sub>2</sub> climatology for the coastal ocean derived from neural network interpolation

2017 ◽  
Author(s):  
Goulven G. Laruelle ◽  
Peter Landschützer ◽  
Nicolas Gruber ◽  
Jean-Louis Tison ◽  
Bruno Delille ◽  
...  
Keyword(s):  
Neural Network ◽  
Spatial Resolution ◽  
Open Ocean ◽  
Global Perspective ◽  
Strong Increase ◽  
Spatial And Temporal Variability ◽  
Continental Margins ◽  
Surface Ocean ◽  
Shelf Seas ◽  
Artificial Neural Network Method

Abstract. In spite of the recent strong increase in the number of measurements of the partial pressure of CO2 in the surface ocean (pCO2), the air-sea CO2 balance of the continental shelf seas remains poorly quantified. This is a consequence of these regions remaining strongly under-sampled both in time and space, and of surface pCO2 exhibiting much higher temporal and spatial variability in these regions compared to the open ocean. Here, we use a modified version of a two-step artificial neural network method (SOM-FFN, Landschützer et al., 2013) to interpolate the pCO2 data along the continental margins with a spatial resolution of 0.25 degrees and with monthly resolution from 1998 until 2014. The most important modifications compared to the original SOM-FFN method are (i) the much higher spatial resolution, and (ii) the inclusion of sea-ice as a predictor of pCO2. The validity of our interpolation, both in space and time, is assessed by comparing the SOM-FFN outputs with pCO2 measurements extracted from the SOCATv3.0 and LDVEO2014 datasets. The new coastal pCO2 product confirms a previously suggested general meridional trend of the annual mean pCO2 in all the continental shelves with high values in the tropics and dropping to values beneath those of the atmosphere at higher latitudes. But significant differences in the seasonality across the ocean basins exist. The shelves of the western and northern Pacific, as well as the shelves in the temperate North Atlantic display particularly pronounced seasonal variations in pCO2, while the shelves in the southeastern Atlantic and in the South Pacific reveal a much smaller seasonality. Overall, the seasonality in shelf pCO2 cannot solely be explained by temperature-induced changes in solubility, but are also the result of seasonal changes in circulation, mixing, and biological productivity. Finally, thanks to this product having been extended to cover open ocean areas as well, it can be readily merged with existing global open ocean products to produce a true global perspective of the spatial and temporal variability of surface ocean pCO2.

Sign in / Sign up

Export Citation Format

Share Document