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  • 1
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    Zooplankton‐derived dissolved organic matter composition and its bioavailability to natural prokaryotic communities (2022)
    De Corte, Daniele ; Varela, Marta M. ; Louro, Angeles M. ; [et al.]
    John Wiley & Sons, Inc. | Hoboken, USA
    Details
    Publication Date: 2023-12-14
    Description: Zooplankton grazing onphytoplankton promotes the release of particulate and dissolved organic matter (DOM) into the water column and therefore plays a key role in organic matter cycling in aquatic systems. Prokaryotes are the main DOM consumers in the ocean by actively remineralizing and transforming it, contributing to its molecular diversification. To explore the molecular composition of zooplankton‐derived DOM and its bioavailability to natural prokaryotic communities, the DOM generated by a mixed zooplankton community in the coastal Atlantic off Spain was used as substrate for a natural prokaryotic community and monitored over a ~ 5‐d incubation experiment. The molecular composition of solid‐phase extracted DOM was characterized via Fourier‐transform ion cyclotron resonance mass spectrometry. After ~ 4 d in the zooplankton‐derived DOM amended incubation, the prokaryotic community demonstrated a 17‐fold exponential increase in cell number. The prokaryotic growth resulted in a reduction in bulk dissolved organic carbon concentration and the zooplankton‐derived DOM was considerably transformed at molecular and bulk elemental levels over the incubation period. The C : N ratio (calculated from the obtained molecular formulae) increased while the functional diversity decreased over the incubation time. In addition, molecular indices pointed to a reduced bioavailability of DOM at the end of the experiment. These findings show that zooplankton excreta are a source of labile organic matter that is quickly metabolized by the prokaryotic community. Therefore, a fraction of carbon is shunted from transfer to secondary consumers similarly to the viral shunt, suggesting that the zooplankton–prokaryotic interactions play an important role in the ocean's carbon cycle.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: Xunta de Galicia http://dx.doi.org/10.13039/501100010801
    Keywords: ddc:577.7 ; Spain ; coastal Atlantic ; zooplankton–prokaryotic interactions ; ocean’s carbon cycle
    Language: English
    Type: doc-type:article
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  • 2
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    The detection of bacterial exometabolites in marine dissolved organic matter through ultrahigh‐resolution mass spectrometry (2022)
    John Wiley & Sons, Inc. | Hoboken, USA
    Details
    Publication Date: 2022-10-01
    Description: Bacteria play a key role in sustaining the chemodiversity of marine dissolved organic matter (DOM), yet there is limited direct evidence of a major contribution of bacterial exometabolites to the DOM pool. This study tests whether molecular formulae of intact exometabolites can be detected in natural DOM via untargeted Fourier‐transform ion cyclotron resonance mass spectrometry (FT‐ICR‐MS). We analyzed a series of quantitative mixtures of solid‐phase extracted DOM from the deep ocean, of a natural microbial community and selected model strains of marine bacteria. Under standard instrument settings (200 broadband scans, mass range 92–1000 Da), 77% of molecular formulae were shared between the mesocosm and marine DOM. However, there was 〈 10% overlap between pure bacterial exometabolome with marine DOM, and in mixing ratios closest to mimicking natural environments (1% bacterial DOM, 99% marine DOM), only 4% of the unique bacterial exometabolites remained detectable. Further experiments with the bacterial exometabolome DOM mixtures using enhanced instrument settings resulted in increased detection of the exometabolites at low concentrations. At 1000 and 10,000 accumulated scans, 23% and 29% of the unique molecular formulae were detectable at low concentrations, respectively. Moreover, windowing a specific mass range encompassing a representative fraction of exometabolites tripled the number of unique detected formulae at low concentrations. Routine FT‐ICR‐MS settings are thus not always sufficient to distinguish bacterial exometabolome patterns from a seawater DOM background. To observe these patterns at higher sensitivity, we recommend a high scan number coupled with windowing a characteristic region of the molecular fingerprint.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Keywords: ddc:551.46 ; ddc:579.3 ; ddc:
    Language: English
    Type: doc-type:article
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  • 3
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    Transformation of dissolved organic matter by two Indo‐Pacific sponges (2022)
    John Wiley & Sons, Inc. | Hoboken, USA
    Details
    Publication Date: 2023-01-27
    Description: Dissolved organic matter (DOM) is the largest organic carbon reservoir in the ocean and an integral component of biogeochemical cycles. The role of free‐living microbes in DOM transformation has been studied thoroughly, whereas little attention has been directed towards the influence of benthic organisms. Sponges are efficient filter feeders and common inhabitants of many benthic communities circumglobally. Here, we investigated how two tropical coral reef sponges shape marine DOM. We compared bacterial abundance, inorganic and organic nutrients in off reef, sponge inhalant, and sponge exhalant water of Melophlus sarasinorum and Rhabdastrella globostellata. DOM and bacterial cells were taken up, and dissolved inorganic nitrogen was released by the two Indo‐Pacific sponges. Both sponge species utilized a common set of 142 of a total of 3040 compounds detected in DOM on a molecular formula level via ultrahigh‐resolution mass spectrometry. In addition, species‐specific uptake was observed, likely due to differences in their associated microbial communities. Overall, the sponges removed presumably semi‐labile and semi‐refractory compounds from the water column, thereby competing with pelagic bacteria. Within minutes, sponge holobionts altered the molecular composition of surface water DOM (inhalant) into a composition similar to deep‐sea DOM (exhalent). The apparent radiocarbon age of DOM increased consistently from off reef and inhalant to exhalant by about 900 14C years for M. sarasinorum. In the pelagic, similar transformations require decades to centuries. Our results stress the dependence of DOM lability definition on the respective environment and illustrate that sponges are hotspots of DOM transformation in the ocean.
    Description: Helmholtz Institute for Functional Marine Biodiversity at the University of Oldenburg
    Description: Ministry for Science and Culture of Lower Saxony http://dx.doi.org/10.13039/501100010570
    Description: Carl‐von‐Ossietzky University Oldenburg
    Description: Alfred‐Wegener‐Institute, Helmholtz‐Center for Polar and Marine Research
    Description: Volkswagen Foundation http://dx.doi.org/10.13039/501100001663
    Description: https://doi.org/10.5061/dryad.m0cfxpp6v
    Keywords: ddc:577.7 ; Indo-Pacific sponges ; dissolved organic matter ; biogeochemical cycles
    Language: English
    Type: doc-type:article
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  • 4
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    Biodegradability of hydrothermally altered deep-sea dissolved organic matter (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Chemistry, ELSEVIER SCIENCE BV, 217, ISSN: 0304-4203
    Details
    Publication Date: 2020-10-07
    Description: Deep-sea dissolved organic matter (DOM) constitutes a huge carbon reservoir in the worlds' oceans that – despite its abundance – is virtually unused as a substrate by marine heterotrophs. Heating within hydrothermal systems induces major molecular modifications of deep-sea DOM. Here, we tested the hypothesis that hydrothermal heating of deep-sea DOM enhances bioavailability. Aliquots of DOM extracted from the deep North Pacific (North Equatorial Pacific Intermediate Water; NEqPIW) were re-dissolved in artificial seawater and subjected to temperatures of 100 and 200 °C (40 MPa) using Dickson-type reactors. In agreement with earlier findings we observed a temperature-related drop in dissolved organic carbon (DOC) concentration (−6.1% at 100 °C, −21.0% at 200 °C) that predominantly affected the solid-phase extractable (SPE-DOC) fraction (−18.2% at 100 °C, −51.4% at 200 °C). Fourier-transform ion cyclotron resonance mass spectrometric (FT-ICR-MS) analysis confirmed a temperature-related reduction of average molecular mass, O/C ratios, double bond equivalents (DBE) and a relative increase in aromaticity (AImod). This thermally altered DOM was added (25 μmol L−1 DOC) to deep-water samples from the South West Pacific (Kermadec Arc, RV Sonne / SO253, 32° 37.706′ S | 179° 38.728′ W) and incubated with the prevailing natural microbial community. After 16 days at 4 °C in the dark, prokaryotic cell counts in incubations containing the full spectrum of thermally-degraded DOM (extractable and non-extractable compounds) had increased considerably (on average 21× for DOM100°C and 27× for DOM200°C). In contrast, prokaryotic growth in incubations to which only solid-phase extractable thermally-altered DOM was added was not enhanced compared to control incubations. The experiments demonstrate that temperature-driven degradation of deep-sea recalcitrant DOM within hydrothermal systems turns fractions of it accessible to microbes. The thermally-produced DOM compounds that stimulate microbial growth are not retained on reversed-phase resins (SPE-DOM) and are likely low-molecular mass organic acids. Despite the comprehensive compositional modifications of the solid-phase extractable (SPE-DOM) fraction through heating, it remains inaccessible to microbes at the investigated concentration levels. The microbial incubation resulted in only minor and mostly insignificant overall changes in SPE-DOM molecular composition and concentration.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 5
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    Iron Promotes the Retention of Terrigenous Dissolved Organic Matter in Subtidal Permeable Sediments (2024)
    American Chemical Society (ACS)
    In:  EPIC3Environmental Science and Technology, American Chemical Society (ACS), ISSN: 0013-936X
    Details
    Publication Date: 2024-04-08
    Description: Marine permeable sediments are important sites for organic matter turnover in the coastal ocean. However, little is known about their role in trapping dissolved organic matter (DOM). Here, we examined DOM abundance and molecular compositions (9804 formulas identified) in subtidal permeable sediments along a near- to offshore gradient in the German North Sea. With the salinity increasing from 30.1 to 34.6 PSU, the DOM composition in bottom water shifts from relatively higher abundances of aromatic compounds to more highly unsaturated compounds. In the bulk sediment, DOM leached by ultrapure water (UPW) from the solid phase is 54 ± 20 times more abundant than DOM in porewater, with higher H/C ratios and a more terrigenous signature. With 0.5 M HCl, the amount of leached DOM (enriched in aromatic and oxygen-rich compounds) is doubled compared to UPW, mainly due to the dissolution of poorly crystalline Fe phases (e.g., ferrihydrite and Fe monosulfides). This suggests that poorly crystalline Fe phases promote DOM retention in permeable sediments, preferentially terrigenous, and aromatic fractions. Given the intense filtration of seawater through the permeable sediments, we posit that Fe can serve as an important intermediate storage for terrigenous organic matter and potentially accelerate organic matter burial in the coastal ocean.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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