Dataset Information

Evidence of Anomalously Low ?(13)C of Marine Organic Matter in an Arctic Fjord.

ABSTRACT: Accurate estimation of relative carbon deposition (marine vs. terrestrial) is required for understanding the global carbon budget, particularly in the Arctic region, which holds disproportionate importance with respect to global carbon cycling. Although the sedimentary organic matter (SOM) concentration and its isotopic composition are important tools for such calculations, uncertainties loom over estimates provided by organic-geochemical bulk parameters. We report carbon and nitrogen concentrations and isotopes (?(13)C and ?(15)N) of SOM at an Arctic fjord namely Kongsfjorden. We find that the bound inorganic nitrogen (ammonium attached to the clay minerals) forms a significant proportion of total nitrogen concentration (~77% in the inner fjord to ~24% in the outer part). On removing the bound nitrogen, the C/N ratio shows that the SOM in the inner fjord is made up of terrestrial carbon while the outer fjord shows mixed marine-terrestrial signal. We further show that the marine organic matter is unusually more depleted in (13)C (~-24‰) than the terrestrial organic matter (~-22.5‰). This particular finding also helps explain high ?(13)C values of SOM as noted by earlier studies in central Arctic sediments despite a high terrestrial contribution.

SUBMITTER: Kumar V

PROVIDER: S-EPMC5101485 | biostudies-other | 2016 Nov

REPOSITORIES: biostudies-other

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Evidence of Anomalously Low δ<sup>13</sup>C of Marine Organic Matter in an Arctic Fjord.

Kumar Vikash V Tiwari Manish M Nagoji Siddhesh S Tripathi Shubham S

Scientific reports 20161109

Accurate estimation of relative carbon deposition (marine vs. terrestrial) is required for understanding the global carbon budget, particularly in the Arctic region, which holds disproportionate importance with respect to global carbon cycling. Although the sedimentary organic matter (SOM) concentration and its isotopic composition are important tools for such calculations, uncertainties loom over estimates provided by organic-geochemical bulk parameters. We report carbon and nitrogen concentrat ...[more]

PMID: 27827457

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Project description:Marine algae produce a variety of glycans, which fulfill diverse biological functions and fuel the carbon and energy demands of heterotrophic microbes. A common approach to analysis of marine organic matter uses acid to hydrolyze the glycans into measurable monosaccharides. The monosaccharides may be derived from different glycans that are built with the same monosaccharides, however, and this approach does not distinguish between glycans in natural samples. Here we use enzymes to digest selectively and thereby quantify laminarin in particulate organic matter. Environmental metaproteome data revealed carbohydrate-active enzymes from marine flavobacteria as tools for selective hydrolysis of the algal ?-glucan laminarin. The enzymes digested laminarin into glucose and oligosaccharides, which we measured with standard methods to establish the amounts of laminarin in the samples. We cloned, expressed, purified, and characterized three new glycoside hydrolases (GHs) of Formosa bacteria: two are endo-?-1,3-glucanases, of the GH16 and GH17 families, and the other is a GH30 exo-?-1,6-glucanase. Formosa sp. nov strain Hel1_33_131 GH30 (FbGH30) removed the ?-1,6-glucose side chains, and Formosa agariphila GH17A (FaGH17A) and FaGH16A hydrolyzed the ?-1,3-glucose backbone of laminarin. Specificity profiling with a library of glucan oligosaccharides and polysaccharides revealed that FaGH17A and FbGH30 were highly specific enzymes, while FaGH16A also hydrolyzed mixed-linked glucans with ?-1,4-glucose. Therefore, we chose the more specific FaGH17A and FbGH30 to quantify laminarin in two cultured diatoms, namely, Thalassiosira weissflogii and Thalassiosira pseudonana, and in seawater samples from the North Sea and the Arctic Ocean. Combined, these results demonstrate the potential of enzymes for faster, stereospecific, and sequence-specific analysis of select glycans in marine organic matter.IMPORTANCE Marine algae synthesize substantial amounts of the glucose polymer laminarin for energy and carbon storage. Its concentrations, rates of production by autotrophic organisms, and rates of digestion by heterotrophic organisms remain unknown. Here we present a method based on enzymes that hydrolyze laminarin and enable its quantification even in crude substrate mixtures, without purification. Compared to the commonly used acid hydrolysis, the enzymatic method presented here is faster and stereospecific and selectively cleaves laminarin in mixtures of glycans, releasing only glucose and oligosaccharides, which can be easily quantified with reducing sugar assays.

Dataset Information

Evidence of Anomalously Low ?(13)C of Marine Organic Matter in an Arctic Fjord.

Publications

Evidence of Anomalously Low δ<sup>13</sup>C of Marine Organic Matter in an Arctic Fjord.

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