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Compound-specific ?¹⁵N composition of free amino acids in moss as indicators of atmospheric nitrogen sources.

ABSTRACT: Haplocladium microphyllum moss samples were collected in Nanchang, China. Free amino acid (FAA) concentrations and N isotope compositions (?¹⁵N_FAA) in the samples were determined and compared with the bulk N concentrations and ?¹⁵N_bulk values. The aim was to determine whether ?¹⁵N_FAA values in moss (which are very variable) indicate the sources of atmospheric N. The ?¹⁵N_FAA values among individual FAA varied widely (from -19.3‰ to +16.1‰), possibly because of the different sources of N and isotope fractionation in amino acids metabolic pathways. Total ¹⁵N-enrichment for the individual FAAs was equal to total ¹⁵N-depletion relative to ?¹⁵N_bulk. The concentration-weighted mean ?¹⁵N value for total FAAs (TFAA) (?¹⁵N_TFAA) was -3.1‰?±?3.2‰, which was similar to ?¹⁵N_bulk (-4.0‰?±?2.9‰). We concluded that a N isotope balance occurred during amino acid metabolism and that little isotope disparity occurred between the concentration-weighted TFAA and bulk N. We concluded that ?¹⁵N_TFAA ? ?¹⁵N_bulk ? ?¹⁵N_source. The mean ?¹⁵N_alanine (-4.1‰), ?¹⁵N_glutamate (-4.2‰), and ?¹⁵N_lysine (-4.0‰) were similar to the mean ?¹⁵N_bulk, which we attributed to little isotope fractionation occurring during their in situ the metabolic pathways. This suggests that ?¹⁵N_alanine, ?¹⁵N_glutamate, and ?¹⁵N_lysine in moss can be used to indicate the sources of atmospheric N deposition.

SUBMITTER: Zhu RG

PROVIDER: S-EPMC6156404 | biostudies-literature | 2018 Sep

REPOSITORIES: biostudies-literature

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Compound-specific δ15N composition of free amino acids in moss as indicators of atmospheric nitrogen sources.

Zhu Ren-Guo RG Xiao Hua-Yun HY Zhang Zhongyi Z Lai Yuanyuan Y

Scientific reports 20180925 1

Haplocladium microphyllum moss samples were collected in Nanchang, China. Free amino acid (FAA) concentrations and N isotope compositions (δ15NFAA) in the samples were determined and compared with the bulk N concentrations and δ15Nbulk values. The aim was to determine whether δ15NFAA values in moss (which are very variable) indicate the sources of atmospheric N. The δ15NFAA values among individual FAA varied ...[more]

PMID: 30254224

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Project description:BackgroundThe use of enriched stable isotopes is of outstanding importance in chemical metrology as it allows the application of isotope dilution mass spectrometry (IDMS). Primary methods based on IDMS ensure the quality of the analytical measurements and traceability of the results to the international system of units. However, the synthesis of isotopically labelled molecules from enriched stable isotopes is an expensive and a difficult task. Either chemical and biochemical methods to produce labelled molecules have been proposed, but so far, few cost-effective methods have been described.ResultsThe aim of this study was to use the microalgae Chlamydomonas reinhardtii to produce, at laboratory scale, 15N-labelled amino acids with a high isotopic enrichment. To do that, a culture media containing 15NH4Cl was used. No kinetic isotope effect (KIE) was observed. The labelled proteins biosynthesized by the microorganism were extracted from the biomass and the 15N-labelled amino acids were obtained after a protein hydrolysis with HCl. The use of the wall deficient strain CC503 cw92 mt+ is fit for purpose, as it only assimilates ammonia as nitrogen source, avoiding isotope contamination with nitrogen from the atmosphere or the reagents used in the culture medium, and enhancing the protein extraction efficiency compared to cell-walled wild type Chlamydomonas. The isotopic enrichment of the labelled amino acids was calculated from their isotopic composition measured by gas chromatography mass spectrometry (GC-MS). The average isotopic enrichment for the 16 amino acids characterized was 99.56 ± 0.05% and the concentration of the amino acids in the hydrolysate ranged from 18 to 90 µg/mL.ConclusionsPreviously reported biochemical methods to produce isotopically labelled proteins have been applied in the fields of proteomics and fluxomics. For these approaches, low amounts of products are required and the isotopic enrichment of the molecules has never been properly determined. So far, only 13C-labelled fatty acids have been isolated from labelled microalga biomass as valuable industrial products. In this study, we propose Chlamydomonas reinhardtii CC503 as a feasible microorganism and strain to produce labelled biomass from which a standard containing sixteen 15N-labelled amino acids could be obtained.

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Compound-specific ?¹⁵N composition of free amino acids in moss as indicators of atmospheric nitrogen sources.

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Compound-specific δ<sup>15</sup>N composition of free amino acids in moss as indicators of atmospheric nitrogen sources.

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Compound-specific ?15N composition of free amino acids in moss as indicators of atmospheric nitrogen sources.

Publications

Compound-specific δ<sup>15</sup>N composition of free amino acids in moss as indicators of atmospheric nitrogen sources.

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OmicsDI is part of the ELIXIR infrastructure

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Compound-specific ?¹⁵N composition of free amino acids in moss as indicators of atmospheric nitrogen sources.