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Isotopic labelling of cultured macroalgae and isolation of 13 C-labelled cell wall polysaccharides for trophic investigations

Abstract : Macroalgae are considered as major primary producers in coastal environments, acting as a global carbon sink. This abundant biomass contains up to 50% of storage or cell wall polysaccharides, which therefore represent a reservoir of organic matter for potential algal consumers. Tracking of natural isotopic abundance (δ 13 C vs. δ 15 N) in macroalgae-colonized habitats such as kelp forests and rocky shores previously evidenced the importance of the algal resource to support local and adjacent trophic webs mostly via the microbial detrital pathway. However, such bulk isotopic measures of natural abundances cannot inform precisely on the microbial actors and processes at play for the degradation of selected algal compounds. To overcome these limitations, we developed a stable isotope labelling procedure for cultures of the brown alga Laminaria digitata and tested its ability to yield labelled polysaccharides. Sporophytes of L. digitata were grown in controlled conditions for three months in seawater regularly amended with 13 C-labelled sodium bicarbonate. Elemental analysisisotope ratio mass spectrometry of algal specimens showed a significant enrichment after 10 days of treatment, reaching a maximum of At% C = 3.5321% after 80 days. Sequential polysaccharide extraction from this labelled algal biomass allowed retrieving both alginate and fucose-containing sulphated polysaccharide fractions with high isotopic enrichment (At% 13 C = 3.6279% and 3.5868%, respectively). This labelling protocol opens the way for future studies combining coastal ecosystems trophic interactions and microbial activities towards macroalgal biomass degradation.
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https://hal.archives-ouvertes.fr/hal-03035113
Contributor : François Thomas <>
Submitted on : Wednesday, December 2, 2020 - 9:05:41 AM
Last modification on : Monday, February 1, 2021 - 12:06:02 PM
Long-term archiving on: : Wednesday, March 3, 2021 - 6:27:33 PM

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François Thomas, Nolwen Le Duff, Cédric Leroux, Laurence Dartevelle, Pascal Riera. Isotopic labelling of cultured macroalgae and isolation of 13 C-labelled cell wall polysaccharides for trophic investigations. Advances in Botanical Research, 2020, ⟨10.1016/bs.abr.2019.11.005⟩. ⟨hal-03035113⟩

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