Production and Characterization of the Intra‐ and Extracellular Carbohydrates and Polymeric Substances (EPS) of Three Sea‐Ice Diatom Species, and Evidence for a Cryoprotective Role for EPS

<jats:p>Diatoms and their associated extracellular polymeric substances (<jats:styled-content style="fixed-case">EPS</jats:styled-content>) are major constituents of the microalgal assemblages present within sea ice. Yields and chemical composition of soluble and cell‐associated polysaccharides produced by three sea‐ice diatoms, <jats:italic><jats:styled-content style="fixed-case">S</jats:styled-content>ynedropsis</jats:italic> sp., <jats:italic><jats:styled-content style="fixed-case">F</jats:styled-content>ragilariopsis curta</jats:italic>, and <jats:italic><jats:styled-content style="fixed-case">F</jats:styled-content>. cylindrus</jats:italic>, were compared. Colloidal carbohydrates (<jats:styled-content style="fixed-case">CC</jats:styled-content>) contained heteropolysaccharides rich in mannose, xylose, galactose, and glucose. <jats:italic>Synedropsis</jats:italic> sp. <jats:styled-content style="fixed-case">CC</jats:styled-content> consisted mainly of carbohydrates &lt;8 kDa size, with relatively soluble EPS, compared to high proportions of less‐soluble <jats:styled-content style="fixed-case">EPS</jats:styled-content> produced by both <jats:italic><jats:styled-content style="fixed-case">F</jats:styled-content>ragilariopsis</jats:italic> spp. <jats:italic><jats:styled-content style="fixed-case">F</jats:styled-content>. curta</jats:italic> colloidal <jats:styled-content style="fixed-case">EPS</jats:styled-content> contained high concentrations of amino sugars (<jats:styled-content style="fixed-case">AS</jats:styled-content>). Both <jats:italic><jats:styled-content style="fixed-case">F</jats:styled-content>ragilariopsis</jats:italic> species had high yields of hot bicarbonate (HB) soluble <jats:styled-content style="fixed-case">EPS</jats:styled-content>, rich in xylose, mannose, galactose, and fucose (and <jats:styled-content style="fixed-case">AS</jats:styled-content> in <jats:italic><jats:styled-content style="fixed-case">F</jats:styled-content>. cylindrus</jats:italic>). All species had frustule‐associated <jats:styled-content style="fixed-case">EPS</jats:styled-content> rich in glucose–mannose. Nutrient limitation resulted in declines in <jats:styled-content style="fixed-case">EPS</jats:styled-content> yields and in glucose content of all <jats:styled-content style="fixed-case">EPS</jats:styled-content> fractions. Significant similarities between <jats:styled-content style="fixed-case">EPS</jats:styled-content> fractions from cultures and different components of natural <jats:styled-content style="fixed-case">EPS</jats:styled-content> from Antarctic sea ice were found. Increased salinity (52) reduced growth, but increased yields of <jats:styled-content style="fixed-case">EPS</jats:styled-content> in <jats:italic>Fragilariopsis cylindrus</jats:italic>. Ice formation was inhibited by<jats:italic><jats:styled-content style="fixed-case">F</jats:styled-content>. cylindrus</jats:italic>,<jats:styled-content style="fixed-case"> EPS</jats:styled-content>, and by enhanced <jats:styled-content style="fixed-case">EPS</jats:styled-content> content (additional xanthan gum) down to −12°C, with growth rate reduced in the presence of xanthan. Differences in the production and composition of <jats:styled-content style="fixed-case">EPS</jats:styled-content> between <jats:italic>Synedropsis</jats:italic> sp. and <jats:italic><jats:styled-content style="fixed-case">F</jats:styled-content>ragilariopsis</jats:italic> spp., and the association between <jats:styled-content style="fixed-case">EPS</jats:styled-content>, freezing and cell survival, supports the hypothesis that <jats:styled-content style="fixed-case">EPS</jats:styled-content> production is a strategy to assist polar ice diatoms to survive the cold and saline conditions present in sea ice.</jats:p>