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

• Published in: Journal of Phycology
• Main Authors: Aslam, Shazia N., Cresswell‐Maynard, Tania, Thomas, David N., Underwood, Graham J. C.
• Other Authors: U.K. Natural Environment Research Council
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2012
• Subjects: Antarctic; Antarc*; Sea ice
• Online Access: http://dx.doi.org/10.1111/jpy.12004; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fjpy.12004; https://onlinelibrary.wiley.com/doi/pdf/10.1111/jpy.12004

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