Production, characterisation and novel roles of sea-ice diatom exopolymers (EPS)

Lead Research Organisation: University of Essex
Department Name: Biological Sciences

Abstract

Sea ice covers up to 13% of the world's surface and is a unique environment, supporting a diverse microbial community. During ice formation in autumn, microorganisms are confined to hypersaline brine channels, where salinity reaches over 20% and temperatures can drop to below -20oC. Despite the harsh environmental conditions the algal biomass is surprisingly high, with diatoms representing a major component to this unique community. It has been determined that sea ice diatoms produced large amounts of extracellular polymeric substances (EPS) or mucilages, that fill the brine channels. These mucilages are thought to help the diatoms to survive in the harsh conditions of the sea ice channels. The cells that remain metabolically active in this hypersaline brine at ultra low temperatures are living in an environment of such reduced free energy that the system is virtually locked up at the molecular level. It is suggested that the extracellular polymeric substances (EPS) may confer general benefits to ice diatoms, such as cryoprotection, salinity barriers and a localised microclimate. In this proposal, experiments and sampling will be carried out in the field (Antarctica) and in laboratory cultures to determine the abundance and composition of this diatom EPS, measure the protective properties of EPS, and determine how EPS aids the survival of diatoms in conditions that are inhospitable to life. We aim to answer the question how is sustained metabolic activity possible and what role EPS might play in cellular tolerance of these conditions? The outcomes from this research will enable scientists to understand how microbes can survive in extreme environments.

Publications

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Chin JP (2010) Solutes determine the temperature windows for microbial survival and growth. in Proceedings of the National Academy of Sciences of the United States of America

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Meiners K (2011) Physico-ecobiogeochemistry of East Antarctic pack ice during the winter-spring transition in Deep Sea Research Part II: Topical Studies in Oceanography

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Underwood GJ (2013) Broad-scale predictability of carbohydrates and exopolymers in Antarctic and Arctic sea ice. in Proceedings of the National Academy of Sciences of the United States of America

 
Description We have now published the first pathway describing the biosynthesis pathways of EPS in any diatom, using the polar diatom Fragilariopsis cyclindrus. the work describes both field data, cell physiology, EPS biochemistry and RNA transcriptomic analysis, and reveals the ability of the diatom to reprogramme different elements of its EPS pathway in response to changing temperature and salinity conditions found in sea ice.

Secondly, we have published the first study showing the response of water column bacteria to melting sea ice diatom EPS in first year ice, finding significant differences in the rates of utilisation of different elements of the organic matter "menu" provided by the ice EPS, and different species of bacterial growing on these. This is important in understanding the contribution of sea-ice organic matter to carbon cycling in the warming arctic ocean.
Exploitation Route First published pathway for EPS production in diatoms, a key algal group
Sectors Chemicals,Manufacturing, including Industrial Biotechology

URL https://www.nature.com/articles/s41396-017-0039-z