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

海冰覆盖了世界表面的13%，是一个独特的环境，支持着多样化的微生物群落。在秋季结冰期间，微生物被限制在高盐盐水通道中，其中盐度可达20%以上，温度可降至-20℃以下。尽管环境条件恶劣，但藻类生物量惊人地高，硅藻是这个独特群落的主要组成部分。已经确定，海冰硅藻产生了大量的细胞外聚合物质（EPS）或粘液，填满了盐水通道。这些粘液被认为有助于硅藻在海冰通道的恶劣条件下生存。在这种超低温的高盐盐水中保持代谢活性的细胞生活在一个自由能如此减少的环境中，以至于系统实际上被锁定在分子水平上。研究表明，胞外聚合物质（EPS）可能会给冰硅藻带来普遍的好处，如低温保护、盐度屏障和局部小气候。在本提案中，将在野外（南极洲）和实验室培养中进行实验和取样，以确定这种硅藻EPS的丰度和组成，测量EPS的保护特性，并确定EPS如何帮助硅藻在不适合生命的条件下生存。我们的目标是回答这样的问题：持续的代谢活动是如何可能的，以及EPS在这些条件下的细胞耐受性中可能发挥什么作用？这项研究的结果将使科学家能够了解微生物如何在极端环境中生存。

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.