Microalgae produce copious amounts of structurally diverse polysaccharides, some are bound within cells and cell walls, while others are secreted into the surrounding seawater. A fraction of the secreted polysaccharides assembles into particles promoting aggregation and in turn formation of aggregates increases the export of carbon into the deep ocean via sinking. However, specific polysaccharides contributing to particle formation and carbon export remain unknown. Here, we studied microalgae polysaccharide composition in a system of reduced complexity consisting of lab grown monospecific cultures of the centric diatom species Thalassiosira weissflogii and Chaetoceros socialis. We followed the abundance and dynamics of five specific polysaccharide types in the dissolved and particulate organic matter (DOM and POM) for two weeks. Polysaccharides were detected using monoclonal antibodies (mAbs) specific for β-1,4-mannan, β-1,4-xylan, arabinogalactan, and two fucose-containing sulfated polysaccharide (FCSP) epitopes. Additionally, glycan composition of all samples was analyzed by monosaccharide analysis. The time series revealed polysaccharides partition differently between the dissolved and particulate carbon pools. β-1,4-xylan and β-1,4-mannan were mainly present in POM, possibly as cell wall polymers, while FCSPs were found in both DOM and POM. The data showed that the main glycan component secreted by diatoms was fucose-containing polysaccharide, which accumulated in DOM over time. Roller tank experiments were used to induce aggregate formation finding FCSP transitioned from DOM to POM under aggregating conditions. These results suggest that diatom-secreted FCSPs are involved in the formation of aggregates, which promote the formation of particles, and potentially carbon export.

中文翻译：

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硅藻分泌硫酸化岩藻聚糖可能有助于海洋聚集体的形成

微藻会产生大量结构多样的多糖，一些多糖结合在细胞和细胞壁内，而另一些则分泌到周围的海水中。一部分分泌的多糖组装成促进聚集的颗粒，而聚集体的形成又增加了碳通过下沉进入深海的输出。然而，有助于颗粒形成和碳输出的特定多糖仍然未知。在这里，我们研究了复杂性降低的系统中的微藻多糖组成，该系统由中心硅藻物种 Thalassiosira weissflogii 和 Chaetoceros socialis 的实验室培养单特异性培养物组成。我们跟踪了溶解和颗粒状有机物质（DOM 和 POM）中五种特定多糖类型的丰度和动态两周。使用对 β-1,4-甘露聚糖、β-1,4-木聚糖、阿拉伯半乳聚糖和两种含岩藻糖的硫酸化多糖 (FCSP) 表位特异的单克隆抗体 (mAb) 检测多糖。此外，所有样品的聚糖组成都通过单糖分析进行了分析。时间序列显示多糖在溶解碳池和颗粒碳池之间的分配不同。β-1,4-木聚糖和 β-1,4-甘露聚糖主要存在于 POM 中，可能作为细胞壁聚合物，而 FCSPs 存在于 DOM 和 POM 中。数据表明，硅藻分泌的主要聚糖成分是含岩藻糖的多糖，随着时间的推移，它会在 DOM 中积累。辊槽实验用于诱导聚集体形成，发现 FCSP 在聚集条件下从 DOM 转变为 POM。