Interactions between phytoplankton and bacteria play major roles in global biogeochemical cycles and oceanic nutrient fluxes. These interactions occur in the microenvironment surrounding phytoplankton cells, known as the phycosphere. Bacteria in the phycosphere use either chemotaxis or attachment to benefit from algal excretions. Both processes are regulated by quorum sensing (QS), a cell–cell signalling mechanism that uses small infochemicals to coordinate bacterial gene expression. However, the role of QS in regulating bacterial attachment in the phycosphere is not clear. Here, we isolated a Sulfitobacter pseudonitzschiae F5 and a Phaeobacter sp. F10 belonging to the marine Roseobacter group and an Alteromonas macleodii F12 belonging to Alteromonadaceae, from the microbial community of the ubiquitous diatom Asterionellopsis glacialis. We show that only the Roseobacter group isolates (diatom symbionts) can attach to diatom transparent exopolymeric particles. Despite all three bacteria possessing genes involved in motility, chemotaxis, and attachment, only S. pseudonitzschiae F5 and Phaeobacter sp. F10 possessed complete QS systems and could synthesize QS signals. Using UHPLC–MS/MS, we identified three QS molecules produced by both bacteria of which only 3‐oxo‐C_16:1‐HSL strongly inhibited bacterial motility and stimulated attachment in the phycosphere. These findings suggest that QS signals enable colonization of the phycosphere by algal symbionts.

中文翻译：

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法定人数感测调节了藻圈中“游泳或坚持”的生活方式。

浮游植物与细菌之间的相互作用在全球生物地球化学循环和海洋营养通量中起主要作用。这些相互作用发生在浮游植物细胞周围的微环境中，称为浮游植物。藻圈中的细菌利用趋化性或附着性来受益于藻类排泄物。这两个过程均受群体感应（QS）调控，群体感应是一种细胞间信号传导机制，使用小的信息化学物质来协调细菌基因的表达。但是，QS在调节藻圈中细菌附着方面的作用尚不清楚。在这里，我们分离出了拟杆菌S5和假细菌。F10属于海洋Roseobacter组和Macerodinas macleodiiF12属于Alteromonadaceae，来自无处不在的硅藻Asterionellopsis glacialis的微生物群落。我们表明，只有玫瑰杆菌群分离物（硅藻共生体）可以附着在硅藻透明的外聚合物颗粒上。尽管所有三种细菌拥有参与运动，趋化性和附件，只有基因S. pseudonitzschiae F5和Phaeobacter SP。F10拥有完整的QS系统，可以合成QS信号。使用UHPLC-MS / MS，我们鉴定了两种细菌产生的三个QS分子，其中只有3-oxo-C _16：1‐HSL强烈抑制细菌运动，并刺激其在藻圈中的附着。这些发现表明，QS信号使藻类共生菌能够在藻圈定居。