Data_Sheet_1_Differential acclimation kinetics of the two forms of type IV chromatic acclimaters occurring in marine Synechococcus cyanobacteria.PDF

Synechococcus, the second most abundant marine phytoplanktonic organism, displays the widest variety of pigment content of all marine oxyphototrophs, explaining its ability to colonize all spectral niches occurring in the upper lit layer of oceans. Seven Synechococcus pigment types (PTs) have been described so far based on the phycobiliprotein composition and chromophorylation of their light-harvesting complexes, called phycobilisomes. The most elaborate and abundant PT (3d) in the open ocean consists of cells capable of type IV chromatic acclimation (CA4), i.e., to reversibly modify the ratio of the blue light-absorbing phycourobilin (PUB) to the green light-absorbing phycoerythrobilin (PEB) in phycobilisome rods to match the ambient light color. Two genetically distinct types of chromatic acclimaters, so-called PTs 3dA and 3dB, occur at similar global abundance in the ocean, but the precise physiological differences between these two types and the reasons for their complementary niche partitioning in the field remain obscure. Here, photoacclimation experiments in different mixes of blue and green light of representatives of these two PTs demonstrated that they differ by the ratio of blue-to-green light required to trigger the CA4 process. Furthermore, shift experiments between 100% blue and 100% green light, and vice-versa, revealed significant discrepancies between the acclimation pace of the two types of chromatic acclimaters. This study provides novel insights into the finely tuned adaptation mechanisms used by Synechococcus cells to colonize the whole underwater light field.

聚球藻（Synechococcus）是全球丰度排名第二的海洋浮游植物，其色素组成多样性为所有海洋产氧光合自养生物之最，这解释了它能够定植于海洋上层透光层中所有光谱生态位的能力。截至目前，研究人员已根据其捕光复合物——藻胆体（phycobilisome）的藻胆蛋白组成与辅基化修饰特征，定义了7种聚球藻色素型（PTs）。开阔大洋中结构最复杂、丰度最高的色素型为3d型，该类群细胞具备IV型颜色适应（CA4）能力，即可逆调节藻胆体杆中吸收蓝光的藻尿胆素（PUB）与吸收绿光的藻红胆素（PEB）的比例，以匹配环境光色。全球海洋中，两类遗传背景迥异的颜色适应型类群（即PT 3dA与PT 3dB）丰度相当，但二者间确切的生理差异，以及它们在野外实现互补性生态位分化的原因仍不明确。本研究针对这两类色素型的代表菌株开展了不同蓝绿光配比下的光适应实验，结果表明二者在触发CA4过程所需的蓝光-绿光比例上存在差异。此外，在100%蓝光与100%绿光之间的光质转换实验（及反向转换）中，两类颜色适应型类群的适应速率存在显著分歧。本研究为聚球藻细胞用以定植整个水下光场的精细调控适应机制提供了全新见解。