Data_Sheet_1_Diversity and Spatial Distribution of Chromophytic Phytoplankton in the Bay of Bengal Revealed by RuBisCO Genes (rbcL).docx

Phytoplankton are the basis of primary production and play important roles in regulating energy export in marine ecosystems. Compared to other regions, chromophytic phytoplankton are considerably understudied in the Bay of Bengal (BOB). Here, we investigated community structure and spatial distribution of chromophytic phytoplankton in the BOB by using RuBisCO genes (Form ID rbcL). High throughput sequencing of rbcL genes revealed that diatoms, cyanobacteria (Cyanophyceae), Pelagophyceae, Haptophyceae, Chrysophyceae, Eustigamatophyceae, Xanthophyceae, Cryptophyceae, Dictyochophyceae, and Pinguiophyceae were the most abundant groups recovered in the BOB. Abundances and distribution of diatoms and Pelagophyceae were further verified using quantitative PCR analyses which showed the dominance of these groups near the Equator region (p < 0.01) where upwelling was likely the source of nutrients. Further, redundancy analysis demonstrated that temperature was an important environmental driver in structuring distributions of Cyanophyceae and dominant chromophytic phytoplankton. Morphological identification and quantification confirmed the dominance of diatoms, and also detected other cyanobacteria and dinoflagellates that were missing in our molecular characterizations. Pearson’s correlations of these morphologically identified phytoplankton with environmental gradients also indicated that nutrients and temperature were key variables shaping community structure. Combination of molecular characterization and morphological identification provided a comprehensive overview of chromophytic phytoplankton. This is the first molecular study of chromophytic phytoplankton accomplished in the BOB, and our results highlight a combination of molecular analysis targeting rbcL genes and microscopic detection in examining phytoplankton composition and diversity.

浮游植物（phytoplankton）是初级生产的基础，在调控海洋生态系统的能量输出过程中发挥着关键作用。与其他海域相比，孟加拉湾（Bay of Bengal, BOB）内的有色浮游植物（chromophytic phytoplankton）相关研究仍较为匮乏。本研究采用核酮糖-1,5-二磷酸羧化酶/加氧酶基因（RuBisCO genes，rbcL型，Form ID rbcL）作为分子标记，对孟加拉湾内有色浮游植物的群落结构与空间分布展开了调查。

对rbcL基因的高通量测序（high-throughput sequencing）结果显示，本研究在孟加拉湾中检出的优势类群包括硅藻（diatoms）、蓝细菌（Cyanophyceae，蓝藻纲）、海囊藻纲（Pelagophyceae）、定鞭藻纲（Haptophyceae）、金藻纲（Chrysophyceae）、真眼点藻纲（Eustigamatophyceae）、黄藻纲（Xanthophyceae）、隐藻纲（Cryptophyceae）、网粘藻纲（Dictyochophyceae）以及厚丝藻纲（Pinguiophyceae）。

研究进一步通过定量PCR（quantitative PCR）验证了硅藻与海囊藻纲的丰度及分布特征，结果表明这两类群在赤道附近海域占据绝对优势（p < 0.01），该区域的上升流大概率为其提供了营养盐。

冗余分析（redundancy analysis）证实，温度是调控蓝藻纲以及优势有色浮游植物类群分布的核心环境驱动因子。形态学鉴定与计数结果不仅证实了硅藻的优势地位，还检出了分子表征中未被发现的其他蓝细菌与甲藻（dinoflagellates）。

针对上述形态学鉴定得到的浮游植物与环境梯度的皮尔逊相关分析（Pearson’s correlations）同样显示，营养盐与温度是塑造浮游植物群落结构的关键变量。结合分子表征与形态学鉴定的研究策略，可为有色浮游植物的类群组成与多样性分析提供全面的认知。

本研究是孟加拉湾内首个针对有色浮游植物的分子生物学研究，结果凸显了靶向rbcL基因的分子分析与显微镜检测相结合的方法，在探究浮游植物组成与多样性方面的应用价值。