Supplementary Material for: Temporal and Vertical Variation in Microbial Community Composition in Response to Physicochemical Characteristics in a Water Column of Highly Eutrophied Jinhae Bay, South Korea

Microbial communities play an essential role in marine biogeochemical cycles. Physical and biogeochemical changes in Jinhae Bay, the most anthropogenically eutrophied bay on the coasts of South Korea, are well described, but less is known about the associated changes in microbial communities. Temporal and vertical variation in microbial communities at three depths (surface, middle, and bottom) at seven time points (June to December) at the J1 sampling site were investigated on the MiSeq platform based on the 16S rRNA gene. Overall, the microbial community was dominated by Proteobacteria, Cyanobacteria, and Bacteroidetes from June to November, whereas Firmicutes were dominant in December, especially in the middle and bottom layers. The results indicate that the microbial community composition strongly varied with temporal changes in the physicochemical water properties. Moreover, the community composition differed markedly between the surface and middle layers and the bottom layer in the summer, when the water column was strongly stratified and bottom water hypoxia developed. A redundancy analysis suggested a significant correlation between physicochemical variables (i.e., temperature, salinity, and oxygen concentration) and microbial community composition. This study indicates that temporal changes in water conditions and eutrophication-induced hypoxia effectively shape the structure of the microbial community.

微生物群落在海洋生物地球化学循环中发挥着至关重要的作用。韩国沿岸受人类活动驱动富营养化程度最高的镇海湾（Jinhae Bay），其物理与生物地球化学变化已得到充分研究，但相关的微生物群落变化却鲜为人知。本研究基于16S rRNA基因，利用MiSeq测序平台，对J1采样点处7个时间节点（6月至12月）、3个深度层次（表层、中层和底层）的微生物群落时间与垂直分布变化进行了探究。整体而言，6月至11月的微生物群落以变形菌门（Proteobacteria）、蓝细菌门（Cyanobacteria）和拟杆菌门（Bacteroidetes）为优势类群；而12月的优势类群则为厚壁菌门（Firmicutes），尤其在中层和底层水体中更为显著。研究结果表明，微生物群落组成随水体理化性质的时间变化呈现显著差异。此外，夏季水体出现强烈分层且底层水体发生缺氧时，表层与中层的群落组成与底层存在显著差异。冗余分析（Redundancy Analysis）结果显示，水温、盐度与溶解氧浓度等理化因子与微生物群落组成之间存在显著相关性。本研究表明，水体环境的时间变化以及富营养化引发的缺氧现象，可有效塑造微生物群落的结构组成。