The cosmopolitan algae Phaeocystis globosa forms harmful algal blooms frequently in a number of tropical and subtropical coastal regions in the past two decades. During the bloom, the giant colony, which is formed by P. globosa, is the dominant morphotype. However, the microenvironment and the microbial composition in the intracolonial fluid are poorly understood. Here, we used high-throughput 16S rRNA amplicon sequencing to examine the bacterial composition and predicted functions in intracolonial fluid. Compared with the bacterial consortia in ambient seawater, intracolonial fluids possessed the lower levels of microbial richness and diversity, implying selectivity of bacteria by the unique intracolonial microenvironment enclosed within the P. globosa polysaccharide envelope. The bacterial consortia in intracolonial fluid were dominated by Balneola (48.6% of total abundance) and Labrezia (28.5%). The bacteria and microbial function enriched in intracolonial fluid were involved in aromatic benzenoid compounds degradation, DMSP and DMS production and consumption, and antibacterial compounds synthesis. We suggest that the P. globosa colonial envelope allows for the formation of a specific microenvironment; thus, the unique microbial consortia inhabiting intracolonial fluid has close interaction with P. globosa cells, which may benefit colony development.

世界性的藻类 球藻在过去的二十年里，在一些热带和亚热带沿海地区经常形成有害的藻华。在盛开期间，巨大的菌落由球状假单胞菌, 是显性形态型。然而，人们对菌落内液中的微环境和微生物组成知之甚少。在这里，我们使用高通量 16S rRNA 扩增子测序来检查菌落液中的细菌组成和预测功能。与周围海水中的细菌聚生体相比，菌落内流体的微生物丰富度和多样性水平较低，这意味着细菌的选择性受到封闭在内部的独特菌落内微环境的影响。球状假单胞菌多糖包膜。菌落内菌群主要由巴尔尼奥拉 （总丰度的 48.6%）和 拉布雷齐亚(28.5%)。菌落液中富含的细菌和微生物功能参与了芳香族苯类化合物的降解、DMSP 和 DMS 的产生和消耗以及抗菌化合物的合成。我们建议将球状假单胞菌殖民地外壳允许形成特定的微环境；因此，居住在菌落内液中的独特微生物群落与球状假单胞菌 细胞，这可能有利于集落发育。