Biotic interactions dominate plankton communities, yet the microbial consortia associated with harmful algal blooms (HABs) have not been well-described. Here, high-throughput amplicon sequencing of ribosomal genes was used to quantify the dynamics of bacterial (16S) and phytoplankton assemblages (18S) associated with blooms and cultures of two harmful algae, Alexandrium fundyense and Dinophysis acuminata. Experiments were performed to assess changes in natural bacterial and phytoplankton communities in response to the filtrate from cultures of these two harmful algae. Analysis of prokaryotic sequences from ecosystems, experiments, and cultures revealed statistically unique bacterial associations with each HAB. The dinoflagellate, Alexandrium, was strongly associated with multiple genera of Flavobacteria including Owenweeksia spp., Maribacter spp., and individuals within the NS5 marine group. While Flavobacteria also dominated Dinophysis-associated communities, the relative abundance of Alteromonadales bacteria strongly co-varied with Dinophysis abundances during blooms and Ulvibacter spp. (Flavobacteriales) and Arenicella spp. (Gammaproteobacteria) were associated with cells in culture. Eukaryotic sequencing facilitated the discovery of the endosymbiotic, parasitic dinoflagellate, Amoebophrya spp., that had not been regionally described but represented up to 17% of sequences during Alexandrium blooms. The presence of Alexandrium in field samples and in experiments significantly altered the relative abundances of bacterial and phytoplankton by both suppressing and promoting different taxa, while this effect was weaker in Dinophysis. Experiments specifically revealed a negative feedback loop during blooms whereby Alexandrium filtrate promoted the abundance of the parasite, Amoebophrya spp. Collectively, this study demonstrates that HABs formed by Alexandrium and Dinophysis harbor unique prokaryotic and eukaryotic microbiomes that are likely to, in turn, influence the dynamics of these HABs.

生物相互作用在浮游生物群落中占主导地位，但与有害藻华（HABs）有关的微生物群落尚未得到充分描述。在这里，高通量核糖体基因的扩增子测序来定量细菌（16S）与开花和两个有害藻类，培养物相关的动力学和浮游植物组合（18S）亚历山大芬迪湾亚历山大藻和鳍藻喜树。进行实验以评估天然细菌和浮游植物群落对这两种有害藻类培养物产生的滤液的反应。对来自生态系统，实验和培养的原核生物序列的分析揭示了每个HAB在统计学上独特的细菌关联。鞭毛藻，亚历山大，与黄细菌的多个属密切相关，包括Owenweeksia spp。，Maribacter spp。和NS5海洋群内的个体。虽然黄杆菌也占据鳍藻-相关的社区，Alteromonadales细菌具有强烈的共同变化的相对丰度鳍藻华和中丰度Ulvibacter属。（Flavobacteriales）和Arenicella spp。（丙型杆菌）与培养中的细胞有关。真核测序有助于发现内共生寄生性鞭毛虫，变形虫属，这在区域上没有描述，但在此过程中最多代表了17％的序列。亚历山大绽放。野外样品和实验中亚历山大藻的存在通过抑制和促进不同的分类单元而显着改变了细菌和浮游植物的相对丰度，而在恐龙学中这种作用较弱。实验特别揭示了开花期间的负反馈回路，从而亚历山大滤液提高了寄生虫Amoebophrya spp的丰度。总体而言，这项研究表明，由亚历山大和恐龙物理所形成的HAB包含独特的原核和真核微生物组，这很可能反过来影响这些HAB的动力学。