Institute of Hydrobiology, Jinan University, Guangzhou, Guangdong, China.
Center for Fundamental and Applied Microbiomics, Biodesign Institute, Arizona State University, Tempe, AZ 85287, USA.
Harmful Algae. 2019 Feb;82:9-18. doi: 10.1016/j.hal.2018.12.006. Epub 2018 Dec 29.
Cyanobacterial blooms are intensifying global ecological hazards. The fine structure and dynamics of bloom community are critical to understanding bloom development but little understood. Here, the questions whether dominant bloomers have high diversity and whether dominant OTUs (operational taxonomical units) compete with one another were addressed. 16S rRNA gene amplicons from an annual bloom at five locations in Harsha Lake (Ohio, USA) showed cyanobacteria were the dominant phylum, and co-existing major bacterial phyla included Proteobacteria, Bacteroidetes, Actinoacteria, and Verrucomicrobia. On the genus level, the initial dominance by Dolichospermum in June yielded to Planktothrix in July, which were replaced by Microcystis and Cylindrospermopsis in August throughout the bloom. Based on the number of verified unique OTUs (a within-genus biodiversity metric), dominant genera tended to have high within-genus diversity. For example, Dolichospermum had 57 unique OTUs, Planktothrix had 36, Microcystis had 12, and Cylindrospermopsis had 4 unique OTUs. Interestingly, these different OTUs showed different dynamics and association with other OTUs. First, no between-OTU competitions were observed during the bloom cycle, and dominant OTUs were abundant throughout the bloom. Such biodiversity of OTUs and their dynamics were verified in Microcystis aeruginosa with two microcystin synthetase genes (mcyA and mcyG): the relative abundance of both genes varied during the bloom based on quantitative PCR. Two Dolichospermum circinale OTUs and one P. rubescens OTU were most abundant and persistently present throughout the entire bloom. Second, these OTUs differed in the OTUs they were associated with. Third, these OTUs tended to have different levels of association with the environmental factors, even they belonged to the same genera. These findings suggest the structure and dynamics of a cyanobacterial bloom community is complex, with only few OTUs dominating the bloom. Thus, high-resolution molecular characterization will be necessary to understand bloom development.
蓝藻水华正在加剧全球生态危害。了解水华群落的精细结构和动态对于理解水华的发展至关重要，但目前对此知之甚少。本研究旨在探讨优势藻种是否具有高度多样性，以及优势 OTU（操作分类单元）是否相互竞争的问题。从美国俄亥俄州哈沙湖（Harsha Lake）五个地点的年度水华采集的 16S rRNA 基因扩增子显示，蓝藻是优势门，共存的主要细菌门包括变形菌门、拟杆菌门、放线菌门和疣微菌门。在属水平上，6 月时优势藻种是束丝藻属（Dolichospermum），7 月时优势藻种变为束丝藻属（Planktothrix），8 月时整个水华过程中优势藻种变为微囊藻属（Microcystis）和柱孢藻属（Cylindrospermopsis）。基于经证实的独特 OTU 数量（属内生物多样性指标），优势属往往具有较高的属内多样性。例如，束丝藻属有 57 个独特 OTU，束丝藻属有 36 个，微囊藻属有 12 个，柱孢藻属有 4 个独特 OTU。有趣的是，这些不同的 OTU 表现出不同的动态和与其他 OTU 的关联。首先，在水华周期中没有观察到 OTU 之间的竞争，而且优势 OTU 在整个水华过程中都很丰富。这种 OTU 的生物多样性及其动态在铜绿微囊藻的两个微囊藻毒素合成酶基因（mcyA 和 mcyG）中得到了验证：基于定量 PCR，这两个基因的相对丰度在水华期间发生了变化。两个束丝藻 circinaleOTU 和一个 P. rubescensOTU 最为丰富，并在整个水华过程中一直存在。其次，这些 OTU 与不同的 OTU 相关联。第三，这些 OTU 与环境因素的关联程度不同，即使它们属于同一属。这些发现表明，蓝藻水华群落的结构和动态是复杂的，只有少数 OTU 主导水华。因此，需要进行高分辨率的分子特征分析，以了解水华的发展。
