Novel diversity of polar Cyanobacteria revealed by genome-resolved metagenomics

Benthic microbial mats dominated by Cyanobacteria are important features of polar lakes. Although culture-independent studies have provided important insights into their diversity, only a handful of genomes of polar Cyanobacteria have been sequenced to date. Here, we applied a genome-resolved metagenomics approach to data obtained from Arctic, sub-Antarctic, and Antarctic microbial mats. We recovered 22 unique metagenome-assembled genomes (MAGs) of Cyanobacteria, most of which are only distantly related to genomes that have been sequenced so far. These include i) lineages that are common in polar microbial mats such as the filamentous taxa Pseudanabaena, Leptolyngbya, Microcoleus/Tychonema, and Phormidium; ii) the less common taxa Crinalium and Chamaesiphon; iii) an enigmatic Chroococcales lineage only distantly related to Microcystis; and iv) an early branching lineage in the order Gloeobacterales that is almost exclusively restricted to the cold biosphere, for which we propose the name Candidatus Sivonenia alaskensis. Our results show that genome-resolved metagenomics is a powerful tool for expanding our understanding of the diversity of Cyanobacteria, especially in understudied remote and extreme environments.

以蓝细菌（Cyanobacteria）为优势类群的底栖微生物垫是极地湖泊的重要特征。尽管免培养研究已为其多样性解析提供了重要见解，但迄今为止已测序的极地蓝细菌基因组仍寥寥无几。本研究将基因组解析宏基因组学（genome-resolved metagenomics）方法应用于源自北极、亚南极及南极微生物垫的测序数据，成功获得22个独特的蓝细菌宏基因组组装基因组（metagenome-assembled genomes，MAGs），其中绝大多数与已测序的蓝细菌基因组亲缘关系甚远。这些基因组涵盖的类群包括：i）极地微生物垫中常见的丝状类群，如假鱼腥藻属（Pseudanabaena）、细鞘丝藻属（Leptolyngbya）、微鞘藻属/提恩藻属（Microcoleus/Tychonema）以及席藻属（Phormidium）；ii）较为少见的克里纳藻属（Crinalium）和管孢藻属（Chamaesiphon）；iii）与微囊藻属（Microcystis）亲缘关系较远的神秘色球藻目（Chroococcales）类群；iv）胶杆菌目（Gloeobacterales）下的一个早期分化类群，该类群几乎仅分布于低温生物圈，我们将其命名为*Candidatus Sivonenia alaskensis*。本研究结果表明，基因组解析宏基因组学是拓展我们对蓝细菌多样性认知的有力工具，尤其针对研究不足的偏远极端环境。