Novel diversity of polar Cyanobacteria revealed by genome-resolved metagenomics. CCAMBIO 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.