Metagenomics reveals global-scale contrasts in nitrogen cycling and cyanobacterial light-harvesting mechanisms in glacier cryoconite

• Published in: Microbiome
• Main Authors: Takumi Murakami, Nozomu Takeuchi, Hiroshi Mori, Yuu Hirose, Arwyn Edwards, Tristram Irvine-Fynn, Zhongqin Li, Satoshi Ishii, Takahiro Segawa
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2022
• Subjects: Glacier ecosystem; Cryoconite; Metagenomics; Denitrification; Cyanobacteria; Phycobilisome; Microbial ecology; QR100-130; Arctic; Antarctic; Antarc*
• Online Access: https://doi.org/10.1186/s40168-022-01238-7; https://doaj.org/article/261b7f03438f490f81235825783fb2b7

Abstract Background Cryoconite granules are mineral–microbial aggregates found on glacier surfaces worldwide and are hotspots of biogeochemical reactions in glacier ecosystems. However, despite their importance within glacier ecosystems, the geographical diversity of taxonomic assemblages and metabolic potential of cryoconite communities around the globe remain unclear. In particular, the genomic content of cryoconite communities on Asia’s high mountain glaciers, which represent a substantial portion of Earth’s ice masses, has rarely been reported. Therefore, in this study, to elucidate the taxonomic and ecological diversities of cryoconite bacterial consortia on a global scale, we conducted shotgun metagenomic sequencing of cryoconite acquired from a range of geographical areas comprising Polar (Arctic and Antarctic) and Asian alpine regions. Results Our metagenomic data indicate that compositions of both bacterial taxa and functional genes are particularly distinctive for Asian cryoconite. Read abundance of the genes responsible for denitrification was significantly more abundant in Asian cryoconite than the Polar cryoconite, implying that denitrification is more enhanced in Asian glaciers. The taxonomic composition of Cyanobacteria, the key primary producers in cryoconite communities, also differs between the Polar and Asian samples. Analyses on the metagenome-assembled genomes and fluorescence emission spectra reveal that Asian cryoconite is dominated by multiple cyanobacterial lineages possessing phycoerythrin, a green light-harvesting component for photosynthesis. In contrast, Polar cryoconite is dominated by a single cyanobacterial species Phormidesmis priestleyi that does not possess phycoerythrin. These findings suggest that the assemblage of cryoconite bacterial communities respond to regional- or glacier-specific physicochemical conditions, such as the availability of nutrients (e.g., nitrate and dissolved organic carbon) and light (i.e., incident shortwave radiation). Conclusions Our genome-resolved ...