Revealing keystone arctic microbial genomes

Abstract

Microbial community composition in the North Polar waters varies greatly throughout the year. From what it is known so far, spring melting of the ice and increase in light disposal spur the bloom of phytoplankton. During summer, bacterial populations, mainly heterotrophic and photoheterotrophic, feed on the nutrients derived from such bloom. With fall’s shorter light hours and colder seawater temperatures, the bacterial community shifts towards chemolithoautotrophic microorganisms, that will prevail during winter. In 2013 Tara Oceans navigated Arctic waters during spring, summer and the beginning of fall (May to October), extensively sampling the microbial plankton communities. Here, we show the reconstruction of 2555 bacterial and archaeal metagenomic assembled genomes (MAGs) from 41 microbial metagenomes, covering the whole Arctic Ocean from spring to early fall at different water depths. Together with the physicochemical information of all stations we are capable of linking habitat preferences (generalists vs specialist) of the different prokaryotic taxa around the North Pole with at the maximum resolution possible, the genome level. Of the reconstructed prokaryotic MAGs, 96 are considered to be high-quality draft-like genomes (>90% genome completeness, <5% contamination), revealing several potential new phyla, including unexpected taxa such as Dehaloccocoidetes, a group that had never been described in polar oceans waters. Moreover, the metabolic capacity of these uncultured prokaryotic genomes reveals the ubiquity of chemolithoautotrophic metabolisms in this environment through the different seasons, harboring different pathways for CO2 fixation. This finding represents a major breakthrough in our understanding of potential prokaryotic endemism’s and the carbon fluxes in Arctic polar waters, pointing out to a greater impact than previously considered