Phylogeography and ecogenomics of 'Ca. Fonsibacter' (SAR11-IIIb)

Financial support: Czech Science Foundation (GACR); Project No.: 22-03662S, Duration: 2022-2025

Principal Investigator: Michaela Salcher

Team Members: Clafy Fernandes, Markus Haber, Cecilia Chiriac, Rohit Ghai, Ievgen Lebeda, Alžběta Férová

Microbes affiliated to SAR11 (‘Ca. Pelagibacterales’) dominate in marine (SAR11-I, II, IV, V), brackish (SAR11-IIIa) and freshwater (SAR11-IIIb) systems and are challenging to cultivate due to their oligotrophic lifestyle and unusual nutrient requirements. A first culture of freshwater SAR11-IIIb was described only 2 years ago (‘Ca. Fonsibacter’). We have recently isolated 13 SAR11-IIIb strains by high-throughput dilution-to-extinction and aim at 50 additional cultures. State-of-the-art genomics will be combined with experiments to tackle their microdiversity, topdown control by protists and interactions with other microbes (WP1). Sampling of lakes on the southern hemisphere will counterbalance the uneven global sampling of mainly northern countries. Long-read metagenomics will enable sophisticated phylogeographic analyses of highquality genomes of metagenomes (MAGs) and cultures (WP2). The evolution of freshwater SAR11 will be addressed with SAR11 MAGs originating from freshwaters branching within marine lineages and strains gained from the brackish Baltic Sea (WP3).

We aim to characterize the ecology, microdiversity, global biogeography and evolutionary history of ‘Ca. Fonsibacter’ (freshwater SAR11-IIIb) by using high-throughput dilution-toextinction cultivation, experimental characterization, and whole-genome-sequencing together with long-read metagenomics.