Cyanobacterial symbionts diverged in the late Cretaceous towards lineage-specific nitrogen fixation factories in single-celled phytoplankton
- Cornejo-Castillo, Francisco M;
- Cabello, Ana M;
- Salazar, Guillem;
- Sánchez-Baracaldo, Patricia;
- Lima-Mendez, Gipsi;
- Hingamp, Pascal;
- Alberti, Adriana;
- Sunagawa, Shinichi;
- Bork, Peer;
- de Vargas, Colomban;
- Raes, Jeroen;
- Bowler, Chris;
- Wincker, Patrick;
- Zehr, Jonathan P;
- Gasol, Josep M;
- Massana, Ramon;
- Acinas, Silvia G
- et al.
Published Web Location
https://www.nature.com/articles/ncomms11071Abstract
The unicellular cyanobacterium UCYN-A, one of the major contributors to nitrogen fixation in the open ocean, lives in symbiosis with single-celled phytoplankton. UCYN-A includes several closely related lineages whose partner fidelity, genome-wide expression and time of evolutionary divergence remain to be resolved. Here we detect and distinguish UCYN-A1 and UCYN-A2 lineages in symbiosis with two distinct prymnesiophyte partners in the South Atlantic Ocean. Both symbiotic systems are lineage specific and differ in the number of UCYN-A cells involved. Our analyses infer a streamlined genome expression towards nitrogen fixation in both UCYN-A lineages. Comparative genomics reveal a strong purifying selection in UCYN-A1 and UCYN-A2 with a diversification process ∼91 Myr ago, in the late Cretaceous, after the low-nutrient regime period occurred during the Jurassic. These findings suggest that UCYN-A diversified in a co-evolutionary process, wherein their prymnesiophyte partners acted as a barrier driving an allopatric speciation of extant UCYN-A lineages.
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