Cyanobacterial symbionts diverged in the late Cretaceous towards lineage-specific nitrogen fixation factories in single-celled phytoplankton

• Published in: Nature Communications
• Main Authors: Cornejo-Castillo, Francisco M., Cabello, Ana María, Salazar, Guillem, Gasol, Josep M., Massana, Ramon, Acinas, Silvia G.
• Other Authors: European Molecular Biology Laboratory, Agence Nationale de la Recherche (France), France Génomique, Consejo Superior de Investigaciones Científicas (España), Ministerio de Ciencia e Innovación (España)
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Nature Publishing Group 2016
• Subjects: Cornejo; South Atlantic Ocean
• Online Access: http://hdl.handle.net/10261/131710; https://doi.org/10.1038/ncomms11071; https://doi.org/10.13039/501100001665; https://doi.org/10.13039/501100003339; https://doi.org/10.13039/501100004837; https://doi.org/10.13039/100013060

Cornejo-Castillo, Francisco M. . et al.-- 9 pages, 3 figures, 1 table, supplementary data, supplementary information http://dx.doi.org/10.1038/ncomms11071.-- This article is contribution number 37 of Tara Oceans 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 This work was supported by the Spanish Ministry of Science and Innovation grant CGL2011-26848/BOS MicroOcean PANGENOMICS, and TANIT (CONES 2010-0036) from the Agència de Gestió d'Ajuts Universitaris i Recerca to S.G.A. This research was further supported by European Molecular Biology Laboratory (EMBL), Investissements d'avenir grants Oceanomics (ANR-11-BTBR-OOO8) and France Génomique (ANR-10-INBS-09-08). F.M.C.-C. and A.M.C. held FPI (MICINN) fellowships and G.S. held PhD JAE-Predoc (CSIC) fellowship. S.G.A. was supported by FP7-OCEAN-2011 project ‘Micro B3’ Peer Reviewed