Delineating ecologically significant taxonomic units from global patterns of marine picocyanobacteria

摘要: Prochlorococcus and Synechococcus are the two most abundant widespread phytoplankton in global ocean. To better understand factors controlling their biogeography, a reference database of high-resolution taxonomic marker petB, encoding cytochrome b6, was used to recruit reads out 109 metagenomes from Tara Oceans expedition. An unsuspected novel genetic diversity unveiled within both genera, even for well-characterized clades, 136 divergent petB sequences were successfully assembled metagenomic reads, significantly enriching database. We then defined Ecologically Significant Taxonomic Units (ESTUs)—that is, organisms belonging same clade occupying common oceanic niche. Three major ESTU assemblages identified along cruise transect eight Synechococcus. Although HLIIIA HLIVA ESTUs codominated iron-depleted areas Pacific Ocean, CRD1 yet-to-be cultured EnvB prevalent clades this area, with three different distinct ecological niches regard iron availability temperature. Sharp community shifts also observed over short geographic distances—for example, around Marquesas Islands or between southern Indian Atlantic Oceans—pointing tight correlation specific physico-chemical parameters. Together, study demonstrates that there is previously overlooked, ecologically meaningful, fine-scale some currently picocyanobacterial ecotypes, bringing insights into ecology, diversity, biology phototrophs on Earth.