Coexistence rather than predation affects the microbiome associated with Synechococcus ribotypes

Planktonic cyanobacteria belonging to the genus Synechococcus are ubiquitouslydistributed in marine and freshwaters, coexisting and competing in the microbialcontinuum. Interplays among phylogenetically different Synechococcus clades andassociated bacterial communities can affect their ecological fate and susceptibility toprotistan predation. In this study, we experimentally promoted different levels of microbialinteractions by mixing Synechococcus ribotypes (MW101C3 and LL), with and withoutnanoflagellate grazers (Poterioochromonas). The beta-diversity of the Synechococcusassociated microbiome indicated that the presence of the LL ribotype was the main factordetermining community composition changes (41% of total variance), and prevailed overthe effect of protistan predation (18% of total variance). We elucidated that speciescoexistence may promote microbial diversity by increasing the overall complexity of cell-to-cellinteractions, thus highlighting the ecological relevance of such emerging factors.