Fig. 6

Maximum likelihood phylogenetic tree of Cas1 (a) and a schematic view of symbiotic interactions and niche adaptations in picocyanobacteria (b). a Picocyanobacterial Cas1 sequences are indicated by red circles at node tips. Ultrafast bootstrap values are displayed at selected nodes. Different CRISPR-Cas subtypes are represented by distinct colors. b Picocyanobacteria are represented in red or green depending on their pigmentation. Co-occurring heterotrophic bacteria are presented in brown. The degree of cell aggregation distinguishes the four ecologically significant ecotypes into unicellular or colonial lifestyles. The symbiotic interactions between picocyanobacteria and heterotrophs are illustrated with arrows indicating the direction of the interactions