Single cells and microcolonies of freshwater picocyanobacteria: a common ecology

Picocyanobacteria (Pcy) single-cells and microcolonies are common in lakes throughout the world, and abundant across a wide spectrum of trophic conditions. The single-celled Pcy populations tend to be predominant in large, deep oligo-mesotrophic lakes, while the microcolonies find optimal conditions in warmer, shallower and more nutrient rich lakes. Microcolonies of different size (from 5 to 50 cells) constitute a gradient without a net separation from single-celled types. Considering microcolonies as transitional forms from single-cells to colonial morphotypes it is conceivable to propose a common ecology where local communities are not isolated but linked by dispersal of multiple, potentially interactive, species. In this review abiotic forcing and biotic regulation of Pcy community structure and dynamics are examined to offer an updated view of Pcy ecology.