Freshwater Picocyanobacteria: Single Cells, Microcolonies and Colonial Forms

Abstract

This chapter deals with some taxonomic and ecological aspects of picocyanobacteria (Pcy) single-cells, microcolonies and other colonial (CPcy), that are common in lakes throughout the world, and abundant across a wide spectrum of trophic conditions. We discussed phenotypic diversity of Pcy in conjunction with a genotypic approach in order to resolve whether a similar morphology also reflects a phylogenetic relationship. Microcolonies of different size (from 5 to 50 cells) constitute a gradient without a net separation from single-celled types and should be considered Pcy, as transition forms from single-cell to colonial morphotypes. The single-celled Pcy populations tend to be predominant in large, deep oligo-mesotrophic lakes, while the CPcy find optimal conditions in warmer, shallower and more nutrient rich lakes. The knowledge of Pcy diversity in pelagic and littoral zone habitats is a key to understand the dominance of certain genotypes in the water column and of their ubiquity. We devoted some paragraphs to analyse the factors (biotic and abiotic) which can influence the dynamics of the different Pcy forms and we have approached the study of their common ecology.