Relationships between genetic diversity and niche-partitioning of Synechococcus populations in Mediterranean coastal lagoons, systems of transition between freshwater and marine ecosystems

Coastal lagoons are morphologically and ecologically complex ecosystems, subject to constantly changing environmental conditions generally of much greater magnitude than it is recorded in the open sea. Due to their transitional nature, they usually display a number of specific features (ie. high nutrient concentrations, light spectral quality, salinity range) which are potentially influencing strategies of adaptation of photosynthetic microorganisms. The unicellular cyanobacteria Synechococcus is a major component of marine and freshwater picophytoplankton. Its genetic diversity is well documented for these ecosystems, but knowledge about biodiversity and distribution of this genus in transitional waters remains scarce. The phylogenetic analysis of a library of 240 Synechococcus environmental clones (16S rDNA sequences) isolated from different coastal lagoons reveals that these transitional waters are populated with diverse Synechococcus strains including members from freshwater lakes, brackish, coastal and marine (sub-clusters 5.1 and 5.2) waters. This phylogenetic analysis was combined with an analysis of population genetics in order to understand the relationships between patterns of community structure and environmental parameters.