There is a current gap between molecular and ecological microbiology as the abundant and ecosystem-relevant microbes are scarcely characterized in regards to their metabolism, cell-division, expression, DNA exchange and repair. In this project strains belonging to the most widespread and abundant aquatic bacteria will be established as models to test hypotheses derived from computational predictions of genomic data (retrieved from metagenomes, and cultured and single cells). These often oligotrophic bacteria play a central role in the cycling of dissolved organic matter and determining which carbon compounds are used by these bacteria will serve as a resource for aquatic chemists and biogeochemists working to define the carbon cycle in greater mechanistic detail and at large geographical scales. Comparative genomics and experiments will also reveal the traits underlying their transition between biomes (i.e. from marine to freshwaters). Moreover, studies target towards evolution in controlled experimental settings can help towards understanding homologous recombination and adaptation in oligotrophic bacteria with streamlined genomes.