A study published in Genome Biology, led by Anders Andersson at KTH Royal Institute of Technology/SciLifeLab, shows that the closest relatives of bacterial plankton in the Baltic Sea are not found in oceans or freshwater lakes, but in other brackish environments. The researchers used DNA sequencing and advanced algorithms to reconstruct the genomes of a number of bacterial plankton. The genomes may not yet answer where these plankton came from, but they will help scientists to better understand brackish ecosystems.