Hochschule Mannheim 1 article published in JoVE Biology Natural Transformation, Protein Expression, and Cryoconservation of the Filamentous Cyanobacterium Phormidium lacuna Nora Weber1, Michael Hofmeister1, Nadja Wunsch1, Anja Kohler1, Anne-Kristin Kaster2, Jon Vollmers2, Ben Kachel3, Matthias Mack3, Tilman Lamparter1 1Botanical Institute, Karlsruhe Institute of Technology KIT, 2Institute for Biological Interfaces 5 (IBG 5), Karlsruhe Institute of Technology KIT, 3Institut für Technische Mikrobiologie, Hochschule Mannheim Phormidium lacuna is a filamentous cyanobacterium that was isolated from marine rockpools. This article describes the isolation of filaments from natural sources, DNA extraction, genome sequencing, natural transformation, expression of sfGFP, cryoconservation, and motility methods.