For proliferation, phages have to take over major cell functions while the bacterial hosts have developed a whole array of countermeasures to prevent the foreign intruders from doing so. Lysogenic phages therefore had to evolve mechanisms to enter the cells unrecognized, establish themselves as genetic element and to take control when necessary. Many of the mechanisms by which such phages affect their host are still elusive, and, in addition, most phages possess numerous genes encoding unknown proteins that are or may be involved in host control. The Shewanella lysogenic phage LambdaSo harbors a gene cluster encoding six relatively small (50 – 120 aa) uncharacterized proteins, which affect cell elongation and enable or suppress cell lysis. In this project we combine biochemical, genetic and fluorescence microscopy approaches to unravel the mechanism by which these small phage effectors control elementary functions of the host.