In general, we focus on the molecular mechanisms of bacterial membrane transport systems and particularly on potassium-translocating systems. K+ homeostasis in bacteria is essential for the survival of an individual cell and of a bacterial community. Among others, K+ uptake and release are required for osmoadaptation upon host invasion and electrical signalling within a bacterial biofilm. Thus, several bacterial K+ translocation systems have been suggested as general pathogenicity factors and are potential targets for newly developed drugs. We are aiming at elucidating the proteins’ mechanisms of K+ translocation as well as identifying molecules that regulate their function. Currently, we are focusing on three major topics: The molecular mechanisms of bacterial osmoadaptation, the control of potassium homeostasis by the second messenger cyclic di-AMP, and the role of potassium channels in bacterial cell-cell communication.