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The essential micronutrient manganese (Mn) functions as redox-active cofactor in active sites of enzymes and, thus, is involved in various physiological reactions. Moreover, in oxygenic photosynthetic organisms, Mn is of special importance, since it is central to the oxygen-evolving complex in photosystem II. Although Mn is an essential micronutrient, increased amounts are detrimental to the organism; thus, only a small window exists for beneficial concentrations. Accordingly, Mn homeostasis must be carefully maintained. In contrast to the well-studied uptake mechanisms in cyanobacteria, it is largely unknown how Mn is distributed to the different compartments inside the cell. We identified a protein with so far unknown function as a hypothetical Mn transporter in the cyanobacterial model strain