In silico analysis revealed that SsTroA is a putative lipoprotein (Fig. 1B) . The amino-terminal signal sequence of such lipoproteins is distinguishable by the presence of a lipobox motif at the signal sequence cleavage site. The conserved lipobox motif is usually characterized as L 23 -[A/S/T] 22 -[G/A] 21 -C +1 and lipid modification is achieved through a covalent linkage of a diacylglyceride to the conserved cysteine residue. Indeed, the cysteine residue is absolutely conserved in all bacterial lipoproteins [34, 35] . SsTroA contains a typical type II signal peptide for Sec-dependent transport. Its presumptive lipobox sequence is LGAC, containing the indispensible cysteine in position 30, indicating that SsTroA is not released into the environment but rather inserted into the plasma membrane via a diacylglyceryl anchor. Alignment of sequences also revealed that the metal binding site of SsTroA is very similar to Mn-specific SBPs (Fig. 1B) . These data suggested that the SsTroA should physiologically bind Mn 2+ .