Abstract
Mycoplasma pneumoniae, the causative agent of atypical pneumonia, is one of the bacteria with the smallest genomes that are nonetheless capable of independent life. Because of their longstanding close association with their human host, the bacteria have undergone reductive evolution and lost most biosynthetic abilities. Therefore, they depend on nutrients provided by the host that have to be taken up by the cell. Indeed, M. pneumoniae has a large set of hitherto unexplored transporters and lipoproteins that may be implicated in transport processes. Together, these proteins account for about 17% of the protein complement of M. pneumoniae. In the natural habitat of M. pneumoniae, human lung epithelial surfaces, phospholipids are the major available carbon source. Thus, the uptake and utilization of glycerol and glycerophosphodiesters that are generated by the activity of lipases are important for the nutrition of M. pneumoniae in its common habitat. In this study, we have investigated the roles of several potential transport proteins and lipoproteins in the utilization of glycerol and glycerophosphodiesters. On the basis of experiments with the corresponding mutant strains, our results demonstrate that the newly identified GlpU transport protein (MPN421) is responsible for the uptake of the glycerophosphodiester glycerophosphocholine, which is then intracellularly cleaved to glycerol-3-phosphate and choline. In addition, the proteins MPN076 and MPN077 are accessory factors in glycerophosphocholine uptake. Moreover, the lipoproteins MPN133 and MPN284 are essential for the uptake of glycerol. Our data suggest that they may act as binding proteins for glycerol and deliver glycerol molecules to the glycerol facilitator GlpF.