The cytoskeletal proteins MreB and FtsZ and the peptidoglycan hydrolase PBP4 act together in longitudinally dividing bacterium Candidatus Thiosymbion oneisti

Candidatus Thiosymbion oneisti is a rod-shaped gamma proteobacterium bound on the cuticle of its nematode host Laxus Oneistus by one pole. Compared to other rods, the growth and division of Ca. T. oneisti do not follow the canonical mode. It widens and divides by longitudinal fission. Escherichia coli and Ca. T. oneisti are genetically very similar and both share most of the known proteins involved in cell division. Three of them were investigated and described in this thesis. FtsZ, the bacterial tubulin-homolog, of Ca. T. oneisti shows temperature-sensitive characteristics when it is expressed in E. coli. The temperature sensitivity of Ca. T. oneisti FtsZ is likely an adaptation to the preferred temperature of less than 30 °C of its host the nematode L. oneistus. Ca. T. oneisti MreB localizes at the medial along the length axis of the cells. Co-labeling with antibodies against the cell division protein FtsZ revealed that MreB localization precedes that of FtsZ. Inhibition of the function of MreB by A22 prevented localization of FtsZ and synthesis of septal peptidoglycan. The PG layer of Ca. T. oneisti has an unusually high peptide cross-linkage of 67% but relatively short glycan chains with an average length of 12 disaccharides. Curiously, it has only two predicted endopeptidases, MepA and PBP4. Cellular localization of symbiont PBP4 by fluorescently labeled antibodies reveals its polar localization and its accumulation at the constriction sites, suggesting that PBP4 is involved in PG biosynthesis during septum formation.