Secretion Machineries of L pneumophila Central to Its Life and to Pathogenesis

The importance of protein secretion for L. pneumophila is highlighted by the presence of a wide variety of secretion systems. The two major ones known to be involved in virulence are the icm/dot type IV secretion system and the lsp type II secretion system. However, L. pneumophila possesses several additional ones, such as a second type IV system named lvh, a type I secretion system called lss, a twin arginine translocation pathway, and several tra-like systems. In addition to these conserved secretory pathways, strain Paris encodes a type V secretion system specific to this strain.

15.3 Specific Features of the Legionella Genomes | 325 Type IV Secretion Systems in Legionella

Many bacterial pathogens encode type IV secretion systems. However L. pneumophila and Coxiella burnetii are the only ones known to encode a type IVB secretion system similar to the Tra/Trb system of IncI plasmids. In addition L. pneumophila also encodes type IVA systems similar to the Agrobacterium tumefaciens Vir system, like other bacterial pathogens. The type IVB secretion system in Legionella is the icm (intracellular multiplication; Marra et al. 1992) and/or dot (defective organelle trafficking; Berger and Isberg 1993) system. It is required for intra-cellular growth in human macrophages as well as in amoebae and for intracellular trafficking. The type IVA secretion systems are the lvh (Legionella vir homologue) system and several tra systems, which are homologous to Tra proteins of the Escherichia coli F plasmid.

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