Regulation, integrase-dependent excision, and horizontal transfer of genomic islands in Legionella pneumophila.
Legionella pneumophila is a Gram-negative freshwater agent which multiplies in specialized nutrient-rich vacuoles of amoebae. When replicating in human alveolar macrophages, Legionella can cause Legionnaires' disease. Recently, we identified a new type of conjugation/type IVA secretion system (T4ASS) in L. pneumophila Corby (named trb-tra). Analogous versions of trb-tra are localized on the genomic islands Trb-1 and Trb-2. Both can exist as an episomal circular form, and Trb-1 can be transferred horizontally to other Legionella strains by conjugation. In our current work, we discovered the importance of a site-specific integrase (Int-1, lpc2818) for the excision and conjugation process of Trb-1. Furthermore, we identified the genes lvrRABC (lpc2813 to lpc2816) to be involved in the regulation of Trb-1 excision. In addition, we demonstrated for the first time that a Legionella genomic island (LGI) of L. pneumophila Corby (LpcGI-2) encodes a functional type IV secretion system. The island can be transferred horizontally by conjugation and is integrated site specifically into the genome of the transconjugants. LpcGI-2 generates three different episomal forms. The predominant episomal form, form A, is generated integrase dependently (Lpc1833) and transferred by conjugation in a pilT-dependent manner. Therefore, the genomic islands Trb-1 and LpcGI-2 should be classified as integrative and conjugative elements (ICEs). Coculture studies of L. pneumophila wild-type and mutant strains revealed that the int-1 and lvrRABC genes (located on Trb-1) as well as lpc1833 and pilT (located on LpcGI-2) do not influence the in vivo fitness of L. pneumophila in Acanthamoeba castellanii.
Centre for Biological Security, Division 2 (ZBS2), Cellular Interactions of Bacterial Pathogens Working Group, Robert Koch Institute, Berlin, Germany.
Monika
M
Lautner
Eva
E
Schunder
Vroni
V
Herrmann
Klaus
K
Heuner
D048248:Acanthamoeba castellanii / Q000382:microbiology; D058947:Bacterial Secretion Systems / Q000235:genetics*; D002876:Chromosomes, Bacterial; D003227:Conjugation, Genetic; D022761:Gene Transfer, Horizontal; D044404:Genomic Islands; D006801:Humans; D019426:Integrases / Q000378:metabolism; D016952:Legionella pneumophila / Q000235:genetics* / Q000378:metabolism*; D010957:Plasmids; D011995:Recombination, Genetic
D058947:Bacterial Secretion Systems; D019426:Integrases