title: Evidence for acquisition of Legionella type IV secretion substrates via interdomain horizontal gene transfer.
abstract: Intracellular pathogens exploit host cell functions to create a replication niche inside eukaryotic cells. The causative agent of Legionnaires' disease, the gamma-proteobacterium Legionella pneumophila, resides and replicates within a modified vacuole of protozoan and mammalian cells. L. pneumophila translocates effector proteins into host cells through the Icm-Dot complex, a specialized type IVB secretion system that is required for intracellular growth. To find out if some effector proteins may have been acquired through interdomain horizontal gene transfer (HGT), we performed a bioinformatic screen that searched for eukaryotic motifs in all open reading frames of the L. pneumophila Philadelphia-1 genome. We found 44 uncharacterized genes with many distinct eukaryotic motifs. Most of these genes contain G+C biases compared to other L. pneumophila genes, supporting the theory that they were acquired through HGT. Furthermore, we found that several of them are expressed and up-regulated in stationary phase in an RpoS-dependent manner. In addition, at least seven of these gene products are translocated into host cells via the Icm-Dot complex, confirming their role in the intracellular environment. Reminiscent of the case with most Icm-Dot substrates, most of the strains containing mutations in these genes grew comparably to the parent strain intracellularly. Our findings suggest that in L. pneumophila, interdomain HGT may have been a major mechanism for the acquisition of determinants of infection.
authors.affiliation: Integrated Program in Cellular, Molecular & Biophysical Studies, New York, New York 10032, USA.
authors.forename: Karim Suwwan
authors.initials: KS
authors.lastname: de Felipe
authors.forename: Sergey
authors.initials: S
authors.lastname: Pampou
authors.forename: Oliver S
authors.initials: OS
authors.lastname: Jovanovic
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Pericone
authors.forename: Senna F
authors.initials: SF
authors.lastname: Ye
authors.forename: Sergey
authors.initials: S
authors.lastname: Kalachikov
authors.forename: Howard A
authors.initials: HA
authors.lastname: Shuman
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D019295:Computational Biology; D022761:Gene Transfer, Horizontal; D005798:Genes, Bacterial; D016680:Genome, Bacterial; D016952:Legionella pneumophila / Q000235:genetics* / Q000378:metabolism; D016366:Open Reading Frames / Q000235:genetics; D021381:Protein Transport
chemical_list: D001426:Bacterial Proteins