title: Genomic diversification in strains of Rickettsia felis Isolated from different arthropods.
abstract: Rickettsia felis (Alphaproteobacteria: Rickettsiales) is the causative agent of an emerging flea-borne rickettsiosis with worldwide occurrence. Originally described from the cat flea, Ctenocephalides felis, recent reports have identified R. felis from other flea species, as well as other insects and ticks. This diverse host range for R. felis may indicate an underlying genetic variability associated with host-specific strains. Accordingly, to determine a potential genetic basis for host specialization, we sequenced the genome of R. felis str. LSU-Lb, which is an obligate mutualist of the parthenogenic booklouse Liposcelis bostrychophila (Insecta: Psocoptera). We also sequenced the genome of R. felis str. LSU, the second genome sequence for cat flea-associated strains (cf. R. felis str. URRWXCal2), which are presumably facultative parasites of fleas. Phylogenomics analysis revealed R. felis str. LSU-Lb diverged from the flea-associated strains. Unexpectedly, R. felis str. LSU was found to be divergent from R. felis str. URRWXCal2, despite sharing similar hosts. Although all three R. felis genomes contain the pRF plasmid, R. felis str. LSU-Lb carries an additional unique plasmid, pLbaR (plasmid of L. bostrychophila associated Rickettsia), nearly half of which encodes a unique 23-gene integrative conjugative element. Remarkably, pLbaR also encodes a repeats-in-toxin-like type I secretion system and associated toxin, heretofore unknown from other Rickettsiales genomes, which likely originated from lateral gene transfer with another obligate intracellular parasite of arthropods, Cardinium (Bacteroidetes). Collectively, our study reveals unexpected genomic diversity across three R. felis strains and identifies several diversifying factors that differentiate facultative parasites of fleas from obligate mutualists of booklice.
authors.affiliation: Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland jgillespie@som.umaryland.edu.
authors.forename: Joseph J
authors.initials: JJ
authors.lastname: Gillespie
authors.affiliation: Department of Biology, Western Carolina University.
authors.forename: Timothy P
authors.initials: TP
authors.lastname: Driscoll
authors.affiliation: Department of Pathobiological Sciences, Louisiana State University, School of Veterinary Medicine.
authors.forename: Victoria I
authors.initials: VI
authors.lastname: Verhoeve
authors.affiliation: Department of Pathobiological Sciences, Louisiana State University, School of Veterinary Medicine.
authors.forename: Tadanobu
authors.initials: T
authors.lastname: Utsuki
authors.affiliation: Department of Entomology, Louisiana State University Agricultural Center, Baton Rouge, Louisiana.
authors.forename: Claudia
authors.initials: C
authors.lastname: Husseneder
authors.affiliation: Department of Pathobiological Sciences, Louisiana State University, School of Veterinary Medicine.
authors.forename: Vladimir N
authors.initials: VN
authors.lastname: Chouljenko
authors.affiliation: Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland.
authors.forename: Abdu F
authors.initials: AF
authors.lastname: Azad
authors.affiliation: Department of Pathobiological Sciences, Louisiana State University, School of Veterinary Medicine.
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Macaluso
mesh_terms: D000818:Animals; D001181:Arthropods / Q000382:microbiology; D001426:Bacterial Proteins / Q000235:genetics*; D002415:Cats; D022761:Gene Transfer, Horizontal; D023281:Genomics; D006460:Hemolysin Proteins / Q000235:genetics*; D006801:Humans; D010802:Phylogeny; D010957:Plasmids / Q000235:genetics; D041161:Rickettsia felis / Q000235:genetics* / Q000472:pathogenicity; D012288:Rickettsiaceae Infections / Q000235:genetics* / Q000382:microbiology* / Q000635:transmission; D005423:Siphonaptera / Q000382:microbiology
chemical_list: D001426:Bacterial Proteins; D006460:Hemolysin Proteins; C087744:ApxI toxin, Bacteria
keywords: RTX-type I secretion system; Rickettsiales amplified genetic element; booklouse; flea; genomes; phylogeny; plasmid; transitional group rickettsiae