Honors College Theses

Publication Date



Biology (B.S.B.)

Document Type and Release Option

Thesis (open access)

Faculty Mentor

Dr. Marina Eremeeva


Background: Spotted Fever group rickettsiae are obligate intracellular arthropod-borne bacteria. Rickettsiae are globally distributed yet typically confined to the distribution of their vector(s). Rickettsia rickettsii and Rickettsia philipii are closely related human pathogens endemic to the United States and cause similar febrile illness with differing morbidity and mortality. Genomic comparison found the presence of a 19 kilobase insert containing eleven genes in Rickettsia philipii. The functions of proteins encoded by this insert are speculated to affect virulence and pathogenicity.

Materials and Methods: Bioinformatic analysis was performed to identify functional motifs in four proteins encoded by the insert. Homologous proteins from other bacterial systems with similar motifs were identified and their similarity was analyzed. Primers were designed and polymerase chain reaction was performed to examine target gene presence in R. philipii isolates and other Rickettsia.

Results: Functional domains were predicted and analyzed for 4 proteins encoded by the insert. The nearest relatives with similar domains were identified for each target protein, and their putative functions were assigned based on phylogenetic clustering and published information.. Eleven genes were detected in all R. philipii isolates, but none in R. rickettsii. Only several genes were detected in other Rickettsia species.

Conclusion and Discussion: The 11 genes annotated in the chromosomal insert were detected in all isolates of R. philipii, indicating that they are conserved in this species. If transcribed and expressed, 3 of 11 genes may be a part of a regulatory pathway advantageous for the intracellular lifestyle of R. philipii.