Isolation of Cell Lines and a Rickettsial Endosymbiont from the Soft Tick Carios capensis (Acari: Argasidae: Ornithodorinae)

Abstract

Soft ticks are medically important ectoparasites of birds and mammals that are found throughout the world. This report describes isolation and partial characterization of two embryonic cell lines, CCE2 and CCE3, from the seabird soft tick Carios capensis (Neumann). Sequencing of the mitochondrial 16S rRNAgene and karyology conÞrmed the lines were derived from C. capensis. CCE3 cells were diploid with a modal chromosome number of20. The population doubling time for cell lines CCE2 and 3 in passage 40 was 6Ð9 d. A rickettsial endosymbiont, RCCE3, was co-isolated along with line CCE3. Nucleotide sequences of polymerase chain reaction (PCR) products generated using primers speciÞc for rickettsial 17-kDa antigen, outer membrane protein (omp) A, ompB, and citrate synthase genes along with phylogenetic analyses demonstrated that RCCE3 is a previously uncultured endosymbiont. The rickettsia was identiÞed as a symbiont ofC. capensis, closely related to rickettsiae previously detected by PCR in C. capensis, Ornithodoros moubata (Murray) and Hemaphysalis sulcata Canestrini & Fanzago, a hard tick. RCCE3 caused a cytopathic effect in C. capensis host cells, and it was transferred to Ixodes scapularis Say cell line ISE6 for maintenance. The rickettsial endosymbiont was eliminated from CCE3 by treatment with oxytetracycline. Cell lines fromC. capensis will be useful to researchers investigating interactions between soft ticks and microorganisms, soft tick physiology, and molecular biology. The rickettsia adds to the growing number ofRickettsia species that have been isolated in tick cell culture, and it is available for characterization.