A rickettsial isolate was obtained from a partially engorged Ixodes pacificus female, which was collected from Humboldt County, California. The isolate was provisionally named Rickettsia endosymbiont Ixodes pacificus (REIP). The REIP isolate displayed the highest nucleotide sequence identity to Rickettsia species phylotype G021 in I. pacificus (99%, 99%, and 100% for ompA, 16S rRNA, and gltA, respectively), a bacterium that was previously identified in I. pacifiucs by PCR. Analysis of sequences from complete opening frames of five genes, 16S rRNA, gltA, ompA, ompB, and sca4, provided inference to the bacteria's classification among other Rickettsia species. The REIP isolate displayed 99.8%, 99.4%, 99.2%, 99.5%, and 99.6% nucleotide sequence identity for 16S rRNA, gltA, ompA, ompB, and sca4 gene, respectively, with genes of ‘R. monacensis’ str. IrR/Munich, indicating the REIP isolate is closely related to ‘R. monacensis’. Our suggestion was further supported by phylogenetic analysis using concatenated sequences of 16S rRNA, gltA, ompA, ompB, and sca4 genes, concatenated sequences of dksA-xerC, mppA-purC, and rpmE-tRNAfMet intergenic spacer regions. Both phylogenetic trees implied that the REIP isolate is most closely related to ‘R. monacensis’ str. IrR/Munich. We propose the bacterium be considered as ‘Rickettsia monacensis’ str. Humboldt for its closest phylogenetic relative (=DSM 103975 T = ATCC TSD-94 T).
Bibliographical noteFunding Information:
This research was supported by National Institutes of Health grant 1R15AI099902-01 . We would like to express our great appreciation to the veterinarian and staff at McKinleyville Animal Care Center, McKinleyville, CA, for donating partially engorged Ixodes pacificus females for our research.
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- Ixodes pacificus
- Multi-spacer sequence typing
- Multilocus sequence typing
- Phylogenetic analysis
- ‘Rickettsia monacensis’ str. Humboldt