Candidatus Rickettsia uralica and Candidatus Rickettsia thierseensis are genetic variants of one species

The spotted fever group is the largest group in the Rickettsia genus, and new candidate species of this group are found throughout the world. Candidatus Rickettsia thierseensis was observed in a single Ixodes ricinus in Austria in 2020. However, sequences of five genes (total length: 5305 bp) of the Candidatus R. thierseensis were nearly identical to those available for Candidatus Rickettsia uralica identified in Ixodes trianguliceps and small mammals in Russia in 2015. To confirm the identity of these species, appropriate fragments of seven genetic loci from four isolates of Candidatus R. uralica were sequenced and compared with the Candidatus R. thierseensis sequences. Additionally, the groEL gene fragment was first sequenced for Candidatus R. uralica. In this analysis, Candidatus R. uralica and Candidatus R. thierseensis demonstrated 100% identity in the 23S-5S IGS region (354 bp) and in fragments of the 16S rRNA (991 bp), gltA (1119 bp), and htrA (463 bp) genes, differing by only one substitution in each of the ompA (3696 bp), ompB (4871 bp), and sca4 (2971 bp) gene fragments. Thus, Candidatus R. uralica and Candidatus R. thierseensis are likely the same species based on comparative sequence analysis.

Automated summary

A new candidate species of the spotted fever group, Candidatus Rickettsia thierseensis, was found in Austria and its gene sequences were highly similar to Candidatus Rickettsia uralica identified in Russia. Comparative sequence analysis confirmed that Candidatus R. uralica and Candidatus R. thierseensis are likely the same species.