Infection among Ixodid Ticks Exhibits Species Dependence and Suggests a Vertical Pattern of Transmission.

Members of the genus are Gram-positive bacteria without cell walls. Some species can cause disease in arthropods such as bees, whereas others provide their host with resistance to pathogens. Ticks also harbour , but their role has not been elucidated yet. Here, the infection status and genetic diversity of in ticks were investigated using samples collected from different geographic regions in Japan. A total of 712 ticks were tested for infection by PCR targeting 16S rDNA, and species were genetically characterized based on 16S rDNA, ITS, , and gene sequences. A total of 109 samples originating from eight tick species were positive for infection, with infection rates ranging from 0% to 84% depending on the species. A linear mixed model indicated that tick species was the primary factor associated with infection. Moreover, certain alleles that are highly adapted to specific tick species may explain the high infection rates in and . A comparison of the alleles obtained suggests that horizontal transmission between tick species may not be a frequent event. These findings provide clues to understand the transmission cycle of species in wild tick populations and their roles in host ticks.