Abstract
Members of the genus Spiroplasma are Gram-positive bacteria without cell walls. Some Spiroplasma species can cause disease in arthropods such as bees, whereas others provide their host with resistance to pathogens. Ticks also harbour Spiroplasma, but their role has not been elucidated yet. Here, the infection status and genetic diversity of Spiroplasma in ticks were investigated using samples collected from different geographic regions in Japan. A total of 712 ticks were tested for Spiroplasma infection by PCR targeting 16S rDNA, and Spiroplasma species were genetically characterized based on 16S rDNA, ITS, dnaA, and rpoB gene sequences. A total of 109 samples originating from eight tick species were positive for Spiroplasma 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 Spiroplasma infection. Moreover, certain Spiroplasma alleles that are highly adapted to specific tick species may explain the high infection rates in Ixodes ovatus and Haemaphysalis kitaokai. 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 Spiroplasma species in wild tick populations and their roles in host ticks.
Highlights
Members of the genus Spiroplasma are Gram-positive bacteria without cell walls
Among the 20 different tick species, eight tick species were positive for Spiroplasma infection, and the highest infection rate was observed in I. ovatus (84%; 67/80), followed by H. kitaokai
Female ticks were positive for the infection in I. turdus, D. taiwanensis, and H. flava, while only one male was positive in A. testudinarium
Summary
Members of the genus Spiroplasma are Gram-positive bacteria without cell walls. They are known as symbionts of arthropods and plants and are classified into three major clades based on the 16S ribosomal RNA gene (rDNA) sequence: Ixodetis, Citri-ChrysopicolaMirum (CCM), and Apis [1,2]. Spiroplasma is one of the most common endosymbionts with a wide range of hosts, including insects, arachnids, crustaceans, and plants [3]. Some Spiroplasma species affect the sex ratio by inducing male killing in hosts such as flies, butterflies, and ladybird beetles [7,8,9,10]. Several Spiroplasma species are known to cause disease in arthropods such as bees and plants [6,17,18]. A wide range of symbiotic relationships involving Spiroplasma have been observed [5,7,8,14,15,16]
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