Spatiotemporal and tissue-specific dynamics of bacterial communities in adult female Ixodes ricinus during a four-year period.

INTRODUCTION: The hard tick Ixodes ricinus serves as vector for life-threatening tick-borne diseases (TBDs) such as Lyme borreliosis, relapsing fever, and tick-borne encephalitis. Due to the ticks` ability to adjust to climate changes, their habitat is expanding quickly across Europe, and the incidences of TBD´s are increasing. Therefore, to better understand and control TBDs it is essential to expand the knowledge about the ticks´ microbiome, particularly the spatiotemporal and tissue-specific dynamics of I. ricinus bacterial community. This study was designed to investigate the differences in the detected bacterial communities according to the locations, where ticks had been collected, according to ticks´ tissue types and to seasonal impacts. MATERIALS AND METHODS: A total of 723 adult female I. ricinus were collected from two locations in Bavaria over a four-year period. A defined number of individual ticks were dissected; DNA was extracted from tissue samples or complete ticks, and subsequently 16S rRNA-gene amplicon sequencing was performed. RESULTS AND DISCUSSION: No clear impact of the seasons was detected across the complete four-year period. However, a yearly seasonal pattern was observed in spring (Sp) compared to autumn (Au). Particularly, Sp22, Sp23 and Sp24 showed no difference in effective richness. These results are consistent with previous studies. While the species richness changed between different locations, the effective richness did not. Specific tissue samples of the ticks recovered by dissection (salivary glands, midgut, exoskeleton) carried significant, distinct bacterial communities. The genus Candidatus Midichloria was most abundant and was detected in all tissue types. Borrelia spp. were not detected in any of the collected samples, besides in the mock communities, possibly due to limitations in 16S rRNA gene analysis.