Widespread distribution and high prevalence of an alpha‐proteobacterial symbiont in the tick Ixodes ricinus

SummaryThe tick Ixodes ricinus is responsible for the trans-mission of a number of bacterial, protozoan and viraldiseases to humans and animals in Europe and sˇ C ˇ e˘ Northern Africa. Female I. ricinus from England, Swit-zerland and Italy have been found to harbour an intra-cellular a -proteobacterium, designated IricES1, withinthe cells of the ovary. IricES1 is the only prokaryoteknown to exist within the mitochondria of any animalor multicellular organism. To further examine the dis-tribution, prevalence and mode of transmission ofIricES1, we performed polymerase chain reactionscreening of I. ricinus adults fr om 12 countries acr ossits geographic distribution, including tick coloniesthat have been maintained in the laboratory for vary-ing periods of time. IricES1 was detected in 100% offield-collected female ticks from all countries exam-ined ( n = 128), while 44% of males were found to beinfected ( n = 108). Those males that are infectedappear to harbour fewer bacteria than females.Sequencing of fragments of the 16S rRNA and