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

Abstract

SummaryThe tick Ixodes ricinus is responsible for the transmission of a number of bacterial, protozoan and viral diseases to humans and animals in Europe and š Č ȇ Northern Africa. Female I. ricinus from England, Switzerland and Italy have been found to harbour an intracellular a-proteobacterium, designated IricES1, within the cells of the ovary. IricES1 is the only prokaryote known to exist within the mitochondria of any animal or multicellular organism. To further examine the distribution, prevalence and mode of transmission of IricES1, we performed polymerase chain reaction screening of I. ricinus adults from 12 countries across its geographic distribution, including tick colonies that have been maintained in the laboratory for varying periods of time. IricES1 was detected in 100% of field-collected female ticks from all countries examined (n = 128), while 44% of males were found to be infected (n = 108). Those males that are infected appear to harbour fewer bacteria than females. Sequencing of fragments of the 16S rRNA and gyrB genes revealed very low nucleotide diversity among various populations of IricES1. Transmission of IricES1 from engorged adult females to eggs was found to be 100% (n = 31). In tick colonies that had been maintained in the laboratory for several years, a relatively low prevalence was found in females (32%; n = 25). To our knowledge, IricES1 is the most widespread and highly prevalent of any tick-associated symbiont.

‘Candidatus Midichloria mitochondrii’, an endosymbiont of the tick Ixodes ricinus with a unique intramitochondrial lifestyle

“…We believe the information currently available for one member of this clade, IricES1, meets the criteria required for the description of new genera and species (for uncultured bacteria, see Murray & Stackebrandt, 1995;see also Zeigler, 2003). In brief, the information available is (i) sequences of two genes ; this study), (ii) localization in the host tissues by in situ hybridization and electron microscopy ; this study), (iii) detailed ultrastructural observations , (iv) prevalence studies throughout European and North African populations of the host species (Lo et al, 2006) and (v) PCR evidence for efficient vertical transmission (Lo et al, 2006).…”

“…Sequencing of the 16S rRNA and gyrB genes from ticks from 11 different countries from across the distribution of I. ricinus showed a low level of variability in both genes. One substitution in 380 bases was found in the 16S rRNA gene sequence and two substitutions in 519 bases were found in the gyrB gene sequence (Lo et al, 2006).…”

“…This symbiont of I. ricinus has provisionally been designated IricES1 . IricES1 has been observed in the ovaries of females of I. ricinus with 100 % prevalence, while lower prevalence is reported in male ticks (Lo et al, 2006). In females, the bacterium inhabits the cytoplasm of ovarian cells and possesses the peculiar ability to invade and destroy the host's mitochondria.…”

“CandidatusAnadelfobacter veles” and “CandidatusCyrtobacter comes,” Two NewRickettsialesSpecies Hosted by the Protist CiliateEuplotes harpa(Ciliophora, Spirotrichea)

“…Many authors agree that this clade should be considered a new family of Rickettsiales (for example, see references 2 and 15). However, a formal description is still lacking for the clade that, at present, contains only one "Candidatus" species, namely, "Candidatus Midichloria mitochondrii" (41), an intracellular bacterium inhabiting the perimitochondrial space of the tick Ixodes ricinus, the European vector of Lyme disease (2,23), and of many other hard ticks (8). For this reason, we will refer to this family-level cluster as the "Candidatus Midichloria" clade.…”

In vitro feeding assays for hard ticks

“…There is a greater need to modify the membrane thickness to accommodate the different hypostome lengths of adult stages of some of the economically important tick species than for the hypostomes of the nymphs and larvae ( Figure Id). tick-endosymbiotic Rickettsia [20] and the more recently identified symbionts [21][22][23][24] to tick survival and fecundity can be investigated as the symbionts can be selectively knocked out using antibiotics added to the blood in the feeding assay. Knowledge obtained in relation to these topics from studies on ticks can also be of relevance to insect vectors of disease.…”