Presence, genetic variability, and potential significance of “Candidatus Midichloria mitochondrii” in the lone star tick Amblyomma americanum

Amanda Jo Williams-Newkirk, Lori A. Rowe, Tonya R. Mixson-Hayden, Gregory A. Dasch

We used next generation sequencing to detect the bacterium "Candidatus Midichloria mitochondrii" for the first time in lone star ticks (Amblyomma americanum) from the eastern United States. 177 individuals and 11 tick pools from seven sites in four states were tested by pyrosequencing with barcoded 16S rRNA gene eubacterial primers targeting variable regions 5-3. Average infection prevalence was 0.15 across all surveyed populations (range 0-0.29) and only the site with the smallest sample size (n = 5) was negative. Three genotypes differing by 2.6-4.1 % in a 271 bp region of 16S rRNA gene were identified. Two variants co-occurred in sites in North Carolina and New York, but were not observed in the same tick at those sites. The third genotype was found only in Georgia. Phylogenetic analysis of this fragment indicated that the three variants are more closely related to "Candidatus Midichloria mitochondrii" genotypes from other tick species than to each other. This variation suggests that multiple independent introductions occurred in A. americanum which may provide insight into bacterial spread within its ecosystem and parasitism on this tick. Whether the presence of this bacterium affects acquisition or maintenance of other pathogens and symbionts in A. americanum or the survival, biology and evolution of the tick itself is unknown.