Bacterial communities of four sympatric ixodid tick species from the eastern United States. tick metagenome

Variation in animal-associated bacterial communities may arise due to factors both intrinsic and extrinsic to the host, e.g. sex, species, diet, and environmental exposure. Additionally, bacterial community relationships may reflect the phylogeny of their hosts as a result of phylosymbiotic processes. Among ixodid ticks, important vectors of many human, livestock, and wildlife diseases worldwide, the bacterial communities of many species remain minimally described and the degree of interspecific exchange of non-vertebrate pathogens is largely unexplored. We pyrosequenced 16S rRNA gene amplicons from 130 adult ticks from four sympatric species native to the eastern United States (Amblyomma americanum, A. maculatum, Dermacentor variabilis, and Ixodes scapularis) to determine the relatedness of their bacterial communities and to identify sex and species-specific assemblages. While bacterial alpha-diversity was similar across tick species, the patterns of bacterial operational taxonomic unit (OTU) occurrence and abundance were generally tick species specific. No bacterial OTU was common to all four tick species. Sex-specific communities were observed only within A. americanum and I. scapularis. Bacterial community relatedness quantified by weighted UniFrac was consistent with the host tick phylogeny generated from mitochondrial genes (Mantel test, r=0.67, p<0.05). However, the patterns derived from alternative metrics highlight the possibility that other mechanisms, such as niche adaptation to specific hosts or environmental conditions, may also influence the membership and structure of tick bacterial communities. We also report the first observations of two genotypes of the potential endosymbiont, Candidatus ‘Midichloria mitochondrii’, in A. maculatum.