Bacterial microbiome of the Lone Star tick, Amblyomma americanum, from Arkansas, United States




Zhang, Yan
Mitchell, Elizabeth
Allen, Michael


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Objective: Amblyomma americanum (the Lone Star tick), an aggressive, human-biting tick abundant in the southern, central, and eastern regions of the United States, is an important vector for many bacterial pathogens, including Rickettsia, Ehrlichia, and Francisella spp. Additionally, these ticks harbor many commensals and symbionts. The state of Arkansas has a disproportionately high incidence of several tick-borne, bacterial diseases. In order to better understand the community structure in which both pathogenic and non-pathogenic, tick-borne bacteria exist, we characterized the bacterial microbiome of A. americanum ticks collected from multiple sites in Arkansas. In addition to knowing the underlying bacterial communities within these ticks, the resultant data provide information which can potentially be useful in establishing effective interventions to control tick-borne diseases. Materials and Methods: Genomic DNA was extracted from a total of 87 questing A. americanum ticks (42 females, 21 males, and 24 nymphs) collected in Arkansas during April-June 2015, and the V4 hypervariable region of the 16S rRNA gene was targeted using the Illumina MiSeq® sequencing platform to investigate the tick bacterial microbiomes. Raw sequence data were processed with open access mothur software. Sequences with 97% similarity were grouped into operational taxonomic units (OTUs) and assigned to differenct taxonomic levels by matching to the Greengenes database. Results: The genus Coxiella, which includes a commonly found bacterial endosymbiont, was detected in all ticks tested, with variable distribution among the females (80%), males (0.17%) and nymphs (65%). The genus Rickettsia, which contains several known pathogens, was detected in all nymphal tick pools (0.10% to 0.90%) and about half of the female ticks (0.20% to 2.10%) but was not found in any males. Of interest, more than three-fourths of the male ticks had high abundance of unclassified bacteria within the Enterobacteriaceae family, while few females carried this group of bacteria. Conclusions: These data demonstrate that differences in the bacterial communities are present, when comparing both life stage and sex of A. americanum ticks from Arkansas. The female ticks exhibited significantly less bacterial diversity and contained numerically dominant levels of Coxiella spp. bacteria, when compared to the males.