Characterization of the bacterial communities of life stages of free living lone star ticks (Amblyomma americanum).

Amanda Jo Williams-Newkirk,Lori A Rowe,Gregory A Dasch,Tonya R Mixson-Hayden,Ulrike G Munderloh

doi:10.1371/journal.pone.0102130

Abstract

The lone star tick (Amblyomma americanum) is an abundant and aggressive biter of humans, domestic animals, and wildlife in the southeastern-central USA and an important vector of several known and suspected zoonotic bacterial pathogens. However, the biological drivers of bacterial community variation in this tick are still poorly defined. Knowing the community context in which tick-borne bacterial pathogens exist and evolve is required to fully understand the ecology and immunobiology of the ticks and to design effective public health and veterinary interventions. We performed a metagenomic survey of the bacterial communities of questing A. americanum and tested 131 individuals (66 nymphs, 24 males, and 41 females) from five sites in three states. Pyrosequencing was performed with barcoded eubacterial primers targeting variable 16S rRNA gene regions 5–3. The bacterial communities were dominated by Rickettsia (likely R. amblyommii) and an obligate Coxiella symbiont, together accounting for 6.7–100% of sequences per tick. DNAs from Midichloria, Borrelia, Wolbachia, Ehrlichia, Pseudomonas, or unidentified Bacillales, Enterobacteriaceae, or Rhizobiales groups were also detected frequently. Wolbachia and Midichloria significantly co-occurred in Georgia (p<0.00001), but not in other states. The significance of the Midichloria-Wolbachia co-occurrence is unknown. Among ticks collected in Georgia, nymphs differed from adults in both the composition (p = 0.002) and structure (p = 0.002) of their bacterial communities. Adults differed only in their community structure (p = 0.002) with males containing more Rickettsia and females containing more Coxiella. Comparisons among adult ticks collected in New York and North Carolina supported the findings from the Georgia collection despite differences in geography, collection date, and sample handling, implying that the differences detected are consistent attributes. The data also suggest that some members of the bacterial community change during the tick life cycle and that some sex-specific attributes may be detectable in nymphs.

Highlights

Ticks transmit a greater diversity of pathogens to humans and domestic animals than any other vector group [1], and the lone star tick (Amblyomma americanum) is the most common humanbiting tick in the southeastern United States [2]
Analysis of variance (ANOVA) detected no difference in the mean level of dissimilarity between bacterial communities originating from the same tick DNA but amplified with different polymerases (Platinum 1 and Accuprime, Platinum 2 and Accuprime) and bacterial communities that originated from the same amplification of the same tick DNA (Platinum 1 and Platinum 2) (Jaccard: F(2,75) = 2.74, p.0.07; Bray-Curtis: F(2,75) = 1.40, p.0.25)
The ticks were all questing, field-collected individuals obtained from five sites in three states; as such they are probably at least representative of the diversity of bacterial communities that occur in A. americanum found in the eastern states comprising its range

Summary

Introduction

Ticks transmit a greater diversity of pathogens to humans and domestic animals than any other vector group [1], and the lone star tick (Amblyomma americanum) is the most common humanbiting tick in the southeastern United States [2]. Amblyomma americanum is a three-host tick that is nonspecific in its host use in the immature (larval and nymphal) life stages and has a preference for white-tailed deer (Odocoileus virginianus) as adults (reviewed in [6]). As many pathogens are acquired by ticks from their vertebrate hosts, the lack of host specificity throughout much of its life perfectly positions this tick as a vector of multiple zoonotic diseases, including ehrlichioses [7], rickettsioses, tularemia, and perhaps even Southern Tick-Associated Rash Illness (reviewed in [6]). Adult males take multiple smaller blood meals while seeking feeding females [13]

Methods

Results

Conclusion