The drivers of microbiome variation among ticks are understudied but this information may improve our understanding of how tick-borne diseases are transmitted. We compared the microbiome composition of nymphal-stage black-legged ticks (Ixodes scapularis) - the principal vectors of Lyme disease in the northeastern United States - that fed as larvae on Raccoon (Procyon lotor), Opossum (Didelphis virginiana), Skunk (Mephitis mephitis), Red squirrel (Tamiasciurus hudsonicus) and Grey squirrel (Sciurus carolinensis). We performed 16S rDNA amplicon sequencing to characterize bacterial community composition and tested the hypothesis that different blood meal host species vary in their influence on the composition of the I. scapularis microbiome. To test for the effect of host species on bacterial community assemblage, we performed an Analysis of Similarity on the Unifrac distance matrix and used principal coordinates analysis to visualize the relationship between host species and bacterial community similarity. To maximize the between-host species distances we used a canonical analysis of principal coordinates (CAP), which provided a new metric multidimensional scaling using a subset of the principal coordinates (PCOs). This was followed by a “leave one out” approach to attempt to identify the host species of each sample based on the CAP coordinates.
Results/Conclusions
We found a significant effect of blood meal host identity on bacterial community similarity (R = 0.351; p = 0.048) and a highly significant effect of individual hosts (R = 0.432; p < 0.001). A plot of the first two CAPs revealed clear visual separation among several host species and the “leave one out” approach correctly identified the host species of 52/88 (59%) of the samples. The shifts in community composition were due primarily to variation in the relative abundance of five dominant bacterial orders (Actinomycetales, Burkholderiales, Pseudomonadales, Xanthomonadales and Myxococcales), suggesting that host blood altered an existing tick microbiome, rather than being a source of bacterial colonization for these dominant orders. Such a pattern may be consistent with a “filtering” effect due to immune system cells of the host blood. To the best of our knowledge, this is the most comprehensive analysis to date of the contribution of blood meal hosts to the I. scapularis microbiome. The findings are likely to improve our understanding of the role of the microbiome in the colonization of I. scapularis by pathogens such as Borrelia burgdorferi, the primary agent of Lyme disease in the northeastern U.S.