Exploring bacterial community assemblage patterns in disease vectors using pyrosequencing and phylogenetic analyses

Background/Question/Methods   Vector-borne pathogenic bacteria do not occur in isolation; rather, they co-exist with a diverse assemblage of microbes within their insect hosts. Combining bar-tagged pyrosequencing of the 16S rRNA gene with phylogenetic analyses provides a powerful way to explore diversity patterns of vector-associated microbial communities. I used this approach in three separate studies. First, I described the bacterial communities of 230 prairie dog fleas (Oropsylla hirsuta and Oropsylla tuberculata cynomuris) sampled across time, space, and species. Second, I introduced wild-caught fleas (Oropsylla montana) with a diverse bacterial community to captive-reared fleas (also O. montana) with low bacterial diversity and tracked community assemblages over time. Finally, I intensely sampled insects at one site (Honolulu, Hawaii) and compared bacterial communities of disease vectors to bacterial communities associated with overall insect diversity.

Results/Conclusions   Results from the first study suggest that bacterial communities of wild fleas differ dramatically across years, but also significantly differ among prairie dog colonies within years as well. While environmental factors and stochastic processes certainly play a role in community assembly, interactions between community members may also govern assemblage patterns. For example, I found that bacterial communities of insects harboring a specific Rickettsial lineage had significantly less phylodiversity than insects lacking the Rickettsial lineage. Results from the second study show that most bacterial lineages harbored by wild fleas readily transfer to the low-diversity captive-reared fleas, but that phylodiversity loss increases with amount of time kept in captive conditions (e.g. 23 degrees C, 70% relative humidity). Finally, phylogenetic-based comparisons of the bacterial communities of disease vectors to those of other insects suggests that vectors have unique bacterial assemblages relative to other insects, but that some groups of insects are more likely to share lineages with vectors than others. Overall, these studies show the powerful potential of combining high-throughput DNA sequencing with phylogenetic approaches to better understand the microbial ecology of disease vectors.