Field-collected Triatoma sordida from central Brazil display high microbiota diversity that varies with regard to developmental stage and intestinal segmentation

Abstract

Background/MethodologyTriatomine bugs are the vectors of Trypanosoma cruzi, the agent of Chagas disease. Vector control has for decades relied upon insecticide spraying, but insecticide resistance has recently emerged in several triatomine populations. One alternative strategy to reduce T. cruzi transmission is paratransgenesis, whereby symbiotic bacteria are genetically engineered to produce T. cruzi-killing proteins in the vector’s gut. This approach requires in-depth knowledge of the vectors’ natural gut microbiota. Here, we use metagenomics (16S rRNA 454 pyrosequencing) to describe the gut microbiota of field-caught Triatoma sordida–likely the most common peridomestic triatomine in Brazil. For large nymphs (4th and 5th stage) and adults, we also studied separately the three main digestive-tract segments–anterior midgut, posterior midgut, and hindgut.Principal findingsBacteria of four phyla (12 genera) were present in both nymphs (all five stages) and adults, thus defining T. sordida’s ‘bacterial core’: Actinobacteria (Brevibacterium, Corynebacterium, Dietzia, Gordonia, Nitriliruptor, Nocardia, Nocardiopsis, Rhodococcus, and Williamsia), Proteobacteria (Pseudomonas and Sphingobium), and Firmicutes (Staphylococcus). We found some clear differences in bacterial composition and relative abundance among development stages; overall, Firmicutes and Proteobacteria increased, but Actinobacteria decreased, through development. Finally, the bacterial microbiotas of the bugs’ anterior midgut, posterior midgut, and hindgut were sharply distinct.Conclusions/SignificanceOur results identify the ‘bacterial core set’ of T. sordida and reveal important gut microbiota differences among development stages–particularly between 1st–3rd stage nymphs and adults. Further, we show that, within any given development stage, the vectors’ gut cannot be regarded as a single homogeneous environment. Cultivable, non-pathogenic ‘core’ bacterial species may now be tested as candidates for paratransgenic control of T. cruzi transmission by T. sordida.

Ontogeny, species identity and environment dominate microbiome dynamics in wild populations of kissing bugs (Triatominae)

“…Some of our findings contradict the patterns reported by other authors. The most conspicuous example is the ontogenetic decrease of microbiome diversity in North American species, which is supported by Mann et al [40], but contrasts two studies on South American species [38,43]. Oliveira et al [38], reported an increase in microbiome diversity throughout ontogenetic development in T. sordida and Waltmann et al [43] found no ontogenetic effect in T. infestans.…”

“…Previous studies on triatomine microbiomes have provided inconsistent and mutually conflicting results. They have suggested various factors, including ontogeny [38,42], species identity [36,40,42,43,92], sex [34,40], blood meal source [34], and T. cruzi infection [23,35,39,40], as determinants of microbiome composition, whilst another study claimed triatomine microbiomes have no determining factor [33]. Since many were based on limited sample size (e.g.…”

“…Since 2015, twelve studies have investigated triatomine microbiomes using next-generation sequencing (NGS) tools. Unfortunately, the data lacks methodological consistency, having been retrieved from a wide variety of DNA templates, including pooled or individual bodies, entire abdomens, the distal part of the abdomen, whole guts, midguts, faeces, and cultured bacterial colonies [33][34][35][36][37][38][39][40][41][42][43][44], and often further complicated by other variables (e.g. sex, locality, instar, T. cruzi infection status).…”

“…This disparity may stem from inconsistencies between individual sample sets and methodology, but could also reflect Triatominae true biological characteristics. These include lengthy development times through five nymphal instars [38,42], complex physiology of the alimentary tract [38], and accessory feeding strategies, like hemolymphagy (feeding on arthropod haemolymph), kleptohematophagy (stealing a blood meal from another triatomine), and coprophagy (feeding on faeces) known to be employed by some triatomine species [2,[45][46][47][48].…”

“…To date, only a single study [41] has sampled microbiomes from multiple wild populations of any triatomine species. Others have mostly targeted South American vectors in domestic environments or laboratory-reared specimens [34,38,39,43,44], with little consideration for non-urban systems. In this study, we thus focus on wild populations of 5 Triatoma species in southern Texas and Arizona.…”