Microbiomes of North American Triatominae: The Grounds for Chagas Disease Epidemiology

Abstract

Insect microbiomes influence many fundamental host traits, including functions of practical significance such as their capacity as vectors to transmit parasites and pathogens. The knowledge on the diversity and development of the gut microbiomes in various blood feeding insects is thus crucial not only for theoretical purposes, but also for the development of better disease control strategies. In Triatominae (Heteroptera: Reduviidae), the blood feeding vectors of Chagas disease in South America and parts of North America, the investigation of the microbiomes is in its infancy. The few studies done on microbiomes of South American Triatominae species indicate a relatively low taxonomic diversity and a high host specificity. We designed a comparative survey to serve several purposes: (I) to obtain a better insight into the overall microbiome diversity in different species, (II) to check the long term stability of the interspecific differences, (III) to describe the ontogenetic changes of the microbiome, and (IV) to determine the potential correlation between microbiome composition and presence of Trypanosoma cruzi, the causative agent of Chagas disease. Using 16S amplicons of two abundant species from the southern US, and four laboratory reared colonies, we showed that the microbiome composition is determined by host species, rather than locality or environment. The OTUs (Operational Taxonomic Units) determination confirms a low microbiome diversity, with 12-17 main OTUs detected in wild populations of T. sanguisuga and T. protracta. Among the dominant bacterial taxa are Acinetobacter and Proteiniphilum but also the symbiotic bacterium Arsenophonus triatominarum, previously believed to only live intracellularly. The possibility of ontogenetic microbiome changes was evaluated in all six developmental stages and feces of the laboratory reared model Rhodnius prolixus. We detected considerable changes along the host's ontogeny, including clear trends in the abundance variation of the three dominant bacteria, namely Enterococcus, Acinetobacter, and Arsenophonus. Finally, we screened the samples for the presence of Trypanosoma cruzi. Comparing the parasite presence with the microbiome composition, we assessed the possible significance of the latter in the epidemiology of the disease. Particularly, we found a trend toward more diverse microbiomes in Trypanosoma cruzi positive T. protracta specimens.

Comparison of the Bacterial Gut Microbiome of North American Triatoma spp. With and Without Trypanosoma cruzi

“…Previous reports on the bacterial gut microbiome of triatomines have found infection with T. cruzi to be associated with higher bacterial diversity in the gut microbiome (Montoya-Porras et al, 2018;Rodríguez-Ruano et al, 2018). Contrary to those findings, in this study, which included a much larger number of individual samples, we found that microbial species diversity is only weakly structured by triatomine species, and is not structured by T. cruzi infection, sex, collection location, blood meal status, or DTU strain type.…”

“…The overall bacterial microbiome composition of Triatoma spp. presented here has been similarly observed in other studies of triatomine hindguts, in particular, a high proportion of Enterobacteriaceae (da Mota et al, 2012;Gumiel et al, 2015;Rodríguez-Ruano et al, 2018;Waltmann et al, 2019). Additionally, we found a single ASV assigned to the genus Arsenophonus, members of which are reported to be obligate endosymbionts in a number of insect species, including Triatoma spp.…”

“…da Mota et al (2012) report relatively low overall species complexity in the gut microbiomes of South American triatomine bugs. Similar findings are reported for two species of North American Triatoma, in which the authors further conclude that T. cruzi infection leads to apparent increases in bacterial diversity within the triatomine host gut (Rodríguez-Ruano et al, 2018). The finding of increased bacterial diversity in the hindgut of T. cruzi-infected triatomines is consistent with previously reported changes in the gut microbiome and host physiology upon T. cruzi infection in South American triatomines (Vieira et al, 2015;Díaz et al, 2016), though another study found no impact of T. cruzi infection on alpha diversity metrics in both lab-reared and wild triatomine individuals (Waltmann et al, 2019).…”

“…Contrary to those findings, in this study, which included a much larger number of individual samples, we found that microbial species diversity is only weakly structured by triatomine species, and is not structured by T. cruzi infection, sex, collection location, blood meal status, or DTU strain type. The large number of variables in this study may have masked most of the effects that T. cruzi exerts on its host bacterial microbiome, as reported elsewhere (Díaz et al, 2016;Rodríguez-Ruano et al, 2018). However, another study on the effect of T. cruzi infection status on the triatomine gut microbiome found a similar lack of impact on bacterial diversity (Waltmann et al, 2019), suggesting that increased species sampling and controls are necessary to fully appreciate the interaction between T. cruzi and the larger microbial community.…”

“…To date, few studies have examined the gut microbiome of triatomine vectors, and even fewer have looked at Triatoma spp. collected in the United States (da Mota et al, 2012;Gumiel et al, 2015;Díaz et al, 2016;Montoya-Porras et al, 2018;Rodríguez-Ruano et al, 2018;Waltmann et al, 2019). The composition and diversity of insect gut bacteria could play a significant role, not only in the life cycle of the insect itself (Rodríguez-Ruano et al, 2018), but also in relation to the life cycles of the parasites that they vector, including whether the insect is able to competently harbor and/or transmit various microbes to hosts (Engel and Moran, 2013;Goodrich Julia et al, 2014;Teotônio et al, 2019).…”