In vitro Trypanocidal Activity, Genomic Analysis of Isolates, and in vivo Transcription of Type VI Secretion System of Serratia marcescens Belonging to the Microbiota of Rhodnius prolixus Digestive Tract

Geographical, Seasonal, and Growth-Related Dynamics of Gut Microbiota in a Grapevine Pest, Apolygus spinolae (Heteroptera: Miridae)

A number of insects are associated with gut symbiotic microorganisms, wherein symbiotic partners play pivotal metabolic roles for each other such as nutrient supplementation, diet degradation, and pesticide detoxification. Despite the ecological and evolutionary importance of gut microbial communities in insects, their diversity and dynamics remain unclear in many species. The green plant bug Apolygus spinolae, a notorious grapevine pest in Japan, damages grape shoots and severely reduces grape berry yield and quality. The plant bug possesses a simple tubular gut housing ~ 104 bacteria. Here, we investigated geographic, seasonal, and growth-related dynamics of gut microbiota by high-throughput sequencing in 82 individuals (11 nymphs and 71 adults) from five locations in Hokkaido, Japan. In plant bugs, gut microbiota changed dynamically depending on region, season, and developmental stage. Among the gut bacteria, Serratia was consistently and abundantly detected and was significantly affected by seasonal changes. In addition, Caballeronia, known as a specific symbiont in some stinkbug species, was abundantly detected, especially in insects collected in late summer despite A. spinolae complete lack of midgut crypts known as symbiotic organ harboring Caballeronia in other stinkbug species. Considering their prevalence among host bug populations, it is possible these gut microorganisms play a pivotal role in the adaptation of the green plant bug to grapevine fields, although further confirmation through rearing experiments is needed.

Immune signaling pathways in Rhodnius prolixus in the context of Trypanosoma rangeli infection: cellular and humoral immune responses and microbiota modulation

Introduction

Rhodnius prolixus is a hematophagous insect and one of the main vectors for Trypanosoma cruzi and Trypanosoma rangeli parasites in Latin America. Gut microbiota and insect immune responses affect T. cruzi and T. rangeli infection within triatomines. Particularly the Toll and IMD signaling pathways activations and how they orchestrate the antimicrobial peptides (AMPs) expressions in R. prolixus, especially when infected by T. rangeli.

Objectives

Examine how T. rangeli infection modulates R. prolixus cellular and humoral immunity and its impacts on insect microbiota.

Methods

R. prolixus was fed on blood containing epimastigotes of T. rangeli, and infection was quantified in insect tissues. The gene expression of dorsal, cactus, relish, PGRP, and AMPs was examined in the midgut, fat body, and salivary glands by quantitative real-time PCR. Microbiota composition was analyzed using RT-q PCR targeting specific bacterial species. Hemocyte numbers and phenoloxidase activity were quantified to assess cellular immune responses.

Results

T. rangeli infection modulated triatomine immunity in midgut and hemocoel, activating the expression of the NF-kB gene dorsal, associated with the Toll pathway; increasing expression of the gene encoding PGRP receptor, a component involved in the IMD pathway, both in the intestine and fat body; repressing the expression of the relish transcription factor, mainly in salivary glands. Among the R. prolixus AMPs studied, T. rangeli infection repressed all AMP gene expression, other than defensin C which increased mRNA levels. The PO activity was enhanced in the hemolymph of infected insects. T. rangeli infection did not induce hemocyte number alterations compared to control insects. However, an increase in hemocyte microaggregation was detected in infected insects.

Discussion

R. prolixus recognizes T. rangeli infection and triggers humoral and cellular immune responses involving Toll pathway activation, defensin C synthesis, increased phenoloxidase activity, and enhanced hemocyte aggregation. On the other hand, T. rangeli infection suppressed some IMD pathway components, suggesting that, in R. prolixus, this pathway is involved in defensins A and B gene regulation. Importantly, these immune responses altered the bacterial microbiota composition, potentially favoring T. rangeli establishment in the insect vector.

The type II secretion system as an underappreciated and understudied mediator of interbacterial antagonism

Interbacterial antagonism involves all major phyla, occurs across the full range of ecological niches, and has great significance for the environment, clinical arena, and agricultural and industrial sectors. Though the earliest insight into interbacterial antagonism traces back to the discovery of antibiotics, a paradigm shift happened when it was learned that protein secretion systems (e.g., types VI and IV secretion systems) deliver toxic "effectors" against competitors. However, a link between interbacterial antagonism and the Gram-negative type II secretion system (T2SS), which exists in many pathogens and environmental species, is not evident in prior reviews on bacterial competition or T2SS function. A current examination of the literature revealed four examples of a T2SS or one of its known substrates having a bactericidal activity against a Gram-positive target or another Gram-negative. When further studied, the T2SS effectors proved to be peptidases that target the peptidoglycan of the competitor. There are also reports of various bacteriolytic enzymes occurring in the culture supernatants of some other Gram-negative species, and a link between these bactericidal activities and T2SS is suggested. Thus, a T2SS can be a mediator of interbacterial antagonism, and it is possible that many T2SSs have antibacterial outputs. Yet, at present, the T2SS remains relatively understudied for its role in interbacterial competition. Arguably, there is a need to analyze the T2SSs of a broader range of species for their role in interbacterial antagonism. Such investigation offers, among other things, a possible pathway toward developing new antimicrobials for treating disease.

Interaction of Trypanosoma cruzi, Triatomines and the Microbiota of the Vectors-A Review

This review summarizes the interactions between Trypanosoma cruzi, the etiologic agent of Chagas disease, its vectors, triatomines, and the diverse intestinal microbiota of triatomines, which includes mutualistic symbionts, and highlights open questions. T. cruzi strains show great biological heterogeneity in their development and their interactions. Triatomines differ from other important vectors of diseases in their ontogeny and the enzymes used to digest blood. Many different bacteria colonize the intestinal tract of triatomines, but only Actinomycetales have been identified as mutualistic symbionts. Effects of the vector on T. cruzi are indicated by differences in the ability of T. cruzi to establish in the triatomines and in colonization peculiarities, i.e., proliferation mainly in the posterior midgut and rectum and preferential transformation into infectious metacyclic trypomastigotes in the rectum. In addition, certain forms of T. cruzi develop after feeding and during starvation of triatomines. Negative effects of T. cruzi on the triatomine vectors appear to be particularly evident when the triatomines are stressed and depend on the T. cruzi strain. Effects on the intestinal immunity of the triatomines are induced by ingested blood-stage trypomastigotes of T. cruzi and affect the populations of many non-symbiotic intestinal bacteria, but not all and not the mutualistic symbionts. After the knockdown of antimicrobial peptides, the number of non-symbiotic bacteria increases and the number of T. cruzi decreases. Presumably, in long-term infections, intestinal immunity is suppressed, which supports the growth of specific bacteria, depending on the strain of T. cruzi. These interactions may provide an approach to disrupt T. cruzi transmission.

Microbiota in disease-transmitting vectors

Haematophagous arthropods, including mosquitoes, ticks, flies, triatomine bugs and lice (here referred to as vectors), are involved in the transmission of various pathogens to mammals on whom they blood feed. The diseases caused by these pathogens, collectively known as vector-borne diseases (VBDs), threaten the health of humans and animals. Although the vector arthropods differ in life histories, feeding behaviour as well as reproductive strategies, they all harbour symbiotic microorganisms, known as microbiota, on which they depend for completing essential aspects of their biology, such as development and reproduction. In this Review, we summarize the shared and unique key features of the symbiotic associations that have been characterized in the major vector taxa. We discuss the crosstalks between microbiota and their arthropod hosts that influence vector metabolism and immune responses relevant for pathogen transmission success, known as vector competence. Finally, we highlight how current knowledge on symbiotic associations is being explored to develop non-chemical-based alternative control methods that aim to reduce vector populations, or reduce vector competence. We conclude by highlighting the remaining knowledge gaps that stand to advance basic and translational aspects of vector-microbiota interactions.

Microbiomes of Blood-Feeding Triatomines in the Context of Their Predatory Relatives and the Environment

The importance of gut microbiomes has become generally recognized in vector biology. This study addresses microbiome signatures in North American Triatoma species of public health significance (vectors of Trypanosoma cruzi) linked to their blood-feeding strategy and the natural habitat. To place the Triatoma-associated microbiomes within a complex evolutionary and ecological context, we sampled sympatric Triatoma populations, related predatory reduviids, unrelated ticks, and environmental material from vertebrate nests where these arthropods reside. Along with five Triatoma species, we have characterized microbiomes of five reduviids (Stenolemoides arizonensis, Ploiaria hirticornis, Zelus longipes, and two Reduvius species), a single soft tick species, Ornithodoros turicata, and environmental microbiomes from selected sites in Arizona, Texas, Florida, and Georgia. The microbiomes of predatory reduviids lack a shared core microbiota. As in triatomines, microbiome dissimilarities among species correlate with dominance of a single bacterial taxon. These include Rickettsia, Lactobacillus, "Candidatus Midichloria," and Zymobacter, which are often accompanied by known symbiotic genera, i.e., Wolbachia, "Candidatus Lariskella," Asaia, Gilliamella, and Burkholderia. We have further identified a compositional convergence of the analyzed microbiomes in regard to the host phylogenetic distance in both blood-feeding and predatory reduviids. While the microbiomes of the two reduviid species from the Emesinae family reflect their close relationship, the microbiomes of all Triatoma species repeatedly form a distinct monophyletic cluster highlighting their phylosymbiosis. Furthermore, based on environmental microbiome profiles and blood meal analysis, we propose three epidemiologically relevant and mutually interrelated bacterial sources for Triatoma microbiomes, i.e., host abiotic environment, host skin microbiome, and pathogens circulating in host blood. IMPORTANCE This study places microbiomes of blood-feeding North American Triatoma vectors (Reduviidae) into a broader evolutionary and ecological context provided by related predatory assassin bugs (Reduviidae), another unrelated vector species (soft tick Ornithodoros turicata), and the environment these arthropods coinhabit. For both vectors, microbiome analyses suggest three interrelated sources of bacteria, i.e., the microbiome of vertebrate nests as their natural habitat, the vertebrate skin microbiome, and the pathobiome circulating in vertebrate blood. Despite an apparent influx of environment-associated bacteria into the arthropod microbiomes, Triatoma microbiomes retain their specificity, forming a distinct cluster that significantly differs from both predatory relatives and ecologically comparable ticks. Similarly, within the related predatory Reduviidae, we found the host phylogenetic distance to underlie microbiome similarities.

Association of Midgut Bacteria and Their Metabolic Pathways with Zika Infection and Insecticide Resistance in Colombian Aedes aegypti Populations

INTRODUCTION

Aedes aegypti is the vector of several arboviruses such as dengue, Zika, and chikungunya. In 2015-16, Zika virus (ZIKV) had an outbreak in South America associated with prenatal microcephaly and Guillain-Barré syndrome. This mosquito's viral transmission is influenced by microbiota abundance and diversity and its interactions with the vector. The conditions of cocirculation of these three arboviruses, failure in vector control due to insecticide resistance, limitations in dengue management during the COVID-19 pandemic, and lack of effective treatment or vaccines make it necessary to identify changes in mosquito midgut bacterial composition and predict its functions through the infection. Its study is fundamental because it generates knowledge for surveillance of transmission and the risk of outbreaks of these diseases at the local level.

METHODS

Midgut bacterial compositions of females of Colombian Ae. aegypti populations were analyzed using DADA2 Pipeline, and their functions were predicted with PICRUSt2 analysis. These analyses were done under the condition of natural ZIKV infection and resistance to lambda-cyhalothrin, alone and in combination. One-step RT-PCR determined the percentage of ZIKV-infected females. We also measured the susceptibility to the pyrethroid lambda-cyhalothrin and evaluated the presence of the V1016I mutation in the sodium channel gene.

RESULTS

We found high ZIKV infection rates in Ae. aegypti females from Colombian rural municipalities with deficient water supply, such as Honda with 63.6%. In the face of natural infection with an arbovirus such as Zika, the diversity between an infective and non-infective form was significantly different. Bacteria associated with a state of infection with ZIKV and lambda-cyhalothrin resistance were detected, such as the genus Bacteroides, which was related to functions of pathogenicity, antimicrobial resistance, and bioremediation of insecticides. We hypothesize that it is a vehicle for virus entry, as it is in human intestinal infections. On the other hand, Bello, the only mosquito population classified as susceptible to lambda-cyhalothrin, was associated with bacteria related to mucin degradation functions in the intestine, belonging to the Lachnospiraceae family, with the genus Dorea being increased in ZIKV-infected females. The Serratia genus presented significantly decreased functions related to phenazine production, potentially associated with infection control, and control mechanism functions for host defense and quorum sensing. Additionally, Pseudomonas was the genus principally associated with functions of the degradation of insecticides related to tryptophan metabolism, ABC transporters with a two-component system, efflux pumps, and alginate synthesis.

CONCLUSIONS

Microbiota composition may be modulated by ZIKV infection and insecticide resistance in Ae. aegypti Colombian populations. The condition of resistance to lambda-cyhalothrin could be inducing a phenome of dysbiosis in field Ae. aegypti affecting the transmission of arboviruses.

Characterization of cultivable intestinal microbiota in Rhynchophorus palmarum Linnaeus (Coleoptera: Curculionidae) and determination of its cellulolytic activity

Rhynchophorus palmarum Linnaeus is an agricultural pest that affects various palm crops, including coconut (Cocos nucifera) plantations which are prominent in the economy of Northeastern Brazil. Characterization of the intestinal microbiota of R. palmarum, as well as elucidation of aspects related to the biochemistry and physiology of the insect's digestion, is essential for intervention in specific metabolic processes as a form of pest control. Thus, this study aimed to characterize the intestinal microbiota of R. palmarum and investigate its ability to degrade cellulosic substrates, to explore new biological control measures. Intestinal dissection of eight adult R. palmarum insects was performed in a laminar flow chamber, and the intestines were homogenized in sterile phosphate-buffered saline solution. Subsequently, serial dilution aliquots of these solutions were spread on nutritive agar plates for the isolation of bacteria and fungi. The microorganisms were identified by matrix-assisted laser desorption/ionization with a time-of-flight mass spectrometry and evaluated for their ability to degrade cellulose. Fourteen bacterial genera (Acinetobacter, Alcaligenes, Arthrobacter, Bacillus, Citrobacter, Enterococcus, Kerstersia, Lactococcus, Micrococcus, Proteus, Providencia, Pseudomonas, Serratia, and Staphylococcus) and two fungal genera (Candida and Saccharomyces)-assigned to the Firmicutes, Actinobacteria, Proteobacteria, and Ascomycota phyla-were identified. The cellulolytic activity was exhibited by six bacterial and one fungal species; of these, Bacillus cereus demonstrated the highest enzyme synthesis (enzymatic index = 4.6). This is the first study characterizing the R. palmarum intestinal microbiota, opening new perspectives for the development of strategies for the biological control of this insect.

Molecular Detection and Differentiation of Arthropod, Fungal, Protozoan, Bacterial and Viral Pathogens of Honeybees

The honeybee Apis mellifera is highly appreciated worldwide because of its products, but also as it is a pollinator of crops and wild plants. The beehive is vulnerable to infections due to arthropods, fungi, protozoa, bacteria and/or viruses that manage to by-pass the individual and social immune mechanisms of bees. Due to the close proximity of bees in the beehive and their foraging habits, infections easily spread within and between beehives. Moreover, international trade of bees has caused the global spread of infections, several of which result in significant losses for apiculture. Only in a few cases can infections be diagnosed with the naked eye, by direct observation of the pathogen in the case of some arthropods, or by pathogen-associated distinctive traits. Development of molecular methods based on the amplification and analysis of one or more genes or genomic segments has brought significant progress to the study of bee pathogens, allowing for: (i) the precise and sensitive identification of the infectious agent; (ii) the analysis of co-infections; (iii) the description of novel species; (iv) associations between geno- and pheno-types and (v) population structure studies. Sequencing of bee pathogen genomes has allowed for the identification of new molecular targets and the development of specific genotypification strategies.

Long-term spatiotemporal variation of antimicrobial resistance genes within the Serratia marcescens population and transmission of S. marcescens revealed by public whole-genome datasets

The development of antimicrobial resistance (AMR) is accelerated by the selective pressure exerted by the widespread use of antimicrobial drugs, posing an increasing danger to public health. However, long-term spatiotemporal variation in AMR genes in microorganisms, particularly in bacterial pathogens in response to antibiotic consumption, is not fully understood. Here, we used the NCBI RefSeq database to collect 478 whole-genome sequences for Serratia marcescens ranging from 1961 up to 2019, to document global long-term AMR trends in S. marcescens populations. In total, 100 AMR gene subtypes (16 AMR gene types) were detected in the genomes of S. marcescens populations. We identified 3 core resistance genes in S. marcescens genomes, and a high diversity of AMR genes was observed in S. marcescens genomes after corresponding antibiotics were discovered and introduced into clinical practice, suggesting the adaptation of S. marcescens populations to challenges with therapeutic antibiotics. Our findings indicate spatiotemporal variation of AMR genes in S. marcescens populations in relation to antibiotic consumption and suggest the potential transmission of S. marcescens isolates harboring AMR genes among countries and between the environment and the clinic, representing a public health threat that necessitates international solidarity to overcome.

Influence of Serratia marcescens and Rhodococcus rhodnii on the Humoral Immunity of Rhodnius prolixus

Chagas disease is a human infectious disease caused by Trypanosoma cruzi and can be transmitted by triatomine vectors, such as Rhodnius prolixus. One limiting factor for T. cruzi development is the composition of the bacterial gut microbiota in the triatomine. Herein, we analyzed the humoral immune responses of R. prolixus nymphs treated with antibiotics and subsequently recolonized with either Serratia marcescens or Rhodococcus rhodnii. The treatment with antibiotics reduced the bacterial load in the digestive tract, and the recolonization with each bacterium was successfully detected seven days after treatment. The antibiotic-treated insects, recolonized with S. marcescens, presented reduced antibacterial activity against Staphylococcus aureus and phenoloxidase activity in hemolymph, and lower nitric oxide synthase (NOS) and higher defensin C gene (DefC) gene expression in the fat body. These insects also presented a higher expression of DefC, lower prolixicin (Prol), and lower NOS levels in the anterior midgut. However, the antibiotic-treated insects recolonized with R. rhodnii had increased antibacterial activity against Escherichia coli and lower activity against S. aureus, higher phenoloxidase activity in hemolymph, and lower NOS expression in the fat body. In the anterior midgut, these insects presented higher NOS, defensin A (DefA) and DefC expression, and lower Prol expression. The R. prolixus immune modulation by these two bacteria was observed not only in the midgut, but also systemically in the fat body, and may be crucial for the development and transmission of the parasites Trypanosoma cruzi and Trypanosoma rangeli.

Azadirachtin interferes with basal immunity and microbial homeostasis in the Rhodnius prolixus midgut

Rhodnius prolixus is an insect vector of two flagellate parasites, Trypanosoma rangeli and Trypanosoma cruzi, the latter being the causative agent of Chagas disease in Latin America. The R. prolixus neuroendocrine system regulates the synthesis of the steroid hormone ecdysone, which is essential for not only development and molting but also insect immunity. Knowledge for how this modulates R. prolixus midgut immune responses is essential for understanding interactions between the vector, its parasites and symbiotic microbes. In the present work, we evaluated the effects of ecdysone inhibition on R. prolixus humoral immunity and homeostasis with its microbiota, using the triterpenoid natural product, azadirachtin. Our results demonstrated that azadirachtin promoted a fast and lasting inhibitory effect on expression of both RpRelish, a nuclear factor kappa B transcription factor (NF-kB) component of the IMD pathway, and several antimicrobial peptide (AMP) genes. On the other hand, RpDorsal, encoding the equivalent NF-kB transcription factor in the Toll pathway, and the defC AMP gene were upregulated later in azadirachtin treated insects. The treatment also impacted on proliferation of Serratia marcescens, an abundant commensal bacterium. The simultaneous administration of ecdysone and azadirachtin in R. prolixus blood meals counteracted the azadirachtin effects on insect molting and also on expression of RpRelish and AMPs genes. These results support the direct involvement of ecdysone in regulation of the IMD pathway in the Rhodnius prolixus gut.

Targeting the Gut Microbiota in Chagas Disease: What Do We Know so Far?

Chagas disease (CD) is a tropical and still neglected disease caused by Trypanosoma cruzi that affects >8 million of people worldwide. Although limited, emerging data suggest that gut microbiota dysfunction may be a new mechanism underlying CD pathogenesis. T. cruzi infection leads to changes in the gut microbiota composition of vector insects, mice, and humans. Alterations in insect and mice microbiota due to T. cruzi have been associated with a decreased immune response against the parasite, influencing the establishment and progression of infection. Further, changes in the gut microbiota are linked with inflammatory and neuropsychiatric disorders, comorbid conditions in CD. Therefore, this review article critically analyses the current data on CD and the gut microbiota of insects, mice, and humans and discusses its importance for CD pathogenesis. An enhanced understanding of host microbiota will be critical for the development of alternative therapeutic approaches to target CD, such as gut microbiota-directed interventions.

Proteome of the Triatomine Digestive Tract: From Catalytic to Immune Pathways; Focusing on Annexin Expression

Rhodnius prolixus, Panstrongylus megistus, Triatoma infestans, and Dipetalogaster maxima are all triatomines and potential vectors of the protozoan Trypanosoma cruzi responsible for human Chagas' disease. Considering that the T. cruzi's cycle occurs inside the triatomine digestive tract (TDT), the analysis of the TDT protein profile is an essential step to understand TDT physiology during T. cruzi infection. To characterize the protein profile of TDT of D. maxima, P. megistus, R. prolixus, and T. infestans, a shotgun liquid chromatography-tandem mass spectrometry (LC-MS/MS) approach was applied in this report. Most proteins were found to be closely related to metabolic pathways such as gluconeogenesis/glycolysis, citrate cycle, fatty acid metabolism, oxidative phosphorylation, but also to the immune system. We annotated this new proteome contribution gathering it with those previously published in accordance with Gene Ontology and KEGG. Enzymes were classified in terms of class, acceptor, and function, while the proteins from the immune system were annotated by reference to the pathways of humoral response, cell cycle regulation, Toll, IMD, JNK, Jak-STAT, and MAPK, as available from the Insect Innate Immunity Database (IIID). These pathways were further subclassified in recognition, signaling, response, coagulation, melanization and none. Finally, phylogenetic affinities and gene expression of annexins were investigated for understanding their role in the protection and homeostasis of intestinal epithelial cells against the inflammation.

Dynamic of Composition and Diversity of Gut Microbiota in Triatoma rubrofasciata in Different Developmental Stages and Environmental Conditions

Triatoma rubrofasciata (T. rubrofasciata), one kind of triatomine insects, is the vector of Trypanosoma cruzi (T. cruzi), which lead to American trypanosomiasis. Although the gut microbiome may play an essential role in the development and susceptibility of triatomine, there is limited research on the gut microbiota of T. rubrofasciata. To elucidate the effect of the vector's developmental stages and environmental conditions on the gut microbiome, we employed 16S rRNA gene sequencing to profile the gut bacterial community diversity and composition of T. rubrofasciata. Significant shifts were observed in the overall gut microbe diversity and composition across the development of T. rubrofasciata and specific bacteria were detected in different stages. Serratia and Burkholderia-Caballeronia-Paraburkholderia were dominant in the 1^st nymphal stage, while the abundance of Staphylococcus was low in the 1^st nymphal stage. Oceanicaulis were undetectable in the adult stage and Odoribacter peaked in the 2^nd nymphal stage. Moreover, Staphylococcus was correlated negatively with Serratia. Likewise, the total gut microbiota diversity and composition of T. rubrofasciata differentiated significantly by environmental conditions. The ingestion of a bloodmeal increased alpha diversity of gut bacterial communities, and Staphylococcus was more abundant in laboratory-reared bugs whereas Enterococcus enriched in wild-caught bugs. Furthermore, Pantoea was negatively correlated with Staphylococcus, and positively related to Bacillus only. The phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) algorithm showed obvious metagenomic functional differences by environmental conditions, and Chagas disease relevant pathway was enriched in wild-caught T. rubrofasciata.

The Role of Bacterial Symbionts in Triatomines: An Evolutionary Perspective

Insects have established mutualistic symbiotic interactions with microorganisms that are beneficial to both host and symbiont. Many insects have exploited these symbioses to diversify and expand their ecological ranges. In the Hemiptera (i.e., aphids, cicadas, and true bugs), symbioses have established and evolved with obligatory essential microorganisms (primary symbionts) and with facultative beneficial symbionts (secondary symbionts). Primary symbionts are usually intracellular microorganisms found in insects with specialized diets such as obligate hematophagy or phytophagy. Most Heteroptera (true bugs), however, have gastrointestinal (GI) tract extracellular symbionts with functions analogous to primary endosymbionts. The triatomines, are vectors of the human parasite, Trypanosoma cruzi. A description of their small GI tract microbiota richness was based on a few culturable microorganisms first described almost a century ago. A growing literature describes more complex interactions between triatomines and bacteria with properties characteristic of both primary and secondary symbionts. In this review, we provide an evolutionary perspective of beneficial symbioses in the Hemiptera, illustrating the context that may drive the evolution of symbioses in triatomines. We highlight the diversity of the triatomine microbiota, bacterial taxa with potential to be beneficial symbionts, the unique characteristics of triatomine-bacteria symbioses, and the interactions among trypanosomes, microbiota, and triatomines.

The innate immune system of kissing bugs, vectors of chagas disease

Kissing bugs have long served as models to study many aspects of insect physiology. They also serve as vectors for the parasite Trypanosoma cruzi that causes Chagas disease in humans. The overall success of insects is due, in part, to their ability to recognize parasites and pathogens as non-self and to eliminate them using their innate immune system. This immune system comprises physical barriers, cellular responses (phagocytosis, nodulation and encapsulation), and humoral factors (antimicrobial peptides and the prophenoloxidase cascade). Trypanosoma cruzi survives solely in the gastrointestinal (GI) tract of the vector; if it migrates to the hemocoel it is eliminated. Kissing bugs may not mount a vigorous immune response in the GI tract to avoid eliminating obligate symbiotic microbes on which they rely for survival. Here we describe the current knowledge of innate immunity in kissing bugs and new opportunities using genomic and transcriptomic approaches to study the complex triatomine-trypanosome-microbiome interactions.