A Kazal-type inhibitor is modulated by Trypanosoma cruzi to control microbiota inside the anterior midgut of Rhodnius prolixus

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.

Trypanosomes and Gut Microbiota Interactions in Triatomine bugs and Tsetse Flies: A vectorial perspective

Triatomines (kissing bugs) and tsetse flies (genus: Glossina) are natural vectors of Trypanosoma cruzi and Trypanosoma brucei, respectively. T. cruzi is the causative agent of Chagas disease, endemic in Latin America, while T. brucei causes African sleeping sickness disease in sub-Saharan Africa. Both triatomines and tsetse flies are host to a diverse community of gut microbiota that co-exist with the parasites in the gut. Evidence has shown that the gut microbiota of both vectors plays a key role in parasite development and transmission. However, knowledge on the mechanism involved in parasite-microbiota interaction remains limited and scanty. Here, we attempt to analyse Trypanosoma spp. and gut microbiota interactions in tsetse flies and triatomines, with a focus on understanding the possible mechanisms involved by reviewing published articles on the subject. We report that interactions between Trypanosoma spp. and gut microbiota can be both direct and indirect. In direct interactions, the gut microbiota directly affects the parasite via the formation of biofilms and the production of anti-parasitic molecules, while on the other hand, Trypanosoma spp. produces antimicrobial proteins to regulate gut microbiota of the vector. In indirect interactions, the parasite and gut bacteria affect each other through host vector-activated processes such as immunity and metabolism. Although we are beginning to understand how gut microbiota interacts with the Trypanosoma parasites, there is still a need for further studies on functional role of gut microbiota in parasite development to maximize the use of symbiotic bacteria in vector and parasite control.

The interplay between temperature, Trypanosoma cruzi parasite load, and nutrition: Their effects on the development and life-cycle of the Chagas disease vector Rhodnius prolixus

Chagas disease, caused by the protozoan parasite Trypanosoma cruzi transmitted by blood-sucking insects of the subfamily Triatominae, is a major neglected tropical disease affecting 6 to 7 million of people worldwide. Rhodnius prolixus, one of the most important vectors of Chagas disease in Latin America, is known to be highly sensitive to environmental factors, including temperature. This study aimed to investigate the effects of different temperatures on R. prolixus development and life-cycle, its relationship with T. cruzi, and to gather information about the nutritional habits and energy consumption of R. prolixus. We exposed uninfected and infected R. prolixus to four different temperatures ranging from 24°C to 30°C, and monitored their survival, developmental rate, body and blood meal masses, urine production, and the temporal dynamics of parasite concentration in the excreted urine of the triatomines over the course of their development. Our results demonstrate that temperature significantly impacts R. prolixus development, life-cycle and their relationship with T. cruzi, as R. prolixus exposed to higher temperatures had a shorter developmental time and a higher mortality rate compared to those exposed to lower temperatures, as well as a lower ability to retain weight between blood meals. Infection also decreased the capacity of the triatomines to retain weight gained by blood-feeding to the next developmental stage, and this effect was proportional to parasite concentration in excreted urine. We also showed that T. cruzi multiplication varied depending on temperature, with the lowest temperature having the lowest parasite load. Our findings provide important insights into the potential impact of climate change on the epidemiology of Chagas disease, and can contribute to efforts to model the future distribution of this disease. Our study also raises new questions, highlighting the need for further research in order to understand the complex interactions between temperature, vector biology, and parasite transmission.

Expression of Proteins, Glycoproteins, and Transcripts in the Guts of Fasting, Fed, and Trypanosoma cruzi-Infected Triatomines: A Systematic Review

Chagas disease is caused by the hemoflagellate protozoan Trypanosoma cruzi. The main transmission mechanism for the parasite in endemic areas is contact with the feces of an infected triatomine bug. Part of the life cycle of T. cruzi occurs in the digestive tract of triatomines, where vector and parasite engage in a close interaction at a proteomic-molecular level. This interaction triggers replication and differentiation processes in the parasite that can affect its infectivity for the vertebrate host. With the aim of compiling and analyzing information from indexed publications on transcripts, proteins, and glycoproteins in the guts of fasting, fed, and T. cruzi-infected triatomines in the period 2000-2022, a systematic review was conducted following the PRISMA guidelines. Fifty-five original research articles retrieved from PubMed and ScienceDirect were selected; forty-four papers reported 1-26,946 transcripts, and twenty-one studies described 1-2603 peptides/proteins.

Bacteriolytic activity in saliva of the hematophagous Triatoma infestans (Reduviidae) and novel characterization and expression site of a third lysozyme

Saliva of hematophagous insects contains many different compounds, mainly acting as anticoagulants. Investigating the bacteriolytic compounds of the saliva of the bloodsucking Triatoma infestans photometrically between pH 3 and pH 10 using unfed fifth instars and nymphs up to 15 days after feeding, we found bacteriolytic activity against lyophilized Micrococcus luteus was stronger at pH 4 and pH 6. After feeding, the activity level at pH 4 was unchanged, but at pH 6 more than doubled between 3 and 7 days after feeding. In zymographs of the saliva and after incubation at pH 4, bacteriolytic activity against Micrococcus luteus was present at eight lysis zones between 14.1 and 38.5 kDa, showing the strongest activity at 24.5 kDa. After incubation at pH 6, lysis zones only appeared at 15.3, 17, and 31.4 kDa. Comparing zymographs of the saliva of unfed and fed nymphs, bacteriolytic activity at 17 kDa increased after feeding. In total nine lysis bands appeared, also at >30 kDa, so far unreported in the saliva of triatomines. Reverse transcription polymerase chain reaction using oligonucleotides based on the previously described lysozyme gene of T. infestans, TiLys1, verified expression of genes encoding TiLys1 and TiLys2 in the salivary glands, but also of an undescribed third lysozyme, TiLys3, of which the cloned cDNA shares characteristics with other c-type lysozymes of insects. While TiLys1 was expressed in the tissue of all three salivary glands, transcripts of TiLys2 and of TiLys3 seem to be present only in the gland G1 and G3, respectively.

Cloning and functional identification of pmKPI cDNA in Poecilobdella manillensis

BACKGROUND

Kazal-type serine protease inhibitors play a role in physiological processes such as blood coagulation and fibrinolysis. The amino acid residues at the P1 site are different, and they inhibit different types of proteases. The inhibitory mechanism of the protease in the salivary glands of Poecilobdella manillensis is still unclear.

METHODS AND RESULTS

Based on cloning, prokaryotic expression and bioinformatics analysis, we studied the role of Kazal-type serine protease inhibitors in P. manillensis and analyzed their expression by quantitative real-time PCR. The results suggested that the recombinant protein was successfully expressed in the supernatant when a prokaryotic expression vector was constructed and induced with 0.2 mmol/L IPTG at 37 °C for 4 h, and the enzymatic activity was determined. The mature protein encodes 91 amino acids and has a relative molecular weight of 9929.32 Da, and after removing the signal peptide, the theoretical isoelectric point was 8.79. It is an unstable protein without a transmembrane domain. The mature protein contains two Kazal-type domains, in which all P1 residues are Lys, consisting of an α helix and three antiparallel β sheets. The upregulated expression of the mRNA was induced after a meal was provided, and the results showed an increasing and then decreasing trend.

CONCLUSIONS

Taken together, the results indicate that mature proteins from P. manillensis inhibit thrombin activity, laying the foundation for the subsequent in-depth study of the function of genes encoding Kazal-type serine protease inhibitors.

Salivary and Intestinal Transcriptomes Reveal Differential Gene Expression in Starving, Fed and Trypanosoma cruzi-Infected Rhodnius neglectus

Rhodnius neglectus is a potential vector of Trypanosoma cruzi (Tc), the causative agent of Chagas disease. The salivary glands (SGs) and intestine (INT) are actively required during blood feeding. The saliva from SGs is injected into the vertebrate host, modulating immune responses and favoring feeding for INT digestion. Tc infection significantly alters the physiology of these tissues; however, studies that assess this are still scarce. This study aimed to gain a better understanding of the global transcriptional expression of genes in SGs and INT during fasting (FA), fed (FE), and fed in the presence of Tc (FE + Tc) conditions. In FA, the expression of transcripts related to homeostasis maintenance proteins during periods of stress was predominant. Therefore, the transcript levels of Tret1-like and Hsp70Ba proteins were increased. Blood appeared to be responsible for alterations found in the FE group, as most of the expressed transcripts, such as proteases and cathepsin D, were related to digestion. In FE + Tc group, there was a decreased expression of blood processing genes for insect metabolism (e.g., Antigen-5 precursor, Pr13a, and Obp), detoxification (Sult1) in INT and acid phosphatases in SG. We also found decreased transcriptional expression of lipocalins and nitrophorins in SG and two new proteins, pacifastin and diptericin, in INT. Several transcripts of unknown proteins with investigative potential were found in both tissues. Our results also show that the presence of Tc can change the expression in both tissues for a long or short period of time. While SG homeostasis seems to be re-established on day 9, changes in INT are still evident. The findings of this study may be used for future research on parasite-vector interactions and contribute to the understanding of food physiology and post-meal/infection in triatomines.

An Update on the Knowledge of Parasite-Vector Interactions of Chagas Disease

This review focusses on the interactions between the etiologic agent of Chagas disease, Trypanosoma cruzi, and its triatomine vector. The flagellate mainly colonizes the intestinal tract of the insect. The effect of triatomines on trypanosomes is indicated by susceptibility and refractoriness phenomena that vary according to the combination of the strains. Other effects are apparent in the different regions of the gut. In the stomach, the majority of ingested blood trypomastigotes are killed while the remaining transform to round stages. In the small intestine, these develop into epimastigotes, the main replicative stage. In the rectum, the population density is the highest and is where the infectious stage develops, the metacyclic trypomastigote. In all regions of the gut, starvation and feeding of the triatomine affect T. cruzi. In the small intestine and rectum, starvation reduces the population density and more spheromastigotes develop. In the rectum, feeding after short-term starvation induces metacyclogenesis and after long-term starvation the development of specific cells, containing several nuclei, kinetoplasts and flagella. When considering the effects of T. cruzi on triatomines, the flagellate seems to be of low pathogenicity. However, during stressful periods, which are normal in natural populations, effects occur often on the behaviour, eg, in readiness to approach the host, the period of time before defecation, dispersal and aggregation. In nymphs, the duration of the different instars and the mortality rates increase, but this seems to be induced by repeated infections or blood quality by the feeding on infected hosts. Starvation resistance is often reduced by infection. Longevity and reproduction of adults is reduced, but only after infection with some strains of T. cruzi. Only components of the surface coat of blood trypomastigotes induce an immune reaction. However, this seems to act against gut bacteria and favours the development of T. cruzi.

Early Post-Prandial Regulation of Protein Expression in the Midgut of Chagas Disease Vector Rhodnius prolixus Highlights New Potential Targets for Vector Control Strategy

Chagas disease is a vector-borne parasitic disease caused by the flagellated protozoan Trypanosoma cruzi and transmitted to humans by a large group of bloodsucking triatomine bugs. Triatomine insects, such as Rhodnius prolixus, ingest a huge amount of blood in a single meal. Their midgut represents an important interface for triatomine–trypanosome interactions. Furthermore, the development of parasites and their vectorial transmission are closely linked to the blood feeding and digestion; thus, an understanding of their physiology is essential for the development of new strategies to control triatomines. In this study, we used label-free quantitative proteomics to identify and analyze the early effect of blood feeding on protein expression in the midgut of Rhodnius prolixus. We both identified and quantified 124 proteins in the anterior midgut (AM) and 40 in the posterior midgut (PM), which vary significantly 6 h after feeding. The detailed analysis of these proteins revealed their predominant involvement in the primary function of hematophagy, including proteases, proteases inhibitors, amino acids metabolism, primary metabolites processing, and protein folding. Interestingly, our proteomics data show a potential role of the AM in protein digestion. Moreover, proteins related to detoxification processes and innate immunity, which are largely accepted to be triggered by blood ingestion, were mildly modulated. Surprisingly, one third of blood-regulated proteins in the AM have unknown function. This work contributes to the improvement of knowledge on the digestive physiology of triatomines in the early hours post-feeding. It provides key information for selecting new putative targets for the development of triatomine control tools and their potential role in the vector competence, which could be applied to other vector species.

A rhamnose-binding lectin from Rhodnius prolixus and the impact of its silencing on gut bacterial microbiota and Trypanosoma cruzi

Lectins are ubiquitous proteins involved in the immune defenses of different organisms and mainly responsible for non-self-recognition and agglutination reactions. This work describes molecular and biological characterization of a rhamnose-binding lectin (RBL) from Rhodnius prolixus, which possesses a 21 amino acid signal peptide and a mature protein of 34.6 kDa. The in-silico analysis of the primary and secondary structures of RpLec revealed a lectin domain fully conserved among previous insects studied. The three-dimensional homology model of RpLec was similar to other RBL-lectins. Docking predictions with the monosaccharides showed rhamnose and galactose-binding sites comparable to Latrophilin-1 and N-Acetylgalactosamine-binding in a different site. The effects of RpLec gene silencing on levels of infecting Trypanosoma cruzi Dm 28c and intestinal bacterial populations in the R. prolixus midgut were studied by injecting RpLec dsRNA into the R. prolixus hemocoel. Whereas T. cruzi numbers remained unchanged compared with the controls, numbers of bacteria increased significantly. The silencing also induced the up regulation of the R. prolixus defC (defensin) expression gene. These results with RpLec reveal the potential importance of this little studied molecule in the insect vector immune response and homeostasis of the gut bacterial microbiota.

Nitric oxide effects on Rhodnius prolixus's immune responses, gut microbiota and Trypanosoma cruzi development

The immune system of Rhodnius prolixus comprehends the synthesis of different effectors that modulate the intestinal microbiota population and the life cycle of the parasite Trypanosoma cruzi inside the vector midgut. One of these immune responses is the production of reactive nitrogen species (RNS) derived by the action of nitric oxide synthase (NOS). Therefore, we investigated the effects of L-arginine, the substrate for nitric oxide (NO) production and N_ω-Nitro-L-arginine methyl ester hydrochloride (L-NAME), an inhibitor of NOS, added in the insect blood meal. We analyzed the impact of these treatments on the immune responses and development of intestinal bacteria and parasites on R. prolixus nymphs. The L-arginine treatment in R. prolixus nymphs induced a higher NOS gene expression in the fat body and increased NO production, but reduced catalase and antimicrobial activities in the midgut. As expected, L-NAME treatment reduced NOS gene expression in the fat body. In addition, L-NAME treatment diminished catalase activity in the hemolymph and posterior midgut reduced phenoloxidase activity in the anterior midgut and increased the antimicrobial activity in the hemolymph. Both treatments caused a reduction in the cultivatable intestinal microbiota, especially in insects treated with L-NAME. However, T. cruzi development in the insect's digestive tract was suppressed after L-arginine treatment and the opposite was observed with L-NAME, which resulted in higher parasite counts. Therefore, we conclude that induction and inhibition of NOS and NO production are associated with other R. prolixus humoral immune responses, such as catalase, phenoloxidase, and antibacterial activities in different insect organs. These alterations reflect on intestinal microbiota and T. cruzi development.

High-Throughput Identification of the Rhodnius prolixus Midgut Proteome Unravels a Sophisticated Hematophagic Machinery

Chagas disease is one of the most common parasitic infections in Latin America, which is transmitted by hematophagous triatomine bugs, of which Rhodnius prolixus is the vector prototype for the study of this disease. The protozoan parasite Trypanosoma cruzi, the etiologic agent of this disease, is transmitted by the vector to humans through the bite wound or mucosa. The passage of the parasite through the digestive tract of its vector constitutes a key step in its developmental cycle. Herewith, by a using high-throughput proteomic tool in order to characterize the midgut proteome of R. prolixus, we describe a set of functional groups of proteins, as well as the biological processes in which they are involved. This is the first proteomic analysis showing an elaborated hematophagy machinery involved in the digestion of blood, among which, several families of proteases have been characterized. The evaluation of the activity of cathepsin D proteases in the anterior part of the digestive tract of the insect suggested the existence of a proteolytic activity within this compartment, suggesting that digestion occurs early in this compartment. Moreover, several heat shock proteins, blood clotting inhibitors, and a powerful antioxidant enzyme machinery against reactive oxygen species (ROS) and cell detoxification have been identified. Highlighting the complexity and importance of the digestive physiology of insects could be a starting point for the selection of new targets for innovative control strategies of Chagas disease.

Intestinal microbiota - A modulator of the Trypanosoma cruzi-vector-host triad

Chagas disease affects millions of people, and it is a major cause of death in Latin America. Prevention and development of an effective treatment for this infection can be favored by a more thorough understanding of T. cruzi interaction with the microbiome of vectors and hosts. Next-generation sequencing technology vastly broadened the knowledge about intestinal bacteria composition, showing that microbiota within each host (triatomines and mammals) is composed by high diversity of species, although few dominant phyla. This fact may represent an ecological balance that was acquired during the evolutionary process of the microbiome-host complex, and that serves to perpetuate this system. In this context, commensal microbiota is also essential to protect hosts, conferring them resistance to pathogens colonization. However, in some situations, the microbiota is not able to prevent infection but only modulate it. Here we will review the role of the microbiota on the parasite-vector-host triad with a focus on the kinetoplastida of medical importance Trypanosoma cruzi. Novel strategies to control Chagas disease based on intestinal microbiome will also be discussed.

Bacterial community composition in the salivary glands of triatomines (Hemiptera: Reduviidae)

Background

Chagas disease is caused by the parasite Trypanosoma cruzi and is transmitted through triatomines (Hemiptera: Reduviidae). In the last year, many studies of triatomine gut microbiota have outlined its potential role in modulating vector competence. However, little is known about the microbiota present in the salivary glands of triatomines. Bacterial composition of salivary glands in selected triatomine species was investigated, as well as environmental influences on the acquisition of bacterial communities.

Methodology/Principal findings

The diversity of the bacterial communities of 30 pairs of salivary glands of triatomines was studied by sequencing of the V1- V3 variable region of the 16S rRNA using the MiSeq platform (Illumina), and bacteria isolated from skin of three vertebrate hosts were identified based on 16S rRNA gene sequence analysis (targeting the V3–V5 region). In a comparative analysis of microbiota in the salivary glands of triatomine species, operational taxonomic units belonging to Arsenophonous appeared as dominant in Triatoma spp (74% of the total 16S coverage), while these units belonging to unclassified Enterobacteriaceae were dominant in the Rhodnius spp (57% of the total 16S coverage). Some intraspecific changes in the composition of the triatomine microbiota were observed, suggesting that some bacteria may have been acquired from the environment.

Conclusions and significance

Our study revealed the presence of a low-diversity microbiota associated to the salivary glands of the evaluated triatomines. The predominant bacteria genera are associated with triatomine genera and the bacteria can be acquired in the environment in which the insects reside. Further studies are necessary to determine the influence of bacterial communities on vector competence.

Chagas disease is caused by the parasite Trypanosoma cruzi and is transmitted through triatomines (Hemiptera: Reduviidae). It is estimated that over 10 000 people die every year from clinical manifestations of Chagas disease, and more than 25 million people risk acquiring the disease per year. Vector control remains the most effective method to prevent infection. In previous studies, the microbiota affected vector competence, thereby highlighting its potential for vector control. In this study, we demonstrate the presence of cultivable and non-cultivable bacteria in the salivary glands of different species of triatomines. The predominant bacterial genera appear to be specific to certain triatomines, e.g., the operational taxonomic units belonging to Arsenophonus bacterial genus is associated with the Triatoma spp, while these units belonging to unclassified Enterobacteriaceae bacterial family are associated with the Rhodnius spp. The operational taxonomic units found in low relative abundance also varied between species of triatomines and their occurrence could be influenced by the environment in which insects reside as well as inter-bacterial modulation by species-specific manner.

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

BACKGROUND/METHODOLOGY

Triatomine 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 FINDINGS

Bacteria 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/SIGNIFICANCE

Our 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.

Can Triatoma virus inhibit infection of Trypanosoma cruzi (Chagas, 1909) in Triatoma infestans (Klug)? A cross infection and co-infection study

Triatoma virus occurs infecting Triatominae in the wild (Argentina) and in insectaries (Brazil). Pathogenicity of Triatoma virus has been demonstrated in laboratory; accidental infections in insectaries produce high insect mortality. When more than one microorganism enters the same host, the biological interaction among them differs greatly depending on the nature and the infection order of the co-existing species of microorganisms. We studied the possible interactions between Triatoma virus (TrV) and Trypanosoma cruzi (the etiological agent of Chagas disease) in three different situations: (i) when Triatoma virus is inoculated into an insect host (Triatoma infestans) previously infected with T. cruzi, (ii) when T. cruzi is inoculated into T. infestans previously infected with TrV, and (iii) when TrV and T. cruzi are inoculated simultaneously into the same T. infestans individual. Trypanosoma cruzi infection was found in 57% of insects in the control group for T. cruzi, whereas 85% of insects with previous TrV infection were infected with T. cruzi. TrV infection was found in 78.7% of insects in the control group for TrV, whereas insects previously infected with T. cruzi showed 90% infection with TrV. A total of 67.9% of insects presented simultaneous infection with both types of microorganism. Our results suggest that TrV infection could increase adhesion of T. cruzi to the intestinal cells of triatomines, but presence of T. cruzi in intestinal cells would not increase the possibility of entry of TrV into cells. Although this study cannot explain the mechanism through which TrV facilitates the infection of triatomines with T. cruzi, we conclude that after TrV replication, changes at cellular level should occur that increase the adhesion of T. cruzi.

Characterization and expression profiling of serine protease inhibitors in the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

BACKGROUND

Serine protease inhibitors (SPIs) have been found in all living organisms and play significant roles in digestion, development and innate immunity. In this study, we present a genome-wide identification and expression profiling of SPI genes in the diamondback moth, Plutella xylostella (L.), a major pest of cruciferous crops with global distribution and broad resistance to different types of insecticides.

RESULTS

A total of 61 potential SPI genes were identified in the P. xylostella genome, and these SPIs were classified into serpins, canonical inhibitors, and alpha-2-macroglobulins based on their modes of action. Sequence alignments showed that amino acid residues in the hinge region of known inhibitory serpins from other insect species were conserved in most P. xylostella serpins, suggesting that these P. xylostella serpins may be functionally active. Phylogenetic analysis confirmed that P. xylostella inhibitory serpins were clustered with known inhibitory serpins from six other insect species. More interestingly, nine serpins were highly similar to the orthologues in Manduca sexta which have been demonstrated to participate in regulating the prophenoloxidase activation cascade, an important innate immune response in insects. Of the 61 P.xylostella SPI genes, 33 were canonical SPIs containing seven types of inhibitor domains, including Kunitz, Kazal, TIL, amfpi, Antistasin, WAP and Pacifastin. Moreover, some SPIs contained additional non-inhibitor domains, including spondin_N, reeler, and other modules, which may be involved in protein-protein interactions. Gene expression profiling showed gene-differential, stage- and sex-specific expression patterns of SPIs, suggesting that SPIs may be involved in multiple physiological processes in P. xylostella.

CONCLUSIONS

This is the most comprehensive investigation so far on SPI genes in P. xylostella. The characterized features and expression patterns of P. xylostella SPIs indicate that the SPI family genes may be involved in innate immunity of this species. Our findings provide valuable information for uncovering further biological roles of SPI genes in P. xylostella.

Triatomine physiology in the context of trypanosome infection

Triatomines are hematophagous insects that feed on the blood of vertebrates from different taxa, but can occasionally also take fluids from invertebrate hosts, including other insects. During the blood ingestion process, these insects can acquire diverse parasites that can later be transmitted to susceptible vertebrates if they complete their development inside bugs. Trypanosoma cruzi, the etiological agent of Chagas disease, and Trypanosoma rangeli are protozoan parasites transmitted by triatomines, the latter only transmitted by Rhodnius spp. The present work makes an extensive revision of studies evaluating triatomine-trypanosome interaction, with special focus on Rhodnius prolixus interacting with the two parasites. The sequences of events encompassing the development of these trypanosomes inside bugs and the consequent responses of insects to this infection, as well as many pathological effects produced by the parasites are discussed.

Rhodnius prolixus: from physiology by Wigglesworth to recent studies of immune system modulation by Trypanosoma cruzi and Trypanosoma rangeli

This review is dedicated to the memory of Professor Sir Vincent B. Wigglesworth (VW) in recognition of his many pioneering contributions to insect physiology which, even today, form the basis of modern-day research in this field. Insects not only make vital contributions to our everyday lives by their roles in pollination, balancing eco-systems and provision of honey and silk products, but they are also outstanding models for studying the pathogenicity of microorganisms and the functioning of innate immunity in humans. In this overview, the immune system of the triatomine bug, Rhodnius prolixus, is considered which is most appropriate to this dedication as this insect species was the favourite subject of VW's research. Herein are described recent developments in knowledge of the functioning of the R. prolixus immune system. Thus, the roles of the cellular defences, such as phagocytosis and nodule formation, as well as the role of eicosanoids, ecdysone, antimicrobial peptides, reactive oxygen and nitrogen radicals, and the gut microbiota in the immune response of R. prolixus are described. The details of many of these were unknown to VW although his work gives indications of his awareness of the importance to R. prolixus of cellular immunity, antibacterial activity, prophenoloxidase and the gut microbiota. This description of R. prolixus immunity forms a backdrop to studies on the interaction of the parasitic flagellates, Trypanosoma cruzi and Trypanosoma rangeli, with the host defences of this important insect vector. These parasites remarkably utilize different strategies to avoid/modulate the triatomine immune response in order to survive in the extremely hostile host environments present in the vector gut and haemocoel. Much recent information has also been gleaned on the remarkable diversity of the immune system in the R. prolixus gut and its interaction with trypanosome parasites. This new data is reviewed and gaps in our knowledge of R. prolixus immunity are identified as subjects for future endeavours. Finally, the publication of the T. cruzi, T. rangeli and R. prolixus genomes, together with the use of modern molecular techniques, should lead to the enhanced identification of the determinants of infection derived from both the vector and the parasites which, in turn, could form targets for new molecular-based control strategies.

Microbial control of arthropod-borne disease

Arthropods harbor a diverse array of microbes that profoundly influence many aspects of host biology, including vector competence. Additionally, symbionts can be engineered to produce molecules that inhibit pathogens. Due to their intimate association with the host, microbes have developed strategies that facilitate their transmission, either horizontally or vertically, to conspecifics. These attributes make microbes attractive agents for applied strategies to control arthropod-borne disease. Here we discuss the recent advances in microbial control approaches to reduce the burden of pathogens such as Zika, Dengue and Chikungunya viruses, and Trypanosome and Plasmodium parasites. We also highlight where further investigation is warranted.

Triatomine bugs, their microbiota and Trypanosoma cruzi: asymmetric responses of bacteria to an infected blood meal

Background

Triatomine bugs (Hemiptera: Reduviidae) are vectors of the flagellate Trypanosoma cruzi, the causative agent of Chagas disease. The study of triatomine gut microbiota has gained relevance in the last years due to its possible role in vector competence and prospective use in control strategies. The objective of this study is to examine changes in the gut microbiota composition of triatomines in response to a T. cruzi-infected blood meal and identifying key factors determining those changes.

Results

We sampled colony-reared individuals from six triatomine vectors (Panstrongylus megistus, Rhodnius prolixus, Triatoma brasiliensis, T. infestans, T. juazeirensis and T. sherlocki) comparing experimentally T. cruzi strain 0354-challenged and non-challenged insects. The microbiota of gut and gonad tissues was characterized using high throughput sequencing of region V3-V4 of bacterial 16S rRNA gene. The triatomine microbiota had a low intra-individual diversity, and a high inter-individual variation within the same host species. Arsenophonous appeared as the dominant triatomine bacterial symbiont in our study (59% of the total 16S coverage), but there were significant differences in the distribution of bacterial genera among vectors. In Rhodnius prolixus the dominant symbiont was Pectobacterium.

Conclusions

Trypanosoma cruzi-challenge significantly affects microbiota composition, with challenged vectors harbouring a significantly more diverse bacterial community, both in the gut and the gonads. Our results show that blood-feeding with T. cruzi epimastigotes strongly affects microbiota composition in a species-specific manner. We suggest that triatomine-adapted enterobacteria such as Arsenophonus could be used as stable vectors for genetic transformation of triatomine bugs and control of Chagas disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1926-2) contains supplementary material, which is available to authorized users.

Impact of Trypanosoma cruzi on antimicrobial peptide gene expression and activity in the fat body and midgut of Rhodnius prolixus

Background

Rhodnius prolixus is a major vector of Trypanosoma cruzi, the causative agent of Chagas disease in Latin America. In natural habitats, these insects are in contact with a variety of bacteria, fungi, virus and parasites that they acquire from both their environments and the blood of their hosts. Microorganism ingestion may trigger the synthesis of humoral immune factors, including antimicrobial peptides (AMPs). The objective of this study was to compare the expression levels of AMPs (defensins and prolixicin) in the different midgut compartments and the fat body of R. prolixus infected with different T. cruzi strains. The T. cruzi Dm 28c clone (TcI) successfully develops whereas Y strain (TcII) does not complete its life- cycle in R. prolixus. The relative AMP gene expressions were evaluated in the insect midgut and fat body infected on different days with the T. cruzi Dm 28c clone and the Y strain. The influence of the antibacterial activity on the intestinal microbiota was taken into account.

Methods

The presence of T. cruzi in the midgut of R. prolixus was analysed by optical microscope. The relative expression of the antimicrobial peptides encoding genes defensin (defA, defB, defC) and prolixicin (prol) was quantified by RT-qPCR. The antimicrobial activity of the AMPs against Staphylococcus aureus, Escherichia coli and Serratia marcescens were evaluated in vitro using turbidimetric tests with haemolymph, anterior and posterior midgut samples. Midgut bacteria were quantified using colony forming unit (CFU) assays and real time quantitative polymerase chain reaction (RT-qPCR).

Results

Our results showed that the infection of R. prolixus by the two different T. cruzi strains exhibited different temporal AMP induction profiles in the anterior and posterior midgut. Insects infected with T. cruzi Dm 28c exhibited an increase in defC and prol transcripts and a simultaneous reduction in the midgut cultivable bacteria population, Serratia marcescens and Rhodococcus rhodnii. In contrast, the T. cruzi Y strain neither induced AMP gene expression in the gut nor reduced the number of colony formation units in the anterior midgut. Beside the induction of a local immune response in the midgut after feeding R. prolixus with T. cruzi, a simultaneous systemic response was also detected in the fat body.

Conclusions

R. prolixus AMP gene expressions and the cultivable midgut bacterial microbiota were modulated in distinct patterns, which depend on the T. cruzi genotype used for infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1398-4) contains supplementary material, which is available to authorized users.

Characterization of a novel Kazal-type serine proteinase inhibitor of Arabidopsis thaliana

Many different types of serine proteinase inhibitors have been involved in several kinds of plant physiological processes, including defense mechanisms against phytopathogens. Kazal-type serine proteinase inhibitors, which are included in the serine proteinase inhibitor family, are present in several organisms. These proteins play a regulatory role in processes that involve serine proteinases like trypsin, chymotrypsin, thrombin, elastase and/or subtilisin. In the present work, we characterized two putative Kazal-type serine proteinase inhibitors from Arabidopsis thaliana, which have a single putative Kazal-type domain. The expression of these inhibitors is transiently induced in response to leaf infection by Botrytis cinerea, suggesting that they play some role in defense against pathogens. We also evaluated the inhibitory specificity of one of the Kazal-type serine proteinase inhibitors, which resulted to be induced during the local response to B. cinerea infection. The recombinant Kazal-type serine proteinase inhibitor displayed high specificity for elastase and subtilisin, but low specificity for trypsin, suggesting differences in its selectivity. In addition, this inhibitor exhibited a strong antifungal activity inhibiting the germination rate of B. cinerea conidia in vitro. Due to the important role of proteinase inhibitors in plant protection against pathogens and pests, the information about Kazal-type proteinase inhibitors described in the present work could contribute to improving current methods for plant protection against pathogens.

Colonization of Rhodnius prolixus gut by Trypanosoma cruzi involves an extensive parasite killing

Trypanosoma cruzi, the etiological agent of Chagas disease, is ingested by triatomines during their bloodmeal on an infected mammal. Aiming to investigate the development and differentiation of T. cruzi inside the intestinal tract of Rhodnius prolixus at the beginning of infection we fed insects with cultured epimastigotes and blood trypomastigotes from infected mice to determine the amount of recovered parasites after ingestion. Approximately 20% of the ingested parasites was found in the insect anterior midgut (AM) 3 h after feeding. Interestingly, a significant reduction (80%) in the numbers of trypomastigotes was observed after 24 h of infection suggesting that parasites were killed in the AM. Moreover, few parasites were found in that intestinal portion after 96 h of infection. The evaluation of the numbers of parasites in the posterior midgut (PM) at the same periods showed a reduced parasite load, indicating that parasites were not moving from the AM. Additionally, incubation of blood trypomastigotes with extracts from R. prolixus AMs revealed that components of this tissue could induce significant death of T. cruzi. Finally, we observed that differentiation from trypomastigotes to epimastigotes is not completed in the AM; instead we suggest that trypomastigotes change to intermediary forms before their migration to the PM, where differentiation to epimastigotes takes place. The present work clarifies controversial points concerning T. cruzi development in insect vector, showing that parasite suffers a drastic decrease in population size before epimastigonesis accomplishment in PM.