Age, sex, and mating status discrimination in the sand fly Lutzomyia longipalpis using near infra-red spectroscopy (NIRS)

BACKGROUND

Understanding aspects related to the physiology and capacity of vectors is essential for effectively controlling vector-borne diseases. The sand fly Lutzomyia longipalpis has great importance in medical entomology for disseminating Leishmania parasites, the causative agent of Leishmaniasis, one of the main neglected diseases listed by the World Health Organization (WHO). In this respect, it is necessary to evaluate the transmission potential of this species and the success of vector control interventions. Near-infrared spectroscopy (NIRS) has been used to estimate the age of mosquitoes in different conditions (laboratory, semi-field, and conservation), taxonomic analysis, and infection detection. However, no studies are using NIRS for sand flies.

METHODS

In this study, we developed analytic models to estimate the age of L. longipalpis adults under laboratory conditions, identify their copulation state, and evaluate their gonotrophic cycle and diet.

RESULTS

Sand flies were classified with an accuracy of 58-82% in 3 age groups and 82-92% when separating them into young (<8 days) or old (>8 days) insects. The classification between mated and non-mated sandflies was 98-100% accurate, while the percentage of hits of females that had already passed the first gonotrophic cycle was only 59%.

CONCLUSIONS

We consider the age and copula estimation results very promising, as they provide essential aspects of vector capacity assessment, which can be obtained quickly and at a lower cost with NIRS.

Digestive α-L-fucosidase activity in Rhodnius prolixus after blood feeding: effect of secretagogue and nutritional stimuli

Introduction: Rhodnius prolixus (Hemiptera: Reduviidae) is an important vector of Trypanosoma cruzi, the causative agent of Chagas Disease. This insect is a model for the study of insect physiology, especially concerning the digestion of blood. Among the enzymes produced in the midgut of R. prolixus after blood feeding there is a α-L-fucosidase activity. There are very few studies on α-L-fucosidase of insects, and the role of R. prolixus α-L-fucosidase is still not clear. In this work, we tested if the mechanism for production of this enzyme is similar to the observed for proteases, a secretatogue mechanism that respond to the protein contents of the meal. Methods: We tested if specific proteins or sugars elicit this response, which may help to understand the nature of the physiological substrate for this enzyme. Results: In general, our results showed that the Anterior Midgut was the only midgut fraction that responds to the blood meal in terms of α-L-fucosidase production. Besides that, this response was not triggered by midgut distension or by ingestion of the blood cell fraction. Conversely, the enzyme was produced after feeding with the plasma fraction. However, the production of α-L-fucosidase was also triggered by different biochemical stimuli, as protein or fucoidan ingestion. Discussion: This suggested that the production of the enzyme in the anterior midgut was a general physiological response under control of different convergent signals. Besides that, the comparison between different treatments for artificial blood feeding showed that heparinated blood was the choice with minor side effects for the study of the midgut α-L-fucosidase, when compared to defibrinated or citrated blood.

Remote conferences in parasitology and entomology during the pandemic: eliminate or maintain in a post-pandemic world? That is the dilemma!

The COVID-19 pandemic brought enormous challenges for health, scientists and academic world two years ago. Social isolation and the inabilities of face-to-face activities generated the emergence of many educational and scientific initiatives. Remote activities gave information and brought company and affection to people which allowed students and professionals from different parts of the world to integrate. In this report we are showing the experience from three initiatives in South America of scientific dissemination in infectious diseases. We discuss the scope of having a permanent practice for access and integration in science using remote communication, which can give great benefits in unequal societies. KEY WORDS: E- learning; conferences; seminars; pandemic; webinars; parasitology.

Structure and expression of Rhodnius prolixus GH18 chitinases and chitinase-like proteins: Characterization of the physiological role of RpCht7, a gene from subgroup VIII, in vector fitness and reproduction

Chitinases are enzymes responsible for the hydrolysis of glycosidic linkages within chitin chains. In insects, chitinases are typically members of the multigenic glycoside hydrolase family 18 (GH18). They participate in the relocation of chitin during development and molt, and in digestion in detritivores and predatory insects, and they control the peritrophic membrane thickness. Chitin metabolism is a promising target for developing vector control strategies, and knowledge of the roles of chitinases may reveal new targets and illuminate unique aspects of their physiology and interaction with microorganisms. Rhodnius prolixus is an important vector of Chagas disease, which is caused by the parasite Trypanosoma cruzi. In this study, we performed annotation and structural characterization of nine chitinase and chitinase-like protein genes in the R. prolixus genome. The roles of their corresponding transcripts were studied in more depth; their physiological roles were studied through RNAi silencing. Phylogenetic analysis of coding sequences showed that these genes belong to different subfamilies of GH18 chitinases already described in other insects. The expression patterns of these genes in different tissues and developmental stages were initially characterized using RT-PCR. RNAi screening showed silencing of the gene family members with very different efficiencies. Based on the knockdown results and the general lack of information about subgroup VIII of GH18, the RpCht7 gene was chosen for phenotype analysis. RpCht7 knockdown doubled the mortality in starving fifth-instar nymphs compared to dsGFP-injected controls. However, it did not alter blood intake, diuresis, digestion, molting rate, molting defects, sexual ratio, percentage of hatching, or average hatching time. Nevertheless, female oviposition was reduced by 53% in RpCht7-silenced insects, and differences in oviposition occurred within 14–20 days after a saturating blood meal. These results suggest that RpCht7 may be involved in the reproductive physiology and vector fitness of R. prolixus.

Effects of anti-Leishmania compounds in the behavior of the sand fly vector Lutzomyia longipalpis

BACKGROUND

Leishmaniasis is an infectious parasitic disease caused by pathogens of the genus Leishmania transmitted through the bite of adult female sand flies. To reduce case numbers, it is necessary to combine different control approaches, especially those aimed at the sand fly vectors. Innovative forms of control with the use of attractive sugar baits explored the fact that adult sand flies need to feed on sugars of plant origin. Leishmania parasites develop in the gut of sand flies, interacting with the sugars in the diet of adults. Recent studies have shown that sugar baits containing plant-derived compounds can reduce sand fly survival, the number of parasites per gut, and the percentage of infected sand flies. Several synthetic compounds produced from naphthoquinones and pterocarpans have anti-parasitic activity on Leishmania amazonensis and/or Leishmania infantum in cell culture. This work aimed to assess the inclusion of these compounds in sugar baits for blocking transmission, targeting the development of the Leishmania parasite inside the sand fly vector.

RESULTS

We evaluated the attractant or repellent properties of these compounds, as well as of the reference compound N,N'-diethyl-m-toluamide (DEET), in sugar baits. We also observed changes in feeding preference caused by these compounds, looking for anti-feeding or stimulation of ingestion. Pterocarpanquinone L4 and pentamidine showed attractant and repellent properties, respectively.

CONCLUSION

Based on the effects in feeding preference and intake volume, pterocarpanquinone L6, and the pyrazole-derived compound P8 were chosen as the most promising compounds for the future development of anti-Leishmania sugar baits. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

P2X7 Receptor Triggers Lysosomal Leakage Through Calcium Mobilization in a Mechanism Dependent on Pannexin-1 Hemichannels

The P2X7 receptor is a critical purinergic receptor in immune cells. Its activation was associated with cathepsin release into macrophage cytosol, suggesting its involvement in lysosomal membrane permeabilization (LMP) and leakage. Nevertheless, the mechanisms by which P2X7 receptor activation induces LMP and leakage are unclear. This study investigated cellular mechanisms associated with endosomal and lysosomal leakage triggered by P2X7 receptor activation. We found that ATP at 500 μM and 5 mM (but not 50 μM) induced LMP in non-stimulated peritoneal macrophages. This effect was not observed in P2X7-deficient or A740003-pretreated macrophages. We found that the P2X7 receptor and pannexin-1 channels mediate calcium influx that might be important for activating specific ion channels (TRPM2 and two-pore channels) on the membranes of late endosomes and lysosomes leading to LMP leakage and consequent cathepsin release. These findings suggest the critical role of the P2X7 receptor in inflammatory and infectious diseases via lysosomal dysfunction.

Benefits and costs of immune memory in Rhodnius prolixus against Trypanosoma cruzi

There is increasing evidence supporting the immune memory in invertebrates, but the studies are relatively neglected in insect vectors other than mosquitoes. Therefore, we tested two hypotheses: 1) Rhodnius prolixus insects possess immune memory against Trypanosoma cruzi, and 2) their immune memory is costly. The Dm28c and Y strains of T. cruzi were used, the former being more infective than the latter. On the one hand, the triatomines subjected to dual challenges with the Dm28c strain did not show significant differences in survival than those of the heterologous challenge groups control-Dm28c and Y-Dm28c. On the other hand, the insects survived longer after a dual Y-Y challenge than after the corresponding heterologous challenge (control-Y). The Y-Y, Dm28c-Y, and naïve groups showed similar survival. There was more prolonged survival following the Y-Y versus Dm28c-Dm28c dual challenge. The Dm28c-Dm28c group exhibited moulting sooner than the control-Dm28c or naïve group. In contrast, there were no differences in the probability of moulting between the Y-Y and naïve groups. The results suggest that triatomines have immune memory against the Y but not the Dm28c strain. Further investigation on triatomine and T. cruzi interaction is needed to determine if infectivity accelerates or delay growth due to innate immune memory.

High larvicidal efficacy of yeast-encapsulated orange oil against Aedes aegypti strains from Brazil

Background

Botanical substances such as essential oils (EOs) have demonstrated insecticidal properties and are a valid option for vector control. However, free EOs are unreliable as mosquito larvicides due their easy degradation by environmental exposure to ultraviolet light and higher temperatures. Here, we assessed the efficacy of a mosquito larvicide based on orange oil in a yeast-based delivery system against Aedes aegypti strains with different resistance status towards chemical neurotoxic insecticides. This larvicide preparation was physicochemically characterized in a previous report.

Methods

Larvae of four Ae. aegypti strains from different regions of Brazil and different resistance profiles for deltamethrin (pyrethroid) and temephos (organophosphate) were tested against yeast-encapsulated orange oil (YEOO) in laboratory conditions for measurement of LC₅₀ and LC₉₀ values. The same assays were performed with the Belo Horizonte strain under environmental conditions (natural light and temperature). The resistance profiles of these strains were compared to the Rockefeller reference strain in all conditions.

Results

YEOO was found to be a highly active larvicide (LC₅₀ < 50 mg/L) against all Ae. aegypti strains tested in both laboratory conditions (LC₅₀ = 8.1–24.7 mg/L) and environmental conditions with natural light and temperature fluctuation (LC₅₀ = 20.0–49.9 mg/L). Moreover, all strains were considered susceptible (RR < 5) to YEOO, considering resistance ratios calculated based on the Rockefeller strain. The resistance ratios were only higher than 2.5 for LC_90–95 of Belo Horizonte in the laboratory, probably due the higher heterogeneity associated with older egg papers (> 5 months).

Conclusion

YEOO demonstrates high larvicidal activity against Ae. aegypti strains with resistant phenotypes for deltamethrin (PY) and temephos (OP). This larvicidal activity suggests the potential for the development of YEOO as an alternative intervention to synthetic insecticides in integrated vector management programs, for populations with resistance to commonly used insecticides.

Graphic Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04733-2.

Characterization of Glycoside Hydrolase Families 13 and 31 Reveals Expansion and Diversification of α-Amylase Genes in the Phlebotomine Lutzomyia longipalpis and Modulation of Sandfly Glycosidase Activities by Leishmania Infection

Sugar-rich food sources are essential for sandflies to meet their energy demands, achieving more prolonged survival. The digestion of carbohydrates from food is mainly realized by glycoside hydrolases (GH). To identify genes coding for α-glycosidases and α-amylases belonging to Glycoside Hydrolase Family 13 (GH13) and Glycoside Hydrolase Family 31 (GH31) in Lutzomyia longipalpis, we performed an HMMER search against its genome using known sequences from other dipteran species. The sequences retrieved were classified based on BLASTP best hit, analysis of conserved regions by alignment with sequences of proteins with known structure, and phylogenetic analysis comparing with orthologous proteins from other dipteran species. Using RT-PCR analysis, we evaluated the expression of GH13 and GH31 genes, in the gut and rest of the body of females, in four different conditions: non-fed, sugar-fed, blood-fed, and Leishmania mexicana infected females. L. longipalpis has GH13/31 genes that code for enzymes involved in various aspects of sugar metabolism, as carbohydrate digestion, storage, and mobilization of glycogen reserves, proteins involved in transport, control of N-glycosylation quality, as well as others with a putative function in the regulation of myogenesis. These proteins are representatives of GH13 and GH31 families, and their roles seem to be conserved. Most of the enzymes seem to be active with conserved consense sequences, including the expected catalytic residues. α-amylases also demonstrated the presence of calcium and chloride binding sites. L. longipalpis genome shows an expansion in the α-amylase gene family, with two clusters. In contrast, a retraction in the number of α-glucosidases occurred. The expansion of α-amylases is probably related to the specialization of these proteins for different substrates or inhibitors, which might correlate with the higher diversity of plant foods available in the natural habitat of L. longipalpis. The expression of α-glucosidase genes is higher in blood-fed females, suggesting their role in blood digestion. Besides that, in blood-fed females infected with the parasite Leishmania mexicana, these genes were also modulated. Glycoside Hydrolases from families 13 and 31 are essential for the metabolism of L. longipalpis, and GH13 enzymes seem to be involved in the interaction between sandflies and Leishmania.

Characterization of the Temporal Pattern of Blood Protein Digestion in Rhodnius prolixus: First Description of Early and Late Gut Cathepsins

Rhodnius prolixus is one important vector for the parasite Trypanosoma cruzi in Latin America, where Chagas disease is a significant health issue. Although R. prolixus is a model for investigations of vector–parasite interaction and transmission, not much has been done recently to further comprehend its protein digestion. In this work, gut proteolysis was characterized using new fluorogenic substrates, including optimum pH, inhibition profiles, and tissue and temporal expression patterns. Each protease possessed a particular tissue prevalence and activity cycle after feeding. Cathepsin L had a higher activity in the posterior midgut lumen, being characterized by a plateau of high activities during several days in the intermediate phase of digestion. Cathepsin D showed high activity levels in the tissue homogenates and in the luminal content of the posterior midgut, with a single peak 5 days after blood feeding. Aminopeptidases are highly associated with the midgut wall, where the highest activity is located. Assays with proteinaceous substrates as casein, hemoglobin, and serum albumin revealed different activity profiles, with some evidence of biphasic temporal proteolytic patterns. Cathepsin D genes are preferentially expressed in the anterior midgut, while cathepsin L genes are mainly located in the posterior portion of the midgut, with specific sets of genes being differently expressed in the initial, intermediate, or late phases of blood digestion.

Significance Statement

This is the first description in a non-dipteran hematophagous species of a sequential protease secretion system based on midgut cathepsins instead of the most common insect digestive serine proteases (trypsins and chymotrypsins). The midgut of R. prolixus (Hemiptera) shows a different temporal expression of proteases in the initial, intermediate, and late stages of blood digestion. In this respect, a different timing in protease secretion may be an example of adaptative convergence in blood-sucking vectors from different orders. Expanding the knowledge about gut physiology in triatomine vectors may contribute to the development of new control strategies, aiming the blocking of parasite transmission.

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.

Determination of Chitin Content in Insects: An Alternate Method Based on Calcofluor Staining

Chitin is an aminopolysaccharide present in yeast cells and arthropod cuticle and is one of the most abundant biopolymers. The conventional methods for the quantitation of chitin content in biological samples are based on its hydrolysis (acid or enzymatic), and the assessment of the byproduct, glucosamine. However, previously described methodologies are time-consuming, laborious, low throughput, and not applicable to insect samples in many cases. Here we describe a new approach to chitin content quantitation based on calcofluor fluorescent brightener staining of samples, followed by microplate fluorescence readings. Calcofluor is a specific chitin stain commonly used for topological localization of the polymer. The protocol was tested in three important disease vector species, namely Lutzomyia longipalpis, Aedes aegypti, and Rhodnius prolixus, and then compared to a classic colorimetric chitin assessment method. Results show that chitin content in the tested insects can vary largely in a range of 8–4600 micrograms of chitin per insect, depending on species, sex, and instar. Comparisons between measurements from the previous protocol and calcofluor method showed statistically significant differences in some samples. However, the difference might be due to interference in the classic method from non-chitin sources of glucosamine and reducing agents. Furthermore, chitinase hydrolysis reduces the total chitin mass estimated between 36 and 74%, consolidating the fluorescent measurements as actual stained chitin in the same extent that was observed with the standard protocol. Therefore, the calcofluor staining method revealed to be a fast and reliable technique for chitin quantitation in homogenized insect samples.

Development of Leishmania mexicana in Lutzomyia longipalpis in the absence of sugar feeding

The leishmaniases are caused by Leishmania parasites and transmitted through the bites of phlebotomine sand flies. During parasite development inside the vector’s midgut, promastigotes move towards the stomodeal valve, a mechanism that is crucial for transmission. It has been reported that the sugar meal acquired by sand flies during feeding between bloodmeals is essential for the development and migration of parasites. We demonstrated that the distribution of Leishmania mexicana parasites was affected by the sugar meals obtained by the sand flies. Promastigote migration towards the cardia region seems to be only partially based on the stimuli provided by sugar molecules. In the absence of sugars, significant amounts of parasites developed in the hindgut. In addition, sugar meals were important for the survival of sand flies, especially during blood digestion, presumably supporting their energy requirements.

Characterization of α-Glucosidases From Lutzomyia longipalpis Reveals Independent Hydrolysis Systems for Plant or Blood Sugars

Lutzomyia longipalpis is the main vector of Leishmania infantum and exploits different food sources during development. Adults have a diet rich in sugars, and females also feed on blood. The sugar diet is essential for maintaining longevity, infection, and Leishmaniasis transmission. Carbohydrases, including α-glucosidases, are the main enzymes involved in the digestion of sugars. In this context, we studied the modulation of α-glucosidase activities in different feeding conditions and compartments of Lutzomyia longipalpis females, in order to characterize in detail their roles in the physiology of this insect. All tissues showed activity against MUαGlu and sucrose, with highest activities in the midgut and crop. Activity was 1,000 times higher on sucrose than on MUαGlu. Basal activities were observed in non-fed insects; blood feeding induced activity in the midgut contents, and sugar feeding modulated activity in midgut tissues. α-glucosidase activity changed after female exposure to different sugar concentrations or moieties. α-glucosidases from different tissues showed different biochemical properties, with an optimum pH around 7.0–8.0 and K_M between 0.37 and 4.7 mM, when MUαGlu was used as substrate. Using sucrose as substrate, the optimum pH was around 6.0, and K_M ranges between 11 and 800 mM. Enzymes from the crop and midgut tissues showed inhibition in high substrate concentrations (sucrose), with K_I ranging from 39 to 400 mM, which explains the high K_M values found. Chromatographic profiles confirmed that different α-glucosidases are been produced in L. longipalpis in different physiological contexts, with the distinction of at least four α-glucosidases. The results suggest that some of these enzymes are involved in different metabolic processes, like digestion of plant sugars, digestion of blood glycoproteins or glycolipids, and mobilization of energetic storages during starvation.

Microorganism-Based Larval Diets Affect Mosquito Development, Size and Nutritional Reserves in the Yellow Fever Mosquito Aedes aegypti (Diptera: Culicidae)

Background

Mosquito larvae feed on organic detritus from the environment, particularly microorganisms comprising bacteria, protozoa, and algae as well as crustaceans, plant debris, and insect exuviae. Little attention has been paid to nutritional studies in Aedes aegypti larvae.

Objectives

We investigated the effects of yeast, bacteria and microalgae diets on larval development, pupation time, adult size, emergence, survivorship, lifespan, and wing morphology.

Materials and Methods

Microorganisms (or Tetramin^® as control) were offered as the only source of food to recently hatched first instar larvae and their development was followed until the adult stage. Protein, carbohydrate, glycogen, and lipid were analyzed in single larvae to correlate energetic reserve accumulation by larva with the developmental rates and nutritional content observed. FITC-labeled microorganisms were offered to fourth instar larvae, and its ingestion was recorded by fluorescence microscopy and quantitation.

Results and Discussion

Immature stages developed in all diets, however, larvae fed with bacteria and microalgae showed a severe delay in development rates, pupation time, adult emergence and low survivorship. Adult males emerged earlier as expected and had longer survival than females. Diets with better nutritional quality resulted in adults with bigger wings. Asaia sp. and Escherichia coli resulted in better nutrition and developmental parameters and seemed to be the best bacterial candidates to future studies using symbiont-based control. The diet quality was measured and presented different protein and carbohydrate amounts. Bacteria had the lowest protein and carbohydrate rates, yeasts had the highest carbohydrate amount and microalgae showed the highest protein content. Larvae fed with microalgae seem not to be able to process and store these diets properly. Larvae were shown to be able to process yeast cells and store their energetic components efficiently.

Conclusion

Together, our results point that Ae. aegypti larvae show high plasticity to feed, being able to develop under different microorganism-based diets. The important role of Ae. aegypti in the spread of infectious diseases requires further biological studies in order to understand the vector physiology and thus to manage the larval natural breeding sites aiming a better mosquito control.

Biochemical and Functional Characterization of Glycoside Hydrolase Family 16 Genes in Aedes aegypti Larvae: Identification of the Major Digestive β-1,3-Glucanase

Insect β-1,3-glucanases belong to Glycoside Hydrolase Family 16 (GHF16) and are involved in digestion of detritus and plant hemicellulose. In this work, we investigated the role of GHF16 genes in Aedes aegypti larvae, due to their detritivore diet. Aedes aegypti genome has six genes belonging to GHF16 (Aae GH16.1 – Aae GH16.6), containing two to six exons. Sequence analysis suggests that five of these GHF16 sequences (Aae GH16.1, 2, 3, 5, and 6) contain the conserved catalytic residues of this family and correspond to glucanases. All genomes of Nematocera analyzed showed putative gene duplications corresponding to these sequences. Aae GH16.4 has no conserved catalytic residues and is probably a β-1,3-glucan binding protein involved in the activation of innate immune responses. Additionally, Ae. aegypti larvae contain significant β-1,3-glucanase activities in the head, gut and rest of body. These activities have optimum pH about 5–6 and molecular masses between 41 and 150 kDa. All GHF16 genes above showed different levels of expression in the larval head, gut or rest of the body. Knock-down of AeGH16.5 resulted in survival and pupation rates lower than controls (dsGFP and water treated). However, under stress conditions, severe mortalities were observed in AeGH16.1 and AeGH16.6 knocked-down larvae. Enzymatic assays of β-1,3-glucanase in AeGH16.5 silenced larvae exhibited lower activity in the gut and no change in the rest of the body. Chromatographic activity profiles from gut samples after GH16.5 silencing showed suppression of enzymatic activity, suggesting that this gene codes for the digestive larval β-1,3-glucanase of Ae. aegypti. This gene and enzyme are attractive targets for new control strategies, based on the impairment of normal gut physiology.

Transmission blocking sugar baits for the control of Leishmania development inside sand flies using environmentally friendly beta-glycosides and their aglycones

Background

The sand fly Lutzomyia longipalpis is the main vector of American visceral leishmaniasis, a disease caused by parasites of the genus Leishmania. Adults of this insect feed on blood (females only) or sugar from plant sources, but their digestion of carbohydrates is poorly studied. Beta-glycosides as esculin and amygdalin are plant compounds and release toxic compounds as esculetin and mandelonitrile when hydrolyzed. Beta-glucosidase and trehalase are essential enzymes in sand fly metabolism and participate in sugar digestion. It is therefore possible that the toxic portions of these glycosides, released during digestion, affect sand fly physiology and the development of Leishmania.

Results

We tested the oral administration to sand flies of amygdalin, esculin, mandelonitrile, and esculetin in the sugar meal. These compounds significantly decreased the longevity of Lutzomyia longipalpis females and males. Lutzomyia longipalpis adults have significant hydrolytic activities against esculin and feeding on this compound cause changes in trehalase and β-glucosidase activities. Female trehalase activity is inhibited in vitro by esculin. Esculin is naturally fluorescent, so its ingestion may be detected and quantified in whole insects or tissue samples stored in methanol. Mandelonitrile neither affected the amount of sugar ingested by sand flies nor showed repellent activity. Our results show that mandelonitrile significantly reduces the viability of L. amazonensis, L. braziliensis, L. infantum and L. mexicana, in a concentration-dependent manner. Esculetin caused a similar effect, reducing the number of L. infantum and L. mexicana. Female L. longipalpis fed on mandelonitrile had a reduction in the number of parasites and prevalence of infection after seven days of infection with L. mexicana, either by counting in a Neubauer chamber or by qPCR assays.

Conclusions

Glycosides have significant effects on L. longipalpis longevity and metabolism and also affect the development of parasites in culture and inside the insect. These observations might help to conceptualize new vector control strategies using transmission blocking sugar baits.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3122-z) contains supplementary material, which is available to authorized users.

Penicillium citrinum UFV1 β-glucosidases: purification, characterization, and application for biomass saccharification

BACKGROUND

β-Glucosidases are components of the cellulase system, a family of enzymes that hydrolyze the β-1,4 linkages of cellulose. These proteins have been extensively studied due to the possibility of their use in various biotechnological processes. They have different affinities for substrates (depending on their source) and their activities can be used for saccharification of different types of biomass. In this context, the properties and the synergistic capacity of β-glucosidases from different organisms, to supplement the available commercial cellulase cocktails, need a comprehensive evaluation.

RESULTS

Two β-glucosidases belonging to GH3 family were secreted by Penicillium citrinum UFV. PcβGlu1 (241 kDa) and PcβGlu2 (95 kDa) presented acidic and thermo-tolerant characteristics. PcβGlu1 showed Michaelis-Menten kinetics for all substrates tested with K_m values ranging from 0.09 ± 0.01 (laminarin) to 1.7 ± 0.1 mM (cellobiose, C2) and k_cat values ranging from 0.143 ± 0.005 (laminarin) to 8.0 ± 0.2 s^-1 (laminaribiose, Lb). PcβGlu2 showed substrate inhibition for 4-methylumbelliferyl-β-d-glucopyranoside (MUβGlu), p-nitrophenyl-β-d-glucopyranoside (pNPβGlu), cellodextrins (C3, C4, and C5), N-octil-β-d-glucopyranoside, and laminaribiose, with K_m values ranging from 0.014 ± 0.001 (MUβGlu) to 0.64 ± 0.06 mM (C2) and k_cat values ranging from 0.49 ± 0.01 (gentiobiose) to 1.5 ± 0.2 s^-1 (C4). Inhibition constants (K_i) for PcβGlu2 substrate inhibition ranged from 0.69 ± 0.07 (MUβGlu) to 10 ± 1 mM (Lb). Glucose and cellobiose are competitive inhibitors of PcβGlu1 and PcβGlu2 when pNPβGlu is used as a substrate. For PcβGlu1 inhibition, K_i = 1.89 ± 0.08 mM (glucose) and K_i = 3.8 ± 0.1 mM (cellobiose); for PcβGlu2, K_i = 0.83 ± 0.05 mM (glucose) and K_i = 0.95 ± 0.07 mM (cellobiose). The enzymes were tested for saccharification of different biomasses, individually or supplementing a Trichoderma reesei commercial cellulose preparation. PcβGlu2 was able to hydrolyze banana pseudostem and coconut fiber with the same efficiency as the T. reesei cocktail, showing significant synergistic properties with T. reesei enzymes in the hydrolysis of these alternative biomasses.

CONCLUSIONS

The β-glucosidases from P. citrinum UFV1 present different enzymatic properties from each other and might have potential application in several biotechnological processes, such as hydrolysis of different types of biomass.

N-glycosylation influences the catalytic activity of mosquito α-glucosidases associated with susceptibility or refractoriness to Lysinibacillus sphaericus

Cqm1 and Aam1 are α-glucosidases (EC 3.2.1.20) expressed in Culex quinquefasciatus and Aedes aegypti larvae midgut, respectively. These orthologs share high sequence similarity but while Cqm1 acts as a receptor for the Binary (Bin) insecticidal toxin from Lysinibacillus sphaericus, Aam1 does not bind the toxin, rendering Ae. aegypti refractory to this bacterium. Aam1 is heavily glycosylated, contrasting to Cqm1, but little is known regarding how glycosylation impacts on its function. This study aimed to compare the N-glycosylation patterns and the catalytic activities of Aam1 and Cqm1. Mutant proteins were generated where predicted Aam1 N-glycosylation sites (N-PGS) were either inserted into Cqm1 or abrogated in Aam1. The mutants validated four N-PGS which were found to localize externally on the Aam1 structure. These Aam1 and Cqm1 mutants maintained their Bin binding properties, confirming that glycosylation has no role in this interaction. The α-glucosidase activity of both proteins was next investigated, with Aam1 having a remarkably higher catalytic efficiency, influenced by changes in glycosylation. Molecular dynamics showed that glycosylated and nonglycosylated Aam1 models displayed distinct patterns that could influence their catalytic activity. Differential N-glycosylation may then be associated with higher catalytic efficiency in Aam1, enhancing the functional diversity of related orthologs.

Digestion of Yeasts and Beta-1,3-Glucanases in Mosquito Larvae: Physiological and Biochemical Considerations

Aedes aegypti larvae ingest several kinds of microorganisms. In spite of studies regarding mosquito digestion, little is known about the nutritional utilization of ingested cells by larvae. We investigated the effects of using yeasts as the sole nutrient source for A. aegypti larvae. We also assessed the role of beta-1,3-glucanases in digestion of live yeast cells. Beta-1,3-glucanases are enzymes which hydrolyze the cell wall beta-1,3-glucan polyssacharide. Larvae were fed with cat food (controls), live or autoclaved Saccharomyces cerevisiae cells and larval weight, time for pupation and adult emergence, larval and pupal mortality were measured. The presence of S. cerevisiae cells inside the larval gut was demonstrated by light microscopy. Beta-1,3-glucanase was measured in dissected larval samples. Viability assays were performed with live yeast cells and larval gut homogenates, with or without addition of competing beta-1,3-glucan. A. aegypti larvae fed with yeast cells were heavier at the 4^th instar and showed complete development with normal mortality rates. Yeast cells were efficiently ingested by larvae and quickly killed (10% death in 2h, 100% in 48h). Larvae showed beta-1,3-glucanase in head, gut and rest of body. Gut beta-1,3-glucanase was not derived from ingested yeast cells. Gut and rest of body activity was not affected by the yeast diet, but head homogenates showed a lower activity in animals fed with autoclaved S. cerevisiae cells. The enzymatic lysis of live S. cerevisiae cells was demonstrated using gut homogenates, and this activity was abolished when excess beta-1,3-glucan was added to assays. These results show that live yeast cells are efficiently ingested and hydrolyzed by A. aegypti larvae, which are able to fully-develop on a diet based exclusively on these organisms. Beta-1,3-glucanase seems to be essential for yeast lytic activity of A. aegypti larvae, which possess significant amounts of these enzyme in all parts investigated.

Relationship between digestive enzymes and food habit of Lutzomyia longipalpis (Diptera: Psychodidae) larvae: Characterization of carbohydrases and digestion of microorganisms

The sandfly Lutzomyia longipalpis (Lutz and Neiva, 1912) is the main vector of American Visceral Leishmaniasis. In spite of its medical importance and several studies concerning adult digestive physiology, biochemistry and molecular biology, very few studies have been carried out to elucidate the digestion in sandfly larvae. Even the breeding sites and food sources of these animals in the field are largely uncharacterized. In this paper, we describe and characterize several carbohydrases from the gut of L. longipalpis larvae, and show that they are probably not acquired from food. The enzyme profile of this insect is consistent with the digestion of fungal and bacterial cells, which were proved to be ingested by larvae under laboratory conditions. In this respect, sandfly larvae might have a detritivore habit in nature, being able to exploit microorganisms usually encountered in the detritus as a food source.

Phenol oxidases from Rhodnius prolixus: temporal and tissue expression pattern and regulation by ecdysone

Rhodnius prolixus 5th instar nymphs have significant PO enzymatic activity in the anterior midgut, fat body and hemolymph. The tissue with the major amount of PO activity is the anterior midgut while those with higher specific activities are the fat body and hemolymph. In this work the temporal pattern of PO enzymatic activity in different tissues was investigated. In fat body, PO peaks occur at 7, 12 and 16 days after a blood meal. In hemolymph, PO diminishes until day 7, and then recovers by day 14. In the anterior midgut tissue, PO peaks on day 9 and just before ecdysis; a similar pattern was observed in the anterior midgut contents. Some of these activities are dependent on the release of ecdysone, as feeding blood meal containing azadirachtin suppresses them and ecdysone treatment counteracts this effect. These results suggest that during the development of the 5th instar, the insect has natural regulating cycles of basal PO expression and activation, which could be related to the occurrence of natural infections. The differences in temporal patterns of activity and the effects of azadirachtin and ecdysone in each organ suggest that, at least in R. prolixus, different tissues are expressing different PO genes.

Physalin B inhibits Rhodnius prolixus hemocyte phagocytosis and microaggregation by the activation of endogenous PAF-acetyl hydrolase activities

The effects of physalin B (a natural secosteroidal chemical from Physalis angulata, Solanaceae) on phagocytosis and microaggregation by hemocytes of 5th-instar larvae of Rhodnius prolixus were investigated. In this insect, hemocyte phagocytosis and microaggregation are known to be induced by the platelet-activating factor (PAF) or arachidonic acid (AA) and regulated by phospholipase A(2) (PLA(2)) and PAF-acetyl hydrolase (PAF-AH) activities. Phagocytic activity and formation of hemocyte microaggregates by Rhodnius hemocytes were strongly blocked by oral treatment of this insect with physalin B (1mug/mL of blood meal). The inhibition induced by physalin B was reversed for both phagocytosis and microaggregation by exogenous arachidonic acid (10microg/insect) or PAF (1microg/insect) applied by hemocelic injection. Following treatment with physalin B there were no significant alterations in PLA(2) activities, but a significant enhancement of PAF-AH was observed. These results show that physalin B inhibits hemocytic activity by depressing insect PAF analogous (iPAF) levels in hemolymph and confirm the role of PAF-AH in the cellular immune reactions in R. prolixus.