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

Structural and functional comparisons of salivary α-glucosidases from the mosquito vectors Aedes aegypti, Anopheles gambiae, and Culex quinquefasciatus

Mosquito vectors of medical importance both blood and sugar feed, and their saliva contains bioactive molecules that aid in both processes. Although it has been shown that the salivary glands of several mosquito species exhibit α-glucosidase activities, the specific enzymes responsible for sugar digestion remain understudied. We therefore expressed and purified three recombinant salivary α-glucosidases from the mosquito vectors Aedes aegypti, Anopheles gambiae, and Culex quinquefasciatus and compared their functions and structures. We found that all three enzymes were expressed in the salivary glands of their respective vectors and were secreted into the saliva. The proteins, as well as mosquito salivary gland extracts, exhibited α-glucosidase activity, and the recombinant enzymes displayed preference for sucrose compared to p-nitrophenyl-α-D-glucopyranoside. Finally, we solved the crystal structure of the Ae. aegypti α-glucosidase bound to two calcium ions at a 2.3 Ångstrom resolution. Molecular docking suggested that the Ae. aegypti α-glucosidase preferred di- or polysaccharides compared to monosaccharides, consistent with enzymatic activity assays. Comparing structural models between the three species revealed a high degree of similarity, suggesting similar functional properties. We conclude that the α-glucosidases studied herein are important enzymes for sugar digestion in three mosquito species.

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.

A Culex quinquefasciatus strain resistant to the binary toxin from Lysinibacillus sphaericus displays altered enzyme activities and energy reserves

BACKGROUND

The resistance of a Culex quinquefasciatus strain to the binary (Bin) larvicidal toxin from Lysinibacillus sphaericus is due to the lack of expression of the toxin's receptors, the membrane-bound Cqm1 α-glucosidases. A previous transcriptomic profile of the resistant larvae showed differentially expressed genes coding Cqm1, lipases, proteases and other genes involved in lipid and carbohydrate metabolism. This study aimed to investigate the metabolic features of Bin-resistant individuals by comparing the activity of some enzymes, energy reserves, fertility and fecundity to a susceptible strain.

METHODS

The activity of specific enzymes was recorded in midgut samples from resistant and susceptible larvae. The amount of lipids and reducing sugars was determined for larvae and adults from both strains. Additionally, the fecundity and fertility parameters of these strains under control and stress conditions were examined.

RESULTS

Enzyme assays showed that the esterase activities in the midgut of resistant larvae were significantly lower than susceptible ones using acetyl-, butyryl- and heptanoyl-methylumbelliferyl esthers as substrates. The α-glucosidase activity was also reduced in resistant larvae using sucrose and a synthetic substrate. No difference in protease activities as trypsins, chymotrypsins and aminopeptidases was detected between resistant and susceptible larvae. In larval and adult stages, the resistant strain showed an altered profile of energy reserves characterized by significantly reduced levels of lipids and a greater amount of reducing sugars. The fertility and fecundity of females were similar for both strains, indicating that those changes in energy reserves did not affect these reproductive parameters.

CONCLUSIONS

Our dataset showed that Bin-resistant insects display differential metabolic features co-selected with the phenotype of resistance that can potentially have effects on mosquito fitness, in particular, due to the reduced lipid accumulation.

cAMP: A second messenger involved in the mechanism of midgut alkalinization in Lutzomyia longipalpis

The sand fly Lutzomyia longipalpis is the main vector of Leishmania infantum in the Americas. Female sand flies ingest sugar-rich solutions and blood, which are digested in the midgut. Digestion of nutrients is an essential function performed by digestive enzymes, which require appropriate physiological conditions. One of the main aspects that influence enzymatic activity is the gut pH, which must be tightly controlled. Considering second messengers are frequently involved in the coordination of tightly regulated physiological events, we investigated if the second messenger cAMP would participate in the process of alkalinization in the abdominal midgut of female L. longipalpis. In midguts containing the indicator dye bromothymol-blue, cAMP stimulated the alkalinization of the midgut lumen. Through another technique based on the use of fluorescein as a pH indicator, we propose that cAMP is involved in the alkalinization of the midgut by activating HCO3^- transport from the enterocyte's cytoplasm to the lumen. The results strongly suggested that the carrier responsible for this process would be a HCO3^- /Cl^- antiporter located in the enterocytes' apical membrane. Hematophagy promotes the release of alkalinizing hormones in the hemolymph; however, when the enzyme adenylyl cyclase, responsible for cAMP production, was inhibited, we observed that the hemolymph from blood-fed L. longipalpis' females did not stimulate midgut alkalinization. This result indicated that hormone-stimulated alkalinization is mediated by cAMP. In the present study, we provide evidences that cAMP has a key role in the control of intestinal pH.

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.

Comparative RNA-Seq Analyses of Solenopsis japonica (Hymenoptera: Formicidae) Reveal Gene in Response to Cold Stress

Solenopsis japonica, as a fire ant species, shows some predatory behavior towards earthworms and woodlice, and preys on the larvae of other ant species by tunneling into a neighboring colony's brood chamber. This study focused on the molecular response process and gene expression profiles of S. japonica to low (9 °C)-temperature stress in comparison with normal temperature (25 °C) conditions. A total of 89,657 unigenes (the clustered non-redundant transcripts that are filtered from the longest assembled contigs) were obtained, of which 32,782 were annotated in the NR (nonredundant protein) database with gene ontology (GO) terms, gene descriptions, and metabolic pathways. The results were 81 GO subgroups and 18 EggNOG (evolutionary genealogy of genes: Non-supervised Orthologous Groups) keywords. Differentially expressed genes (DEGs) with log₂fold change (FC) > 1 and log₂FC < -1 with p-value ≤ 0.05 were screened for cold stress temperature. We found 215 unigenes up-regulated and 115 unigenes down-regulated. Comparing transcriptome profiles for differential gene expression resulted in various DE proteins and genes, including fatty acid synthases and lipid metabolism, which have previously been reported to be involved in cold resistance. We verified the RNA-seq data by qPCR on 20 up- and down-regulated DEGs. These findings facilitate the basis for the future understanding of the adaptation mechanisms of S. japonica and the molecular mechanisms underlying the response to low temperatures.

Molecular and biological features of Culex quinquefasciatus homozygous larvae for two cqm1 alleles that confer resistance to Lysinibacillus sphaericus larvicides

BACKGROUND

Culex quinquefasciatus resistance to the binary toxin from Lysinibacillus sphaericus larvicides can occur because of mutations in the cqm1 gene that prevents the expression of the toxin receptor, Cqm1 α-glucosidase. In a resistant laboratory-selected colony maintained for more than 250 generations, cqm1_REC and cqm1_REC-2 resistance alleles were identified. The major allele initially found, cqm1_REC , became minor and was replaced by cqm1_REC-2 . This study aimed to investigate the features associated with homozygous larvae for each allele to understand the reasons for the allele replacement and to generate knowledge on resistance to microbial larvicides.

RESULTS

Homozygous larvae for each allele were compared. Both larvae displayed the same level of resistance to the binary toxin (3500-fold); therefore, a change in phenotype was not the reason for the replacement observed. The lack of Cqm1 expression did not reduce the total specific α-glucosidase activity for homozygous cqm1_REC and cqm1_REC-2 larvae, which were statistically similar to the susceptible strain, using artificial or natural substrates. The expression of eight Cqm1 paralog α-glucosidases was demonstrated in resistant and susceptible larvae. Bioassays in which cqm1_REC or cqm1_REC-2 homozygous larvae were reared under stressful conditions showed that most adults produced were cqm1_REC-2 homozygous (69%). Comparatively, in the offspring of a heterozygous sub-colony reared under optimal conditions for 20 generations, the cqm1_REC allele assumed a higher frequency (0.72).

CONCLUSION

Homozygous larvae for each allele exhibited a similar resistant phenotype. However, they presented specific advantages that might favor their selection and can be used in designing resistance management practices. © 2021 Society of Chemical Industry.

Proteomics and ultrastructural analysis of Hermetia illucens (Diptera: Stratiomyidae) larval peritrophic matrix

BACKGROUND

The black soldier fly (Hermetia illucens) has significant economic potential. The larvae can be used in financially viable waste management systems, as they are voracious feeders able to efficiently convert low-quality waste into valuable biomass. However, most studies on H. illucens in recent decades have focused on optimizing their breeding and bioconversion conditions, while information on their biology is limited.

METHODS

About 200 fifth instar well-fed larvae were sacrificed in this work. The liquid chromatography-tandem mass spectrometry and scanning electron microscopy were employed in this study to perform a proteomic and ultrastructural analysis of the peritrophic matrix (PM) of H. illucens larvae.

RESULTS

A total of 565 proteins were identified in the PM samples of H. illucen, of which 177 proteins were predicted to contain signal peptides, bioinformatics analysis and manual curation determined 88 proteins may be associated with the PM, with functions in digestion, immunity, PM modulation, and others. The ultrastructure of the H. illucens larval PM observed by scanning electron microscopy shows a unique diamond-shaped chitin grid texture.

CONCLUSIONS

It is the first and most comprehensive proteomics research about the PM of H. illucens larvae to date. All the proteins identified in this work has been discussed in details, except several unnamed or uncharacterized proteins, which should not be ignored and need further study. A comparison of the ultrastructure between H. illucens larval PM and those of other insects as observed by SEM indicates that the PM displays diverse textures on an ultra-micro scale and we suscept a unique diamond-shaped chitin grid texture may help H. illucens larval to hold more food. This work deepens our understanding of the molecular architecture and ultrastructure of the H. illucens larval PM.

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.

Essential (Mg, Fe, Zn and Cu) and Non-Essential (Cd and Pb) Elements in Predatory Insects (Vespa crabro and Vespa velutina): A Molecular Perspective

The recent introduction of the Asian yellow-legged hornet, Vespa velutina, into Europe has raised concern regarding the threat to honeybees and the competition with the European hornet, Vespa crabro. The aim of this study was to investigated essential (Mg, Fe, Zn, Cu) and non-essential (Cd and Pb) elements in these two species. Element concentrations were determined in the whole body and separately in the head, thorax and abdomen using atomic absorption spectrometry (AAS). The changes in essential element concentration and speciation during metamorphosis were also studied using size exclusion chromatography followed by AAS and proteomic analysis. In both species, the essential elements were more concentrated in the abdomen due to the presence of fat bodies. Magnesium, Fe and Zn concentrations were significantly higher in V. crabro than in V. velutina and could have been related to the higher aerobic energy demand of the former species required to sustain foraging flight. Low concentrations of Cd and Pb were indicative of low environmental exposure. The concentration and speciation of essential elements, particularly Fe, varied among the developmental stages, indicating a modification of ligand preferences during metamorphosis. Overall, the results in the present study provide a better understanding of the hornet metal metabolism and a foundation for additional studies.

Schistocerca piceifrons piceifrons (Orthoptera: Acrididae) as a Source of Compounds of Biotechnological and Nutritional Interest

The Central American locust, Schistocerca piceifrons piceifrons (Walker) is a major agricultural pest in Mexico and Central America. Control measures against this pest have generated much environmental damage and substantial financial costs because chemical insecticides are used. Yet various Orthoptera species also appear to be a potential source of nutrients and a source of bioactive metabolites. Here, we studied the presence of secondary metabolites in the adult stage of S. p. piceifrons by applying different colorimetric techniques. Adults were collected from the southern region of Tamaulipas, Mexico, during September-December 2017. These samples were subjected to sequential processes of eviscerating, drying, pulverizing, extracting, and detecting of metabolites. Extractions were carried out in water, 50% ethanol, and absolute ethanol. The presence of phenolic compounds, alkaloids, tannins, saponins, flavonoids, and quantity of antioxidants against the DPPH (2, 2-diphenyl-1-picrylhydrazyl) and ABTS (2, 2'-azino-bis, 3-ethylbenzothiazoline-6-sulfonic acid) radicals were determined and reported. Proximate analysis showed that S. p. piceifrons has a high protein content (80.26%), low fat content (6.21%), and fiber content (12.56%) similar to other Orthoptera species. Chitin and chitosan contents of S. p. piceifrons were 11.88 and 9.11%, respectively; the recovery percentage of chitosan from chitin was 76.71%. Among the Orthoptera, the protein content of this pest is among the highest while its contents of chitin and chitosan are similar to those of other insect species (e.g., Bombix mori Linnaeus [Lepidoptera: Bombycidae]). Our results suggest this pest species is a potential source of bioactive compounds of biotechnological interest for use by pharmaceutical and food industries.