Wolbachia Modulates Lipid Metabolism in Aedes albopictus Mosquito Cells

Wolbachia enhances the survival of Drosophila infected with fungal pathogens

BACKGROUND

Wolbachia bacteria of arthropods are at the forefront of basic and translational research on multipartite host-symbiont-pathogen interactions. These vertically transmitted microbes are the most widespread endosymbionts on the planet due to factors including host reproductive manipulation and fitness benefits. Importantly, some strains of Wolbachia can inhibit viral pathogenesis within and between arthropod hosts. Mosquitoes carrying the wMel Wolbachia strain of Drosophila melanogaster have a greatly reduced capacity to spread viruses like dengue and Zika to humans. While significant research efforts have focused on viruses, relatively little attention has been given to Wolbachia-fungal interactions despite the ubiquity of fungal entomopathogens in nature.

RESULTS

Here, we demonstrate that Wolbachia increase the longevity of their Drosophila melanogaster hosts when challenged with a spectrum of yeast and filamentous fungal pathogens. We find that this pattern can vary based on host genotype, sex, and fungal species. Further, Wolbachia correlates with higher fertility and reduced pathogen titers during initial fungal infection, indicating a significant fitness benefit. Finally, RNA sequencing results show altered expression of many immune and stress response genes in the context of Wolbachia and fungal infection, suggesting host immunity may be involved in the mechanism.

CONCLUSIONS

This study demonstrates Wolbachia's protective role in diverse fungal pathogen interactions and determines that the phenotype is broad, but with several variables that influence both the presence and strength of the phenotype. It also is a critical step forward to understanding how symbionts can protect their hosts from a variety of pathogens.

Role of Vigilin and RACK1 in dengue virus-Aedes aegypti-Wolbachia interactions

Vigilin is a large and evolutionary conserved RNA-binding protein (RBP), which can interact with RNA through its KH domain. Vigilin is, therefore, a multifunctional protein reported to be associated with RNA transport and metabolism, sterol metabolism, chromosome segregation, carcinogenesis, and heterochromatin-mediated gene silencing. The receptor for activated C kinase 1 (RACK1) is another highly conserved protein involved in many cellular pathways. Functional studies in human cells indicated that RACK1 interacts with Vigilin to promote dengue virus (DENV) replication. Both proteins are associated with the endoplasmic reticulum. Here, we investigated the significance of Vigilin and RACK1 homologs in Aedes aegypti mosquitoes concerning DENV replication and Wolbachia infection. We identified the homologs of the two genes in Ae. aegypti (AeVigilin and AeRACK1), which were upregulated in DENV-infected Aag2 cells and mosquitoes, and silencing them in Aag2 cells resulted in reduced DENV replication. Co-immunoprecipitation showed that AeRACK1 and AeVigilin interact in mosquito cells. Interestingly, we also found upregulation of both genes in a Wolbachia-infected cell line (Aag2.wAlbB). Furthermore, silencing AeVigilin and AeRACK1 in Aag2.wAlbB cells reduced DENV replication but increased Wolbachia density. However, we did not find a significant effect on DENV replication after silencing both genes in Ae. aegypti mosquitoes. Overall, our results support the involvement and significance of AeVigilin and AeRACK1 in DENV replication in Ae. aegypti.IMPORTANCEDengue virus (DENV), transmitted mainly by Aedes aegypti mosquitoes, poses significant health risks. Identifying factors involved in the virus replication in mosquitoes and human hosts is essential for devising control measures. In this study, we show that Vigilin and the receptor for activated C kinase 1 (RACK1), two proteins shown to play a role in the replication of DENV in human cells, are induced in mosquitoes and cell lines following DENV replication. Both proteins reside in the cytoplasm, where they interact similarly to human cells. Silencing the genes in mosquito cells significantly reduced virus replication. Furthermore, we found that both genes are induced in mosquito cells transinfected with Wolbachia, a bacterium that blocks DENV replication. The results help better understand the role of the common factors supporting DENV replication in mosquitoes and human cells.

Symbiotic Bacteria: Wolbachia, Midgut Microbiota in Mosquitoes and Their Importance for Vector Prevention Strategies

Mosquito-borne illnesses pose a significant threat to eradication under existing vector management measures. Chemo-based vector control strategies (use of insecticides) raise a complication of resistance and environmental pollution. Biological control methods are an alternative approach to overcoming this complication arising from insecticides. The mosquito gut microbiome is essential to supporting the factors that involve metabolic regulation and metamorphic development (from juvenile to adult), as well as the induction of an immune response. The induced immune response includes the JAK-STAT, IMD, and Toll pathways due to the microbial interaction with the midgut cells (MG cells) that prevent disease transmission to humans. The aforementioned sequel to the review provides information about endosymbiont Wolbachia, which contaminates insect cells, including germline and somatic cytoplasm, and inhibits disease-causing pathogen development and transmission by competing for resources within the cell. Moreover, it reduces the host population via cytoplasmic incompatibility (CI), feminization, male killing, and parthenogenesis. Furthermore, the Cif factor in Wolbachia is responsible for CI induction that produces inviable cells with the translocating systems and the embryonic defect-causing protein factor, WalE1 (WD0830), which manipulates the host actin. This potential of Wolbachia can be used to design a paratransgenic system to control vectors in the field. An extracellular symbiotic bacterium such as Asaia, which is grown in the growth medium, is used to transfer lethal genes within itself. Besides, the genetically transferred symbiotic bacteria infect the wild mosquito population and are easily manifold. So, it might be suitable for vector control strategies in the future.

Insect Lipid Metabolism in the Presence of Symbiotic and Pathogenic Viruses and Bacteria

Insects, like most animals, have intimate interactions with microorganisms that can influence the insect host's lipid metabolism. In this chapter, we describe what is known so far about the role prokaryotic microorganisms play in insect lipid metabolism. We start exploring microbe-insect lipid interactions focusing on endosymbionts, and more specifically the gut microbiota that has been predominantly studied in Drosophila melanogaster. We then move on to an overview of the work done on the common and well-studied endosymbiont Wolbachia pipientis, also in interaction with other microbes. Taking a slightly different angle, we then look at the effect of human pathogens, including dengue and other viruses, on the lipids of mosquito vectors. We extend the work on human pathogens and include interactions with the endosymbiont Wolbachia that was identified as a natural tool to reduce the spread of mosquito-borne diseases. Research on lipid metabolism of plant disease vectors is up and coming and we end this chapter by highlighting current knowledge in that field.

Wolbachia modify host cell metabolite profiles in response to short-term temperature stress

Wolbachia are common heritable endosymbionts that influence many aspects of ecology and evolution in various insects, yet Wolbachia-mediated intracellular metabolic responses to temperature stress have been largely overlooked. Here, we introduced the Wolbachia strain wLhui from the invasive Liriomyza huidobrensis (Blanchard) into a Drosophila Schneider 2 cell line (S2) and investigated the metabolite profile of wLhui-infected (S2_wLhui) and uninfected cell lines (S2_wu) under short-term exposure to either high (37°C), moderate (27°C), or low (7 and 17°C) temperatures. We find that Wolbachia infection, temperature stress, and their interactions significantly affect cellular metabolic profiles. Most significantly, when comparing the changes in metabolites between S2_wLhui and S2_wu, glycerophospholipids, amino acids, and fatty acids associated with metabolic pathways, microbial metabolism in diverse environments, and other pathways were significantly accumulated at either low or high temperatures. Our findings suggest Wolbachia-induced cellular physiological responses to short-term temperature stress, which may in turn affect the fitness and adaptive ability of its host as an invasive species.

Long-term impacts of egg quiescence and Wolbachia infection on lipid profiles in Aedes aegypti: Ovarian roles in lipid synthesis during reproduction

Wolbachia, an endosymbiotic bacterium, relies on nutrients from its host to complete its life cycle. The presence of Wolbachia strain wAlbB in the mosquito Aedes aegypti during egg or larval stages affects the host's development, leading to the absence of developed and visible ovaries in adult mosquito females. In this study, we investigated the impacts of egg quiescence and Wolbachia infection on lipid profiles of adult Ae. aegypti females, and discerned the role of ovaries in lipid synthesis in the reproductive process. The lipidomes of Wolbachia infected and uninfected female individuals at various developmental stages were quantitatively analyzed by LC-MS/MS. Lipidomic change patterns were systematically further investigated in wAlbB-infected fertile females and infertile females following blood feeding. Prolonged egg quiescence induced a shortage of acyl-carnitine (CAR) and potentially impacted some molecules of diacyl-phospholipid (diacyl-PL) and sphingolipid (SL) in young adult mosquitoes. After the first gonotrophic cycle, infertile females accumulated more CAR and lyso-phospholipid (lyso-PL) than fertile females. Then in the second gonotrophic cycle, the patterns of different lipid groups remained similar between fertile and infertile females. Only a small proportion of molecules of triglyceride (TG), phospholipid (lyso-PL and diacyl-PL) and ceramide (Cer) increased exclusively in fertile females from 0 h to 16 h post blood meal, suggesting that the generation or prescence of these lipids rely on ovaries. In addition, we found cardiolipins (CL) might be impacted by Wolbachia infection at the egg stage, and infected mosquitoes also showed distinct patterns between fertile and infertile females at their second gonotrophic cycle. Our study provides new insights into the long-term influence of Wolbachia on lipid profiles throughout various life stages of mosquitoes. Additionally, it suggests a role played by ovaries in lipid synthesis during mosquito reproduction.

Multidimensional plasma lipid composition and its causal association with type 2 diabetes mellitus: A Mendelian randomization study

BACKGROUND AND AIM

Recent research extends our knowledge of plasma lipid species, building on established links between serum lipid levels and Type 2 Diabetes Mellitus (T2DM) risk. Identifying the causal roles of these lipid species is key to improving T2DM risk assessment.

METHODS AND RESULTS

This study employs Mendelian randomization (MR) to investigate the causal relationship between 179 lipid species across 13 lipid categories and T2DM. Summary-level data were sourced from genome-wide association studies. The primary analytical methods included the inverse variance weighted (IVW) approach and the Wald ratio, complemented by a series of sensitivity analyses to ensure the robustness of results. The IVW analysis reveals a significant causal association between elevated levels of ceramide (d40:2) (OR = 1.071, 95% CI 1.034-1.109, P = 1.36 × 10-4), sphingomyelin (d38:1) (OR = 1.052, 95% CI 1.028-1.077, P = 1.80 × 10-5), and triacylglycerol (56:8) (OR = 1.174, 95% CI 1.108-1.243, P = 4.65 × 10-8), and an increased risk of T2DM. Conversely, Wald ratio analysis indicates that higher levels of phosphatidylcholine (O-16:1_16:0) (OR = 0.928, 95% CI 0.892-0.966, P = 2.37 × 10-4), phosphatidylcholine (O-16:1_20:4) (OR = 0.932, 95% CI 0.897-0.967, P = 2.37 × 10-4), and phosphatidylcholine (O-18:2_20:4) (OR = 0.872, 95% CI 0.812-0.935, P = 1.24 × 10-4) are significantly associated with a reduced risk of T2DM. Furthermore, suggestive causal evidence for 22 additional lipid species was identified.

CONCLUSIONS

This MR study establishes a causal relationship between specific lipid classes in modulating the risk of T2DM. It offers new insights for risk assessment and potential therapeutic targets in T2DM.

A comprehensive review of Wolbachia-mediated mechanisms to control dengue virus transmission in Aedes aegypti through innate immune pathways

The Dengue virus (DENV), primarily spread by Aedes aegypti and also by Aedes albopictus in some regions, poses significant global health risks. Alternative techniques are urgently needed because the current control mechanisms are insufficient to reduce the transmission of DENV. Introducing Wolbachia pipientis into Ae. aegypti inhibits DENV transmission, however, the underlying mechanisms are still poorly understood. Innate immune effector upregulation, the regulation of autophagy, and intracellular competition between Wolbachia and DENV for lipids are among the theories for the mechanism of inhibition. Furthermore, mainly three immune pathways Toll, IMD, and JAK/STAT are involved in the host for the suppression of the virus. These pathways are activated by Wolbachia and DENV in the host and are responsible for the upregulation and downregulation of many genes in mosquitoes, which ultimately reduces the titer of the DENV in the host. The functioning of these immune pathways depends upon the Wolbachia, host, and virus interaction. Here, we summarize the current understanding of DENV recognition by the Ae. aegypti's immune system, aiming to create a comprehensive picture of our knowledge. Additionally, we investigated how Wolbachia regulates the activation of multiple genes associated with immune priming for the reduction of DENV.

A Structural Proteome Screen Identifies Protein Mimicry in Host-Microbe Systems

Host-microbe systems are evolutionary niches that produce coevolved biological interactions and are a key component of global health. However, these systems have historically been a difficult field of biological research due to their experimental intractability. Impactful advances in global health will be obtained by leveraging in silico screens to identify genes involved in mediating interspecific interactions. These predictions will progress our understanding of these systems and lay the groundwork for future in vitro and in vivo experiments and bioengineering projects. A driver of host-manipulation and intracellular survival utilized by host-associated microbes is molecular mimicry, a critical mechanism that can occur at any level from DNA to protein structures. We applied protein structure prediction and alignment tools to explore host-associated bacterial structural proteomes for examples of protein structure mimicry. By leveraging the Legionella pneumophila proteome and its many known structural mimics, we developed and validated a screen that can be applied to virtually any host-microbe system to uncover signals of protein mimicry. These mimics represent candidate proteins that mediate host interactions in microbial proteomes. We successfully applied this screen to other microbes with demonstrated effects on global health, Helicobacter pylori and Wolbachia , identifying protein mimic candidates in each proteome. We discuss the roles these candidates may play in important Wolbachia -induced phenotypes and show that Wobachia infection can partially rescue the loss of one of these factors. This work demonstrates how a genome-wide screen for candidates of host-manipulation and intracellular survival offers an opportunity to identify functionally important genes in host-microbe systems.

Antiviral Wolbachia strains associate with Aedes aegypti endoplasmic reticulum membranes and induce lipid droplet formation to restrict dengue virus replication

Wolbachia are a genus of insect endosymbiotic bacteria which includes strains wMel and wAlbB that are being utilized as a biocontrol tool to reduce the incidence of Aedes aegypti-transmitted viral diseases like dengue. However, the precise mechanisms underpinning the antiviral activity of these Wolbachia strains are not well defined. Here, we generated a panel of Ae. aegypti-derived cell lines infected with antiviral strains wMel and wAlbB or the non-antiviral Wolbachia strain wPip to understand host cell morphological changes specifically induced by antiviral strains. Antiviral strains were frequently found to be entirely wrapped by the host endoplasmic reticulum (ER) membrane, while wPip bacteria clustered separately in the host cell cytoplasm. ER-derived lipid droplets (LDs) increased in volume in wMel- and wAlbB-infected cell lines and mosquito tissues compared to cells infected with wPip or Wolbachia-free controls. Inhibition of fatty acid synthase (required for triacylglycerol biosynthesis) reduced LD formation and significantly restored ER-associated dengue virus replication in cells occupied by wMel. Together, this suggests that antiviral Wolbachia strains may specifically alter the lipid composition of the ER to preclude the establishment of dengue virus (DENV) replication complexes. Defining Wolbachia's antiviral mechanisms will support the application and longevity of this effective biocontrol tool that is already being used at scale.IMPORTANCEAedes aegypti transmits a range of important human pathogenic viruses like dengue. However, infection of Ae. aegypti with the insect endosymbiotic bacterium, Wolbachia, reduces the risk of mosquito to human viral transmission. Wolbachia is being utilized at field sites across more than 13 countries to reduce the incidence of viruses like dengue, but it is not well understood how Wolbachia induces its antiviral effects. To examine this at the subcellular level, we compared how different strains of Wolbachia with varying antiviral strengths associate with and modify host cell structures. Strongly antiviral strains were found to specifically associate with the host endoplasmic reticulum and induce striking impacts on host cell lipid droplets. Inhibiting Wolbachia-induced lipid redistribution partially restored dengue virus replication demonstrating this is a contributing role for Wolbachia's antiviral activity. These findings provide new insights into how antiviral Wolbachia strains associate with and modify Ae. aegypti host cells.

Wolbachia interferes with Zika virus replication by hijacking cholesterol metabolism in mosquito cells

IMPORTANCE

Arthropod-borne viruses are emerging pathogens that are spread widely by mosquitos. Zika virus is an arbovirus that can infect humans and be transmitted from an infected mother to the fetus, potentially leading to microcephaly in infants. One promising strategy to prevent disease caused by arboviruses is to target the insect vector population. Recent field studies have shown that mosquito populations infected with Wolbachia bacteria suppress arbovirus replication and transmission. Here, we describe how intracellular bacteria redirect resources within their host cells and suppress Zika virus replication at the cellular level. Understanding the mechanism behind Wolbachia-induced interference of arbovirus replication could help advance strategies to control arbovirus pathogens in insect vectors and human populations.

The endosymbiotic bacterium Wolbachia (Rickettsiales) alters larval metabolism of the parasitoid Habrobracon hebetor (Hymenoptera: Braconidae)

Infection of intestinal tissues with Wolbachia has been found in Habrobracon hebetor. There are not many studies on the relationship between Habrobracon and Wolbachia, and they focus predominantly on the sex index of an infected parasitoid, its fertility, and behavior. The actual role of Wolbachia in the biology of Habrobracon is not yet clear. The method of complete eradication of Wolbachia in the parasitoid was developed here, and effects of the endosymbiont on the host's digestive metabolism were compared between two lines of the parasitoid (Wolbachia-positive and Wolbachia-negative). In the gut of Wolbachia+ larvae, lipases' activity was higher almost twofold, and activities of acid proteases, esterases, and trehalase were 1.5-fold greater than those in the Wolbachia- line. Analyses of larval homogenates revealed that Wolbachia+ larvae accumulate significantly more lipids and have a lower amount of pyruvate as compared to Wolbachia- larvae. The presented results indicate significant effects of the intracellular symbiotic bacterium Wolbachia on the metabolism of H. hebetor larvae and on the activity of its digestive enzymes.

Patterns of Variation in the Usage of Fatty Acid Chains among Classes of Ester and Ether Neutral Lipids and Phospholipids in the Queensland Fruit Fly

Modern lipidomics has the power and sensitivity to elucidate the role of insects' lipidomes in their adaptations to the environment at a mechanistic molecular level. However, few lipidomic studies have yet been conducted on insects beyond model species such as Drosophila melanogaster. Here, we present the lipidome of adult males of another higher dipteran frugivore, Bactrocera tryoni. We describe 421 lipids across 15 classes of ester neutral lipids and phospholipids and ether neutral lipids and phospholipids. Most of the lipids are specified in terms of the carbon and double bond contents of each constituent hydrocarbon chain, and more ether lipids are specified to this degree than in any previous insect lipidomic analyses. Class-specific profiles of chain length and (un)saturation are broadly similar to those reported in D. melanogaster, although we found fewer medium-length chains in ether lipids. The high level of chain specification in our dataset also revealed widespread non-random combinations of different chain types in several ester lipid classes, including deficits of combinations involving chains of the same carbon and double bond contents among four phospholipid classes and excesses of combinations of dissimilar chains in several classes. Large differences were also found in the length and double bond profiles of the acyl vs. alkyl or alkenyl chains of the ether lipids. Work on other organisms suggests some of the differences observed will be functionally consequential and mediated, at least in part, by differences in substrate specificity among enzymes in lipid synthesis and remodelling pathways. Interrogation of the B. tryoni genome showed it has comparable levels of diversity overall in these enzymes but with some gene gain/loss differences and considerable sequence divergence from D. melanogaster.

Impact of the microbiome on mosquito-borne diseases

Mosquito-borne diseases present a significant threat to human health, with the possibility of outbreaks of new mosquito-borne diseases always looming. Unfortunately, current measures to combat these diseases such as vaccines and drugs are often either unavailable or ineffective. However, recent studies on microbiomes may reveal promising strategies to fight these diseases. In this review, we examine recent advances in our understanding of the effects of both the mosquito and vertebrate microbiomes on mosquito-borne diseases. We argue that the mosquito microbiome can have direct and indirect impacts on the transmission of these diseases, with mosquito symbiotic microorganisms, particularly Wolbachia bacteria, showing potential for controlling mosquito-borne diseases. Moreover, the skin microbiome of vertebrates plays a significant role in mosquito preferences, while the gut microbiome has an impact on the progression of mosquito-borne diseases in humans. As researchers continue to explore the role of microbiomes in mosquito-borne diseases, we highlight some promising future directions for this field. Ultimately, a better understanding of the interplay between mosquitoes, their hosts, pathogens, and the microbiomes of mosquitoes and hosts may hold the key to preventing and controlling mosquito-borne diseases.

Wolbachia enhances the survival of Drosophila infected with fungal pathogens

Wolbachia bacteria of arthropods are at the forefront of basic and translational research on multipartite host-symbiont-pathogen interactions. These microbes are vertically inherited from mother to offspring via the cytoplasm. They are the most widespread endosymbionts on the planet due to their infamous ability to manipulate the reproduction of their hosts to spread themselves in a population, and to provide a variety of fitness benefits to their hosts. Importantly, some strains of Wolbachia can inhibit viral pathogenesis within and between arthropod hosts. Mosquitoes carrying the wMel Wolbachia strain of Drosophila melanogaster have a greatly reduced capacity to spread viruses like dengue and Zika to humans. Therefore, Wolbachia are the basis of several global vector control initiatives. While significant research efforts have focused on viruses, relatively little attention has been given to Wolbachia-fungal interactions despite the ubiquity of fungal entomopathogens in nature. Here, we demonstrate that Wolbachia increase the longevity of their Drosophila melanogaster hosts when challenged with a spectrum of yeast and filamentous fungal pathogens. We find that this pattern can vary based on host genotype, sex, and fungal species. Further, Wolbachia correlates with higher fertility and reduced pathogen titers during initial fungal infection, indicating a significant fitness benefit. This study demonstrates Wolbachia's role in diverse fungal pathogen interactions and determines that the phenotype is broad, but with several variables that influence both the presence and strength of the phenotype. These results enhance our knowledge of the strategies Wolbachia uses that likely contribute to such a high global symbiont prevalence.

Wolbachia-mediated resistance to Zika virus infection in Aedes aegypti is dominated by diverse transcriptional regulation and weak evolutionary pressures

A promising candidate for arbovirus control and prevention relies on replacing arbovirus-susceptible Aedes aegypti populations with mosquitoes that have been colonized by the intracellular bacterium Wolbachia and thus have a reduced capacity to transmit arboviruses. This reduced capacity to transmit arboviruses is mediated through a phenomenon referred to as pathogen blocking. Pathogen blocking has primarily been proposed as a tool to control dengue virus (DENV) transmission, however it works against a range of viruses, including Zika virus (ZIKV). Despite years of research, the molecular mechanisms underlying pathogen blocking still need to be better understood. Here, we used RNA-seq to characterize mosquito gene transcription dynamics in Ae. aegypti infected with the wMel strain of Wolbachia that are being released by the World Mosquito Program in Medellín, Colombia. Comparative analyses using ZIKV-infected, uninfected tissues, and mosquitoes without Wolbachia revealed that the influence of wMel on mosquito gene transcription is multifactorial. Importantly, because Wolbachia limits, but does not completely prevent, replication of ZIKV and other viruses in coinfected mosquitoes, there is a possibility that these viruses could evolve resistance to pathogen blocking. Therefore, to understand the influence of Wolbachia on within-host ZIKV evolution, we characterized the genetic diversity of molecularly barcoded ZIKV virus populations replicating in Wolbachia-infected mosquitoes and found that within-host ZIKV evolution was subject to weak purifying selection and, unexpectedly, loose anatomical bottlenecks in the presence and absence of Wolbachia. Together, these findings suggest that there is no clear transcriptional profile associated with Wolbachia-mediated ZIKV restriction, and that there is no evidence for ZIKV escape from this restriction in our system.

Microbiota in disease-transmitting vectors

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

Differences in proteome perturbations caused by the Wolbachia strain wAu suggest multiple mechanisms of Wolbachia-mediated antiviral activity

Some strains of the inherited bacterium Wolbachia have been shown to be effective at reducing the transmission of dengue virus (DENV) and other RNA viruses by Aedes aegypti in both laboratory and field settings and are being deployed for DENV control. The degree of virus inhibition varies between Wolbachia strains. Density and tissue tropism can contribute to these differences but there are also indications that this is not the only factor involved: for example, strains wAu and wAlbA are maintained at similar intracellular densities but only wAu produces strong DENV inhibition. We previously reported perturbations in lipid transport dynamics, including sequestration of cholesterol in lipid droplets, with strains wMel/wMelPop in Ae. aegypti. To further investigate the cellular basis underlying these differences, proteomic analysis of midguts was carried out on Ae. aegypti lines carrying strains wAu and wAlbA: with the hypothesis that differences in perturbations may underline Wolbachia-mediated antiviral activity. Surprisingly, wAu-carrying midguts not only showed distinct proteome perturbations when compared to non-Wolbachia carrying and wAlbA-carrying midguts but also wMel-carrying midguts. There are changes in RNA processing pathways and upregulation of a specific set of RNA-binding proteins in the wAu-carrying line, including genes with known antiviral activity. Lipid transport and metabolism proteome changes also differ between strains, and we show that strain wAu does not produce the same cholesterol sequestration phenotype as wMel. Moreover, in contrast to wMel, wAu antiviral activity was not rescued by cyclodextrin treatment. Together these results suggest that wAu could show unique features in its inhibition of arboviruses compared to previously characterized Wolbachia strains.

Wolbachia -mediated resistance to Zika virus infection in Aedes aegypti is dominated by diverse transcriptional regulation and weak evolutionary pressures

A promising candidate for arbovirus control and prevention relies on replacing arbovirus-susceptible Aedes aegypti populations with mosquitoes that have been colonized by the intracellular bacterium Wolbachia and thus have a reduced capacity to transmit arboviruses. This reduced capacity to transmit arboviruses is mediated through a phenomenon referred to as pathogen blocking. Pathogen blocking has primarily been proposed as a tool to control dengue virus (DENV) transmission, however it works against a range of viruses, including Zika virus (ZIKV). Despite years of research, the molecular mechanisms underlying pathogen blocking still need to be better understood. Here, we used RNA-seq to characterize mosquito gene transcription dynamics in Ae. aegypti infected with the w Mel strain of Wolbachia that are being released by the World Mosquito Program in Medellín, Colombia. Comparative analyses using ZIKV-infected, uninfected tissues, and mosquitoes without Wolbachia revealed that the influence of w Mel on mosquito gene transcription is multifactorial. Importantly, because Wolbachia limits, but does not completely prevent, replication of ZIKV and other viruses in coinfected mosquitoes, there is a possibility that these viruses could evolve resistance to pathogen blocking. Therefore, to understand the influence of Wolbachia on within-host ZIKV evolution, we characterized the genetic diversity of molecularly barcoded ZIKV virus populations replicating in Wolbachia -infected mosquitoes and found that within-host ZIKV evolution was subject to weak purifying selection and, unexpectedly, loose anatomical bottlenecks in the presence and absence of Wolbachia . Together, these findings suggest that there is no clear transcriptional profile associated with Wolbachia -mediated ZIKV restriction, and that there is no evidence for ZIKV escape from this restriction in our system.

Author Summary

When Wolbachia bacteria infect Aedes aegypti mosquitoes, they dramatically reduce the mosquitoes' susceptibility to infection with a range of arthropod-borne viruses, including Zika virus (ZIKV). Although this pathogen-blocking effect has been widely recognized, its mechanisms remain unclear. Furthermore, because Wolbachia limits, but does not completely prevent, replication of ZIKV and other viruses in coinfected mosquitoes, there is a possibility that these viruses could evolve resistance to Wolbachia -mediated blocking. Here, we use host transcriptomics and viral genome sequencing to examine the mechanisms of ZIKV pathogen blocking by Wolbachia and viral evolutionary dynamics in Ae. aegypti mosquitoes. We find complex transcriptome patterns that do not suggest a single clear mechanism for pathogen blocking. We also find no evidence that Wolbachia exerts detectable selective pressures on ZIKV in coinfected mosquitoes. Together our data suggest that it may be difficult for ZIKV to evolve Wolbachia resistance, perhaps due to the complexity of the pathogen blockade mechanism.

Ovarian transcriptional response to Wolbachia infection in D. melanogaster in the context of between-genotype variation in gene expression

Wolbachia is a maternally transmitted endosymbiotic bacteria that infects a wide variety of arthropod and nematode hosts. The effects of Wolbachia on host biology are far-reaching and include changes in host gene expression. However, previous work on the host transcriptional response has generally been investigated in the context of a single host genotype. Thus, the relative effect of Wolbachia infection versus vs. host genotype on gene expression is unknown. Here, we explicitly test the relative roles of Wolbachia infection and host genotype on host gene expression by comparing the ovarian transcriptomes of 4 strains of Drosophila melanogaster (D. melanogaster) infected and uninfected with Wolbachia. Our data suggest that infection explains a small amount of transcriptional variation, particularly in comparison to variation in gene expression among strains. However, infection specifically affects genes related to cell cycle, translation, and metabolism. We also find enrichment of cell division and recombination processes among genes with infection-associated differential expression. Broadly, the transcriptomic changes identified in this study provide novel understanding of the relative magnitude of the effect of Wolbachia infection on gene expression in the context of host genetic variation and also point to genes that are consistently differentially expressed in response to infection among multiple genotypes.

Wolbachia-Virus interactions and arbovirus control through population replacement in mosquitoes

Following transfer into the primary arbovirus vector Aedes aegypti, several strains of the intracellular bacterium Wolbachia have been shown to inhibit the transmission of dengue, Zika, and chikungunya viruses, important human pathogens that cause significant morbidity and mortality worldwide. In addition to pathogen inhibition, many Wolbachia strains manipulate host reproduction, resulting in an invasive capacity of the bacterium in insect populations. This has led to the deployment of Wolbachia as a dengue control tool, and trials have reported significant reductions in transmission in release areas. Here, we discuss the possible mechanisms of Wolbachia-virus inhibition and the implications for long-term success of dengue control. We also consider the evidence presented in several reports that Wolbachia may cause an enhancement of replication of certain viruses under particular conditions, and conclude that these should not cause any concerns with respect to the application of Wolbachia to arbovirus control.

The buzz in the field: the interaction between viruses, mosquitoes, and metabolism

Among many medically important pathogens, arboviruses like dengue, Zika and chikungunya cause severe health and economic burdens especially in developing countries. These viruses are primarily vectored by mosquitoes. Having surmounted geographical barriers and threat of control strategies, these vectors continue to conquer many areas of the globe exposing more than half of the world's population to these viruses. Unfortunately, no medical interventions have been capable so far to produce successful vaccines or antivirals against many of these viruses. Thus, vector control remains the fundamental strategy to prevent disease transmission. The long-established understanding regarding the replication of these viruses is that they reshape both human and mosquito host cellular membranes upon infection for their replicative benefit. This leads to or is a result of significant alterations in lipid metabolism. Metabolism involves complex chemical reactions in the body that are essential for general physiological functions and survival of an organism. Finely tuned metabolic homeostases are maintained in healthy organisms. However, a simple stimulus like a viral infection can alter this homeostatic landscape driving considerable phenotypic change. Better comprehension of these mechanisms can serve as innovative control strategies against these vectors and viruses. Here, we review the metabolic basis of fundamental mosquito biology and virus-vector interactions. The cited work provides compelling evidence that targeting metabolism can be a paradigm shift and provide potent tools for vector control as well as tools to answer many unresolved questions and gaps in the field of arbovirology.

Differences in gene expression in field populations of Wolbachia-infected Aedes aegypti mosquitoes with varying release histories in northern Australia

Aedes aegypti is the principal mosquito vector of dengue, yellow fever, Zika and chikungunya viruses. The wMel strain of the endosymbiotic bacteria Wolbachia pipientis was introduced into the vector as a novel biocontrol strategy to stop transmission of these viruses. Mosquitoes with Wolbachia have been released in the field in Northern Queensland, Australia since 2011, at various locations and over several years, with populations remaining stably infected. Wolbachia infection is known to alter gene expression in its mosquito host, but whether (and how) this changes over the long-term in the context of field releases remains unknown. We sampled mosquitoes from Wolbachia-infected populations with three different release histories along a time gradient and performed RNA-seq to investigate gene expression changes in the insect host. We observed a significant impact on gene expression in Wolbachia-infected mosquitoes versus uninfected controls. Fewer genes had significantly upregulated expression in mosquitoes from the older releases (512 and 486 from the 2011 and 2013/14 release years, respectively) versus the more recent releases (1154 from the 2017 release year). Nonetheless, a fundamental signature of Wolbachia infection on host gene expression was observed across all releases, comprising upregulation of immunity (e.g. leucine-rich repeats, CLIPs) and metabolism (e.g. lipid metabolism, iron transport) genes. There was limited downregulation of gene expression in mosquitoes from the older releases (84 and 71 genes from the 2011 and 2013/14 release years, respectively), but significantly more in the most recent release (509 from the 2017 release year). Our findings indicate that at > 8 years post-introgression into field populations, Wolbachia continues to profoundly impact expression of host genes, such as those involved in insect immune response and metabolism. If Wolbachia-mediated virus blocking is underpinned by these differential gene expression changes, our results suggest it may remain stable long-term.

Toward novel treatment against filariasis: Insight into genome-wide co-evolutionary analysis of filarial nematodes and Wolbachia

Infectious diseases caused by filarial nematodes are major health problems for humans and animals globally. Current treatment using anti-helminthic drugs requires a long treatment period and is only effective against the microfilarial stage. Most species of filarial nematodes harbor a specific strain of Wolbachia bacteria, which are essential for the survival, development, and reproduction of the nematodes. This parasite-bacteria obligate symbiosis offers a new angle for the cure of filariasis. In this study, we utilized publicly available genome data and putative protein sequences from seven filarial nematode species and their symbiotic Wolbachia to screen for protein-protein interactions that could be a novel target against multiple filarial nematode species. Genome-wide in silico screening was performed to predict molecular interactions based on co-evolutionary signals. We identified over 8,000 pairs of gene families that show evidence of co-evolution based on high correlation score and low false discovery rate (FDR) between gene families and obtained a candidate list that may be keys in filarial nematode-Wolbachia interactions. Functional analysis was conducted on these top-scoring pairs, revealing biological processes related to various signaling processes, adult lifespan, developmental control, lipid and nucleotide metabolism, and RNA modification. Furthermore, network analysis of the top-scoring genes with multiple co-evolving pairs suggests candidate genes in both Wolbachia and the nematode that may play crucial roles at the center of multi-gene networks. A number of the top-scoring genes matched well to known drug targets, suggesting a promising drug-repurposing strategy that could be applicable against multiple filarial nematode species.

Analysing inhibition of dengue virus in Wolbachia-infected mosquito cells following the removal of Wolbachia

Wolbachia pipientis is known to block replication of positive sense RNA viruses. Previously, we created an Aedes aegypti Aag2 cell line (Aag2.wAlbB) transinfected with the wAlbB strain of Wolbachia and a matching tetracycline-cured Aag2.tet cell line. While dengue virus (DENV) was blocked in Aag2.wAlbB cells, we found significant inhibition of DENV in Aag2.tet cells. RNA-Seq analysis of the cells confirmed removal of Wolbachia and lack of expression of Wolbachia genes that could have been due to lateral gene transfer in Aag2.tet cells. However, we noticed a substantial increase in the abundance of phasi charoen-like virus (PCLV) in Aag2.tet cells. When RNAi was used to reduce the PCLV levels, DENV replication was significantly increased. Further, we found significant changes in the expression of antiviral and proviral genes in Aag2.tet cells. Overall, the results reveal an antagonistic interaction between DENV and PCLV and how PCLV-induced changes could contribute to DENV inhibition.

Diversity and dynamics of endosymbionts in a single population of sweet potato weevil, Cylas formicarius (Coleoptera: Brentidae): a preliminary study

Endosymbionts live symbiotically with insect hosts and play important roles in the evolution, growth, development, reproduction, and environmental fitness of hosts. Weevils are one of the most abundant insect groups that can be infected by various endosymbionts, such as Sodalis, Nardonella, and Wolbachia. The sweet potato weevil, Cylas formicarius (Coleoptera: Brentidae), is a notorious pest in sweet potato (Ipomoea batatas L.) cultivation. Currently, little is known about the presence of endosymbionts in C. formicarius. Herein, we assessed the endosymbiont load of a single geographic population of C. formicarius. The results showed that Nardonella and Rickettsia could infect C. formicarius at different rates, which also varied according to the developmental stages of C. formicarius. The relative titer of Nardonella was significantly related to C. formicarius developmental stages. The Nardonella-infecting sweet potato weevils were most closely related to the Nardonella in Sphenophorus levis (Coleoptera, Curculionidae). The Rickettsia be identified in bellii group. These results preliminarily revealed the endosymbionts in C. formicarius and helped to explore the diversity of endosymbionts in weevils and uncover the physiological roles of endosymbionts in weevils.

Targeting Aedes aegypti Metabolism with Next-Generation Insecticides

Aedes aegypti is the primary vector of dengue virus (DENV), zika virus (ZIKV), and other emerging infectious diseases of concern. A key disease mitigation strategy is vector control, which relies heavily on the use of insecticides. The development of insecticide resistance poses a major threat to public health worldwide. Unfortunately, there is a limited number of chemical compounds available for vector control, and these chemicals can have off-target effects that harm invertebrate and vertebrate species. Fundamental basic science research is needed to identify novel molecular targets that can be exploited for vector control. Next-generation insecticides will have unique mechanisms of action that can be used in combination to limit selection of insecticide resistance. Further, molecular targets will be species-specific and limit off-target effects. Studies have shown that mosquitoes rely on key nutrients during multiple life cycle stages. Targeting metabolic pathways is a promising direction that can deprive mosquitoes of nutrition and interfere with development. Metabolic pathways are also important for the virus life cycle. Here, we review studies that reveal the importance of dietary and stored nutrients during mosquito development and infection and suggest strategies to identify next-generation insecticides with a focus on trehalase inhibitors.

Wolbachia RNase HI contributes to virus blocking in the mosquito Aedes aegypti

The endosymbiotic bacterium Wolbachia pipientis blocks replication of several arboviruses in transinfected Aedes aegypti mosquitoes. However, the mechanism of virus blocking remains poorly understood. Here, we characterized an RNase HI gene from Wolbachia, which is rapidly induced in response to dengue virus (DENV) infection. Knocking down w RNase HI using antisense RNA in Wolbachia-transinfected mosquito cell lines and A. aegypti mosquitoes led to increased DENV replication. Furthermore, overexpression of wRNase HI, in the absence of Wolbachia, led to reduced replication of a positive sense RNA virus, but had no effect on a negative sense RNA virus, a familiar scenario in Wolbachia-infected cells. Altogether, our results provide compelling evidence for the missing link between early Wolbachia-mediated virus blocking and degradation of viral RNA. These findings and the successful pioneered knockdown of Wolbachia genes using antisense RNA in cell line and mosquitoes enable new ways to manipulate and study the complex endosymbiont-host interactions.

The Involvement of Atlastin in Dengue Virus and Wolbachia Infection in Aedes aegypti and Its Regulation by aae-miR-989

Endoplasmic reticulum (ER)-shaping atlastin proteins (ATLs) have been demonstrated to play a functional role during flavivirus replication in mammalian cells. For dengue virus (DENV), atlastin is required in the formation of the replication organelles and RNA replication, virion assembly, production of the infectious virus particles, and trafficking or directing the association of vesicle packets with furin. Here, we investigated the involvement of atlastin in DENV replication in the mosquito Aedes aegypti and explored the possibility of its manipulation by the endosymbiotic bacterium Wolbachia to interfere with DENV replication. Results showed the expression of Ae. aegypti atlastin gene (AaATL) was upregulated in DENV-infected Aag2 cells, and its silencing led to reduced DENV replication. Contrary to our assumption that AaATL could be downregulated by Wolbachia, we did not find evidence for that in Wolbachia-infected cell lines, but this was the case in mosquitoes. Further, silencing AaATL did not have any effect on Wolbachia density. Our results also suggest that aae-miR-989 miRNA negatively regulates AaATL. The oversupply of the miRNA mimic led to reduced DENV replication consistent with the positive role of AaATL in DENV replication. Overall, the results favor AaATL's involvement in DENV replication; however, there is no support that the protein is involved in Wolbachia-mediated DENV inhibition. In addition, the results contribute to discerning further possible overlapping functions of ATLs in mosquitoes and mammalian cells. IMPORTANCE Atlastin is a protein associated with the endoplasmic reticulum and has been shown to play a role in replication of flaviviruses in mammalian cells. This study aimed to investigate the role of mosquito Aedes aegypti atlastin (AaATL) in dengue virus replication and maintenance of Wolbachia, an endosymbiotic bacterium, in the mosquito. Our results suggest that AaATL facilitates dengue virus replication in mosquito cells, considering silencing the gene led to reductions in virus replication and virion production. Further, AaATL was found to be regulated by a mosquito microRNA, aae-miR-989. Despite an effect on dengue virus, AaATL silencing did not affect Wolbachia replication and maintenance in mosquito cells. The results shed light on the role of atlastins in mosquito-pathogen interactions and their overlapping roles in mosquito and mammalian cells.

Chronic depletion of vertebrate lipids in Aedes aegypti cells dysregulates lipid metabolism and inhibits innate immunity without altering dengue infectivity

Aedes aegypti is the primary vector of dengue virus (DENV) and other arboviruses. Previous literature suggests that vertebrate and invertebrate lipids and the nutritional status of mosquitoes modify virus infection. Here, we developed a vertebrate lipid-depleted Ae. aegypti cell line to investigate if chronic depletion of vertebrate lipids normally present in a blood meal and insect cell culture medium would impact cell growth and virus infection. Chronic depletion of vertebrate lipids reduced cell size and proliferation, although cells retained equivalent total intracellular lipids per cell by reducing lipolysis and modifying gene expression related to sugar and lipid metabolism. Downregulation of innate immunity genes was also observed. We hypothesized that chronic depletion of vertebrate lipids would impact virus infection; however, the same amount of DENV was produced per cell. This study reveals how Ae. aegypti cells adapt in the absence of vertebrate lipids, and how DENV can replicate equally well in cells that contain predominately vertebrate or invertebrate lipids.

Aedes aegypti is a major threat to public health. Ae. aegypti is the primary vector of dengue virus types 1–4 (DENV 1–4), zika virus (ZIKV), chikungunya virus (CHIKV), and yellow fever virus (YFV). Ae. aegypti acquires arboviruses from a vertebrate host during blood feeding. Blood feeding introduces vertebrate-specific factors into the mosquito that may be important for both mosquito and virus. This study reveals that Ae. aegypti adapts to depletion of vertebrate lipids by inhibiting lipolysis and promoting de novo synthesis of invertebrate lipids, and that DENV can replicate equally well without high concentrations of cholesterol and other vertebrate lipid species. Understanding how disease vectors adapt to nutritional changes will identify novel strategies for vector control and disease mitigation.

Endosymbionts Reduce Microbiome Diversity and Modify Host Metabolism and Fecundity in the Planthopper Sogatella furcifera

Endosymbionts can strongly affect bacterial microbiota in pests. The white-backed planthopper Sogatella furcifera, a notorious pest in rice, is usually co-infected with Cardinium and Wolbachia, but the effects of these endosymbionts together or individually on the host microbiome and fecundity are unclear. Here, we established three S. furcifera lines (Cardinium and Wolbachia double-infected, Cardinium single-infected, and both-uninfected lines) backcrossed to a common nuclear background and found that single and double infections reduced bacterial diversity and changed bacterial community structure across nymph and adult stages and across adult tissues. The endosymbionts differed in densities between adults and nymphs as well as across adult tissues, with the distribution of Cardinium affected by Wolbachia. Both the single infection and particularly the double infection reduced host fecundity. Lines also differed in levels of metabolites, some of which may influence fecundity (e.g., arginine biosynthesis and nicotinamide metabolism). Cardinium in the single-infected line upregulated metabolic levels, while Wolbachia in the double-infected line appeared to mainly downregulate them. Association analysis pointed to possible connections between various bacteria and differential metabolites. These results reveal that Cardinium by itself and in combination with Wolbachia affect bacterial microbiota and levels of metabolites, with likely effects on host fecundity. Many of the effects of these metabolically limited endosymbionts that are dependent on the hosts may be exerted through manipulation of the microbiome.

IMPORTANCE Endosymbionts can profoundly affect the nutrition, immunity, development, and reproduction of insect hosts, but the effects of multiple endosymbiont infections on microbiota and the interaction of these effects with insect host fitness are not well known. By establishing S. furcifera lines with different endosymbiont infection status, we found that Cardinium and the combined Cardinium + Wolbachia infections differentially reduced bacterial diversity as well as changing bacterial community structure and affecting metabolism, which may connect to negative fitness effects of the endosymbionts on their host. These results established the connections between reduced bacterial diversity, decreased fecundity and metabolic responses in S. furcifera.

Production, Transmission, Pathogenesis, and Control of Dengue Virus: A Literature-Based Undivided Perspective

Dengue remains one of the most serious and widespread mosquito-borne viral infections in human beings, with serious health problems or even death. About 50 to 100 million people are newly infected annually, with almost 2.5 billion people living at risk and resulting in 20,000 deaths. Dengue virus infection is especially transmitted through bites of Aedes mosquitos, hugely spread in tropical and subtropical environments, mostly found in urban and semiurban areas. Unfortunately, there is no particular therapeutic approach, but prevention, adequate consciousness, detection at earlier stage of viral infection, and appropriate medical care can lower the fatality rates. This review offers a comprehensive view of production, transmission, pathogenesis, and control measures of the dengue virus and its vectors.

Impacts of fungal entomopathogens on survival and immune responses of Aedes albopictus and Culex pipiens mosquitoes in the context of native Wolbachia infections

Microbial control of mosquitoes via the use of symbiotic or pathogenic microbes, such as Wolbachia and entomopathogenic fungi, are promising alternatives to synthetic insecticides to tackle the rapid increase in insecticide resistance and vector-borne disease outbreaks. This study evaluated the susceptibility and host responses of two important mosquito vectors, Ae. albopictus and Cx. pipiens, that naturally carry Wolbachia, to infections by entomopathogenic fungi. Our study indicated that while Wolbachia presence did not provide a protective advantage against entomopathogenic fungal infection, it nevertheless influenced the bacterial / fungal load and the expression of select anti-microbial effectors and phenoloxidase cascade genes in mosquitoes. Furthermore, although host responses from Ae. albopictus and Cx. pipiens were mostly similar, we observed contrasting phenotypes with regards to susceptibility and immune responses to fungal entomopathogenic infection in these two mosquitoes. This study provides new insights into the intricate multipartite interaction between the mosquito host, its native symbiont and pathogenic microbes that might be employed to control mosquito populations.

Control of mosquitoes via the use of microbes is a promising alternative to synthetic insecticides and a potential solution to tackle the rapid evolution of insecticide resistance in mosquitoes. Recently, a parasitic microbe named Wolbachia has been found to render the mosquito resistant to virus infections and it is currently showing great promise in reducing dengue cases on tests conducted in the field. On the other side of the symbiotic spectrum, we have entomopathogenic fungi, who have evolved to naturally infect and kill insects, and offer a unique potential to control mosquito populations. In this study, we examined the effect that native Wolbachia can have on the mosquito susceptibility to fungal entomopathogens. Our findings show that while Wolbachia does not affect the action of entomopathogenic fungi on mosquitoes, it does influence the expression of important mosquito immune genes, suggesting that Wolbachia has a closer interaction with the mosquito response to microbial infections than previously reported. Furthermore, our study provides new records on the susceptibility of two important mosquito vectors in the USA (Aedes albopictus and Culex pipiens), with Cx. pipiens showing significant resistance to the action of one fungal entomopathogen tested. This article informs on the mosquito susceptibility and interaction with other microbes that will aid in the selection of fungal entomopathogens to control mosquitoes, especially those that carry native microbes such as Wolbachia.

Molecular Rationale of Insect-Microbes Symbiosis-From Insect Behaviour to Mechanism

Insects nurture a panoply of microbial populations that are often obligatory and exist mutually with their hosts. Symbionts not only impact their host fitness but also shape the trajectory of their phenotype. This co-constructed niche successfully evolved long in the past to mark advanced ecological specialization. The resident microbes regulate insect nutrition by controlling their host plant specialization and immunity. It enhances the host fitness and performance by detoxifying toxins secreted by the predators and abstains them. The profound effect of a microbial population on insect physiology and behaviour is exploited to understand the host–microbial system in diverse taxa. Emergent research of insect-associated microbes has revealed their potential to modulate insect brain functions and, ultimately, control their behaviours, including social interactions. The revelation of the gut microbiota–brain axis has now unravelled insects as a cost-effective potential model to study neurodegenerative disorders and behavioural dysfunctions in humans. This article reviewed our knowledge about the insect–microbial system, an exquisite network of interactions operating between insects and microbes, its mechanistic insight that holds intricate multi-organismal systems in harmony, and its future perspectives. The demystification of molecular networks governing insect–microbial symbiosis will reveal the perplexing behaviours of insects that could be utilized in managing insect pests.

Novel Symbiotic Genome-Scale Model Reveals Wolbachia's Arboviral Pathogen Blocking Mechanism in Aedes aegypti

Wolbachia are endosymbiont bacteria known to infect arthropods causing different effects, such as cytoplasmic incompatibility and pathogen blocking in Aedes aegypti. Although several Wolbachia strains have been studied, there is little knowledge regarding the relationship between this bacterium and their hosts, particularly on their obligate endosymbiont nature and its pathogen blocking ability. Motivated by the potential applications on disease control, we developed a genome-scale model of two Wolbachia strains: wMel and the strongest Dengue blocking strain known to date: wMelPop. The obtained metabolic reconstructions exhibit an energy metabolism relying mainly on amino acids and lipid transport to support cell growth that is consistent with altered lipid and cholesterol metabolism in Wolbachia-infected mosquitoes. The obtained metabolic reconstruction was then coupled with a reconstructed mosquito model to retrieve a symbiotic genome-scale model accounting for 1,636 genes and 6,408 reactions of the Aedes aegypti-Wolbachia interaction system. Simulation of an arboviral infection in the obtained novel symbiotic model represents a metabolic scenario characterized by pathogen blocking in higher titer Wolbachia strains, showing that pathogen blocking by Wolbachia infection is consistent with competition for lipid and amino acid resources between arbovirus and this endosymbiotic bacteria.

The Manifold Roles of Sphingolipids in Viral Infections

Sphingolipids are essential components of eukaryotic cells. In this review, we want to exemplarily illustrate what is known about the interactions of sphingolipids with various viruses at different steps of their replication cycles. This includes structural interactions during entry at the plasma membrane or endosomal membranes, early interactions leading to sphingolipid-mediated signal transduction, interactions with internal membranes and lipids during replication, and interactions during virus assembly and budding. Targeted interventions in sphingolipid metabolism - as far as they can be tolerated by cells and organisms - may open novel possibilities to support antiviral therapies. Human immunodeficiency virus type 1 (HIV-1) infections have intensively been studied, but for other viral infections, such as influenza A virus (IAV), measles virus (MV), hepatitis C virus (HCV), dengue virus, Ebola virus, and severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), investigations are still in their beginnings. As many inhibitors of sphingolipid metabolism are already in clinical use against other diseases, repurposing studies for applications in some viral infections appear to be a promising approach.

Aphids harbouring different endosymbionts exhibit differences in cuticular hydrocarbon profiles that can be recognized by ant mutualists

Cuticular hydrocarbons (CHCs) have important communicative functions for ants, which use CHC profiles to recognize mutualistic aphid partners. Aphid endosymbionts can influence the quality of their hosts as ant mutualists, via effects on honeydew composition, and might also affect CHC profiles, suggesting that ants could potentially use CHC cues to discriminate among aphid lines harbouring different endosymbionts. We explored how several strains of Hamiltonella defensa and Regiella insecticola influence the CHC profiles of host aphids (Aphis fabae) and the ability of aphid-tending ants (Lasius niger) to distinguish the profiles of aphids hosting different endosymbionts. We found significant compositional differences between the CHCs of aphids with different infections. Some endosymbionts changed the proportions of odd-chain linear alkanes, while others changed primarily methyl-branched compounds, which may be particularly important for communication. Behavioural assays, in which we trained ants to associate CHC profiles of endosymbiont infected or uninfected aphids with food rewards, revealed that ants readily learned to distinguish differences in aphid CHC profiles associated with variation in endosymbiont strains. While previous work has documented endosymbiont effects on aphid interactions with antagonists, the current findings support the hypothesis that endosymbionts also alter traits that influence communicative interactions with ant mutualists.

Aedes fluviatilis cell lines as new tools to study metabolic and immune interactions in mosquito-Wolbachia symbiosis

In the present work, we established two novel embryonic cell lines from the mosquito Aedes fluviatilis containing or not the naturally occurring symbiont bacteria Wolbachia, which were called wAflu1 and Aflu2, respectively. We also obtained wAflu1 without Wolbachia after tetracycline treatment, named wAflu1.tet. Morphofunctional characterization was performed to help elucidate the symbiont-host interaction in the context of energy metabolism regulation and molecular mechanisms of the immune responses involved. The presence of Wolbachia pipientis improves energy performance in A. fluviatilis cells; it affects the regulation of key energy sources such as lipids, proteins, and carbohydrates, making the distribution of actin more peripheral and with extensions that come into contact with neighboring cells. Additionally, innate immunity mechanisms were activated, showing that the wAflu1 and wAflu1.tet cells are responsive after the stimulus using Gram negative bacteria. Therefore, this work confirms the natural, mutually co-regulating symbiotic relationship between W. pipientis and A. fluviatilis, modulating the host metabolism and immune pathway activation. The results presented here add important resources to the current knowledge of Wolbachia-arthropod interactions.

Blood Meals With Active and Heat-Inactivated Serum Modifies the Gene Expression and Microbiome of Aedes albopictus

The Asian "tiger mosquito" Aedes albopictus is currently the most widely distributed disease-transmitting mosquito in the world. Its geographical expansion has also allowed the expansion of multiple arboviruses like dengue, Zika, and chikungunya, to higher latitudes. Due to the enormous risk to global public health caused by mosquitoes species vectors of human disease, and the challenges in slowing their expansion, it is necessary to develop new and environmentally friendly vector control strategies. Among these, host-associated microbiome-based strategies have emerged as promising options. In this study, we performed an RNA-seq analysis on dissected abdomens of Ae. albopictus females from Manhattan, KS, United States fed with sugar and human blood containing either normal or heat-inactivated serum, to evaluate the effect of heat inactivation on gene expression, the bacteriome transcripts and the RNA virome of this mosquito species. Our results showed at least 600 genes with modified expression profile when mosquitoes were fed with normal vs. heat-inactivated-containing blood. These genes were mainly involved in immunity, oxidative stress, lipid metabolism, and oogenesis. Also, we observed bacteriome changes with an increase in transcripts of Actinobacteria, Rhodospirillaceae, and Anaplasmataceae at 6 h post-feeding. We also found that feeding with normal blood seems to particularly influence Wolbachia metabolism, demonstrated by a significant increase in transcripts of this bacteria in mosquitoes fed with blood containing normal serum. However, no differences were observed in the virome core of this mosquito population. These results suggest that heat and further inactivation of complement proteins in human serum may have profound effect on mosquito and microbiome metabolism, which could influence interpretation of the pathogen-host interaction findings when using this type of reagents specially when measuring the effect of Wolbachia in vector competence.

Sphingolipids: Effectors and Achilles Heals in Viral Infections?

As viruses are obligatory intracellular parasites, any step during their life cycle strictly depends on successful interaction with their particular host cells. In particular, their interaction with cellular membranes is of crucial importance for most steps in the viral replication cycle. Such interactions are initiated by uptake of viral particles and subsequent trafficking to intracellular compartments to access their replication compartments which provide a spatially confined environment concentrating viral and cellular components, and subsequently, employ cellular membranes for assembly and exit of viral progeny. The ability of viruses to actively modulate lipid composition such as sphingolipids (SLs) is essential for successful completion of the viral life cycle. In addition to their structural and biophysical properties of cellular membranes, some sphingolipid (SL) species are bioactive and as such, take part in cellular signaling processes involved in regulating viral replication. It is especially due to the progress made in tools to study accumulation and dynamics of SLs, which visualize their compartmentalization and identify interaction partners at a cellular level, as well as the availability of genetic knockout systems, that the role of particular SL species in the viral replication process can be analyzed and, most importantly, be explored as targets for therapeutic intervention.

Unraveling mosquito metabolism with mass spectrometry-based metabolomics

Nearly half a million people die annually due to mosquito-borne diseases. Despite aggressive mosquito population-control efforts, current strategies are limited in their ability to control these vectors. A better understanding of mosquito metabolism through modern approaches can contribute to the discovery of novel metabolic targets and/or regulators and lead to the development of better mosquito-control strategies. Currently, cutting-edge technologies such as gas or liquid chromatography-mass spectrometry-based metabolomics are considered 'mature technologies' in many life-science disciplines but are still an emerging area of research in medical entomology. This review primarily discusses recent developments and progress in the application of mass spectrometry-based metabolomics to answer multiple biological questions related to mosquito metabolism.

Detection and Identification of Wolbachia pipientis Strains in Mosquito Eggs Using Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) Spectroscopy

The global fight against mosquito-borne viral diseases has in recent years been bolstered by the introduction of the endosymbiotic bacteria Wolbachia to vector populations, which in host mosquitoes suppresses the transmissibility of several viruses. Researchers engaged on this front of the battle often need to know the Wolbachia infection status of individual mosquitoes, as the intervention progresses and the mosquitoes become established in the target population. Previously, we successfully applied attenuated total reflection Fourier transform infrared spectroscopy to the detection of Wolbachia in adult Aedes aegypti mosquitoes; here we apply the same principles to Aedes eggs, with sensitivity and selectivity > 0.95. Further, we successfully distinguish between infections in eggs of the wMel and wMelPop strains of Wolbachia pipientis, with a classification error of 3%. The disruption of host lipid profile by Wolbachia is found to be a key driver in spectral differences between these sample classes.

Wolbachia as translational science: controlling mosquito-borne pathogens

In this review we examine how exploiting the Wolbachia-mosquito relationship has become an increasingly popular strategy for controlling arbovirus transmission. Field deployments of Wolbachia-infected mosquitoes have led to significant decreases in dengue virus incidence via high levels of mosquito population suppression and replacement, emphasizing the success of Wolbachia approaches. Here, we examine how improved knowledge of Wolbachia-host interactions has provided key insight into the mechanisms of the essential phenotypes of pathogen blocking and cytoplasmic incompatibility. And we discuss recent studies demonstrating that extrinsic factors, such as ambient temperature, can modulate Wolbachia density and maternal transmission. Finally, we assess the prospects of using Wolbachia to control other vectors and agricultural pest species.

Intracellular Interactions Between Arboviruses and Wolbachia in Aedes aegypti

Aedes aegypti is inherently susceptible to arboviruses. The geographical expansion of this vector host species has led to the persistence of Dengue, Zika, and Chikungunya human infections. These viruses take advantage of the mosquito’s cell to create an environment conducive for their growth. Arboviral infection triggers transcriptomic and protein dysregulation in Ae. aegypti and in effect, host antiviral mechanisms are compromised. Currently, there are no existing vaccines able to protect human hosts from these infections and thus, vector control strategies such as Wolbachia mass release program is regarded as a viable option. Considerable evidence demonstrates how the presence of Wolbachia interferes with arboviruses by decreasing host cytoskeletal proteins and lipids essential for arboviral infection. Also, Wolbachia strengthens host immunity, cellular regeneration and causes the expression of microRNAs which could potentially be involved in virus inhibition. However, variation in the magnitude of Wolbachia’s pathogen blocking effect that is not due to the endosymbiont’s density has been recently reported. Furthermore, the cellular mechanisms involved in this phenotype differs depending on Wolbachia strain and host species. This prompts the need to explore the cellular interactions between Ae. aegypti-arboviruses-Wolbachia and how different Wolbachia strains overall affect the mosquito’s cell. Understanding what happens at the cellular and molecular level will provide evidence on the sustainability of Wolbachia vector control.

Fat and Happy: Profiling Mosquito Fat Body Lipid Storage and Composition Post-blood Meal

The fat body is considered the insect analog of vertebrate liver and fat tissue. In mosquitoes, a blood meal triggers a series of processes in the fat body that culminate in vitellogenesis, the process of yolk formation. Lipids are stored in the fat body in specialized organelles called lipid droplets that change in size depending on the nutritional and metabolic status of the insect. We surveyed lipid droplets in female Aedes aegypti fat body during a reproductive cycle using confocal microscopy and analyzed the dynamic changes in the fat body lipidome during this process using LC/MS. We found that lipid droplets underwent dynamic changes in volume after the mosquito took a blood meal. The lipid composition found in the fat body is quite complex with 117 distinct lipids that fall into 19 classes and sublcasses. Our results demonstrate that the lipid composition of the fat body is complex as most lipid classes underwent significant changes over the course of the vitellogenic cycle. This study lays the foundation for identifying unknown biochemical pathways active in the mosquito fat body, that are high-value targets for the development of novel mosquito control strategies.

Serratia symbiotica Enhances Fatty Acid Metabolism of Pea Aphid to Promote Host Development

Bacterial symbionts associated with insects are often involved in host development and ecological adaptation. Serratia symbiotica, a common facultative endosymbiont harbored in pea aphids, improves host fitness and heat tolerance, but studies concerning the nutritional metabolism and impact on the aphid host associated with carrying Serratia are limited. In the current study, we showed that Serratia-infected aphids had a shorter nymphal developmental time and higher body weight than Serratia-free aphids when fed on detached leaves. Genes connecting to fatty acid biosynthesis and elongation were up-regulated in Serratia-infected aphids. Specifically, elevated expression of fatty acid synthase 1 (FASN1) and diacylglycerol-o-acyltransferase 2 (DGAT2) could result in accumulation of myristic acid, palmitic acid, linoleic acid, and arachidic acid in fat bodies. Impairing fatty acid synthesis in Serratia-infected pea aphids either by a pharmacological inhibitor or through silencing FASN1 and DGAT2 expression prolonged the nymphal growth period and decreased the aphid body weight. Conversely, supplementation of myristic acid (C14:0) to these aphids restored their normal development and weight gain. Our results indicated that Serratia promoted development and growth of its aphid host through enhancing fatty acid biosynthesis. Our discovery has shed more light on nutritional effects underlying the symbiosis between aphids and facultative endosymbionts.

Mayaro Virus: The Potential Role of Microbiota and Wolbachia

The Mayaro virus (MAYV) is an arbovirus that circulates mainly in tropical forests or rural areas in Latin America and is transmitted mainly by Haemagogus mosquitoes. The objective of this study was to evaluate the vector competence, microbiome, and the presence of Wolbachia in three Aedes albopictus populations infected with MAYV. The vector competence was assessed based on viral infection and transmission by RT-qPCR. In addition, the microbiome was evaluated by amplification of the 16S rRNA V4 region and PCR to detect the presence of Wolbachia (strain wAlbA/wAlbB). Our results show that all three populations were susceptible to MAYV infection. The potential transmission of the MAYV was consistent in all populations of naïve mosquitoes injected (more than 50%). The microbiome analysis revealed 118 OTUs (operational taxonomic unit) from the three populations, 8 phyla, 15 classes, 26 orders, 35 families, 65 genera, and 53 species. All populations had Pseudomonas and Wolbachia as predominant genera. There was no difference between the variables for MAYV and Wolbachia (wAlbA or wAlbB) in the abdomen. However, in the head + thorax samples at 14 dpi, there was a difference between the two populations, indicating a possible correlation between the presence of Wolbachia (wAlbB) and infection. Overall, we show evidence that Ae. albopictus displays significant infection and transmission competence for the MAYV in the laboratory, and its bacterial microbiota play an important role in the host, mainly the strains of Wolbachia. The influence of the intestinal microbiota of Ae. albopictus is poorly known, and a better understanding of these interactions would open new perspectives for disease control through the manipulation of microbial communities. The exact contribution of this mosquito species to the transmission of the MAYV in the field remains to be confirmed.

Wolbachia and Virus Alter the Host Transcriptome at the Interface of Nucleotide Metabolism Pathways

Wolbachia is a maternally transmitted bacterium that manipulates arthropod and nematode biology in myriad ways. The Wolbachia strain colonizing Drosophila melanogaster creates sperm-egg incompatibilities and protects its host against RNA viruses, making it a promising tool for vector control. Despite successful trials using Wolbachia-transfected mosquitoes for dengue control, knowledge of how Wolbachia and viruses jointly affect insect biology remains limited. Using the Drosophila melanogaster model, transcriptomics and gene expression network analyses revealed pathways with altered expression and splicing due to Wolbachia colonization and virus infection. Included are metabolic pathways previously unknown to be important for Wolbachia-host interactions. Additionally, Wolbachia-colonized flies exhibit a dampened transcriptomic response to virus infection, consistent with early blocking of virus replication. Finally, using Drosophila genetics, we show that Wolbachia and expression of nucleotide metabolism genes have interactive effects on virus replication. Understanding the mechanisms of pathogen blocking will contribute to the effective development of Wolbachia-mediated vector control programs.IMPORTANCE Recently developed arbovirus control strategies leverage the symbiotic bacterium Wolbachia, which spreads in insect populations and blocks viruses from replicating. While this strategy has been successful, details of how this "pathogen blocking" works are limited. Here, we use a combination of virus infections, fly genetics, and transcriptomics to show that Wolbachia and virus interact at host nucleotide metabolism pathways.

Wolbachia affects reproduction in the spider mite Tetranychus truncatus (Acari: Tetranychidae) by regulating chorion protein S38-like and Rop

Wolbachia-induced reproductive regulation in hosts has been used to control pest populations, but little is known about the molecular mechanism underlying Wolbachia regulation of host genes. Here, reproductive regulation by Wolbachia in the spider mite Tetranychus truncatus was studied at the molecular level. Infection with Wolbachia resulted in decreasing oviposition and cytoplasmic incompatibility in T. truncatus. Further RNA-seq revealed genes regulated by Wolbachia in T. truncatus. Real-time quantitative polymerase chain reaction (qPCR) showed that genes, including chorion protein S38-like and Rop were down-regulated by Wolbachia. RNA interference (RNAi) of chorion protein S38-like and Rop in Wolbachia-uninfected T. truncatus decreased oviposition, which was consistent with Wolbachia-induced oviposition decrease. Interestingly, suppressing Rop in Wolbachia-infected T. truncatus led to increased Wolbachia titres in eggs; however, this did not occur after RNAi of chorion protein S38-like. This is the first study to show that chorion protein S38-like and Rop facilitate Wolbachia-mediated changes in T. truncatus fertility. In addition, RNAi of Rop turned the body colour of Wolbachia-uninfected T. truncatus black, which indicates that the role of Rop is not limited to the reproductive regulation of T. truncatus.