Omics and the metabolic function of insect-microbial symbioses

Insects to the rescue? Insights into applications, mechanisms, and prospects of insect-driven remediation of organic contaminants

Traditional and emerging contaminants pose significant human and environmental health risks. Conventional physical, chemical, and bioremediation techniques have been extensively studied for contaminant remediation. However, entomo- or insect-driven remediation has received limited research and public attention. Entomo-remediation refers to the use of insects, their associated gut microbiota, and enzymes to remove or mitigate organic contaminants. This novel approach shows potential as an eco-friendly method for mitigating contaminated media. However, a comprehensive review of the status, applications, and challenges of entomo-remediation is lacking. This paper addresses this research gap by examining and discussing the evidence on entomo-remediation of various legacy and emerging organic contaminants. The results demonstrate the successful application of entomo-remediation to remove legacy organic contaminants such as persistent organic pollutants. Moreover, entomo-remediation shows promise in removing various groups of emerging contaminants, including microplastics, persistent and emerging organic micropollutants (e.g., antibiotics, pesticides), and nanomaterials. Entomo-remediation involves several insect-mediated processes, including bio-uptake, biotransfer, bioaccumulation, and biotransformation of contaminants. The mechanisms underlying the biotransformation of contaminants are complex and rely on the insect gut microbiota and associated enzymes. Notably, while insects facilitate the remediation of contaminants, they may also be exposed to the ecotoxicological effects of these substances, which is often overlooked in research. As an emerging field of research, entomo-remediation has several knowledge gaps. Therefore, this review proposes ten key research questions to guide future perspectives and advance the field. These questions address areas such as process optimization, assessment of ecotoxicological effects on insects, and evaluation of potential human exposure and health risks.

Facultative endosymbionts modulate the aphid reproductive performance on wheat cultivars differing in contents of benzoxazinoids

BACKGROUND

Facultative bacterial endosymbionts have the potential to influence the interactions between aphids, their natural enemies, and host plants. Among the facultative symbionts found in populations of the grain aphid Sitobion avenae in central Chile, the bacterium Regiella insecticola is the most prevalent. In this study, we aimed to investigate whether infected and cured aphid lineages exhibit differential responses to wheat cultivars containing varying levels of the benzoxazinoid DIMBOA (2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one), which is a xenobiotic compound produced by plants. Specifically, we examined the reproductive performance responses of the most frequently encountered genotypes of Sitobion avenae when reared on wheat seedlings expressing low, medium, and high concentrations of DIMBOA.

RESULTS

Our findings reveal that the intrinsic rate of population increase (rm ) in cured lineages of Sitobion avenae genotypes exhibits a biphasic pattern, characterized by the lowest rm and an extended time to first reproduction on wheat seedlings with medium levels of DIMBOA. In contrast, the aphid genotypes harbouring Regiella insecticola display idiosyncratic responses, with the two most prevalent genotypes demonstrating improved performance on seedlings featuring an intermediate content of DIMBOA compared to their cured counterparts.

CONCLUSION

This study represents the first investigation into the mediating impact of facultative endosymbionts on aphid performance in plants exhibiting varying DIMBOA contents. These findings present exciting prospects for identifying novel targets for aphid control by manipulating the presence of aphid symbionts. © 2023 Society of Chemical Industry.

Functional and Compositional Changes in Sirex noctilio Gut Microbiome in Different Habitats: Unraveling the Complexity of Invasive Adaptation

The mutualistic symbiosis relationship between the gut microbiome and their insect hosts has attracted much scientific attention. The native woodwasp, Sirex nitobei, and the invasive European woodwasp, Sirex noctilio, are two pests that infest pines in northeastern China. Following its encounter with the native species, however, there is a lack of research on whether the gut microbiome of S. noctilio changed, what causes contributed to these alterations, and whether these changes were more conducive to invasive colonization. We used high-throughput and metatranscriptomic sequencing to investigate S. noctilio larval gut and frass from four sites where only S. noctilio and both two Sirex species and investigated the effects of environmental factors, biological interactions, and ecological processes on S. noctilio gut microbial community assembly. Amplicon sequencing of two Sirex species revealed differential patterns of bacterial and fungal composition and functional prediction. S. noctilio larval gut bacterial and fungal diversity was essentially higher in coexistence sites than in separate existence sites, and most of the larval gut bacterial and fungal community functional predictions were significantly different as well. Moreover, temperature and precipitation positively correlate with most of the highly abundant bacterial and fungal genera. Source-tracking analysis showed that S. noctilio larvae at coexistence sites remain dependent on adult gut transmission (vertical transmission) or recruitment to frass (horizontal transmission). Meanwhile, stochastic processes of drift and dispersal limitation also have important impacts on the assembly of S. noctilio larval gut microbiome, especially at coexistence sites. In summary, our results reveal the potential role of changes in S. noctilio larval gut microbiome in the successful colonization and better adaptation of the environment.

Effect of Ciprofloxacin on the Composition of Intestinal Microbiota in Sarcophaga peregrina (Diptera: Sarcophagidae)

The intestinal bacteria of insects are crucial to the growth and development of the host. It has been found that various physiological processes of insects, such as immune response, metabolism, reproductive ability, and growth and development, involve the gastrointestinal flora. However, many external factors affect the composition of insects' intestinal microorganisms, such as the type of dietary substrate. Sarcophaga peregrina (Robineau-Desvoidy, 1830) (Diptera: Sarcophagidae) is of great significance in medicine and forensic science. In this study, we investigated the effects of ciprofloxacin on the growth and gut microbiota of S. peregrina. The results demonstrated that the maximum body length of larvae was not affected by ciprofloxacin, while the growth rate of body length quickened as the concentration of the drug increased. The weight of the pupa and adult was reduced significantly due to the effect of ciprofloxacin. After analyzing the gut microbiota composition of S. peregrina in different drug groups, it was indicated that Ignatzschineria, Providencia, Wohlfahrtiimonas, Proteus, Myroides, and Bacteroides play important roles in the growth of S. peregrina. However, they still need to be further studied. In general, ciprofloxacin can affect the gut microbial community structure, which in turn affects the fitness of the host.

Population mixing mediates the intestinal flora composition and facilitates invasiveness in a globally invasive fruit fly

BACKGROUND

Changes in population heterozygosity and genetic diversity play important roles in mediating life history traits of organisms; these changes often lead to phenotypic evolution in offspring, which become superior to their parents. In the present study, we examined phenotypic differentiation, the intestinal microbiome composition, and metabolism shift in the oriental fruit fly (Bactrocera dorsalis) by comparing an inbred (monophyletic) original population and an outbred (mixed) invasive population.

RESULTS

The results showed that the outbred population of B. dorsalis had significantly higher biomass, adult longevity, and fecundity than the inbred population. Additionally, intestinal microflora analysis revealed that both Diutina rugosa and Komagataeibacter saccharivorans were significantly enriched in the outbred population with higher genetic heterozygosity. D. rugosa enrichment altered amino acid metabolism in the intestinal tract, and supplementing essential amino acids (e.g. histidine and glutamine) in the diet led to an increase in pupal weight of the outbred population. Additionally, transcriptome analysis revealed that the HSPA1S gene was significantly downregulated in the outbred population. HSPA1S was involved in activation of the JNK-MAPK pathway through negative regulation, caused the upregulation of juvenile hormone (JH), and led to an increase in biomass in the outbred flies.

CONCLUSION

In conclusion, the outbred population had an altered intestinal microbe composition, mediating metabolism and transcriptional regulation, leading to phenotypic differentiation; this may be a potential mechanism driving the global invasion of B. dorsalis. Thus, multiple introductions could lead to invasiveness enhancement in B. dorsalis through population mixing, providing preliminary evidence that changes in the intestinal microbiome can promote biological invasion. Video Abstract.

Colonization Resistance of Symbionts in Their Insect Hosts

The symbiotic microbiome is critical in promoting insect resistance against colonization by exogenous microorganisms. The mechanisms by which symbionts contribute to the host's immune capacity is referred to as colonization resistance. Symbionts can protect insects from exogenous pathogens through a variety of mechanisms, including upregulating the expression of host immune-related genes, producing antimicrobial substances, and competitively excluding pathogens. Concordantly, insects have evolved fine-tuned regulatory mechanisms to avoid overactive immune responses against symbionts or specialized cells to harbor symbionts. Alternatively, some symbionts have evolved special adaptations, such as the formation of biofilms to increase their tolerance to host immune responses. Here, we provide a review of the mechanisms about colonization resistance of symbionts in their insect hosts. Adaptations of symbionts and their insect hosts that may maintain such symbiotic relationships, and the significance of such relationships in the coevolution of symbiotic systems are also discussed to provide insights into the in-depth study of the contribution of symbionts to host physiology and behavior.

300 Million years of coral treaders (Insecta: Heteroptera: Hermatobatidae) back to the ocean in the phylogenetic context of Arthropoda

Among hundreds of insect families, Hermatobatidae (commonly known as coral treaders) is one of the most unique. They are small, wingless predaceous bugs in the suborder Heteroptera. Adults are almost black in colour, measuring about 5 mm in body length and 3 mm in width. Thirteen species are known from tropical coral reefs or rocky shores, but their origin and evolutionary adaptation to their unusual marine habitat were unexplored. We report here the genome and metagenome of Hermatobates lingyangjiaoensis, hitherto known only from its type locality in the South China Sea. We further reconstructed the evolutionary history and origin of these marine bugs in the broader context of Arthropoda. The dated phylogeny indicates that Hexapoda diverged from their marine sister groups approximately 498 Ma and that Hermatobatidae originated 192 Ma, indicating that they returned to an oceanic life some 300 Myr after their ancestors became terrestrial. Their origin is consistent with the recovery of tropical reef ecosystems after the end-Triassic mass extinction, which might have provided new and open niches for them to occupy and thrive. Our analyses also revealed that both the genome changes and the symbiotic bacteria might have contributed to adaptations necessary for life in the sea.

Diesel exhaust particles alter gut microbiome and gene expression in the bumblebee Bombus terrestris

Insect decline is a major threat to ecosystems around the world as they provide many important functions, such as pollination or pest control. Pollution is one of the main reasons for the decline, alongside changes in land use, global warming, and invasive species. While negative impacts of pesticides are well-studied, there is still a lack of knowledge about the effects of other anthropogenic pollutants, such as airborne particulate matter, on insects. To address this, we exposed workers of the bumblebee Bombus terrestris to sublethal doses of diesel exhaust particles (DEPs) and brake dust, orally or via air. After 7 days, we looked at the composition of the gut microbiome and tracked changes in gene expression. While there were no changes in the other treatments, oral DEP exposure significantly altered the structure of the gut microbiome. In particular, the core bacterium Snodgrassella had a decreased abundance in the DEP treatment. Similarly, transcriptome analysis revealed changes in gene expression after oral DEP exposure, but not in the other treatments. The changes are related to metabolism and signal transduction, which indicates a general stress response. Taken together, our results suggest potential health effects of DEP exposure on insects, here shown in bumblebees, as gut dysbiosis may increase the susceptibility of bumblebees to pathogens, while a general stress response may lower available energy resources. Those effects may exacerbate under natural conditions where insects face a multiple-stressor environment.

A bacteriocyte symbiont determines whitefly sex ratio by regulating mitochondrial function

Nutritional symbionts influence host reproduction, but the underlying molecular mechanisms are largely unclear. We previously found that the bacteriocyte symbiont Hamiltonella impacts the sex ratio of the whitefly Bemisia tabaci. Hamiltonella synthesizes folate by cooperation with the whitefly. Folate deficiency by Hamiltonella elimination or whitefly gene silencing distorted whitefly sex ratio, and folate supplementation restored the sex ratio. Hamiltonella deficiency or gene silencing altered histone H3 lysine 9 trimethylation (H3K9me3) level, which was restored by folate supplementation. Genome-wide chromatin immunoprecipitation-seq analysis of H3K9me3 indicated mitochondrial dysfunction in symbiont-deficient whiteflies. Hamiltonella deficiency compromised mitochondrial quality of whitefly ovaries. Repressing ovary mitochondrial function led to distorted whitefly sex ratio. These findings indicate that the symbiont-derived folate regulates host histone methylation modifications, which thereby impacts ovary mitochondrial function, and finally determines host sex ratio. Our study suggests that a nutritional symbiont can regulate animal reproduction in a way that differs from reproductive manipulators.

Diversity and metabolic potentials of microbial communities associated with pollinator and cheater fig wasps in fig-fig wasp mutualism system

Microbial symbionts can influence a myriad of insect behavioral and physiological traits. However, how microbial communities may shape or be shaped by insect interactions with plants and neighboring species remains underexplored. The fig-fig wasp mutualism system offers a unique model to study the roles of microbiome in the interactions between the plants and co-habiting insects because a confined fig environment is shared by two fig wasp species, the pollinator wasp (Eupristina altissima and Eupristina verticillata) and the cheater wasp (Eupristina sp1 and Eupristina sp2). Here, we performed whole genome resequencing (WGS) on 48 individual fig wasps (Eupristina spp.) from Yunnan, China, to reveal the phylogenetic relationship and genetic divergence between pollinator and congeneric cheater wasps associated with the Ficus trees. We then extracted metagenomic sequences to explore the compositions, network structures, and functional capabilities of microbial communities associated with these wasps. We found that the cheaters and pollinators from the same fig species are sister species, which are highly genetically divergent. Fig wasps harbor diverse but stable microbial communities. Fig species dominate over the fig wasp genotype in shaping the bacterial and fungal communities. Variation in microbial communities may be partially explained by the filtering effect from fig and phylogeny of fig wasps. It is worth noting that cheaters have similar microbial communities to their sister pollinators, which may allow cheaters to coexist and gain resources from the same fig species. In terms of metabolic capabilities, some bacteria such as Desulfovibrio and Lachnospiraceae are candidates involved in the nutritional uptake of fig wasps. Our results provide novel insights into how microbiome community and metabolic functions may couple with the fig-wasp mutualistic systems.

Contribution of insect gut microbiota and their associated enzymes in insect physiology and biodegradation of pesticides

Synthetic pesticides are extensively and injudiciously applied to control agriculture and household pests worldwide. Due to their high use, their toxic residues have enormously increased in the agroecosystem in the past several years. They have caused many severe threats to non-target organisms, including humans. Therefore, the complete removal of toxic compounds is gaining wide attention to protect the ecosystem and the diversity of living organisms. Several methods, such as physical, chemical and biological, are applied to degrade compounds, but as compared to other methods, biological methods are considered more efficient, fast, eco-friendly and less expensive. In particular, employing microbial species and their purified enzymes makes the degradation of toxic pollutants more accessible and converts them into non-toxic products by several metabolic pathways. The digestive tract of insects is usually known as a superior organ that provides a nutrient-rich environment to hundreds of microbial species that perform a pivotal role in various physiological and ecological functions. There is a direct relationship between pesticides and insect pests: pesticides reduce the growth of insect species and alter the phyla located in the gut microbiome. In comparison, the insect gut microbiota tries to degrade toxic compounds by changing their toxicity, increasing the production and regulation of a diverse range of enzymes. These enzymes breakdown into their derivatives, and microbial species utilize them as a sole source of carbon, sulfur and energy. The resistance of pesticides (carbamates, pyrethroids, organophosphates, organochlorines, and neonicotinoids) in insect species is developed by metabolic mechanisms, regulation of enzymes and the expression of various microbial detoxifying genes in insect guts. This review summarizes the toxic effects of agrochemicals on humans, animals, birds and beneficial arthropods. It explores the preferential role of insect gut microbial species in the degradation process and the resistance mechanism of several pesticides in insect species. Additionally, various metabolic pathways have been systematically discussed to better understand the degradation of xenobiotics by insect gut microbial species.

Larval gut microbiome of Pelidnota luridipes (Coleoptera: Scarabaeidae): high bacterial diversity, different metabolic profiles on gut chambers and species with probiotic potential

Pelidnota luridipes Blanchard (1850) is a tropical beetle of the family Scarabaeidae, whose larvae live on wood without parental care. Microbiota of mid- and hindgut of larvae was evaluated by culture-dependent and independent methods, and the results show a diverse microbiota, with most species of bacteria and fungi shared between midgut and hindgut. We isolated 272 bacterial and 29 yeast isolates, identified in 57 and 7 species, respectively, while using metabarcoding, we accessed 1,481 and 267 OTUs of bacteria and fungi, respectively. The composition and abundance of bacteria and fungi differed between mid- and hindgut, with a tendency for higher richness and diversity of yeasts in the midgut, and bacteria on the hindgut. Some taxa are abundant in the intestine of P. luridipes larvae, such as Firmicutes, Bacteroidetes, Proteobacteria, and Actinobacteria; as well as Saccharomycetales and Trichosporonales yeasts. Mid- and hindgut metabolic profiles differ (e.g. biosynthesis of amino acids, cofactors, and lipopolysaccharides) with higher functional diversity in the hindgut. Isolates have different functional traits such as secretion of hydrolytic enzymes and antibiosis against pathogens. Apiotrichum siamense L29A and Bacillus sp. BL17B protected larvae of the moth Galleria mellonella, against infection by the pathogens Listeria monocytogenes ATCC19111 and Pseudomonas aeruginosa ATCC 9027. This is the first work with the larval microbiome of a Rutelini beetle, demonstrating its diversity and potential in prospecting microbial products as probiotics. The functional role of microbiota for the nutrition and adaptability of P. luridipes larvae needs to be evaluated in the future.

Bacterial diversity and community structure shapes pederin polymorphism but lacks association with host genotype specificity in the rove beetle, Paederus fuscipes

Paederus beetles are notorious for their irritant haemolymph toxin pederin synthesized by an unculturable bacterial symbiont which causes dermatitis when in contact with human skin. Pederin polymorphism is observed when (+) females carrying the toxin pederin and (-) females lacking this, co-occur in natural populations. Despite reports detecting pederin polymorphism in several Paederina beetles, symbiont infection frequencies in their natural populations and the bacterial diversity differences underlying the polymorphism between these female types are understudied. Herein we report a high prevalence (>80%) of female Paederus fuscipes carrying bacterial ped genes in all six study populations. This finding suggests selection pressure favouring pederin-producing females is crucial for survival in the natural environment. 16S rRNA metabarcoding analysis revealed significant dominance of the unculturable pederin-producing Pseudomonas-like bacterium (Gammaproteobacteria) in (+) females consistent with previous studies. The microbial diversity of the (-) females revealed significant abundance of Apibacter (Bacteroidia) previously undocumented suggesting its importance in the functionality of (-) females. Predicted functions related to metabolisms are enriched in (-) females suggesting fitness advantage possibilities in sustaining the population in the absence of predation. Further investigations on possible genetic basis of host genotype revealed no association of host mtDNA and pederin polymorphism in P. fuscipes.

Microplastic exposure across trophic levels: effects on the host-microbiota of freshwater organisms

BACKGROUND

Microplastics are a pervasive pollutant widespread in the sea and freshwater from anthropogenic sources, and together with the presence of pesticides, they can have physical and chemical effects on aquatic organisms and on their microbiota. Few studies have explored the combined effects of microplastics and pesticides on the host-microbiome, and more importantly, the effects across multiple trophic levels. In this work, we studied the effects of exposure to microplastics and the pesticide deltamethrin on the diversity and abundance of the host-microbiome across a three-level food chain: daphnids-damselfly-dragonflies. Daphnids were the only organism exposed to 1 µm microplastic beads, and they were fed to damselfly larvae. Those damselfly larvae were exposed to deltamethrin and then fed to the dragonfly larvae. The microbiotas of the daphnids, damselflies, and dragonflies were analyzed.

RESULTS

Exposure to microplastics and deltamethrin had a direct effect on the microbiome of the species exposed to these pollutants. An indirect effect was also found since exposure to the pollutants at lower trophic levels showed carry over effects on the diversity and abundance of the microbiome on higher trophic levels, even though the organisms at these levels where not directly exposed to the pollutants. Moreover, the exposure to deltamethrin on the damselflies negatively affected their survival rate in the presence of the dragonfly predator, but no such effects were found on damselflies fed with daphnids that had been exposed to microplastics.

CONCLUSIONS

Our study highlights the importance of evaluating ecotoxicological effects at the community level. Importantly, the indirect exposure to microplastics and pesticides through diet can potentially have bottom-up effects on the trophic webs.

Role of Insect Gut Microbiota in Pesticide Degradation: A Review

Insect pests cause significant agricultural and economic losses to crops worldwide due to their destructive activities. Pesticides are designed to be poisonous and are intentionally released into the environment to combat the menace caused by these noxious pests. To survive, these insects can resist toxic substances introduced by humans in the form of pesticides. According to recent findings, microbes that live in insect as symbionts have recently been found to protect their hosts against toxins. Symbioses that have been formed are between the pests and various microbes, a defensive mechanism against pathogens and pesticides. Insects' guts provide unique conditions for microbial colonization, and resident bacteria can deliver numerous benefits to their hosts. Insects vary significantly in their reliance on gut microbes for basic functions. Insect digestive tracts are very different in shape and chemical properties, which have a big impact on the structure and composition of the microbial community. Insect gut microbiota has been found to contribute to feeding, parasite and pathogen protection, immune response modulation, and pesticide breakdown. The current review will examine the roles of gut microbiota in pesticide detoxification and the mechanisms behind the development of resistance in insects to various pesticides. To better understand the detoxifying microbiota in agriculturally significant pest insects, we provided comprehensive information regarding the role of gut microbiota in the detoxification of pesticides.

Metabolite Profiling of the Social Spider Stegodyphus dumicola Along a Climate Gradient

Animals experience climatic variation in their natural habitats, which may lead to variation in phenotypic responses among populations through local adaptation or phenotypic plasticity. In ectotherm arthropods, the expression of thermoprotective metabolites such as free amino acids, sugars, and polyols, in response to temperature stress, may facilitate temperature tolerance by regulating cellular homeostasis. If populations experience differences in temperatures, individuals may exhibit population-specific metabolite profiles through differential accumulation of metabolites that facilitate thermal tolerance. Such thermoprotective metabolites may originate from the animals themselves or from their associated microbiome, and hence microbial symbionts may contribute to shape the thermal niche of their host. The social spider Stegodyphus dumicola has extremely low genetic diversity, yet it occupies a relatively broad temperature range occurring across multiple climate zones in Southern Africa. We investigated whether the metabolome, including thermoprotective metabolites, differs between populations, and whether population genetic structure or the spider microbiome may explain potential differences. To address these questions, we assessed metabolite profiles, phylogenetic relationships, and microbiomes in three natural populations along a temperature gradient. The spider microbiomes in three genetically distinct populations of S. dumicola showed no significant population-specific pattern, and none of its dominating genera (Borrelia, Diplorickettsia, and Mycoplasma) are known to facilitate thermal tolerance in hosts. These results do not support a role of the microbiome in shaping the thermal niche of S. dumicola. Metabolite profiles of the three spider populations were significantly different. The variation was driven by multiple metabolites that can be linked to temperature stress (e.g., lactate, succinate, or xanthine) and thermal tolerance (e.g., polyols, trehalose, or glycerol): these metabolites had higher relative abundance in spiders from the hottest geographic region. These distinct metabolite profiles are consistent with a potential role of the metabolome in temperature response.

Diatraea saccharalis harbors microorganisms that can affect growth of sugarcane stalk-dwelling fungi

Diatraea saccharalis (Fabricius, 1794) (Lepidoptera: Crambidae), the sugarcane borer, spends most of its life cycle inside the galleries it burrows into sugarcane stalk, where two rot-causing fungi Colletotrichum falcatum (Went, 1893) and Fusarium verticillioides (Nirenberg, 1976) are commonly found. Results have shown that microbiota harbored by D. saccharalis inhibits the growth of F. verticillioides and C. falcatum. D. saccharalis larvae were collected from chemical-free field plants, and yeast and bacteria from third and fourth-instar D. saccharalis regurgitate were isolated onto appropriate media. The percentage of F. verticillioides and C. falcatum mycelial growth inhibition was recorded. Out of 32 yeast isolates, 9 exerted 30 to 40% growth inhibition of C. falcatum or F. verticillioides. When 24 bacterial isolates were confronted with rot-causing fungi, six inhibited C. falcatum growth by 30 to 60%, and 24 isolates inhibited 30 to 60% of F. verticillioides growth. Bacteria and yeast isolates were identified through DNA sequencing of part of 16S rDNA and part of ITS1-5.8S-ITS2, respectively, revealing an abundance of isolates with sequence similarity to Klebsiella and Bacillus and Meyerozyma, which have been used as biological control agents and their ability to promote plant growth has been demonstrated. We have shown that microorganisms from borer regurgitate inhibit phytopathogen growth in vitro. Still, further investigation of the possible functions of D. saccharalis-associated microorganisms may help understand their ecological role in plant-insect-phytopathogen interaction.

The Bee Hemolymph Metabolome: A Window into the Impact of Viruses on Bumble Bees

State-of-the-art virus detection technology has advanced a lot, yet technology to evaluate the impacts of viruses on bee physiology and health is basically lacking. However, such technology is sorely needed to understand how multi-host viruses can impact the composition of the bee community. Here, we evaluated the potential of hemolymph metabolites as biomarkers to identify the viral infection status in bees. A metabolomics strategy based on ultra-high-performance liquid chromatography coupled to high-resolution mass spectrometry was implemented. First, we constructed a predictive model for standardized bumble bees, in which non-infected bees were metabolically differentiated from an overt Israeli acute paralysis virus (IAPV) infection (R²Y = 0.993; Q² = 0.906), as well as a covert slow bee paralysis virus (SBPV) infection (R²Y = 0.999; Q² = 0.875). Second, two sets of potential biomarkers were identified, being descriptors for the metabolomic changes in the bee's hemolymph following viral infection. Third, the biomarker sets were evaluated in a new dataset only containing wild bees and successfully discriminated virus infection versus non-virus infection with an AUC of 0.985. We concluded that screening hemolymph metabolite markers can underpin physiological changes linked to virus infection dynamics, opening promising avenues to identify, monitor, and predict the effects of virus infection in a bee community within a specific environment.

Two Deoxythymidine Triphosphate Synthesis-Related Genes Regulate Obligate Symbiont Density and Reproduction in the Whitefly Bemisia tabaci MED

Deoxythymidine triphosphate (dTTP) is essential for DNA synthesis and cellular growth in all organisms. Here, genetic capacity analysis of the pyrimidine pathway in insects and their symbionts revealed that dTTP is a kind of metabolic input in several host insect/obligate symbiont symbiosis systems, including Bemisia tabaci MED/Candidatus Portiera aleyrodidarum (hereafter Portiera). As such, the roles of dTTP on both sides of the symbiosis system were investigated in B. tabaci MED/Portiera. Dietary RNA interference (RNAi) showed that suppressing dTTP production significantly reduced the density of Portiera, significantly repressed the expression levels of horizontally transferred essential amino acid (EAA) synthesis-related genes, and significantly decreased the reproduction of B. tabaci MED adults as well as the hatchability of their offspring. Our results revealed the regulatory role of dTTP in B. tabaci MED/Portiera and showed that dTTP synthesis-related genes could be potential targets for controlling B. tabaci as well as other sucking pests.

An Insight into Diversity and Functionalities of Gut Microbiota in Insects

The gut microbiota has long been of research interests due to its nutritional importance for many insects. It has been demonstrated that diversity of gut microbiota in insects can be modulated by many factors, including habitats, feeding preference, etc. Besides, the community structure of gut microbiota could also be altered during the different life stages of host insects. With development of conventional culture-dependent technologies and advanced culture-independent technologies, comprehensive and deep understanding of the functions of gut microbiota and their relationship with host insects were achieved, especially for the nutrient metabolic process mediated by them. In this review, we summarized the gut microbiota composition, major methods for gut microbiota characterization, and vital nutrient metabolic process mediated by gut microbiota in different insects. The increasing knowledge on the modulation of gut microbiota will help us for the comprehension of the contribution of gut microbiota to the nutritional metabolism of insects, prompting their growth and health.

Anti-MRSA Activity of Actinomycin X2 and Collismycin A Produced by Streptomyces globisporus WA5-2-37 From the Intestinal Tract of American Cockroach (Periplaneta americana)

Methicillin-resistant Staphylococcus aureus (MRSA) is recognized as one of the serious pathogen that causes acquired infections worldwide. Its emerging need to discover novel, safe and potent anti-MRSA drugs. In this study, primary screening by anti-MRSA activity assay found one strain WA5-2-37 isolated from the intestinal tract of Periplaneta americana, exhibited great activity against MRSA ATCC 43300. The strain WA5-2-37 produced actinomycin X₂ and collismycin A which showed strong inhibition of MRSA with minimum inhibitory concentration (MIC) values of 0.25 and 8 μg/mL. The structures of the pure compounds were elucidated by analysis of mass spectrometry (MS), ¹H and ¹³C nuclear magnetic resonance (NMR). The strain WA5-2-37 was considered as Streptomyces globisporus on the basis of morphological characteristics, genotypic data, and phylogenetic analysis. This is the first reported naturally occurring strain of S. globisporus isolated from the intestinal tract of P. americana, whereas it has almost been found from plants, marine, and soil previously. Moreover, S. globisporus has not been reported to produce any anti-MRSA substances previously, such as actinomycin X₂ and collismycin A. In conclusion, the insect-derived strain of S. globisporus WA5-2-37 was considered of great potential as a new strain of producing actinomycin X₂, collismycin A or other anti-MRSA compounds.

Dynamics of bacterial composition in the locust reproductive tract are affected by the density-dependent phase

The important role that locust gut bacteria play in their host biology is well accepted. Among other roles, gut bacteria are suggested to be involved in the locust swarming phenomenon. In addition, in many insect orders, the reproductive system is reported to serve as a vector for trans-generation bacterial inoculation. Knowledge of the bacterial composition of the locust reproductive tract is, however, practically absent. Here we characterized the reproductive system bacterial composition of gregarious and solitary females. We investigated its temporal dynamics and how it interacts with the locust phase, by comparative sampling and 16S rRNA amplicon sequencing. We revealed that the bacterial composition of the locust female reproductive tract is mostly constructed of three core genera: Micrococcus, Acinetobacter and Staphylococcus. While solitary females maintained a consistent bacterial composition, in the gregarious phase this consortium demonstrated large temporal shifts, mostly manifested by Brevibacterium blooms. These data are in accord with our previous report on the dynamics of locust hindgut bacterial microbiota, further indicating that locust endosymbionts are affected by their host population density. These newly understood dynamics may have implications beyond their contribution to our knowledge of locust ecology, as aggregation and mass migration are prevalent phenomena across many migrating animals.

Insect Sterol Nutrition: Physiological Mechanisms, Ecology, and Applications

Insects, like all eukaryotes, require sterols for structural and metabolic purposes. However, insects, like all arthropods, cannot make sterols. Cholesterol is the dominant tissue sterol for most insects; insect herbivores produce cholesterol by metabolizing phytosterols, but not always with high efficiency. Many insects grow on a mixed-sterol diet, but this ability varies depending on the types and ratio of dietary sterols. Dietary sterol uptake, transport, and metabolism are regulated by several proteins and processes that are relatively conserved across eukaryotes. Sterol requirements also impact insect ecology and behavior. There is potential to exploit insect sterol requirements to (a) control insect pests in agricultural systems and (b) better understand sterol biology, including in humans. We suggest that future studies focus on the genetic mechanism of sterol metabolism and reverse transportation, characterizing sterol distribution and function at the cellular level, the role of bacterial symbionts in sterol metabolism, and interrupting sterol trafficking for pest control.

Topical dsRNA delivery induces gene silencing and mortality in the pea aphid

BACKGROUND

With the growing number of available aphid genomes and transcriptomes, an efficient and easy-to-adapt tool for gene function study is urgently required. RNA interference (RNAi), as a post-transcriptional gene silencing mechanism, is important as a research tool for determining gene functions and has potential as a novel insect control strategy. However, these applications have been hampered by the lack of effective dsRNA delivery approaches in aphids.

RESULTS

Here, we developed a convenient and efficient dsRNA delivery method, topical RNAi, in aphids. An investigation of its dose and time-dependent RNAi efficiencies revealed that with as little as 60 ng dsRNA per adult pea aphid (Acyrthosiphon pisum), the indicator gene, Aphunchback, could be significantly silenced within 2 h of exposure. The method was further validated by successfully silencing other different genes, and it was also efficient toward two other aphid species, Aphis citricidus and Myzus persicae. Furthermore, a noticeable mortality was also observed in pea aphids using topical RNAi-mediated gene silencing, within 4 days post-dsRNA application for four out of seven tested genes.

CONCLUSION

Compared with the currently used dsRNA delivery methods in aphids, microinjection and ingestion, topical RNAi is time- and cost-effective, which could greatly influence RNAi-based gene functional studies and potential candidate gene selection for developing RNAi-based aphid control strategies in the future. © 2019 Society of Chemical Industry.

Drosophila and its gut microbes: a model for drug-microbiome interactions

Drosophila is an excellent system to investigate how the presence and composition of the gut microbiome influences the efficacy of therapeutic drugs and downstream consequences for host health. These opportunities derive from two key attributes of Drosophila. First, Drosophila is amenable for microbiome research, with simple, standardized methods to produce large numbers of microbiologically-sterile flies and flies with a standardized gut microbiome, thereby facilitating experimental reproducibility. Second, Drosophila is a well-established genetic model that is increasingly used to elucidate the molecular and physiological basis of lesions associated with human disease alleles; this provides the opportunity to link microbiome/drug interactions to previously-described processes shaping health and disease. In this way, Drosophila can fast-track understanding of fundamental biology to generate precise hypotheses for testing in mammalian systems. Drosophila is particularly well-suited to investigate the incidence of microbiome/drug interactions mediated by different mechanisms, including microbial drug metabolism (to active, inactive or toxic derivatives), microbial production of compounds that inhibit drug efficacy, and off-target effects of the drug on the microbiome, resulting in dysbiosis and host ill-health. Drosophila can also be used to investigate how interactions between the microbiome and host genotype may shape responses to therapeutic drugs, informing the reliability of precision medicine based exclusively on human genomic markers.

Correlation and causation between the microbiome, Wolbachia and host functional traits in natural populations of drosophilid flies

Resident microorganisms are known to influence the fitness and traits of animals under controlled laboratory conditions, but the relevance of these findings to wild animals is uncertain. This study investigated the host functional correlates of microbiota composition in a wild community of three sympatric species of mycophagous drosophilid flies, Drosophila falleni, Drosophila neotestacea and Drosophila putrida. Specifically, we quantified bacterial communities and host transcriptomes by parallel 16S rRNA gene amplicon sequencing and RNA-Seq of individual flies. Among-fly variation in microbiota composition did not partition strongly by sex or species, and included multiple modules, that is, sets of bacterial taxa whose abundance varied in concert across different flies. The abundance of bacteria in several modules varied significantly with multiple host transcripts, especially in females, but the identity of the correlated host transcriptional functions differed with host species, including epithelial barrier function in D. falleni, muscle function in D. putrida, and insect growth and development in D. neotestacea. In D. neotestacea, which harbours the endosymbionts Wolbachia and Spiroplasma, Wolbachia promotes the abundance of Spiroplasma, and is positively correlated with abundance of Lactobacillales and Bacteroidales. Furthermore, most correlations between host gene expression and relative abundance of bacterial modules were co-correlated with abundance of Wolbachia (but not Spiroplasma), indicative of an interdependence between host functional traits, microbiota composition and Wolbachia abundance in this species. These data suggest that, in these natural populations of drosophilid flies, different host species interact with microbial communities in functionally different ways that can vary with the abundance of endosymbionts.

Transcriptomic analyses uncover emerging roles of mucins, lysosome/secretory addressing and detoxification pathways in insect midguts

The study of insect midgut features has been made possible by the recent availability of transcriptome datasets. These data uncovered the preferential expression of mucus-forming mucins at midgut regions that require protection (e.g. the acidic middle midgut of Musca domestica) or at sites of enzyme immobilization, particularly around the peritrophic membrane of Spodoptera frugiperda. Coleoptera lysosomal peptidases are directed to midgut lumen when over-expressed and targeted to lysosomes by a mechanism other than the mannose 6-phosphate-dependent pathway. We show that this second trend is likely conserved across Annelida, Mollusca, Nematoda, and Arthropoda. Furthermore, midgut transcriptomes of distantly related species reveal a general overexpression of xenobiotic detoxification pathways. In addition to attenuating toxicity of plant-derived compounds and insecticides, we also discuss a role for these detoxification pathways in regulating host-microbiota interactions by metabolizing bacterial secondary metabolites.