Apis cerana gut microbiota contribute to host health though stimulating host immune system and strengthening host resistance to Nosema ceranae

Tetracycline-induced gut community dysbiosis and Israeli Acute Paralysis Virus infection synergistically negatively affect honeybees

Antibiotics are frequently employed to control bacterial diseases in honeybees, but their broad-spectrum action can disrupt the delicate balance of the gut microbiome, leading to dysbiosis. This imbalance in the gut microbiota of honeybees adversely affects their physiological health and weakens their resistance to pathogens, including viruses that significantly threaten honeybee health. In this study, we investigated whether tetracycline-induced gut microbiome dysbiosis promotes the replication of Israeli acute paralysis virus (IAPV), a key virus associated with colony losses and whether IAPV infection exacerbates gut microbiome dysbiosis. Our results demonstrated that tetracycline-induced gut microbiome dysbiosis increases the susceptibility of honeybees to IAPV infection. The viral titer in worker bees with antibiotic-induced gut microbiome dysbiosis prior to IAPV inoculation was significantly higher than in those merely inoculated with IAPV. Furthermore, we observed a synergistic effect between tetracycline and IAPV on the disruption of the honeybee gut microbiome balance. The progression of IAPV replication could, in turn, exacerbate antibiotic-induced gut microbiome dysbiosis in honeybees. Our research provides novel insights into the role of the gut microbiota in host-virus interactions, emphasizing the complex interplay between antibiotic use, gut microbiome health, and viral susceptibility in honeybees. We highlight the crucial role of a balanced gut microbiota in honey bees for their immune response against pathogens and emphasize the importance of careful, safe antibiotic use in beekeeping to protect these beneficial microbes.

Interactions between microsporidia and other members of the microbiome

The microbiome is the collection of microbes that are associated with a host. Microsporidia are intracellular eukaryotic parasites that can infect most types of animals. In the last decade, there has been much progress to define the relationship between microsporidia and the microbiome. In this review, we cover an increasing number of reports suggesting that microsporidia are common components of the microbiome in both invertebrates and vertebrates. These microsporidia infections can range from mutualistic to pathogenic, causing several physiological phenotypes, including death. Infection with microsporidia often causes a disruption in the normal microbiome, with both increases and decreases of bacterial, fungal, viral, and protozoan species being observed. This impact on the microbiome can occur through upregulation and downregulation of innate immunity as well as morphological changes to tissues that impact interactions with these microbes. Other microbes, particularly bacteria, can inhibit microsporidia and have been exploited to control microsporidia infections. These bacteria can function through regulating immunity, secreting anti-microsporidia compounds, and, in engineered versions, expressing double-stranded RNA targeting microsporidia genes. We end this review by discussing potential future directions to further understand the complex interactions between microsporidia and the other members of the microbiome.

Proteomics and Immune Response Differences in Apis mellifera and Apis cerana Inoculated with Three Nosema ceranae Isolates

Nosema ceranae infects midgut epithelial cells of the Apis species and has jumped from its original host A. cerana to A. mellifera worldwide, raising questions about the response of the new host. We compared the responses of these two species to N. ceranae isolates from A. cerana, A. mellifera from Thailand and A. mellifera from France. Proteomics and transcriptomics results were combined to better understand the impact on the immunity of the two species. This is the first combination of omics analyses to evaluate the impact of N. ceranae spores from different origins and provides new insights into the differential immune responses in honeybees inoculated with N. ceranae from original A. cerana. No difference in the antimicrobial peptides (AMPs) was observed in A. mellifera, whereas these peptides were altered in A. cerana compared to controls. Inoculation of A. mellifera or A. cerana with N. ceranae upregulated AMP genes and cellular-mediated immune genes but did not significantly alter apoptosis-related gene expression. A. cerana showed a stronger immune response than A. mellifera after inoculation with different N. ceranae isolates. N. ceranae from A. cerana had a strong negative impact on the health of A. mellifera and A. cerana compared to other Nosema isolates.

Intestinal Microflora Characteristics of Antheraea pernyi (Lepidoptera: Saturniidae) Larvae With Vomit Disease

Antheraea pernyi Guérin-Méneville (Lepidoptera: Saturniidae) is of high economic value as a source of silk, food, and bioactive substances with medicinal properties. A. pernyi larvae are prone to A. pernyi vomit disease (AVD), which results in substantial economic losses during cultivation; however, the relationship between AVD and A. pernyi gut microbiota remains unclear. Here, we investigated the bacterial community in the midgut and feces of A. pernyi larvae with and without AVD using 16S rRNA gene sequencing with Illumina MiSeq technology. Compared with healthy larvae, intestinal bacterial diversity and community richness increased and decreased in larvae with mild and severe AVD, respectively. In addition, the proportion of gut Enterobacter Hormaeche and Edwards(Enterobacteriales: Enterobacteriaceae) and Enterococcus Thiercelin and Jouhaud (Lactobacillales: Enterococcaceae) was higher and lower, respectively, in larvae with mild AVD than those in healthy larvae. A. pernyi vomit disease infection significantly increased the genera with abundance <1%. In the gut of larvae with severe AVD, the proportion of Turicibacter Bosshard et al. (Erysipelotrichales: Turicibacteraceae) increased significantly to 81.53-99.92%, whereas that of Enterobacter decreased compared with healthy larvae. However, the diversity of fecal bacteria was similar between healthy larvae and those with mild AVD. Overall, the findings demonstrate that intestinal microflora in A. pernyi larvae are altered by AVD infection and may cause secondary bacterial infection. This is the first report of the presence of Turicibacter in the intestinal tract of lepidopterans.

Host-microbiome metabolism of a plant toxin in bees

While foraging for nectar and pollen, bees are exposed to a myriad of xenobiotics, including plant metabolites, which may exert a wide range of effects on their health. Although the bee genome encodes enzymes that help in the metabolism of xenobiotics, it has lower detoxification gene diversity than the genomes of other insects. Therefore, bees may rely on other components that shape their physiology, such as the microbiota, to degrade potentially toxic molecules. In this study, we show that amygdalin, a cyanogenic glycoside found in honey bee-pollinated almond trees, can be metabolized by both bees and members of the gut microbiota. In microbiota-deprived bees, amygdalin is degraded into prunasin, leading to prunasin accumulation in the midgut and hindgut. In microbiota-colonized bees, on the other hand, amygdalin is degraded even further, and prunasin does not accumulate in the gut, suggesting that the microbiota contribute to the full degradation of amygdalin into hydrogen cyanide. In vitro experiments demonstrated that amygdalin degradation by bee gut bacteria is strain-specific and not characteristic of a particular genus or species. We found strains of Bifidobacterium, Bombilactobacillus, and Gilliamella that can degrade amygdalin. The degradation mechanism appears to vary since only some strains produce prunasin as an intermediate. Finally, we investigated the basis of degradation in Bifidobacterium wkB204, a strain that fully degrades amygdalin. We found overexpression and secretion of several carbohydrate-degrading enzymes, including one in glycoside hydrolase family 3 (GH3). We expressed this GH3 in Escherichia coli and detected prunasin as a byproduct when cell lysates were cultured with amygdalin, supporting its contribution to amygdalin degradation. These findings demonstrate that both host and microbiota can act together to metabolize dietary plant metabolites.

In-depth investigation of microRNA-mediated cross-kingdom regulation between Asian honey bee and microsporidian

Asian honey bee Apis cerana is the original host for Nosema ceranae, a unicellular fungal parasite that causes bee nosemosis throughout the world. Currently, interaction between A. cerana and N. ceranae is largely unknown. Our group previously prepared A. c. cerana workers’ midguts at 7 days post inoculation (dpi) and 10 dpi with N. ceranae spores as well as corresponding un-inoculated workers’ midguts, followed by cDNA library construction and a combination of RNAs-seq and small RNA-seq. Meanwhile, we previously prepared clean spores of N. ceranae, which were then subjected to cDNA library construction and deep sequencing. Here, based on the gained high-quality transcriptome datasets, N. ceranae differentially expressed mRNAs (DEmiRNAs) targeted by host DEmiRNAs, and A. c. cerana DEmRNAs targeted by microsporidian DEmiRNAs were deeply investigated, with a focus on targets involved in N. ceranae glycolysis/glyconeogenesis as well as virulence factors, and A. c. cerana energy metabolism and immune response. In A. c. cerana worker’s midguts at 7 (10) dpi (days post inoculation), eight (seven) up-regulated and six (two) down-regulated miRNAs were observed to target 97 (44) down-regulated and 60 (15) up-regulated N. ceranae mRNAs, respectively. Additionally, two up-regulated miRNAs (miR-60-y and miR-676-y) in host midgut at 7 dpi could target genes engaged in N. ceranae spore wall protein and glycolysis/gluconeogenesis, indicating potential host miRNA-mediated regulation of microsporidian virulence factor and energy metabolism. Meanwhile, in N. ceranae at 7 (10) dpi, 121 (110) up-regulated and 112 (104) down-regulated miRNAs were found to, respectively, target 343 (247) down-regulated and 138 (110) down-regulated mRNAs in A. c. cerana workers’ midguts. These targets in host were relevant to several crucial cellular and humoral immune pathways, such as phagasome, endocytosis, lysosomes, regulation of autophagy, and Jak–STAT signaling pathway, indicative of the involvement of N. ceranae DEmiRNAs in regulating these cellular and humoral immune pathways. In addition, N. ceranae miR-21-x was up-regulated at 7 dpi and had a target relative to oxidative phosphorylation, suggesting that miR-21-x may be used as a weapon to modulate this pivotal energy metabolism pathway. Furthermore, potential targeting relationships between two pairs of host DEmiRNAs-microsporidian DEmRNAs and two pairs of microsporidian DEmiRNAs-host DEmRNAs were validated using RT-qPCR. Our findings not only lay a foundation for exploring the molecular mechanism underlying cross-kingdom regulation between A. c. cerana workers and N. ceranae, but also offer valuable insights into Asian honey bee-microsporidian interaction.

Significant compositional and functional variation reveals the patterns of gut microbiota evolution among the widespread Asian honeybee populations

The gut microbiome is a crucial element that facilitates a host’s adaptation to a changing environment. Compared to the western honeybee Apis mellifera, the Asian honeybee, Apis cerana populations across its natural range remain mostly semi-feral and are less affected by bee management, which provides a good system to investigate how gut microbiota evolve under environmental heterogeneity on large geographic scales. We compared and analyzed the gut microbiomes of 99 Asian honeybees, from genetically diverged populations covering 13 provinces across China. Bacterial composition varied significantly across populations at phylotype, sequence-discrete population (SDP), and strain levels, but with extensive overlaps, indicating that the diversity of microbial community among A. cerana populations is driven by nestedness. Pollen diets were significantly correlated with both the composition and function of the gut microbiome. Core bacteria, Gilliamella and Lactobacillus Firm-5, showed antagonistic turnovers and contributed to the enrichment in carbohydrate transport and metabolism. By feeding and inoculation bioassays, we confirmed that the variations in pollen polysaccharide composition contributed to the trade-off of these core bacteria. Progressive change, i.e., nestedness, is the foundation of gut microbiome evolution among the Asian honeybee. Such a transition during the co-diversification of gut microbiomes is affected by environmental factors, diets in general, and pollen polysaccharides in particular.

Prospects for probiotics in social bees

Social corbiculate bees are major pollinators. They have characteristic bacterial microbiomes associated with their hives and their guts. In honeybees and bumblebees, worker guts contain a microbiome composed of distinctive bacterial taxa shown to benefit hosts. These benefits include stimulating immune and metabolic pathways, digesting or detoxifying food, and defending against pathogens and parasites. Stressors including toxins and poor nutrition disrupt the microbiome and increase susceptibility to opportunistic pathogens. Administering probiotic bacterial strains may improve the health of individual bees and of hives, and several commercial probiotics are available for bees. However, evidence for probiotic benefits is lacking or mixed. Most bacterial species used in commercial probiotics are not native to bee guts. We present new experimental results showing that cultured strains of native bee gut bacteria colonize robustly while bacteria in a commercial probiotic do not establish in bee guts. A defined community of native bee gut bacteria resembles unperturbed native gut communities in its activation of genes for immunity and metabolism in worker bees. Although many questions remain unanswered, the development of natural probiotics for honeybees, or for commercially managed bumblebees, is a promising direction for protecting the health of managed bee colonies.

This article is part of the theme issue ‘Natural processes influencing pollinator health: from chemistry to landscapes’.

Understanding effects of floral products on bee parasites: Mechanisms, synergism, and ecological complexity

Floral nectar and pollen commonly contain diverse secondary metabolites. While these compounds are classically thought to play a role in plant defense, recent research indicates that they may also reduce disease in pollinators. Given that parasites have been implicated in ongoing bee declines, this discovery has spurred interest in the potential for 'medicinal' floral products to aid in pollinator conservation efforts. We review the evidence for antiparasitic effects of floral products on bee diseases, emphasizing the importance of investigating the mechanism underlying antiparasitic effects, including direct or host-mediated effects. We discuss the high specificity of antiparasitic effects of even very similar compounds, and highlight the need to consider how nonadditive effects of multiple compounds, and the post-ingestion transformation of metabolites, mediate the disease-reducing capacity of floral products. While the bulk of research on antiparasitic effects of floral products on bee parasites has been conducted in the lab, we review evidence for the impact of such effects in the field, and highlight areas for future research at the floral product-bee disease interface. Such research has great potential both to enhance our understanding of the role of parasites in shaping plant-bee interactions, and the role of plants in determining bee-parasite dynamics. This understanding may in turn reveal new avenues for pollinator conservation.

The Role of Nosema ceranae (Microsporidia: Nosematidae) in Honey Bee Colony Losses and Current Insights on Treatment

Honeybee populations have locally and temporally declined in the last few years because of both biotic and abiotic factors. Among the latter, one of the most important reasons is infection by the microsporidia Nosema ceranae, which is the etiological agent of type C nosemosis. This species was first described in Asian honeybees (Apis cerana). Nowadays, domestic honeybees (Apis mellifera) worldwide are also becoming infected due to globalization. Type C nosemosis can be asymptomatic or can cause important damage to bees, such as changes in temporal polyethism, energy and oxidative stress, immunity loss, and decreased average life expectancy. It causes drastic reductions in workers, numbers of broods, and honey production, finally leading to colony loss. Common treatment is based on fumagillin, an antibiotic with side effects and relatively poor efficiency, which is banned in the European Union. Natural products, probiotics, food supplements, nutraceuticals, and other veterinary drugs are currently under study and might represent alternative treatments. Prophylaxis and management of affected colonies are essential to control the disease. While N. ceranae is one potential cause of bee losses in a colony, other factors must also be considered, especially synergies between microsporidia and the use of insecticides.

Pesticide-induced disturbances of bee gut microbiotas

Social bee gut microbiotas play key roles in host health and performance. Worryingly, a growing body of literature shows that pesticide exposure can disturb these microbiotas. Most studies examine changes in taxonomic composition in Western honey bee (Apis mellifera) gut microbiotas caused by insecticide exposure. Core bee gut microbiota taxa shift in abundance after exposure but are rarely eliminated, with declines in Bifidobacteriales and Lactobacillus near melliventris abundance being the most common shifts. Pesticide concentration, exposure duration, season and concurrent stressors all influence whether and how bee gut microbiotas are disturbed. Also, the mechanism of disturbance-i.e. whether a pesticide directly affects microbial growth or indirectly affects the microbiota by altering host health-likely affects disturbance consistency. Despite growing interest in this topic, important questions remain unanswered. Specifically, metabolic shifts in bee gut microbiotas remain largely uninvestigated, as do effects of pesticide-disturbed gut microbiotas on bee host performance. Furthermore, few bee species have been studied other than A. mellifera, and few herbicides and fungicides have been examined. We call for these knowledge gaps to be addressed so that we may obtain a comprehensive picture of how pesticides alter bee gut microbiotas, and of the functional consequences of these changes.

The Pass-on Effect of Tetracycline-Induced Honey Bee (Apis mellifera) Gut Community Dysbiosis

Gut microbial community plays an important role in the regulation of insect health. Antibiotic treatment is powerful to fight bacterial infections, while it also causes collateral damage to gut microbiome, which may have long-lasting consequences for host health. However, current studies on honey bees mainly focus on the impact of direct exposure to antibiotics on individual bees, and little is known about the impact of social transmission of antibiotic-induced gut community disorder in honey bee colonies. In order to provide insight into the potential pass-on effect of antibiotic-induced dysbiosis, we colonized newly emerged germ-free workers with either normal or tetracycline-treated gut community and analyzed the gut bacteria composition. We also treated workers with low dosage of tetracycline to evaluate its impact on honey bee gut microbiota. Our results showed that the tetracycline-treated gut community caused disruption of gut community in their receivers, while the direct exposure to the low dosage of tetracycline had no significant effect. In addition, no significant difference was observed on the mortality rate of A. mellifera workers with different treatments. These results suggest that though the residue of antibiotic treatment may not have direct effect on honey bee gut community, the gut microbiota dysbiosis caused by high dosage of antibiotic treatment has a cascade effect on the gut community of the nestmates in honeybee colonies.

Nosema apis and N. ceranae Infection in Honey bees: A Model for Host-Pathogen Interactions in Insects

There has been increased focus on the role of microbial attack as a potential cause of recent declines in the health of the western honey bee, Apis mellifera. The Nosema species, N. apis and N. ceranae, are microsporidian parasites that are pathogenic to honey bees, and infection by these species has been implicated as a key factor in honey bee losses. Honey bees infected with both Nosema spp. display significant changes in their biology at the cellular, tissue, and organismal levels impacting host metabolism, immune function, physiology, and behavior. Infected individuals lead to colony dysfunction and can contribute to colony disease in some circumstances. The means through which parasite growth and tissue pathology in the midgut lead to the dramatic physiological and behavioral changes at the organismal level are only partially understood. In addition, we possess only a limited appreciation of the elements of the host environment that impact pathogen growth and development. Critical for answering these questions is a mechanistic understanding of the host and pathogen machinery responsible for host-pathogen interactions. A number of approaches are already being used to elucidate these mechanisms, and promising new tools may allow for gain- and loss-of-function experiments to accelerate future progress.

Enterococcus faecium Regulates Honey Bee Developmental Genes

Honey bees provide essential pollination services to the terrestrial ecosystem and produce important agricultural products. As a beneficial lactic acid bacterium, Enterococcus faecium is often supplied as a probiotic for honey bees and other animals. However, the underlying mechanisms of its actions and possible safety risks are not well understood. We present the first complete genome sequence of E. faecium isolated from the honey bee gut using nanopore sequencing, and investigate the effects and mechanisms of interactions between E. faecium and honey bees via transcriptome and miRNA analysis. E. faecium colonization increased honey bee gut weight. Transcriptome analysis showed that developmental genes were up-regulated. In accordance, the target genes of the down-regulated miRNAs were enriched in developmental pathways. We describe how E. faecium increases honey bee gut weight at the transcriptional and post-transcriptional levels, and add insights about how miRNAs mediate host and bacteria interactions.

Transcriptome analysis of Apis mellifera under benomyl stress to discriminate the gene expression in response to development and immune systems

The health and safety of the honeybees are seriously threatened due to the abuse of chemical pesticides in modern agriculture and apiculture. In this study, the RNA Seq approach was used to assess the effects of the honeybees treated with benomyl. The results showed that there were a total of 11,902 differentially expressed genes (DEGs). Among them, 5,759 DEGs were up-regulated and involved in the functions of immunity, detoxification, biological metabolism, and regulation. The DEGs were clustered in the GO terms of epidermal structure and response to external stimuli, and most of the DEGs were enriched in 15 pathways, such as light conduction, MAPK, calcium ion pathway, and so on. Moreover, the pathway of the toll signal transduction was activated. The data investigated that the expression of functional genes involved in the growth, development, foraging, and immunity of honeybees were significantly affected by benomyl stress, which would seriously threaten the health of the honeybees. This study provided a theoretical basis for revealing the response mechanism of honeybees to pesticides stress.

Heliconius Butterflies Host Characteristic and Phylogenetically Structured Adult-Stage Microbiomes

Lepidoptera (butterflies and moths) are diverse and ecologically important, yet we know little about how they interact with microbes as adults. Due to metamorphosis, the form and function of their adult-stage microbiomes might be very different from those of microbiomes in the larval stage (caterpillars). We studied adult-stage microbiomes of Heliconius and closely related passion-vine butterflies (Heliconiini), which are an important model system in evolutionary biology. To characterize the structure and dynamics of heliconiine microbiomes, we used field collections of wild butterflies, 16S rRNA gene sequencing, quantitative PCR, and shotgun metagenomics. We found that Heliconius butterflies harbor simple and abundant bacterial communities that are moderately consistent among conspecific individuals and over time. Heliconiine microbiomes also exhibited a strong signal of the host phylogeny, with a major distinction between Heliconius and other butterflies. These patterns were largely driven by differing relative abundances of bacterial phylotypes shared among host species and genera, as opposed to the presence or absence of host-specific phylotypes. We suggest that the phylogenetic structure in heliconiine microbiomes arises from conserved host traits that differentially filter microbes from the environment. While the relative importance of different traits remains unclear, our data indicate that pollen feeding (unique to Heliconius) is not a primary driver. Using shotgun metagenomics, we also discovered trypanosomatids and microsporidia to be prevalent in butterfly guts, raising the possibility of antagonistic interactions between eukaryotic parasites and colocalized gut bacteria. Our discovery of characteristic and phylogenetically structured microbiomes provides a foundation for tests of adult-stage microbiome function, a poorly understood aspect of lepidopteran biology.IMPORTANCE Many insects host microbiomes with important ecological functions. However, the prevalence of this phenomenon is unclear because in many insect taxa, microbiomes have been studied in only part of the life cycle, if at all. A prominent example is butterflies and moths, in which the composition and functional role of adult-stage microbiomes are largely unknown. We comprehensively characterized microbiomes in adult passion-vine butterflies. Butterfly-associated bacterial communities are generally abundant in guts, consistent within populations, and composed of taxa widely shared among hosts. More closely related butterflies harbor more similar microbiomes, with the most dramatic shift in microbiome composition occurring in tandem with a suite of ecological and life history traits unique to the genus Heliconius Butterflies are also frequently infected with previously undescribed eukaryotic parasites, which may interact with bacteria in important ways. These findings advance our understanding of butterfly biology and insect-microbe interactions generally.