Project description:The honey bee, Apis mellifera, pollinates a wide variety of essential crops in numerous ecosystems around the world but faces many modern challenges. Among these, the microsporidian pathogen Nosema ceranae is one of the primary detriments to honey bee health. Nosema infects the honey bee gut, which harbors a highly specific, coevolved microbiota heavily involved in bee immune function and nutrition. Here, we extend previous work investigating interactions between the honey bee gut microbiome and N. ceranae by studying experimentally infected bees that were returned to their colonies and sampled 5, 10, and 21 days post-infection. We measured Nosema load with quantitative PCR and characterized microbiota with 16S rRNA gene amplicon sequencing. We found significant colony level variation in infection levels, and subtle differences between the microbiota of colonies with high infection levels versus those with low infection levels. Two exact sequence variants of Gilliamella, a core gut symbiont that has previously been associated with gut dysbiosis, were significantly more abundant in bees from colonies with high Nosema loads versus those with low Nosema loads. These bacteria deserve further study to determine if they facilitate more intense infection by Nosema ceranae.
Project description:BackgroundGut microbial communities can contribute positively and negatively to host health. So far, eight core bacterial taxonomic clusters have been reported in honey bees. These bacteria are involved in host metabolism and defenses. Nosema ceranae is a gut intracellular parasite of honey bees which destroys epithelial cells and gut tissue integrity. Studies have shown protective impacts of honey bee gut microbiota towards N. ceranae infection. However, the impacts of N. ceranae on the relative abundance of honey bee gut microbiota remains unclear, and has been confounded during prior infection assays which resulted in the co-inoculation of bacteria during Nosema challenges. We used a novel method, the suppression of N. ceranae with specific siRNAs, to measure the impacts of Nosema on the gut microbiome.ResultsSuppressing N. ceranae led to significant positive effects on microbial abundance. Nevertheless, 15 bacterial taxa, including three core taxa, were negatively correlated with N. ceranae levels. In particular, one co-regulated group of 7 bacteria was significantly negatively correlated with N. ceranae levels.ConclusionsN. ceranae are negatively correlated with the abundance of 15 identified bacteria. Our results provide insights into interactions between gut microbes and N. ceranae during infection.
Project description:Nosema ceranae is a honey bee gut parasite that has recently spilled to another honey bee host through trading. The impact of infection on the native host is minor, which is substantial in the novel host. In this study, artificial inoculation simulated the parasite transmission from the native to the novel host. We found that the parasite initiated proliferation earlier in the novel host than in the native host. Additionally, parasite gene expression was significantly higher when infecting the novel host compared with the native host, leading to a significantly higher number of spores. Allele frequencies were similar for spores of parasites infecting both native and novel hosts. This suggests that the high number of spores found in the novel host was not caused by a subset of more fit spores from native hosts. Native hosts also showed a higher number of up-regulated genes in response to infection when compared with novel hosts. Our data further showed that native hosts suppressed parasite gene expression and arguably sacrificed cells to limit the parasite. The results provide novel insights into host defenses and gene selection during a parasite spillover event.
Project description:In order to study the effects of Nosema ceranae infection on honey bee microRNA (miRNA) expression, we deep-sequenced honey bee miRNAs daily across a full 6-day parasite reproduction cycle. Seventeen miRNAs were differentially expressed in honey bees infected by N. ceranae that potentially target over 400 genes predicted to primarily involve ion binding, signaling, the nucleus, transmembrane transport, and DNA binding. Based on Enzyme Code analysis, nine biological pathways were identified by screening target genes against the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, seven of which involved metabolism. Our results suggest that differentially expressed miRNAs regulate metabolism related genes of host honey bees in response to N. ceranae infection.
Project description:Nosema ceranae, a newly introduced parasite of the honey bee, Apis mellifera, is contributing to worldwide colony losses. Other Nosema species, such as N. apis, tend to be associated with increased defecation and spread via a fecal-oral pathway, but because N. ceranae does not induce defecation, it may instead be spread via an oral-oral pathway. Cages that separated older infected bees from young uninfected bees were used to test whether N. ceranae can be spread during food exchange. When cages were separated by one screen, food could be passed between the older bees and the young bees, but when separated by two screens, food could not be passed between the two cages. Young uninfected bees were also kept isolated in cages, as a solitary control. After 4 days of exposure to the older bees, and 10 days to incubate infections, young bees were more likely to be infected in the 1-Screen Test treatment vs. the 2-Screen Test treatment (P=0.0097). Young bees fed by older bees showed a 13-fold increase in mean infection level relative to young bees not fed by older bees (1-Screen Test 40.8%; 2-Screen Test 3.4%; Solo Control 2.8%). Although fecal-oral transmission is still possible in this experimental design, oral-oral infectivity could help explain the rapid spread of N. ceranae worldwide.
Project description:Honey bee (Apis mellifera) health has been severely impacted by multiple environmental stressors including parasitic infection, pesticide exposure, and poor nutrition. The decline in bee health is therefore a complex multifactorial problem which requires a holistic investigative approach. Within the exposome paradigm, the combined exposure to the environment, drugs, food, and individuals' internal biochemistry affects health in positive and negative ways. In the context of the exposome, honey bee hive infection with parasites such as Nosema ceranae is also a form of environmental exposure. In this study, we hypothesized that exposure to xenobiotic pesticides and other environmental chemicals increases susceptibility to N. ceranae infection upon incidental exposure to the parasite. We further queried whether these exposures could be linked to changes in conserved metabolic biological pathways. From 30 hives sampled across 10 sites, a total of 2,352 chemical features were found via gas chromatography-time of flight mass spectrometry (GC-TOF) in extracts of honey bees collected from each hive. Of these, 20 pesticides were identified and annotated, and found to be significantly associated with N. ceranae infection. We further determined that infected hives were linked to a greater number of xenobiotic exposures, and the relative concentration of the exposures were not linked to the presence of a N. ceranae infection. In the exposome profiles of the bees, we also found chemicals inherent to known biological metabolic pathways of Apis mellifera and identified 9 dysregulated pathways. These findings have led us to posit that for hives exposed to similar chemicals, those that incur multiple, simultaneous xenobiotic stressors have a greater incidence of infection with N. ceranae. Mechanistically, our results suggests the overwhelming nature of these exposures negatively affects the biological functioning of the bee, and could explain how the decline in bee populations is associated with pesticide exposures.
Project description:The research aims to give new insights on the effect of administering selected bacterial strains, isolated from honey bee gut, and/or a commercial plant extract blend (HiveAlive®) on Nosema ceranae. Analyses were first performed under laboratory conditions such as different infective doses of N. ceranae, the effect of single strains and their mixture and the influence of pollen administration. Daily survival and feed consumption rate were recorded and pathogen development was analysed using qPCR and microscope counts. Biomarkers of immunity and physiological status were also evaluated for the different treatments tested using one bacterial strain, a mixture of all the bacteria and/or a plant extract blend as treatments. The results showed an increase of abaecin transcript levels in the midgut of the honey bees treated with the bacterial mixture and an increased expression of the protein vitellogenin in the haemolymph of honey bees treated with two separate bacterial strains (Bifidobacterium coryneforme and Apilactobacillus kunkeei). A significant effectiveness in reducing N. ceranae was shown by the bacterial mixture and the plant extract blend regardless of the composition of the diet. This bioactivity was seasonally linked. Quantitative PCR and microscope counts showed the reduction of N. ceranae under different experimental conditions. The antiparasitic efficacy of the treatments at field conditions was studied using a semi-field approach which was adapted from research on insecticides for the first time, to analyse antiparasitic activity against N. ceranae. The approach proved to be reliable and effective in validating data obtained in the laboratory. Both the mixture of beneficial bacteria and its association with Hive Alive® are effective in controlling the natural infection of N. ceranae in honey bee colonies.
Project description:The microsporidium Nosema ceranae is a newly prevalent parasite of the European honey bee (Apis mellifera). Although this parasite is presently spreading across the world into its novel host, the mechanisms by it which affects the bees and how bees respond are not well understood. We therefore performed an extensive characterization of the parasite effects at the molecular level by using genetic and biochemical tools. The transcriptome modifications at the midgut level were characterized seven days post-infection with tiling microarrays. Then we tested the bee midgut response to infection by measuring activity of antioxidant and detoxification enzymes (superoxide dismutases, glutathione peroxidases, glutathione reductase, and glutathione-S-transferase). At the gene-expression level, the bee midgut responded to N. ceranae infection by an increase in oxidative stress concurrent with the generation of antioxidant enzymes, defense and protective response specifically observed in the gut of mammals and insects. However, at the enzymatic level, the protective response was not confirmed, with only glutathione-S-transferase exhibiting a higher activity in infected bees. The oxidative stress was associated with a higher transcription of sugar transporter in the gut. Finally, a dramatic effect of the microsporidia infection was the inhibition of genes involved in the homeostasis and renewal of intestinal tissues (Wnt signaling pathway), a phenomenon that was confirmed at the histological level. This tissue degeneration and prevention of gut epithelium renewal may explain early bee death. In conclusion, our integrated approach not only gives new insights into the pathological effects of N. ceranae and the bee gut response, but also demonstrate that the honey bee gut is an interesting model system for studying host defense responses.
Project description:Vairimorpha (Nosema) ceranae is the most common eukaryotic gut pathogen in honey bees. Infection is typically chronic but may result in mortality. Gut microbiota is a factor that was recently noted for gut infectious disease development. Interestingly, studies identified positive, instead of negative, associations between core bacteria of honey bee microbiota and V. ceranae infection. To investigate the effects of the positive associations, we added isomaltooligosaccharide (IMO), a prebiotic sugar also found in honey, to enhance the positive associations, and we then investigated the infection and the gut microbiota alterations using qPCR and 16S rRNA gene sequencing. We found that infected bees fed IMO had significantly higher V. ceranae spore counts but lower mortalities. In microbiota comparisons, V. ceranae infections alone significantly enhanced the overall microbiota population in the honey bee hindgut and feces; all monitored core bacteria significantly increased in the quantities but not all in the population ratios. The microbiota alterations caused by the infection were enhanced with IMO, and these alterations were similar to the differences found in bees that naturally have longer lifespans. Although our results did not clarify the causations of the positive associations between the infections and microbiota, the associations seemed to sustain the host survival and benefit the pathogen. Enhancing indigenous gut microbe to control nosema disease may result in an increment of bee populations but not the control of the pathogen. This interaction between the pathogen and microbiota potentially enhances disease transmission and avoids the social immune responses that diseased bees die prematurely to curb the disease from spreading within colonies.
Project description:Apis cerana is the original host for Nosema ceranae, a widespread fungal parasite resulting in honey bee nosemosis, which leads to severe losses to the apiculture industry throughout the world. However, knowledge of N. ceranae infecting eastern honey bees is extremely limited. Currently, the mechanism underlying N. ceranae infection is still largely unknown. Based on our previously gained high-quality transcriptome datasets derived from N. ceranae spores (NcCK group), N. ceranae infecting Apis cerana cerana workers at seven days post inoculation (dpi) and 10 dpi (NcT1 and NcT2 groups), comparative transcriptomic investigation was conducted in this work, with a focus on virulence factor-associated differentially expressed genes (DEGs). Microscopic observation showed that the midguts of A. c. cerana workers were effectively infected after inoculation with clean spores of N. ceranae. In total, 1411, 604, and 38 DEGs were identified from NcCK vs. NcT1, NcCK vs. NcT2, and NcT1 vs. NcT2 comparison groups. Venn analysis showed that 10 upregulated genes and nine downregulated ones were shared by the aforementioned comparison groups. The GO category indicated that these DEGs were involved in a series of functional terms relevant to biological process, cellular component, and molecular function such as metabolic process, cell part, and catalytic activity. Additionally, KEGG pathway analysis suggested that the DEGs were engaged in an array of pathways of great importance such as metabolic pathway, glycolysis, and the biosynthesis of secondary metabolites. Furthermore, expression clustering analysis demonstrated that the majority of genes encoding virulence factors such as ricin B lectins and polar tube proteins displayed apparent upregulation, whereas a few virulence factor-associated genes such as hexokinase gene and 6-phosphofructokinase gene presented downregulation during the fungal infection. Finally, the expression trend of 14 DEGs was confirmed by RT-qPCR, validating the reliability of our transcriptome datasets. These results together demonstrated that an overall alteration of the transcriptome of N. ceranae occurred during the infection of A. c. cerana workers, and most of the virulence factor-related genes were induced to activation to promote the fungal invasion. Our findings not only lay a foundation for clarifying the molecular mechanism underlying N. ceranae infection of eastern honey bee workers and microsporidian-host interaction.