Microbial symbionts of honeybees: a promising tool to improve honeybee health

Synergistic resistance of honeybee (Apis mellifera) and their gut microorganisms to fluvalinate stress

Fluvalinate is widely used in the control of Varroa destructor, but its residues in colonies threaten honeybees. The effect of fluvalinate-induced dysbiosis on honeybee-related gene expression and the gut microenvironment of honeybees has not yet been fully elucidated. In this study, two-day-old larvae to seven-day-old adult worker bees were continuously fed different amounts of fluvalinate-sucrose solutions (0, 0.5, 5, and 50 mg/kg), after which the expression levels of two immune-related genes (Hymenoptaecin and Defensin1) and three detoxication-related genes (GSTS3, CAT, and CYP450) in worker bees (1, 7, and 20 days old) were measured. The effect of fluvalinate on the gut microbes of worker bees at seven days old also was explored using 16S rRNA Illumina deep sequencing. The results showed that exposure of honeybees to the insecticide fluvalinate affected their gene expression and gut microbial composition. As the age of honeybees increased, the effect of fluvalinate on the expression of Hymenoptaecin, CYP450, and CAT decreased, and the abundance of honeybee gut bacteria was affected by increasing the fluvalinate concentration. These findings provide insights into the synergistic defense of honeybee hosts against exogenous stresses in conjunction with honeybee gut microbes.

Episyrphus balteatus symbiont variation across developmental stages, living states, two sexes, and potential horizontal transmission from prey or environment

Introduction

Episyrphus balteatus is one representative Syrphidae insect which can provide extensive pollination and pest control services. To date, the symbiont composition and potential acquisition approaches in Syrphidae remain unclear.

Methods

Herein, we investigated microbiota dynamics across developmental stages, different living states, and two sexes in E. balteatus via full-length 16S rRNA genes sequencing, followed by an attempt to explore the possibility of symbiont transmission from prey Megoura crassicauda to the hoverfly.

Results

Overall, Proteobacteria and Firmicutes were the dominant bacteria phyla with fluctuating relative abundances across the life stage. Cosenzaea myxofaciens is dominant in adulthood, while Enterococcus silesiacus and Morganella morganii dominate in larvae and pupae of E. balteatus, respectively. Unexpectedly, Serratia symbiotica, one facultative endosymbiont commonly harbored in aphids, was one of the predominant bacteria in larvae of E. balteatus, just behind Enterococcus silesiacus. In addition, S. symbiotica was also surprisingly most dominated in M. crassicauda aphids (92.1% relative abundance), which are significantly higher than Buchnera aphidicola (4.7% relative abundance), the primary obligate symbiont of most aphid species. Approximately 25% mortality was observed among newly emerged adults, of which microbiota was also disordered, similar to normally dying individuals. Sexually biased symbionts and 41 bacteria species with pairwise co-occurrence in E. balteatus and 23 biomarker species for each group were identified eventually. Functional prediction showed symbionts of hoverflies and aphids, both mainly focusing on metabolic pathways. In brief, we comprehensively explored the microbiome in one Syrphidae hoverfly using E. balteatus reared indoors on M. morganii as the model, revealed its dominated symbiont species, identified sexually biased symbionts, and found an aphid facultative endosymbiont inhabited in the hoverfly. We also found that the dominated symbiotic bacteria in M. crassicauda are S. symbiotica other than Buchnera aphidicola.

Discussion

Taken together, this study provides new valuable resources about symbionts in hoverflies and prey aphids jointly, which will benefit further exploring the potential roles of microbiota in E. balteatus.

Gut microbial diversity in Apis cerana indica and Apis florea colonies: a comparative study

Introduction

Honey bee gut microbiota have an important role in host health, nutrition, host-symbiont interaction, and interaction behavior with the surrounding environment. Recent discoveries of strain-level variation, characteristics of protective and nutritional capabilities, and reports of eco-physiological significance to the microbial community have emphasized the importance of honey bee gut microbiota. Many regions of Asia and Africa are inhabited by the dwarf honey bee, Apis florea. Studying its microflora and potential for pollination is therefore of foremost importance.

Methods

In the present investigation, we aimed to explore the gut bacteriobiome composition of two distinct honey bee species, Apis florea and Apis cerana indica using high throughput sequencing. Functional predictions of bee gut bacterial communities using PICRUSt2 was carried out.

Results and discussion

The phylum Proteobacteria dominated the bacterial community in both A. cerana indica (50.1%) and A. florea (86.7%), followed by Firmicutes (26.29 and 12.81%), Bacteroidetes (23.19 and 0.04%) and Actinobacteria (0.4 and 0.02%) respectively. The gut bacteria of A. cerana indica was more diverse than that of A. florea. The observed variations in bacterial genomic diversity among these critical pollinator species may have been influenced by the apiary management techniques, ecological adaptation factors or habitat size. These variations can have a significant effect in understanding host-symbiont interactions and functioning of gut microbiota highlighting the importance of metagenomic survey in understanding microbial community ecology and evolution. This is the first comparative study on variation in bacterial diversity between two Asian honey bees.

Beneficial bacteria as biocontrol agents for American foulbrood disease in honey bees (Apis mellifera)

American foulbrood (AFB) is a cosmopolitan bacterial disease that affects honey bee (Apis mellifera) larvae and causes great economic losses in apiculture. Currently, no satisfactory methods are available for AFB treatment mainly due to the difficulties to eradicate the tenacious spores produced by the etiological agent of AFB, Paenibacillus larvae (Bacillales, Paenibacillaceae). This present review focused on the beneficial bacteria that displayed antagonistic activities against P. larvae and demonstrated potential in AFB control. Emphases were placed on commensal bacteria (genus Bacillus and lactic acid bacteria in particular) in the alimentary tract of honey bees. The probiotic roles lactic acid bacteria play in combating the pathogenic P. larvae and the limitations referring to the application of these beneficial bacteria were addressed.

The promise of probiotics in honeybee health and disease management

Over the last decades, losses of bee populations have been observed worldwide. A panoply of biotic and abiotic factors, as well as the interplay among them, has been suggested to be responsible for bee declines, but definitive causes have not yet been identified. Among pollinators, the honeybee Apis mellifera is threatened by various diseases and environmental stresses, which have been shown to impact the insect gut microbiota that is known to be fundamental for host metabolism, development and immunity. Aimed at preserving the gut homeostasis, many researches are currently focusing on improving the honeybee health through the administration of probiotics e.g., by boosting the innate immune response against microbial infections. Here, we review the knowledge available on the characterization of the microbial diversity associated to honeybees and the use of probiotic symbionts as a promising approach to maintain honeybee fitness, sustaining a healthy gut microbiota and enhancing its crucial relationship with the host immune system.

Probiotics as a promising prophylactic tool to reduce levels of toxic or potentially toxic elements in bees

Bees are precious living beings for our planet. Thanks to their essential service of pollination, these insects allow the maintenance of biodiversity and the variety and amount of food available. Unfortunately, we are observing an increasingly devastating reduction of bee families and other pollinating insects for factors related to human activities, environmental pollution, diseases and parasites, compromise of natural habitats, and climate change. We show that probiotics can protect bees from element pollution. We collected bees, beeswax, honey, pollen, and propolis directly from hives in a rural area of central Italy to investigate the content of 41 elements in control (not supplemented with probiotics) and experimental (supplemented with probiotics) groups. Our data show a significantly lower concentration of some elements (Ba, Be, Cd, Ce, Co, Cu, Pb, Sn, Tl, and U) in experimental bees than in control groups, indicating a possible beneficial effect of probiotics in reducing the absorption of chemicals. This study presents the first data on element levels after probiotics have been fed to bees and provides the basis for future research in several activities relating to the environment, agriculture, economy, territory, and medicine.

Chlorothalonil alters the gut microbiota and reduces the survival of immature honey bees reared in vitro

BACKGROUND

Chlorothalonil is a nonsystemic fungicide, and it is one of the most widely detected pesticides in bee hives. The effect of chlorothalonil on the survival, weight, and gut microbiota of immature Apis mellifera L. reared in vitro was studied.

RESULTS

Larvae were fed 1, 2, 4, 8, and 16 μg/mL chlorothalonil and compared with larvae fed the negative control (diet without any additives), positive control (45 mg/L dimethoate), and solvent control (2% acetone). Compared with the control groups, the survival of the 2, 4, 8, and 16 μg/mL chlorothalonil treatments was significantly reduced. The no-observed-adverse-effect concentration of chlorothalonil was 1 μg/mL. Chlorothalonil had no significant effect on larval weight. The gut bacterial community composition of newly emerged bees was determined by PacBio 16S rDNA gene sequencing. linear discriminant analysis effect size (LEFSe) analysis showed that Pseudomonadales and Burkholderiales were affected by exposure to chlorothalonil.

CONCLUSION

Chlorothalonil reduced the survival of honey bee larvae and altered the gut microbiota of newly emerged bees. The risk of pesticides to honey bees is related to their toxicity and exposure dose.

Recent Advances in the Biocontrol of Nosemosis in Honey Bees (Apis mellifera L.)

Nosemosis is a disease triggered by the single-celled spore-forming fungi Nosema apis and Nosema ceranae, which can cause extensive colony losses in honey bees (Apis mellifera L.). Fumagillin is an effective antibiotic treatment to control nosemosis, but due to its toxicity, it is currently banned in many countries. Accordingly, in the beekeeping sector, there is a strong demand for alternative ecological methods that can be used for the prevention and therapeutic control of nosemosis in honey bee colonies. Numerous studies have shown that plant extracts, RNA interference (RNAi) and beneficial microbes could provide viable non-antibiotic alternatives. In this article, recent scientific advances in the biocontrol of nosemosis are summarized.

Functional Properties and Antimicrobial Activity from Lactic Acid Bacteria as Resources to Improve the Health and Welfare of Honey Bees

Simple Summary

Honey bees play a pivotal role in the sustainability of ecosystems and biodiversity. Many factors including parasites, pathogens, pesticide residues, forage losses, and poor nutrition have been proposed to explain honey bee colony losses. Lactic acid bacteria (LAB) are normal inhabitants of the gastrointestinal tract of honey bees and their role has been consistently reported in the literature. In recent years, there have been numerous scientific evidence that the intestinal microbiota plays an essential role in honey bee health. Management strategies, based on supplementation of the gut microbiota with probiotics, may be important to increase stress tolerance and disease resistance. In this review, recent scientific advances on the use of LABs as microbial supplements in the diet of honey bees are summarized and discussed.

Abstract

Honey bees (Apis mellifera) are agriculturally important pollinators. Over the past decades, significant losses of wild and domestic bees have been reported in many parts of the world. Several biotic and abiotic factors, such as change in land use over time, intensive land management, use of pesticides, climate change, beekeeper’s management practices, lack of forage (nectar and pollen), and infection by parasites and pathogens, negatively affect the honey bee’s well-being and survival. The gut microbiota is important for honey bee growth and development, immune function, protection against pathogen invasion; moreover, a well-balanced microbiota is fundamental to support honey bee health and vigor. In fact, the structure of the bee’s intestinal bacterial community can become an indicator of the honey bee’s health status. Lactic acid bacteria are normal inhabitants of the gastrointestinal tract of many insects, and their presence in the honey bee intestinal tract has been consistently reported in the literature. In the first section of this review, recent scientific advances in the use of LABs as probiotic supplements in the diet of honey bees are summarized and discussed. The second section discusses some of the mechanisms by which LABs carry out their antimicrobial activity against pathogens. Afterward, individual paragraphs are dedicated to Chalkbrood, American foulbrood, European foulbrood, Nosemosis, and Varroosis as well as to the potentiality of LABs for their biological control.

Lactobacillus salivarius A3iob Reduces the Incidence of Varroa destructor and Nosema Spp. in Commercial Apiaries Located in the Northwest of Argentina

Lactobacillus salivarius A3iob was administered to productive colonies belonging to commercial apiaries of small beekeepers (around 30-50 hives each one), from four departments of the province of Jujuy (Argentina): Yala, Tilquiza, El Carmen, and Los Alisos. The incidence of Varroa destructor and Nosema spp., before and after winter, was monitored during 2 years of study (2014-2015). Depending on the geographical location of each apiary and the application time, a monthly dose of the bacteria (10⁵ CFU/mL) reduced the levels of varroasis between 50 and 80%. Interestingly, L. salivarius A3iob cells remitted the percentage of the mites to undetectable values in an apiary treated with flumethrin (at Yala, Yungas region).On the other hand, the spore levels of Nosema spp. in the lactobacilli-treated colonies also depended on the apiary and the year of application, but a significant decrease was mainly observed in the post-winter period. However, at Rivera (El Carmen's department), no significant changes were detected in both parameters.These results obtained after 2 years of work suggest that delivering L. salivarius A3iob cells to the bee colonies can become a new eco-friendly tool to cooperate with the control of these bees' pests.

A combination of Tropilaelaps mercedesae and imidacloprid negatively affects survival, pollen consumption and midgut bacterial composition of honey bee

Tropilaelaps mercedesae is not only a major threat to honey bees in Asia but also a potential risk to global apiculture due to trade. Imidacloprid is a systemic insecticide that negatively affects individual bees. Moreover, the health of honey bees may be threatened by imidacloprid exposure and T. mercedesae infestation. We studied the effects of T. mercedesae and imidacloprid on the survival, food consumption and midgut bacterial diversity of Apis mellifera in the laboratory. Illumina 16S rRNA gene sequencing was used to determine the bacterial composition in the honey bee midgut. T. mercedesae decreased survival in parasitized honey bees compared with nonparasitized honey bees, but there was no significant difference in food consumption. The imidacloprid 50 μg/L diet significantly decreased syrup consumption of A. mellifera compared with the control diet. The combination of T. mercedesae infestation and imidacloprid 50 μg/L exposure reduced survival and increased pollen consumption of A. mellifera. T. mercedesae infestation or a combination of T. mercedesae infestation and exposure to 25 μg/L imidacloprid affected the midgut bacterial composition of honey bees. T. mercedesae infestation and imidacloprid exposure may reduce the survival and affect honey bee health.

Insight into probiotic properties of lactic acid bacterial endosymbionts of Apis mellifera L. derived from the Polish apiary

Taking into account that fructophilic lactic acid bacteria (FLAB) can play an important role in the health of honey bees and can be used as probiotics, phenotypic properties of probiotic interest of Lactobacillus kunkeei (12 strains) and Fructobacillus fructossus bacteria (2 strains), isolated from Apis mellifera gastrointestinal tract, have been studied. We have evaluated survival of tested FLAB in honey bee gut, their susceptibility to antibiotics (ampicillin, erythromycin, tylosin), cell surface hydrophobicity, auto-aggregation ability, co-aggregation with model pathogenic bacteria, biofilm formation capacity, and effect of studied FLAB, added to sucrose syrup bee diet, on longevity of honey bees. The tested FLAB exhibited good gastrointestinal tract tolerance and high antibiotic susceptibility, which are important criteria in the screening of probiotic candidates. It was also found that all FLAB studied have high cell surface hydrophobicity and fulfil next selection criterion for their use as probiotics. Symbionts of A. mellifera showed also auto- and co-aggregation capacities regarded as valuable features for biofilm formation and inhibition of pathogens adhesion to the bee gut cells. Biofilm-development ability is a desired characteristic of probiotic lactic acid bacteria. As indicated by quantitative crystal violet-stained microplate assay and confocal laser scanning microscopy imaging, all studied A. mellifera gut isolates exhibit a biofilm positive phenotype. Moreover, it was also documented, on honey bees kept in cages, that supplementation of A. mellifera sucrose diet with FLAB decreases mortality and improves significantly longevity of honey bees. Presented research showed that A. mellifera FLAB symbionts are good candidates for application as probiotics.

Microbiota dysbiosis in honeybee (Apis mellifera L.) larvae infected with brood diseases and foraging bees exposed to agrochemicals

American foulbrood (AFB) disease and chalkbrood disease (CBD) are important bacterial and fungal diseases, respectively, that affect honeybee broods. Exposure to agrochemicals is an abiotic stressor that potentially weakens honeybee colonies. Gut microflora alterations in adult honeybees associated with these biotic and abiotic factors have been investigated. However, microbial compositions in AFB- and CBD-infected larvae and the profile of whole-body microbiota in foraging bees exposed to agrochemicals have not been fully studied. In this study, bacterial and fungal communities in healthy and diseased (AFB/CBD) honeybee larvae were characterized by amplicon sequencing of bacterial 16S rRNA gene and fungal internal transcribed spacer1 region, respectively. The bacterial and fungal communities in disordered foraging bees poisoned by agrochemicals were analysed. Our results revealed that healthy larvae were significantly enriched in bacterial genera Lactobacillus and Stenotrophomonas and the fungal genera Alternaria and Aspergillus. The enrichment of these microorganisms, which had antagonistic activities against the etiologic agents for AFB and CBD, respectively, may protect larvae from potential infection. In disordered foraging bees, the relative abundance of bacterial genus Gilliamella and fungal species Cystofilobasidium macerans were significantly reduced, which may compromise hosts' capacities in nutrient absorption and immune defence against pathogens. Significantly higher frequency of environmentally derived fungi was observed in disordered foraging bees, which reflected the perturbed microbiota communities of hosts. Results from PICRUSt and FUNGuild analyses revealed significant differences in gene clusters of bacterial communities and fungal function profiles. Overall, results of this study provide references for the composition and function of microbial communities in AFB- and CBD-infected honeybee larvae and foraging bees exposed to agrochemicals.

Efficiency of probiotic supplements in the dynamics of economically useful indicators of honey-bee colonies

In the modern world, the problem of honey-bee colonies’ death is acute. An intensive search is underway for environmentally friendly preparations that could stimulate the bees’ resistance to various diseases, as well as have a beneficial effect on the body, thereby contributing to an increase in honey productivity. Preparations based on live probiotics bacteria of Lactobacillus and Bacillus subtilis genus are currently becoming increasingly popular. The use of probiotics in beekeeping allows to destroy pathogenic microflora, strengthen immunity and activate the body’s metabolic processes. The aim of the study was to determine the influence efficiency of probiotic preparations complex ApiVrach, SpasiPchel, Pche-loNormoSil during the period of spring development on the economically useful traits of honey-bee colonies. Studies have found that when probiotics are added to sugar syrup in the spring, the brood growth of bee colonies and their honey productivity are activated. The flight activity of bees when feeding with probiotic preparations increased by 43.6% from the control group. When assessing the dynamics of the bee colony’s strength, it was found that the usage of “ApiVrach” + “PcheloNormoSil” combination allows increasing the amount of sealed brood by 4 times, and the strength of the bee colony - by 1.5 times. Also, this combination of preparations made it possible to obtain the largest amount of total honey yield by 19.2% more than the control group, by 3.0% more than the group that received the ApiVrach + SpasiPchel complex and by 1.1% more than when using ApiVrach.

Strains of Lactobacillus spp. reduce chalkbrood in Apis mellifera

Beekeeping activities have increased recently in Argentina, a country that is a major consumer of honey and other products from hives. With the advancement of monoculture areas in Argentina and worldwide, beekeepers move from one area to another in search of floral resources, thus spreading diseases such as chalkbrood, caused by the fungus Ascosphaera apis. Although there are few effective antifungals for the control of chalkbrood, different natural products have been investigated in recent years. Current research is focusing on the intestinal microbiota for the prevention of different pathogens and parasites. In this work, we analyzed the in vivo probiotic effect of three lactic acid bacteria (genus Lactobacillus spp.) isolated from pollen bread from apiaries of Jujuy province on A. apis strains from Spanish and Argentine provinces. Special hives were made for the assays, and a protective effect was observed in larvae of bees fed lactic acid bacteria added to sugar syrup at 10⁵ CFU/mL concentrations, administered from May to September in two consecutive years. The results showed that the three lactic acid bacteria reduced larval mummification by percentages greater than 80%. Therefore, this work brings a first approximation of the in vivo probiotic effect of lactic bacteria against A. apis.

Hydrolytic Profile of the Culturable Gut Bacterial Community Associated With Hermetia illucens

Larvae of the black soldier fly (BSF) Hermetia illucens (L.) convert organic waste into high valuable insect biomass that can be used as alternative protein source for animal nutrition or as feedstock for biodiesel production. Since insect biology and physiology are influenced by the gut microbiome, knowledge about the functional role of BSF-associated microorganisms could be exploited to enhance the insect performance and growth. Although an increasing number of culture-independent studies are unveiling the microbiota structure and composition of the BSF gut microbiota, a knowledge gap remains on the experimental validation of the contribution of the microorganisms to the insect growth and development. We aimed at assessing if BSF gut-associated bacteria potentially involved in the breakdown of diet components are able to improve host nutrition. A total of 193 bacterial strains were obtained from guts of BSF larvae reared on a nutritious diet using selective and enrichment media. Most of the bacterial isolates are typically found in the insect gut, with major representatives belonging to the Gammaproteobacteria and Bacilli classes. The hydrolytic profile of the bacterial collection was assessed on compounds typically present in the diet. Finally, we tested the hypothesis that the addition to a nutritionally poor diet of the two isolates Bacillus licheniformis HI169 and Stenotrophomonas maltophilia HI121, selected for their complementary metabolic activities, could enhance BSF growth. B. licheniformis HI169 positively influenced the larval final weight and growth rate when compared to the control. Conversely, the addition of S. maltophilia HI121 to the nutritionally poor diet did not result in a growth enhancement in terms of larval weight and pupal weight and length in comparison to the control, whereas the combination of the two strains positively affected the larval final weight and the pupal weight and length. In conclusion, we isolated BSF-associated bacterial strains with potential positive properties for the host nutrition and we showed that selected isolates may enhance BSF growth, suggesting the importance to evaluate the effect of the bacterial administration on the insect performance.

The trisaccharide melezitose impacts honey bees and their intestinal microbiota

In general, honey bees (Apis mellifera L.) feed on honey produced from collected nectar. In the absence of nectar, during certain times of the year or in monocultural landscapes, honey bees forage on honeydew. Honeydew is excreted by different herbivores of the order Hemiptera that consume phloem sap of plant species. In comparison to nectar, honeydew is composed of a higher variety of sugars and additional sugars with higher molecular weight, like the trisaccharide melezitose that can be a major constituent of honeydew. However, melezitose-containing honey is known to cause malnutrition in overwintering honey bees. Following the hypothesis that melezitose may be the cause for the so called ‘honeydew flow disease’, three independent feeding experiments with caged bees were conducted in consecutive years. Bees fed with melezitose showed increased food uptake, higher gut weights and elevated mortality compared to bees fed a control diet. Moreover, severe disease symptoms, such as swollen abdomen, abdomen tipping and impaired movement were observed in melezitose-fed bees. 16S-amplicon sequencing indicated that the melezitose diet changed the species composition of the lactic acid bacteria community within the gut microbiota. Based on these results, we conclude that melezitose cannot be easily digested by the host and may accumulate in the hindgut. Within cages or during winter, when there is no opportunity for excretion, the accumulated melezitose can cause severe intestinal symptoms and death of the bees, probably as result of poor melezitose metabolism capabilities in the intestinal microbiota. These findings confirm the causal relation between the trisaccharide melezitose and the honeydew flow disease and indicate a possible mechanism of pathogenesis.

Peptide Hormones in the Insect Midgut

Insects produce many peptide hormones that play important roles in regulating growth, development, immunity, homeostasis, stress, and other processes to maintain normal life. As part of the digestive system, the insect midgut is also affected by hormones secreted from the prothoracic gland, corpus allatum, and various neuronal cells; these hormones regulate the secretion and activity of insects’ digestive enzymes and change their feeding behaviors. In addition, the insect midgut produces certain hormones when it recognizes various components or pathogenic bacteria in ingested foods; concurrently, the hormones regulate other tissues and organs. In addition, intestinal symbiotic bacteria can produce hormones that influence insect signaling pathways to promote host growth and development; this interaction is the result of long-term evolution. In this review, the types, functions, and mechanisms of hormones working on the insect midgut, as well as hormones produced therein, are reviewed for future reference in biological pest control.

Honeybee gut microbiota dysbiosis in pesticide/parasite co-exposures is mainly induced by Nosema ceranae

Honeybees ensure a key ecosystem service by pollinating many agricultural crops and wild plants. However, in the past few decades, managed bee colonies have been declining in Europe and North America. Researchers have emphasized both parasites and pesticides as the most important factors. Infection by the parasite Nosema ceranae and exposure to pesticides can contribute to gut dysbiosis, impacting the honeybee physiology. Here, we examined and quantified the effects of N. ceranae, the neonicotinoid thiamethoxam, the phenylpyrazole fipronil and the carboxamide boscalid, alone and in combination, on the honeybee gut microbiota. Chronic exposures to fipronil and thiamethoxam alone or combined with N. ceranae infection significantly decreased honeybee survival whereas the fungicide boscalid had no effect on uninfected bees. Interestingly, increased mortality was observed in N. ceranae-infected bees after exposure to boscalid, with synergistic negative effects. Regarding gut microbiota composition, co-exposure to the parasite and each pesticide led to decreased abundance of Alphaproteobacteria, and increased abundance of Gammaproteobacteria. The parasite also induced an increase of bacterial alpha-diversity (species richness). Our findings demonstrated that exposure of honeybees to N. ceranae and/or pesticides play a significant role in colony health and is associated with the establishment of a dysbiotic gut microbiota.

Characteristics of Microbial Communities of Pachygrontha antennata (Hemiptera: Pachygronthidae) in Relation to Habitat Variables

The microbial community interacts with the environment and the health and immune function of its host both directly and indirectly. However, very few studies about microbial communities have considered habitat and external environmental variables. This study examined environmental influences on the microbial community of Pachygrontha antennata, which is found in various habitats (e.g., urban, forested, and agricultural areas). The results demonstrated that the composition of the microbial community differed according to land use, while the bacterial diversity did not. In urban areas with high environmental heterogeneity, microbial community diversity tended to be high. Furthermore, bacteria in forests and agricultural areas (e.g., Paraburkholderia, Burkholderia) have been found to be highly correlated with habitat variables. Therefore, we suggest that habitat variables should be considered in future symbiotic studies.

Effects of Tropilaelaps mercedesae on midgut bacterial diversity of Apis mellifera

Tropilaelaps mercedesae is an ectoparasite of Apis mellifera in Asia and is considered a major threat to honey bee health. Herein, we used the Illumina MiSeq platform 16S rDNA Amplicon Sequencing targeting the V3-V4 regions and analysed the effects on the midgut bacterial communities of honey bees infested with T. mercedesae. The overall bacterial community in honey bees infested with T. mercedesae were observed at different developmental stages. Honey bee core intestinal bacterial genera such as Gilliamella, Lactobacillus and Frischella were detected. Tropilaelapsmercedesae infestation changed the bacterial communities in the midgut of A. mellifera. Tropilaelapsmercedesae-infested pupae had greatly increased relative abundances of Micrococcus and Sphingomonas, whereas T. mercedesae-infested 15-day-old workers had significantly reduced relative abundance of non-core microbes: Corynebacterium, Sphingomonas, Acinetobacter and Enhydrobacter compared to T. mercedesae-infested newly emerged bees. The bacterial community was significantly changed at the various T. mercedesae-infested developmental stages of A. mellifera. Tropilaelapsmercedesae infestation also changed the non-core bacterial community from larvae to newly emerged honey bees. Bacterial communities were significantly different between T. mercedesa-infested and non-mite-infested 15-day-old workers. Lactobacillus was dominant in T. mercedesae-infested 15-day-old workers compared to non-mite-infested 15-day-old workers.

Gut and Whole-Body Microbiota of the Honey Bee Separate Thriving and Non-thriving Hives

The recent worldwide decline of honey bee colonies is a major ecological problem which also threatens pollinated crop production. Several interacting stressors such as environmental pressures and pathogens are suspected. Recently, the gut microbiota has emerged as a critical factor affecting bee health and fitness. We profiled the bacterial communities associated with the gut and whole body of worker bees to assess whether non-thriving colonies could be separated from thriving hives based on their microbial signature. The microbiota of thriving colonies was characterised by higher diversity and higher relative abundance of bacterial taxa involved in sugar degradation that were previously associated with healthy bees (e.g. Commensalibacter sp. and Bartonella apis). In contrast, the microbiota of non-thriving bees was depleted in health-associated species (e.g. Lactobacillus apis), and bacterial taxa associated with disease states (e.g. Gilliamella apicola) and pollen degradation (e.g. G. apicola and Bifidobacterium asteroides) were present in higher abundance compared to thriving colonies. Gut and whole-body microbiota shared a similar dominant core but their comparison showed differences in composition and relative abundance. More differences in taxon relative abundance between gut and whole body were observed in non-thriving bees, suggesting that microbiota associated with other bee organs might also be different. Thus, microbiota profiling could be used as a diagnostic tool in beekeeping practices to predict hive health and guide hive management.

The Herbicide Glyphosate Negatively Affects Midgut Bacterial Communities and Survival of Honey Bee during Larvae Reared in Vitro

Effects of glyphosate on survival, developmental rate, larval weight, and midgut bacterial diversity of Apis mellifera were tested in the laboratory. Larvae were reared in vitro and fed diet containing glyphosate 0.8, 4, and 20 mg/L. The dependent variables were compared with negative control and positive control (dimethoate 45 mg/L). Brood survival decreased in 4 or 20 mg/L glyphosate treatments but not in 0.8 mg/L, and larval weight decreased in 0.8 or 4 mg/L glyphosate treatments. Exposure to three concentrations did not affect the developmental rate. Furthermore, the intestinal bacterial communities were determined using high-throughput sequencing targeting the V3-V4 regions of the 16S rDNA. All core honey bee intestinal bacterial phyla such as Proteobacteria (30.86%), Firmicutes (13.82%), and Actinobacteria (11.88%) were detected, and significant changes were found in the species diversity and richness in 20 mg/L glyphosate group. Our results suggest that high concentrations of glyphosate are deleterious to immature bees.

Gram-Positive Bacteria with Probiotic Potential for the Apis mellifera L. Honey Bee: The Experience in the Northwest of Argentina

Apis mellifera L. is one of the most important natural pollinators of significant crops and flowers around the world. It can be affected by different types of illnesses: american foulbrood, nosemosis, varroasis, viruses, among others. Such infections mainly cause a reduction in honey production and in extreme situations, the death of the colony. Argentina is the world's second largest honey exporter and the third largest honey producer, after China and Turkey. Given both the prominence of the honey bee in nature and the economic importance of apiculture in Argentina and the world, it is crucial to develop efficient and sustainable strategies to control honey bee diseases and to improve bee colony health. Gram-positive bacteria, such as lactic acid bacteria, mainly Lactobacillus, and Bacillus spp. are promising options. In the Northwest of Argentina, several Lactobacillus and Bacillus strains from the honey bee gut and honey were isolated by our research group and characterized by using in vitro tests. Two strains were selected because of their potential probiotic properties: Lactobacillus johnsonii CRL1647 and Bacillus subtilis subsp. subtilis Mori2. Under independent trials with both experimental and commercial hives, it was determined that each strain was able to elicit probiotic effects on bee colonies reared in the northwestern region of Argentina. One result was the increase in egg-laying by the queen which therefore produced an increase in bee number and, consequently, a higher honey yield. Moreover, the beneficial bacteria reduced the incidence of two important bee diseases: nosemosis and varroosis. These results are promising and extend the horizon of probiotic bacteria to the insect world, serving beekeepers worldwide as a natural tool that they can administer as is, or combine with other disease-controlling methods.

Empirical, Metagenomic, and Computational Techniques Illuminate the Mechanisms by which Fungicides Compromise Bee Health

Growers often use fungicide sprays during bloom to protect crops against disease, which exposes bees to fungicide residues. Although considered "bee-safe," there is mounting evidence that fungicide residues in pollen are associated with bee declines (for both honey and bumble bee species). While the mechanisms remain relatively unknown, researchers have speculated that bee-microbe symbioses are involved. Microbes play a pivotal role in the preservation and/or processing of pollen, which serves as nutrition for larval bees. By altering the microbial community, it is likely that fungicides disrupt these microbe-mediated services, and thereby compromise bee health. This manuscript describes the protocols used to investigate the indirect mechanism(s) by which fungicides may be causing colony decline. Cage experiments exposing bees to fungicide-treated flowers have already provided the first evidence that fungicides cause profound colony losses in a native bumble bee (Bombus impatiens). Using field-relevant doses of fungicides, a series of experiments have been developed to provide a finer description of microbial community dynamics of fungicide-exposed pollen. Shifts in the structural composition of fungal and bacterial assemblages within the pollen microbiome are investigated by next-generation sequencing and metagenomic analysis. Experiments developed herein have been designed to provide a mechanistic understanding of how fungicides affect the microbiome of pollen-provisions. Ultimately, these findings should shed light on the indirect pathway through which fungicides may be causing colony declines.

Honey Bee Gut Microbiome Is Altered by In-Hive Pesticide Exposures

Honey bees (Apis mellifera) are the primary pollinators of major horticultural crops. Over the last few decades, a substantial decline in honey bees and their colonies have been reported. While a plethora of factors could contribute to the putative decline, pathogens, and pesticides are common concerns that draw attention. In addition to potential direct effects on honey bees, indirect pesticide effects could include alteration of essential gut microbial communities and symbionts that are important to honey bee health (e.g., immune system). The primary objective of this study was to determine the microbiome associated with honey bees exposed to commonly used in-hive pesticides: coumaphos, tau-fluvalinate, and chlorothalonil. Treatments were replicated at three independent locations near Blacksburg Virginia, and included a no-pesticide amended control at each location. The microbiome was characterized through pyrosequencing of V2-V3 regions of the bacterial 16S rRNA gene and fungal ITS region. Pesticide exposure significantly affected the structure of bacterial but not fungal communities. The bee bacteriome, similar to other studies, was dominated by sequences derived from Bacilli, Actinobacteria, α-, β-, γ-proteobacteria. The fungal community sequences were dominated by Ascomycetes and Basidiomycetes. The Multi-response permutation procedures (MRPP) and subsequent Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) analysis indicated that chlorothalonil caused significant change to the structure and functional potential of the honey bee gut bacterial community relative to control. Putative genes for oxidative phosphorylation, for example, increased while sugar metabolism and peptidase potential declined in the microbiome of chlorothalonil exposed bees. The results of this field-based study suggest the potential for pesticide induced changes to the honey bee gut microbiome that warrant further investigation.

Gut microbial communities of social bees

The gut microbiota can have profound effects on hosts, but the study of these relationships in humans is challenging. The specialized gut microbial community of honey bees is similar to the mammalian microbiota, as both are mostly composed of host-adapted, facultatively anaerobic and microaerophilic bacteria. However, the microbial community of the bee gut is far simpler than the mammalian microbiota, being dominated by only nine bacterial species clusters that are specific to bees and that are transmitted through social interactions between individuals. Recent developments, which include the discovery of extensive strain-level variation, evidence of protective and nutritional functions, and reports of eco-physiological or disease-associated perturbations to the microbial community, have drawn attention to the role of the microbiota in bee health and its potential as a model for studying the ecology and evolution of gut symbionts.

The effects of Bt Cry1Ie toxin on bacterial diversity in the midgut of Apis mellifera ligustica (Hymenoptera: Apidae)

The honey bee has been regarded as a key species in the environmental risk assessment of biotech crops. Here, the potential adverse effects of Cry1Ie toxin on the midgut bacteria of the worker bees (Apis mellifera ligustica) were investigated under laboratory conditions. Newly emerged bees were fed with different concentrations of Cry1Ie toxin syrups (20 ng/mL, 200 ng/mL, and 20 μg/mL), pure sugar syrup, and 48 ppb of imidacloprid syrups, then sampled after 15 and 30 d. We characterized the dominant midgut bacteria and compared the composition and structure of the midgut bacterial community in all samples using the Illumina MiSeq platform targeting the V3–V4 regions of 16S rDNA. No significant differences in the diversity of the midgut bacteria were observed between the five treatments. This work was the first to show the effects of Cry1Ie toxin on honey bees, and our study provided a theoretical basis for the biosafety assessment of transgenic Cry1Ie maize.

Microbial ecology-based methods to characterize the bacterial communities of non-model insects

Among the animals of the Kingdom Animalia, insects are unparalleled for their widespread diffusion, diversity and number of occupied ecological niches. In recent years they have raised researcher interest not only because of their importance as human and agricultural pests, disease vectors and as useful breeding species (e.g. honeybee and silkworm), but also because of their suitability as animal models. It is now fully recognized that microorganisms form symbiotic relationships with insects, influencing their survival, fitness, development, mating habits and the immune system and other aspects of the biology and ecology of the insect host. Thus, any research aimed at deepening the knowledge of any given insect species (perhaps species of applied interest or species emerging as novel pests or vectors) must consider the characterization of the associated microbiome. The present review critically examines the microbiology and molecular ecology techniques that can be applied to the taxonomical and functional analysis of the microbiome of non-model insects. Our goal is to provide an overview of current approaches and methods addressing the ecology and functions of microorganisms and microbiomes associated with insects. Our focus is on operational details, aiming to provide a concise guide to currently available advanced techniques, in an effort to extend insect microbiome research beyond simple descriptions of microbial communities.

Virus Infections of Honeybees Apis Mellifera

The health and vigour of honeybee colonies are threatened by numerous parasites (such as Varroa destructor and Nosema spp.) and pathogens, including viruses, bacteria, protozoa. Among honeybee pathogens, viruses are one of the major threats to the health and well-being of honeybees and cause serious concern for researchers and beekeepers. To tone down the threats posed by these invasive organisms, a better understanding of bee viral infections will be of crucial importance in developing effective and environmentally benign disease control strategies. Here we summarize recent progress in the understanding of the morphology, genome organization, transmission, epidemiology and pathogenesis of eight honeybee viruses: Deformed wing virus (DWV) and Kakugo virus (KV); Sacbrood virus (SBV); Black Queen cell virus (BQCV); Acute bee paralysis virus (ABPV); Kashmir bee virus (KBV); Israeli Acute Paralysis Virus (IAPV); Chronic bee paralysis virus (CBPV). The review has been designed to provide researchers in the field with updated information about honeybee viruses and to serve as a starting point for future research.

Systems biology of host-microbe metabolomics

The human gut microbiota performs essential functions for host and well‐being, but has also been linked to a variety of disease states, e.g., obesity and type 2 diabetes. The mammalian body fluid and tissue metabolomes are greatly influenced by the microbiota, with many health‐relevant metabolites being considered ‘mammalian–microbial co‐metabolites’. To systematically investigate this complex host–microbial co‐metabolism, a systems biology approach integrating high‐throughput data and computational network models is required. Here, we review established top‐down and bottom‐up systems biology approaches that have successfully elucidated relationships between gut microbiota‐derived metabolites and host health and disease. We focus particularly on the constraint‐based modeling and analysis approach, which enables the prediction of mechanisms behind metabolic host–microbe interactions on the molecular level. We illustrate that constraint‐based models are a useful tool for the contextualization of metabolomic measurements and can further our insight into host–microbe interactions, yielding, e.g., in potential novel drugs and biomarkers. WIREs Syst Biol Med 2015, 7:195–219. doi: 10.1002/wsbm.1301

For further resources related to this article, please visit the WIREs website.

Conflict of interest: The authors have declared no conflicts of interest for this article.

Characterization of gut bacteria at different developmental stages of Asian honey bees, Apis cerana

Previous surveys have shown that adult workers of the Asian honey bee Apis cerana harbor four major gut microbes (Bifidobacterium, Snodgrassella alvi, Gilliamella apicola, and Lactobacillus). Using quantitative PCR we characterized gut bacterial communities across the life cycle of A. cerana from larvae to workers. Our results indicate that the presence and quantity of these four bacteria were low on day 1, increased rapidly after day 5, and then peaked during days 10-20. They stabilized from days 20-25 or days 25-30, then dropped to a low level at day 30. In addition, the larvae infected by Sacbrood virus or European foulbrood had significantly lower copies of 16S rRNA genes than healthy individuals.

Bifidobacterium commune sp. nov. isolated from the bumble bee gut

Bifidobacteria were isolated from the gut of Bombus lapidarius, Bombus terrestris and Bombus hypnorum bumble bees by direct isolation on modified trypticase phytone yeast extract agar. The MALDI-TOF MS profiles of four isolates (LMG 28292(T), R-53560, R-53124, LMG 28626) were found to be identical and did not cluster with the profiles of established Bifidobacterium species. Analysis of the 16S rRNA gene sequence of strain LMG 28292(T) revealed that LMG 28292(T) is most closely related to the Bifidobacterium bohemicum type strain (96.8%), which was also isolated from bumble bee gut specimens. The hsp60 gene of strain LMG 28292(T) shows 85.8% sequence similarity to that of the B. bohemicum type strain. The (GTG)5-PCR profiles and the hsp60 sequences of all four isolates were indistinguishable; however, three different phenotypes were observed among the four isolates by means of the API 50CHL microtest system. Based on the phylogenetic, genotypic and phenotypic data, we propose to classify the four isolates within the novel species Bifidobacterium commune sp. nov., with LMG 28292(T) (= DSM 28792(T)) as the type strain.

Paratransgenesis feasibility in the honeybee (Apis mellifera) using Fructobacillus fructosus commensal

AIMS

To establish the molecular tools for honeybee paratransgenesis.

METHODS AND RESULTS

Commensal bacteria were isolated from two honeybees. Based on 16S ribosomal RNA sequence analysis, some isolates were identified as Fructobacillus fructosus, Lactobacillus kunkeei, Gilliamella apicola, Acinetobacter spp, Arthrobacter spp and Pseudomonas spp. Rolling circle and theta replicons were successfully introduced into F. fructosus and Lact. kunkeei. Green fluorescent protein was expressed into both species. The 7·3 Kb Lactococcus lactis subsp. cremoris MG1363 operon encoding a cluster of five genes involved in the metabolism of galactose via the Leloir pathway was functionally expressed into a non-galactose-fermenting strain of F. fructosus enabling it to grow on galactose as a sole carbon source.

CONCLUSIONS

Fructophilic lactic acid bacteria, F. fructosus and Lact. kunkeei, are amenable to extensive genetic manipulations.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study demonstrating the feasibility of genetically engineering honeybee commensals, thus establishing the tools necessary for honeybee paratransgenesis.

Draft Genome of Chilean Honeybee (Apis mellifera) Gut Strain Lactobacillus kunkeei MP2

Here, we report the first draft genome sequence of Lactobacillus kunkeei strain MP2, isolated from a Chilean honeybee gut. The sequenced genome has a total size of 1.58 Mb distributed into 44 contigs and 1,356 protein-coding sequences.