Micro"bee"ota: Honey Bee Normal Microbiota as a Part of Superorganism

Effects of a supplemented diet containing 7 probiotic strains (Honeybeeotic) on honeybee physiology and immune response: analysis of hemolymph cytology, phenoloxidase activity, and gut microbiome

BACKGROUND

In this study, a probiotic mixture (Honeybeeotic) consisting of seven bacterial strains isolated from a unique population of honeybees (Apis mellifera ligustica) was used. That honeybee population was located in the Roti Abbey locality of the Marche Region in Italy, an area isolated from human activities, and genetic contamination from other honeybee populations. The aim was to investigate the effects of this probiotic mixture on the innate immunity and intestinal microbiome of healthy common honeybees in two hives of the same apiary. Hive A received a diet of 50% glucose syrup, while hive B received the same syrup supplemented with the probiotics, both administered daily for 1 month. To determine whether the probiotic altered the immune response, phenoloxidase activity and hemolymph cellular subtype count were investigated. Additionally, metagenomic approaches were used to analyze the effects on gut microbiota composition and function, considering the critical role the gut microbiota plays in modulating host physiology.

RESULTS

The results revealed differences in hemocyte populations between the two hives, as hive A exhibited higher counts of oenocytoids and granulocytes. These findings indicated that the dietary supplementation with the probiotic mixture was safe and well-tolerated. Furthermore, phenoloxidase activity significantly decreased in hive B (1.75 ± 0.19 U/mg) compared to hive A (3.62 ± 0.44 U/mg, p < 0.005), suggesting an improved state of well-being in the honeybees, as they did not require activation of immune defense mechanisms. Regarding the microbiome composition, the probiotic modulated the gut microbiota in hive B compared to the control, retaining core microbiota components while causing both positive and negative variations. Notably, several genes, particularly KEGG genes involved in amino acid metabolism, carbohydrate metabolism, and branched-chain amino acid (BCAA) transport, were more abundant in the probiotic-fed group, suggesting an effective nutritional supplement for the host.

CONCLUSIONS

This study advocated that feeding with this probiotic mixture induces beneficial immunological effects and promoted a balanced gut microbiota with enhanced metabolic activities related to digestion. The use of highly selected probiotics was shown to contribute to the overall well-being of the honeybees, improving their immune response and gut health.

The neonicotinoid acetamiprid reduces larval and adult survival in honeybees (Apis mellifera) and interacts with a fungicide mixture

Plant protection products (PPPs1), which are frequently used in agriculture, can be major stressors for honeybees. They have been found abundantly in the beehive, particularly in pollen. Few studies have analysed effects on honeybee larvae, and little is known about effects of insecticide-fungicide-mixtures, although this is a highly realistic exposure scenario. We asked whether the combination of a frequently used insecticide and fungicides would affect developing bees. Honeybee larvae (Apis mellifera carnica) were reared in vitro on larval diets containing different PPPs at two concentrations, derived from residues found in pollen. We used the neonicotinoid acetamiprid, the combined fungicides boscalid/dimoxystrobin and the mixture of all three substances. Mortality was assessed at larval, pupal, and adult stages, and the size and weight of newly emerged bees was measured. The insecticide treatment in higher concentrations significantly reduced larval and adult survival. Interestingly, survival was not affected by the high concentrated insecticide-fungicides-mixture However, negative synergistic effects on adult survival were caused by the low concentrated insecticide-fungicides-mixture, which had no effect when applied alone. The lower concentrated combined fungicides led to significantly lighter adult bees, although the survival was unaffected. Our results suggest that environmental relevant concentrations can be harmful to honeybees. To fully understand the interaction of different PPPs, more combinations and concentrations should be studied in social and solitary bees with possibly different sensitivities.

Distinct Communities and Differing Dispersal Routes in Bacteria and Fungi of Honey Bees, Honey, and Flowers

Microbiota, the communities of microbes on and in organisms or organic matter, are essential for the functioning of ecosystems. How microbes are shared and transmitted delineates the formation of a microbiota. As pollinators forage, they offer a route to transfer microbes among the flowering plants, themselves, and their nests. To assess how the two components of the microbiota, bacteria and fungi, in pollination communities are shared and transferred, we focused on the honey bee Apis mellifera and collected honey bee, honey (representing the hive microbiota), and flower samples three times during the summer in Finland. We identified the bacteria and fungi by DNA metabarcoding. To determine the impact of honey bees' flower choices on the honey bee and hive microbiota, we identified also plant DNA in honey. The bacterial communities of honey bees, honey, and flowers all differ greatly from each other, while the fungal communities of honey bees and honey are very similar, yet different from flowers. The time of the summer and the sampling area influence all these microbiota. For flowers, the plant identity impacts both bacterial and fungal communities' composition the most. For the dispersal pathways of bacteria to honey bees, they are acquired directly from the honey and indirectly from flowers through the honey, while fungi are directly transmitted to honey bees from flowers. Overall, the distinctiveness of the microbiota of honey bees, honey, and the surrounding flowers suggests the sharing of microbes among them occurs but plays a minor role for the established microbiota.

Gut microbiota influences onset of foraging-related behavior but not physiological hallmarks of division of labor in honeybees

Gut microbes can impact cognition and behavior, but whether they regulate the division of labor in animal societies is unknown. We addressed this question using honeybees since they exhibit division of labor between nurses and foragers and because their gut microbiota can be manipulated. Using automated behavioral tracking and controlling for co-housing effects, we show that gut microbes influence the age at which bees start expressing foraging-like behaviors in the laboratory but have no effects on the time spent in a foraging arena and number of foraging trips. Moreover, the gut microbiota did not influence hallmarks of behavioral maturation such as body weight, cuticular hydrocarbon profile, hypopharyngeal gland size, gene expression, and the proportion of bees maturing into foragers. Overall, this study shows that the honeybee gut microbiota plays a role in controlling the onset of foraging-related behavior without permanent consequences on colony-level division of labor and several physiological hallmarks of behavioral maturation.

IMPORTANCE

The honeybee is emerging as a model system for studying gut microbiota-host interactions. Previous studies reported gut microbiota effects on multiple worker bee phenotypes, all of which change during behavioral maturation-the transition from nursing to foraging. We tested whether the documented effects may stem from an effect of the microbiota on behavioral maturation. The gut microbiota only subtly affected maturation: it accelerated the onset of foraging without affecting the overall proportion of foragers or their average output. We also found no effect of the microbiota on host weight, cuticular hydrocarbon (CHC) profile, hypopharyngeal gland size, and the expression of behavioral maturation-related genes. These results are inconsistent with previous studies reporting effects of the gut microbiota on bee weight and CHC profile. Our experiments revealed that co-housed bees tend to converge in behavior and physiology, suggesting that spurious associations may emerge when rearing environments are not replicated sufficiently or accounted for analytically.

Honey bee colonies can buffer short-term stressor effects of pollen restriction and fungicide exposure on colony development and the microbiome

Honey bees (Apis mellifera) have to withstand various environmental stressors alone or in combination in agriculture settings. Plant protection products are applied to achieve high crop yield, but residues of their active substances are frequently detected in bee matrices and could affect honey bee colonies. In addition, intensified agriculture could lead to resource limitation for honey bees. This study aimed to compare the response of full-sized and nucleus colonies to the combined stressors of fungicide exposure and resource limitation. A large-scale field study was conducted simultaneously at five different locations across Germany, starting in spring 2022 and continuing through spring 2023. The fungicide formulation Pictor® Active (active ingredients boscalid and pyraclostrobin) was applied according to label instructions at the maximum recommended rate on oil seed rape crops. Resource limitation was ensured by pollen restriction using a pollen trap and stressor responses were evaluated by assessing colony development, brood development, and core gut microbiome alterations. Furthermore, effects on the plant nectar microbiome were assessed since nectar inhabiting yeast are beneficial for pollination. We showed, that honey bee colonies were able to compensate for the combined stressor effects within six weeks. Nucleus colonies exposed to the combined stressors showed a short-term response with a less favorable brood to bee ratio and reduced colony development in May. No further impacts were observed in either the nucleus colonies or the full-sized colonies from July until the following spring. In addition, no fungicide-dependent differences were found in core gut and nectar microbiomes, and these differences were not distinguishable from local or environmental effects. Therefore, the provision of sufficient resources is important to increase the resilience of honey bees to a combination of stressors.

Bee-Associated Beneficial Microbes-Importance for Bees and for Humans

Bees are one of the best-known and, at the same time, perhaps the most enigmatic insects on our planet, known for their organization and social structure, being essential for the pollination of agricultural crops and several other plants, playing an essential role in food production and the balance of ecosystems, being associated with the production of high-value-added inputs, and a unique universe in relation to bees' microbiota. In this review, we summarize information regarding on different varieties of bees, with emphasis on their specificity related to microbial variations. Noteworthy are fructophilic bacteria, a lesser-known bacterial group, which use fructose fermentation as their main source of energy, with some strains being closely related to bees' health status. The beneficial properties of fructophilic bacteria may be extendable to humans and other animals as probiotics. In addition, their biotechnological potential may ease the development of new-generation antimicrobials with applications in biopreservation. The concept of "One Health" brings together fundamental and applied research with the aim of clarifying that the connections between the different components of ecosystems must be considered part of a mega-structure, with bees being an iconic example in that the healthy functionality of their microbiota is directly and indirectly related to agricultural production, bee health, quality of bee products, and the functional prosperity for humans and other animals. In fact, good health of bees is clearly related to the stable functionality of ecosystems and indirectly relates to humans' wellbeing, a concept of the "One Health".

Microbiota Analysis of Ejaculated Honey Bee Drone Semen and the Effect of Semen Collection Method on Bacterial Loads

Artificial insemination in queen honey bees is the only tool that provides complete control over mating for research and breeding purposes, making it essential in genetic improvement and conservation programs in this species. The aims of this study were to characterize drone semen bacterial loads by culture-dependent and independent methods and to describe their variation depending on the method of semen collection, the colony and the apiary. In the first experiment, the bacterial loads of semen collected from the seminal vesicles or from ejaculates was studied using culture-dependent methods. The collection method had a significant influence on the overall bacterial count in semen. Out of the 42 semen samples analyzed, 26 (61.9%) tested positive for bacterial isolation. This encompassed the entirety of samples obtained from the seminal vesicles (21 of 21), whereas only 23.8% of those derived from ejaculates (5 out of 21) showed bacterial isolation. In the second experiment, next-generation sequencing techniques were used to describe the microbiome of ejaculated drone semen for the first time. The most abundant phyla were Proteobacteria, Firmicutes, Bacteroidota and Actinobacteriota, while the most abundant genera were Lactobacillus, Staphylococcus, Prevotella, Alloprevotella and Streptococcus. The results showed that the apiary had a significant effect on the community structure composition and abundance of the seminal microbiota, and significative differences in abundance were observed for the genera Sphingomonas, Methylobacterium-Methylorubrum, Bifidobacterium and Alloprevotella. Significant differences were also observed in the richness of the microbiota between apiaries and colonies.

Prospects of probiotics in beekeeping: a review for sustainable approach to boost honeybee health

Honeybees are vital for global crop pollination, making indispensable contributions to agricultural productivity. However, these vital insects are currently facing escalating colony losses on a global scale, primarily attributed to parasitic and pathogenic attacks. The prevalent response to combat these infections may involve the use of antibiotics. Nevertheless, the application of antibiotics raises concerns regarding potential adverse effects such as antibiotic resistance and imbalances in the gut microbiota of bees. In response to these challenges, this study reviews the utilization of a probiotic-supplemented pollen substitute diet to promote honeybee gut health, enhance immunity, and overall well-being. We systematically explore various probiotic strains and their impacts on critical parameters, including survival rate, colony strength, honey and royal jelly production, and the immune response of bees. By doing so, we emphasize the significance of maintaining a balanced gut microbial community in honeybees. The review also scrutinizes the factors influencing the gut microbial communities of bees, elucidates the consequences of dysbiosis, and evaluates the potential of probiotics to mitigate these challenges. Additionally, it delineates different delivery mechanisms for probiotic supplementation and elucidates their positive effects on diverse health parameters of honeybees. Given the alarming decline in honeybee populations and the consequential threat to global food security, this study provides valuable insights into sustainable practices aimed at supporting honeybee populations and enhancing agricultural productivity.

The Bee Gut Microbiota: Bridging Infective Agents Potential in the One Health Context

The bee gut microbiota plays an important role in the services the bees pay to the environment, humans and animals. Alongside, gut-associated microorganisms are vehiculated between apparently remote habitats, promoting microbial heterogeneity of the visited microcosms and the transfer of the microbial genetic elements. To date, no metaproteomics studies dealing with the functional bee microbiota are available. Here, we employ a metaproteomics approach to explore a fraction of the bacterial, fungal, and unicellular parasites inhabiting the bee gut. The bacterial community portrays a dynamic composition, accounting for specimens of human and animal concern. Their functional features highlight the vehiculation of virulence and antimicrobial resistance traits. The fungal and unicellular parasite fractions include environment- and animal-related specimens, whose metabolic activities support the spatial spreading of functional features. Host proteome depicts the major bee physiological activities, supporting the metaproteomics strategy for the simultaneous study of multiple microbial specimens and their host-crosstalks. Altogether, the present study provides a better definition of the structure and function of the bee gut microbiota, highlighting its impact in a variety of strategies aimed at improving/overcoming several current hot topic issues such as antimicrobial resistance, environmental pollution and the promotion of environmental health.

Shotgun Metagenomics Reveals Minor Micro"bee"omes Diversity Defining Differences between Larvae and Pupae Brood Combs

Bees represent not only a valuable asset in agriculture, but also serve as a model organism within contemporary microbiology. The metagenomic composition of the bee superorganism has been substantially characterized. Nevertheless, traditional cultural methods served as the approach to studying brood combs in the past. Indeed, the comb microbiome may contribute to determining larval caste differentiation and hive immunity. To further this understanding, we conducted a shotgun sequencing analysis of the brood comb microbiome. While we found certain similarities regarding species diversity, it exhibits significant differentiation from all previously described hive metagenomes. Many microbiome members maintain a relatively constant ratio, yet taxa with the highest abundance level tend to be ephemeral. More than 90% of classified metagenomes were Gammaproteobacteria, Bacilli and Actinobacteria genetic signatures. Jaccard dissimilarity between samples based on bacteria genus classifications hesitate from 0.63 to 0.77, which for shotgun sequencing indicates a high consistency in bacterial composition. Concurrently, we identified antagonistic relationships between certain bacterial clusters. The presence of genes related to antibiotic synthesis and antibiotic resistance suggests potential mechanisms underlying the stability of comb microbiomes. Differences between pupal and larval combs emerge in the total metagenome, while taxa with the highest abundance remained consistent. All this suggests that a key role in the functioning of the comb microbiome is played by minor biodiversity, the function of which remains to be established experimentally.

Composition and diversity of bacterial communities associated with honey bee foragers from two contrasting environments

The honey bee is associated with a diverse community of microbes (viruses, bacteria, fungi, and protists), commonly known as the microbiome. Here, we present data on honey bee microbiota from two localities having different surrounding landscapes - mountain (the Rhodope Mountains) and lowland (the Danube plain). The bacterial communities of abdomen of adult bees were studied using amplicon sequencing of the 16S rRNA gene. The composition and dominance structure and their variability within and between localities, alpha and beta diversity, and core and differential taxa were compared at different hierarchical levels (operational taxonomic units to phylum). Seven genera (Lactobacillus, Gilliamella, Bifidobacterium, Commensalibacter, Bartonella, Snodgrassella, and Frischella), known to include core gut-associated phylotypes or species clusters, dominated (92-100%) the bacterial assemblages. Significant variations were found in taxa distribution across both geographical regions and within each apiary. Lactobacillus (Firmicutes) prevailed significantly in the mountain locality followed by Gilliamella and Bartonella (Proteobacteria). Bacteria of four genera, core (Bartonella and Lactobacillus) and non-core (Pseudomonas and Morganella), dominated the bee-associated assemblages of the Danube plain locality. Several ubiquitous bacterial genera (e.g., Klebsiella, Serratia, and Providencia), some species known also as potential and opportunistic bee pathogens, had been found in the lowland locality. Beta diversity analyses confirmed the observed differences in the bacterial communities from both localities. The occurrence of non-core taxa contributes substantially to higher microbial richness and diversity in bees from the Danube plain locality. We assume that the observed differences in the microbiota of honey bees from both apiaries are due to a combination of factors specific for each region. The surrounding landscape features of both localities and related vegetation, anthropogenic impact and land use intensity, the beekeeping management practices, and bee health status might all contribute to observed differences in bee microbiota traits.

Delivery mechanism can enhance probiotic activity against honey bee pathogens

Managed honey bee (Apis mellifera) populations play a crucial role in supporting pollination of food crops but are facing unsustainable colony losses, largely due to rampant disease spread within agricultural environments. While mounting evidence suggests that select lactobacilli strains (some being natural symbionts of honey bees) can protect against multiple infections, there has been limited validation at the field-level and few methods exist for applying viable microorganisms to the hive. Here, we compare how two different delivery systems-standard pollen patty infusion and a novel spray-based formulation-affect supplementation of a three-strain lactobacilli consortium (LX3). Hives in a pathogen-dense region of California are supplemented for 4 weeks and then monitored over a 20-week period for health outcomes. Results show both delivery methods facilitate viable uptake of LX3 in adult bees, although the strains do not colonize long-term. Despite this, LX3 treatments induce transcriptional immune responses leading to sustained decreases in many opportunistic bacterial and fungal pathogens, as well as selective enrichment of core symbionts including Bombilactobacillus, Bifidobacterium, Lactobacillus, and Bartonella spp. These changes are ultimately associated with greater brood production and colony growth relative to vehicle controls, and with no apparent trade-offs in ectoparasitic Varroa mite burdens. Furthermore, spray-LX3 exerts potent activities against Ascosphaera apis (a deadly brood pathogen) likely stemming from in-hive dispersal differences, whereas patty-LX3 promotes synergistic brood development via unique nutritional benefits. These findings provide a foundational basis for spray-based probiotic application in apiculture and collectively highlight the importance of considering delivery method in disease management strategies.

Extracts of Talaromyces purpureogenus Strains from Apis mellifera Bee Bread Inhibit the Growth of Paenibacillus spp. In Vitro

Honey bees coexist with fungi that colonize hive surfaces and pollen. Some of these fungi are opportunistic pathogens, but many are beneficial species that produce antimicrobial compounds for pollen conservation and the regulation of pathogen populations. In this study, we tested the in vitro antimicrobial activity of Talaromyces purpureogenus strains isolated from bee bread against Paenibacillus alvei (associated with European foulbrood disease) and three Aspergillus species that cause stonebrood disease. We found that methanol extracts of T. purpureogenus strains B18 and B195 inhibited the growth of P. alvei at a concentration of 0.39 mg/mL. Bioactivity-guided dereplication revealed that the activity of the crude extracts correlated with the presence of diketopiperazines, a siderophore, and three unknown compounds. We propose that non-pathogenic fungi such as Talaromyces spp. and their metabolites in bee bread could be an important requirement to prevent disease. Agricultural practices involving the use of fungicides can disrupt the fungal community and thus negatively affect the health of bee colonies.

Effect of honey bee forage plants in Tunisia on diversity and antibacterial potential of lactic acid bacteria and bifidobacteria from Apis mellifera intermissa and its products

Lactic acid bacteria and bifidobacteria (LAB and Bifido), isolated from the gastrointestinal tract of Apis mellifera intermissa (BGIT), honey (H), propolis (P) and bee bread (BB) of hives set in different vegetations (wildflowers, caraway, orange blossom, Marrubium vulgare, Eucalyptus and Erica cinerea), were subjected to analysis of their antibacterial potential. Isolates able to inhibit Staphylococcus aureus were selected and identified with MALDI-TOF MS leading to 154 strains representing 12 LAB and Bifido species. Lactiplantibacillus plantarum, Pediococcus pentosaceus and Enterococcus faecalis were predominantly found in all matrices. BGIT showed the highest LAB and Bifido diversity with exclusive occurrences of five species (including Bifidobacterium asteroides and Limosilactobacillus fermentum). Honey was the second origin harboring an important variety of LAB species of which Apilactobacillus kunkeei and Enterococcus mundtii were characteristic of both H and BGIT. Principal components analysis revealed associations between antibacterial activities of LAB and Bifido, matrices and honey bee forage plants. Inhibition trends of S. aureus and Citrobacter freundii were highlighted with: L. plantarum from BGIT, P, H of bees feeding on E. cinerea; Pediococcus pentosaceus from BGIT, P, BB associated with E. cinerea; and Bifidobacterium asteroides from BGIT/orange blossom system. However, Enterococcus faecium associated with BGIT/Eucalyptus system antagonized Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii. Our findings highlighted noteworthy effects of bee forage plants on the antibacterial activity of LAB and Bifido. Our approach could be useful to identify multiple conditions promoting antibacterial potency of LAB and Bifido under the combined effects of feeding plants and living matrices.

The Ascosphaera apis Infection (Chalkbrood Disease) Alters the Gut Bacteriome Composition of the Honeybee

The declining honeybee populations are a significant risk to the productivity and security of agriculture worldwide. Although there are many causes of these declines, parasites are a significant one. Disease glitches in honeybees have been identified in recent years and increasing attention has been paid to addressing the issue. Between 30% and 40% of all managed honeybee colonies in the USA have perished annually over the past few years. American foulbrood (AFB) and European foulbrood (EFB) have been reported as bacterial diseases, Nosema as a protozoan disease, and Chalkbrood and Stonebrood as fungal diseases. The study aims to compare the bacterial community related to the Nosema ceranae and Ascosphaera apis infection on the gut of the honeybee and compare it with the weakly active honeybees. The Nosema-infected honeybees contain the phyla Proteobacteria as the significantly dominant bacterial phyla, similar to the weakly active honeybees. In contrast, the Ascosphaera (Chalkbrood) infected honeybee contains large amounts of Firmicutes rather than Proteobacteria.