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

A Review of Diet and Foraged Pollen Interactions with the Honeybee Gut Microbiome

The honeybee Apis mellifera is a globally vital pollinator for flowering plants and crops, but it is currently facing mounting threats to survival due to habitat anthropization, emerging pathogens, and climate change. Over the past decade, increasing research efforts to understand and combat these challenges have led to an exploration of the honeybee gut microbiome-a relatively simple and highly conserved community of commensals which has a range of effects on the host. Researchers have now unravelled the main functional roles of this microbiome which include innate immune system stimulation, metabolism of dietary compounds, and mediation of host development and behaviour. Key amongst these is its role in aiding nutrition through the metabolism of complex carbohydrates and by degradation of otherwise indigestible pollen compounds. Increasingly, research is indicating that a diverse and high-quality pollen diet is key to maintaining healthy colonies and a stable microbiome. However, colonies can struggle to meet these dietary needs, particularly if they are located in anthropized ecosystems. Disruptions to honeybee diets or a reduction in the availability of diverse foraging options can significantly alter the composition of the microbiome, shifting it towards an abnormal state that leaves the honeybee more vulnerable to infection. Seasonal changes, primarily the overwintering period, also induce shifts in microbiome composition and are periods of time when a colony is particularly vulnerable to pathogenic infection. A comprehensive understanding of the effect these variables have on both microbiome composition and colony health is key to tackling the unprecedented environmental challenges that honeybees now face. This review summarises recent research which has elucidated the functional role of the gut microbiome in metabolism and how the composition of this bacterial community can alter due to seasonal change, anthropized landscapes, and dietary shifts. Finally, we also discuss recent studies investigating the effect that dietary supplementation has on the gut microbiome and the application of probiotic candidates for improving colony resilience and strength.

Probiotic effects on ectoparasitic mite infestations in honey bees (Apis mellifera) are modulated by environmental conditions and route of administration

Beneficial bacteria can improve the health of managed honey bees (Apis mellifera) via immune system support as well as direct inhibition of pathogens. However, our understanding of how environmental factors and delivery methods impact treatment outcomes is limited. Here, we evaluated how supplementation of a three-strain lactobacilli consortium (Lactiplantibacillus plantarum Lp39, Apilactobacillus kunkeei BR-1, and Lacticaseibacillus rhamnosus; LX3) affects ectoparasitic mite (Varroa destructor) and bacterial (Paenibacillus larvae) load. We measured this effect following delivery of LX3 in either edible (protein patty) or topical (spray) forms and did so across three distinct habitats (forage-rich, agricultural, and urban). Results demonstrate significant control of mite infestation levels following patty delivery, relative to untreated patty controls. Spray methods, by contrast, were ineffective. Specifically, a control group that received only an uninoculated patty carried more mites than any other group, suggesting excess protein within hives is a catalyst for mite proliferation. This effect, whereby the excess-protein group had the highest parasite load, was pronounced in the most natural (forage-rich) environment type, indicating a significant site-by-treatment interaction. No influence of LX3 on P. larvae loads was observed in the asymptomatic colonies studied, which is likely attributable to the already low levels of pathogenic spores present and challenges associated with detection limits. In summary, this multi-site field study suggests that an LX3-infusion of standard protein patties is an effective method to control Varroa destructor infestations in commercial honey bee colonies.IMPORTANCECommercial beekeeping operations typically have a narrow profit range that depends on maintaining healthy hives throughout the season. Unfortunately, parasitic Varroa mites and bacterial pathogens can contribute to colony losses. The plight of honey bees can in turn affect the price and availability of produce on the agri-food market. There is therefore a need for innovation in the beekeeping industry to help secure bee livestock from season to season. One relatively new approach to sustainable beekeeping is the use of beneficial bacterial supplements that beekeepers can feed to or otherwise apply to hives in aid of the bee's natural health and abilities as mediated through their gut-brain axis. Our multi-site field study applies this approach. We find that a pollen protein patty is an effective vehicle for delivering probiotic bacteria to commercial honey bee colonies and for helping to keep Varroa destructor infestation levels in check.

Selection of Probiotics for Honey Bees: The In Vitro Inhibition of Paenibacillus larvae, Melissococcus plutonius, and Serratia marcescens Strain Sicaria by Host-Specific Lactobacilli and Bifidobacteria

Host-specific Lactobacillus and Bifidobacterium species constitute the core microbiota of the honey bee digestive tract and are recognized for their probiotic properties. One of the properties of these bacteria is the inhibition of bacterial pathogens such as Paenibacillus larvae and Melissococcus plutonius, the causative agents of American and European foulbrood, respectively. Additionally, Serratia marcescens has emerged as a relevant opportunistic pathogen. Although several previously published studies have examined the inhibition of selected bacterial pathogens of bees by members of the bee physiological microbiota, none have simultaneously investigated the inhibition of multiple clinical isolates of P. larvae, M. plutonius, and S. marcescens using a wide range of bifidobacterial and lactobacilli strains isolated from various locations within a single country. Thus, this study evaluated the antimicrobial potential of Lactobacillus and Bifidobacterium strains against these pathogens, with a focus on strain-dependent inhibition. A total of 111 bacterial strains (62 Lactobacillus and 49 Bifidobacterium) were isolated from the digestive tracts of honey bees collected from eight sites across the Czech Republic. Using 16S rRNA gene sequencing, the isolates were classified and tested in vitro against four P. larvae isolates, one M. plutonius isolate, and the S. marcescens strain sicaria in modified BHI medium. Twenty-eight strains (~26%) exhibited strong inhibition (≥21 mm) against at least two P. larvae isolates, while 12 strains showed moderate inhibition (16-20 mm) against all four isolates. Inhibition of M. plutonius and S. marcescens was observed in three and twenty strains, respectively. The most effective strains belonged to Bifidobacterium asteroides, B. choladohabitans, B. polysaccharolyticum, Lactobacillus apis, L. helsingborgensis, L. kullabergensis, and L. melliventris. These results underscore the strain-dependent nature of antimicrobial activity and highlight the importance of selecting probiotic strains with broad-spectrum pathogen inhibition to support honey bee health.

Probiotic Potential of Enterococcus lactis GL3 Strain Isolated from Honeybee (Apis mellifera L.) Larvae: Insights into Its Antimicrobial Activity Against Paenibacillus larvae

This study aimed to address the need for effective probiotics and antibacterial agents to combat American foulbrood disease in honeybees, caused by Paenibacillus larvae. In the context of declining honeybee populations due to pathogens, we isolated eight lactic acid bacteria (LAB) strains from honeybee larvae (Apis mellifera L.) and evaluated their probiotic potential and inhibitory effects against P. larvae. Methods included probiotic property assessments, such as acid and bile salt resistance, hydrophobicity, auto-aggregation, co-aggregation with P. larvae, antioxidant capacities, osmotolerance to 50% sucrose, and antibiotic susceptibility. Results indicated that the GL3 strain exhibited superior probiotic attributes and potent inhibitory effects on P. larvae. Whole-genome sequencing revealed GL3 to be an Enterococcus lactis strain with genetic features tailored to the honeybee larval gut environment. Pangenome analysis highlighted genetic diversity among E. lactis strains, while molecular docking analysis identified aborycin, a lasso peptide produced by GL3, as a promising inhibitor of bacterial cell wall synthesis. These findings suggested that GL3 was a promising probiotic candidate and antibacterial agent for honeybee health management, warranting further investigation into its in vivo efficacy and potential applications in beekeeping practices.

Effects of synergistic fermentation of tea bee pollen with bacteria and enzymes on growth and intestinal health of Apis cerana cerana

While the health benefits of lactic acid bacteria (LAB)-fermented feed on farmed animals are well-established, its potential benefits for honeybees, specifically Apis cerana cerana, remain largely unexplored. The present study aimed to optimize an enzymatic hydrolysis process for tea bee pollen, employing a complex enzyme comprising acid cellulase and pectinase, followed by fermentation with Limosilactobacillus reuteri LP4. A. c. cerana workers were subsequently fed tea bee pollen processed with this optimized method. Under the optimal processing condition of fermented tea bee pollen, the pH value was 4.41, the protein content was 27.75 %, and the viable count of LAB was 2.31×10⁹ CFU/g. No molds and yeasts as well as pathogens were detected. Compared to the unfermented pollen, honey bee workers administrated with fermented tea pollen with L. reuteri LP4 showed significantly increased survival rate by 24.34 % on day 15. Moreover, the relative abundances of Lactobacillus and Bifidobacterium were elevated, while those of Enterococcus and Bacteroides were diminished. Concurrently, the relative expression levels of immune-related genes including Abaecin, PPO, Defensin, and Vg were significantly upregulated. These findings provide a scientific foundation for application of fermented feeds to enhance the health of A. c. cerana populations and contribute to the sustainable development of apiculture in China.

Examination of intestinal microbiota abundance of honey bees supplemented and unsupplemented with probiotic bacteria by QPCR

The aim of this study is to compare the bacterial load in the guts of honey bees supported and unsupplemented with probiotic supplements. To investigate the effects of a commercial bee probiotic containing different Lactobacillus species and different spice extracts on the composition of the gut microbiota of honey bees, QPCR counts of Lactobacillus spp. and Firmicutes phylum gene copies in gut mixtures from 12 different bee groups with and without probiotic supplementation were performed. There was a significant difference between the levels of Lactobacillus spp. in the guts of both groups. When Lactobacillus spp. levels in the guts of honey bees not given probiotics were compared to the Lactobacillus spp. levels in the guts of honey bees given probiotics, it was determined that there was an approximately 5.5-fold difference. However, it was observed that there was no significant difference in the Firmicutes load in the bee guts of both groups. These findings show that the applied probiotic formulation significantly affects the intestinal microbiome of healthy individuals and provides a proportional change in microbial abundance, especially in terms of Lactobacillus spp.

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

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

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 Improving Effects of Probiotic-Added Pollen Substitute Diets on the Gut Microbiota and Individual Health of Honey Bee (Apis mellifera L.)

Honey bee (Apis mellifera L.) health is crucial for honey bee products and effective pollination, and it is closely associated with gut bacteria. Various factors such as reduced habitat, temperature, disease, and diet affect the health of honey bees by disturbing the homeostasis of the gut microbiota. In this study, high-throughput 16S rRNA gene sequencing was used to analyze the gut microbiota of honey bees subjected to seven diets over 5 days. Lactobacillus dominated the microbiota in all diets. Cage experiments (consumption, head protein content, and vitellogenin gene expression level) were conducted to verify the effect of the diet. Through a heatmap, the Diet2 (probiotic-supplemented) group was clustered together with the Beebread and honey group, showing high consumption (177.50 ± 26.16 mg/bee), moderately higher survival duration (29.00 ± 2.83 days), protein content in the head (312.62 ± 28.71 µg/mL), and diet digestibility (48.41 ± 1.90%). Additionally, we analyzed the correlation between gut microbiota and health-related indicators in honey bees fed each diet. Based on the overall results, we identified that probiotic-supplemented diets increased gut microbiota diversity and positively affected the overall health of individual honey bees.

Evaluation of Functional Properties of Some Lactic Acid Bacteria Strains for Probiotic Applications in Apiculture

This study evaluates the suitability of three lactic acid bacteria (LAB) strains-Lactiplantibacillus plantarum, Lactobacillus acidophilus, and Apilactobacillus kunkeei-for use as probiotics in apiculture. Given the decline in bee populations due to pathogens and environmental stressors, sustainable alternatives to conventional treatments are necessary. This study aimed to assess the potential of these LAB strains in a probiotic formulation for bees through various in vitro tests, including co-culture interactions, biofilm formation, auto-aggregation, antioxidant activity, antimicrobial activity, antibiotic susceptibility, and resistance to high osmotic concentrations. This study aimed to assess both the individual effects of the strains and their combined effects, referred to as the LAB mix. Results indicated no mutual antagonistic activity among the LAB strains, demonstrating their compatibility with multi-strain probiotic formulations. The LAB strains showed significant survival rates under high osmotic stress and simulated gastrointestinal conditions. The LAB mix displayed enhanced biofilm formation, antioxidant activity, and antimicrobial efficacy against different bacterial strains. These findings suggest that a probiotic formulation containing these LAB strains could be used for a probiotic formulation, offering a promising approach to mitigating the negative effects of pathogens. Future research should focus on in vivo studies to validate the efficacy of these probiotic bacteria in improving bee health.

Engineering Gut Symbionts: A Way to Promote Bee Growth?

Bees play a crucial role as pollinators, contributing significantly to ecosystems. However, the honeybee population faces challenges such as global warming, pesticide use, and pathogenic microorganisms. Promoting bee growth using several approaches is therefore crucial for maintaining their roles. To this end, the bacterial microbiota is well-known for its native role in supporting bee growth in several respects. Maximizing the capabilities of these microorganisms holds the theoretical potential to promote the growth of bees. Recent advancements have made it feasible to achieve this enhancement through the application of genetic engineering. In this review, we present the roles of gut symbionts in promoting bee growth and collectively summarize the engineering approaches that would be needed for future applications. Particularly, as the engineering of bee gut symbionts has not been advanced, the dominant gut symbiotic bacteria Snodgrassella alvi and Gilliamella apicola are the main focus of the paper, along with other dominant species. Moreover, we propose engineering strategies that will allow for the improvement in bee growth with listed gene targets for modification to further encourage the use of engineered gut symbionts to promote bee growth.

Enhancing Honey Bee Health: Evaluating Pollen Substitute Diets in Field and Cage Experiments

Honey bees (Apis mellifera L.) play vital roles as agricultural pollinators and honey producers. However, global colony losses are increasing due to multiple stressors, including malnutrition. Our study evaluated the effects of four pollen substitute diets (Diet 1, Diet 2, Diet 3, and Control) through field and cage experiments, analyzing 11 parameters and 21 amino acids. Notably, Diet 1 demonstrated significantly superior performance in the field experiment, including the number of honey bees, brood area, consumption, preference, colony weight, and honey production. In the cage experiment, Diet 1 also showed superior performance in dried head and thorax weight and vitellogenin (vg) gene expression levels. Canonical discriminant and principle component analyses highlighted Diet 1's distinctiveness, with histidine, diet digestibility, consumption, vg gene expression levels, and isoleucine identified as key factors. Arginine showed significant correlations with a wide range of parameters, including the number of honey bees, brood area, and consumption, with Diet 1 exhibiting higher levels. Diet 1, containing apple juice, soytide, and Chlorella as additive components, outperformed the other diets, suggesting an enhanced formulation for pollen substitute diets. These findings hold promise for the development of more effective diets, potentially contributing to honey bee health.