HomeIdeaThe ecological role of bees and their microbiome

The ecological role of bees and their microbiome

Bees and Apoidea are vital for the reproduction of wild plants and agricultural production. Their protection is fundamental for the health of the environment, for food security and the global economy, as is remembered every May 20th, on the occasion of the World Day of bees and other pollinating insects, such as wasps, bumblebees, butterflies, moths and beetles. (1,2) As with humans, the intestinal microbiome also plays a decisive role in bees.

1) The ecological role of bees

The bees are often associated withApis mellifera, the species commonly raised for honey production. However, the Apoidei family, to which bees belong, has at least 20.000 species worldwide, with around 2.000 species present in Europe and over 1.000 in Italy, such as bees of the Bombus genus.

This vast biodiversity reflects the ecological importance of Apoidea, which evolved in parallel with angiosperm plants around 100-120 million years ago. (3)

1.1) Symbiosis and evolution

The symbiotic relationship between plants, microorganisms and apoidea has led to the co-evolution of flowers and pollinators:

– plants develop attractively colored flowers, containing many volatile chemical substances and scents, as an extremely sophisticated form of activity and dialogue with the animal world,

– Apoidea, in turn, have adapted to collect nectar and pollen from flowers (Khalifa et al., 2021, Schöner et al., 2015). (4)

This interaction ensures plant reproduction through pollination and also contributes to the genetic diversity of plants, which is essential for the resilience of ecosystems.

1.2) Characteristics of Apoidea and pollination

The apoidea, thanks to their unique anatomical structure, are among the most efficient pollinators.

The hind legs of the worker bee (and only this one) are equipped with a 'brush' which collects the pollen and a 'basket' for collecting and transporting the pollen.

Their feathery down it is easily charged with static electricity, attracting pollen as they approach the flowers.

The digestive tract it is divided into various parts: the ingluvium or super sac (continuation of the esophagus) is a thin-walled, finely pleated sac, which is used to transport and store food. It can extend to occupy a large part of the abdomen.

These characteristics make Apoidea indispensable for the fertilization of many plant species, on which the production of fruit, vegetables and seeds depends.

2) Biodiversity and beekeeping crisis

The decline in bee populations It has a direct impact on biodiversity, food production and the health of ecosystems. The global decline in biodiversity is mainly caused by intensive agriculture, which depends on synthetic pesticides and heavy mechanization, which we have already covered extensively. (5,6,7) The result is a simplification of habitats with a direct impact on various animal groups.

Climate change, characterized by milder winters and alterations in the seasons cause additional stress, creating a discrepancy between the activities of insects and the flowering of plants, threatening their survival.

Beekeeping contributes to the conservation of bees. In addition to providing products such as honey, wax and propolis, it allows the conservation of local bee species and biodiversity.

3) Ecosystem and microbiota

In the bee ecosystem, the intestinal microbiota modulates the digestion of food and the synthesis of essential nutrients and affects the efficiency of immune defenses against pathogens.

The microbiota can be significantly influenced by the soil microbiota through direct and indirect interactions with plants and organic materials that bees collect during their search for food.

Phytochemicals present in plants, for example, can modulate the composition of the intestinal microbiota of bees, improving their health and resistance to diseases.

Through interactions microbiome-host we can understand how bees adapt to a wide range of environments, optimizing their health through an ongoing dialogue with the microbes and chemicals present in their habitat.

4) Microbial synergies in the bee intestine, the study

Microbiome research and its interkingdom connections represents a topic of both ecological and biomedical relevance.

A recent study (Quinn et al. 2024) published in Nature microbiology analyzes the symbiotic interaction between the honey bee and its intestinal microbiota, with a particular focus on Snodgrassella alvi, a Betaproteobacteria that feeds on organic acids.

The authors of the study highlight how S. alvi adapts and thrives in the intestine of Apis mellifera, using specific nutrients and actively modifying tryptophan metabolism. It demonstrates an advanced symbiosis, enriching our understanding of how host nutrients influence microbial colonization. (8)

4.1) Host-microbiota interactions

S. alvi stands out in the intestinal microbiome of bees for its adaptation to a diet that excludes saccharides, in favor of host-derived organic acids. In particular, it focuses on how host-secreted metabolites, such as organic acids, are critical for the colonization and survival of S. alvi in ​​the honeybee gut.

The interactions mutualistic between intestinal bacteria and their animal hosts, where the exchange of metabolites impacts nutrition, intestinal health and immune function. An adaptation that illustrates the specificity of its nutritional needs and its role within the intestinal microbial community.

The digestive system of the honey bee, with its relatively simple and stable gut microbiota, offers an ideal model to examine these interactions in detail. The analysis reveals that S. alvi exploits organic acids such as citrate, glycerate and 3-hydroxy-3-methylglutarate, essential for its growth and survival, demonstrating a refined symbiotic interaction.

4.2) Materials and methods

The research uses a controlled approach, colonizing bees with a single strain of S. alvi and limiting the bees' diet to substrates that are not digestible by the bacterium, to demonstrate that S. alvi assimilates organic acids synthesized by bees from dietary sugars.

A systematic review highlights how S. alvi does not depend on diet or cross-feeding with other microbes, but rather on the catabolism of simple carbohydrates by the host.

At first, the strains were grown on specific agar and identified by 16S ribosomal RNA gene sequencing. For colonization, honey bees were raised under controlled conditions and inoculated with the bacteria. Rigorous measures were taken to validate bee sterility and quantify pollen consumption.

To study the microbiome advanced instruments and techniques such as isotope tracing, qPCR (real time PCR or quantitative PCR) were used to quantify bacterial loads and analyze metabolic interactions, extraction and analysis of metabolites via GC-MS (Gas chromatography-mass spectrometry), specific preparations for transmission electron microscopy (TEM) and NanoSIMS mass spectrometry for ultrastructural and metabolite transfer analysis to observe interactions at the cellular level.

The experiments Isotope tracing assays evaluated the uptake of substrates by the bacteria. Finally, methods include a phylogenetic analysis of the kynureninase gene family and statistical methodologies for data analysis, highlighting the detailed and systematic methodology employed to explore host-microbiota interactions. (8)

4.3) Results

The results of the study demonstrate that Snodgrassella alvi is able to colonize the honey bee gut even in the absence of other nutrients, using host-derived organic acids, regardless of the presence of pollen or interaction with other microbes.

The research further demonstrates that S. alvi can influence tryptophan metabolism by converting Kynurenine to Anthranilate, suggesting a specific metabolic niche and a symbiotic interaction in the broader metabolic context of the gut, evolutionarily adapted between the honey bee and S. alvi. (8)

Gabriele Sapienza

Cover image from http://beesciencenews.com/2019/11/21/microbial-war-against-american-foulbrood/

Footnotes

(1) Dario Dongo, Andrea Adelmo della Penna. World Bee Day, world bee day. No eligible policy. GIFT (Great Italian Food Trade).

(2) WWF. World Bee Day. https://www.wwf.it/pandanews/animali/giornata-mondiale-delle-api/

(3) Khalifa, Shaden AM, Esraa H. Elshafiey, Aya A. Shetaia, Aida A. Abd El-Wahed, Ahmed F. Algethami, Syed G. Musharraf, Mohamed F. AlAjmi, Chao Zhao, Saad HD Masry, Mohamed M Abdel-Daim, and et al. 2021. “Overview of Bee Pollination and Its Economic Value for Crop Production” Insects 12, no. 8:688 https://doi.org/10.3390/insects12080688

(4) Schöner, Michael & Schöner, Caroline & Simon, Ralph & Grafe, Ulmar & Puechmaille, Sebastien & Ji, Liaw & Kerth, G.. (2015). Bats Are Acoustically Attracted to Mutualistic Carnivorous Plants. Current Biology. 25. 1-6. DOI:10.1016/j.cub.2015.05.054

(5) Dario Dongo. Impact of pesticide adjuvants on bee olfaction. GIFT (Great Italian Food Trade).

(6) Dario Dongo. The effect derives from pesticides on bees, trees and plants distant from cultivated land. GIFT (Great Italian Food Trade).

(7) Dario Dongo, Gioele Luchese. Pesticides, green light from the EU Court of Justice to national bans. Let's save the bees. GIFT (Great Italian Food Trade).

(8) Quinn, A., El Chazli, Y., Escrig, S. et al. Host-derived organic acids enable gut colonization of the honey bee symbiont Snodgrassella alvi. Nat Microbiol (2024). https://doi.org/10.1038/s41564-023-01572-y

Trainee Assistant Researcher | Website

Graduated in Agriculture, with experience in sustainable agriculture and permaculture, laboratory and ecological monitoring.

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