Researchers uncover metabolic codependency enabling bees to thrive on nutrient-poor diet
Scientists have new evidence that honey bees and their gut microbes engage in a form of metabolic symbiosis that is vital to the bees’ health and survival. As solitary foragers feeding on the nutritionally inconsistent pollen from flowers, honey bees face a constant struggle to obtain all the amino acids, lipids, vitamins and minerals they need from this largely protein-based diet.
Now a study published this month in Nature Microbiology reveals that specialized gut bacteria help honey bees fill the nutritional gaps in pollen by synthesizing beneficial fatty acids, vitamins and essential amino acids. These nutrients are then absorbed into the bee’s tissues to sustain growth, development, reproduction and defense against pathogens and parasites. The researchers also identified the specific bacterial genes and metabolites involved in this process.
Honey bees lack metabolic pathways present in other insects
Many studies have mapped out the honey bee microbiome – the community of microorganisms living symbiotically in their digestive tracts. The bee gut houses specialized bacteria that are not found in solitary insects like fruit flies or mosquitoes. But exactly why honey bees rely so heavily on bacterial symbionts has been unclear.
The researchers on the latest study believe they now understand why: honey bees lack certain metabolic pathways for deriving essential nutrients from pollen that are present in other insects.
Co-lead author Dr. Kasie Raymann at University of Texas at Austin explains: “Whereas flies make their own vitamins, lipids, and amino acids, bees have outsourced these essential metabolic pathways to their microbiome. This allows them to thrive on a nutritionally poor diet.”
Study co-lead Professor Nancy Moran emphasizes the food processing role of the bee gut microbes: “They are provisioning the bee with nutrients it cannot get directly from flower pollen.”
Carbohydrates in bee bread fuel bacterial nutrient production
A key insight was learning that worker bees facilitate this nutrient exchange through the pollen they collect. Bees don’t directly consume raw pollen collected from flowers. Instead they process it into “bee bread” – adding nectar, digestive enzymes and packing it into cells.
This extra nectar transforms the pollen into a nutritious substrate that gut microbes can feed on for energy. The bacteria break down and ferment carbohydrates in the bee bread to power their own metabolism. This includes the biosynthesis of B-vitamins, essential amino acids and beneficial fatty acids lacking in the pollen itself.
Genetic analysis defines bacterial contributions
To define the specific contributions of bacteria, the researchers analyzed the gut microbiome’s genetic blueprints along with metabolites absorbed into bee tissues. This allowed them to match bacterial genes for making particular nutrients with the nutrients themselves detected inside bees.
Some key findings showing what gut microbes provide:
- B-vitamin synthesis from 5 main bacterial species
- Essential amino acids from a common species Gilliamella apicola
- Beneficial fatty acids 10(R)-hydroxystearic acid produced by Schmidhempelia bombi
Bees and bacteria depend on each other
These and other ingredients synthesized by gut microbes forage bees then distribute to the rest of the colony. A healthy, well-nourished microbiome producing these nutrients translates into well-fed bees better equipped to perform colony duties – like rearing larvae, building honeycomb and foraging over long distances.
At the same time bees have specialized structures and behaviors for maintaining bacterial symbionts. Their honey stomach stores nectar used to produce bee bread for bacteria. And nurses feed bacteria-rich food to newborn bees ensuring they acquire an early gut microbiome.
So bees and bacteria depend completely on each other for health and survival – disrupting this relationship can weaken immunity and productivity. Many factors harming bee health like pesticides, parasites and malnutrition may act in part by damaging gut microbes.
Findings may guide probiotic treatments
Professor Moran’s microbiology team sees practical applications from better understanding bee-bacteria interdependency:
“As we learn how gut microbes benefit bees, this information can guide probiotic treatments to revitalize bee hives that are struggling. Identifying core bee bacteria and what they each contribute enables selecting the best strains for bee health.”
Probiotics involving formulations of key gut bacteria species are already being researched to counter disorder-causing pathogens and improve immunity against disease. Such approaches may become vital for protecting both managed honey bees in agriculture and wild bees from mounting stresses.
The researchers also now want to understand if other specialized bees relying solely on nutrient-poor pollen diets form similar partnerships with gut microbes. Beyond bees, they hope to uncover parallels in other creatures heavily populated by microbial partners.
“Symbiotic relationships between animals and beneficial bacteria are turning out to be very common,” notes Dr. Raymann. “And in many cases, these microbes are providing vital functions their hosts cannot perform alone.”
Key Takeaways: Bee-Bacteria Symbiosis Study
|What bees lack
|What gut bacteria provide
|Bee structures that aid bacteria
|Metabolic pathways to derive essential nutrients from pollen
|B-vitamins, beneficial fatty acids, essential amino acids
|Honey stomach to produce bee bread
|Food fed to larvae to transmit microbiome
More supporting research will further define the precise impacts of the bee gut microbiome. But this discovery of metabolic codependency underscores the integral role of microbial partners in bee health. Fostering the right community with probiotics and nutrition may be key to ensuring both robust agriculture pollination and healthy wild bee populations.
Ongoing declines prompt urgency about protecting bees
This research comes at a time when both honey bees and wild native bees face escalating threats resulting in rising colony losses and local extinctions.
Over the last century managed honey bee colonies needed for vital food crop pollination have declined by 60%. And North America has lost over 40% of its bee diversity since 1990 as once common bumble bees and solitary bees vanish across their historic ranges.
Understanding the gut bacteria so vital to bee welfare may provide insights and tools for reversing these trends. It also reveals how the health of these critical pollinators hinges on microbes we are just beginning to understand.
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