Invisible food workers: Scientists create sterol-mix dietary supplement for bee survival

A new study has found that engineering a food supplement can prevent the declining bee population by boosting reproduction. The researchers used the yeast Yarrowia lipolytica to produce a specific mix of six sterols, which bees require for development. The “superfood” was incorporated into their diet during a feeding trial, which led to a significant number of new larvae.

The study in Nature shows how the newly engineered supplement offers a way to enhance colony resilience without depleting natural floral resources. The compounds — 24-methylenecholesterol, campesterol, isofucosterol, ß-sitosterol, cholesterol, and desmosterol — comprise the majority of bee tissues.

“Our study demonstrates how we can harness synthetic biology to solve real-world ecological challenges. Most of the pollen sterols used by bees are not available naturally in quantities that could be harvested on a commercial scale, making it otherwise impossible to create a nutritionally complete feed that is a substitute for pollen,” comments senior author, professor Geraldine Wright at the Department of Biology, University of Oxford.

Researchers from the UK-based Royal Botanic Gardens Kew and the University of Greenwich, with the Technical University of Denmark, also led the study.

They suggest that since the yeast biomass also contains essential proteins and lipids, it has the potential to be expanded into bee feed. 

Additionally, researchers underline that their findings enable the survival of bees and food businesses reliant on beekeeping.  

They suggest the supplement could be available to farmers in two years. However, the researchers say more large studies are needed to check on the long-term impacts of colony health and pollination efficacy.

Artificial pollen is nutritionally insufficient

Bee populations are vulnerable and threatened by climate change and agricultural expansion due to the depletion of floral diversity. Their diet mainly consists of pollen, which contains specific lipids, or sterols, required for development.

Worker bees feeding in the Oxford Bee Lab (Image credits: Caroline Wood).However, the researchers warn that artificial pollen is nutritionally inferior. These supplements are made of protein, flour, sugar, and oil, which lack the right sterol compounds. The team explains that beekeepers resort to artificial pollen because the varieties of natural pollen are insufficient.

Meanwhile, the study’s engineered Y. lipolytica’s sterol mixture proved successful over a three-month feeding trial. Compared to the control, the sterol-enriched diet group had 15 times more larvae reach the viable pupal stage.

Additionally, the colonies feeding on the enriched diet were noted to be more likely to care for and rear the eggs and larvae by the end of the three-month period, unlike the control, which ceased brood production after 90 days.

Finally, the researchers found the bees only transfer the most biologically necessary sterols to their young, as the profile of larvae in colonies fed with engineered yeast matched the naturally foraged colonies.

“For bees, the difference between the sterol-enriched diet and conventional bee feeds would be comparable to the difference for humans between eating balanced, nutritionally complete meals and eating meals missing essential nutrients like essential fatty acids,” says lead author Dr. Elynor Moore, Department of Biology, University of Oxford (now at Delft University of Technology, the Netherlands).

“Using precision fermentation, we are now able to provide bees with a tailor-made feed that is nutritionally complete at the molecular level.”

Identifying and harvesting sterols

Before the study was carried out, researchers did not know precisely which sterols in pollen were necessary for bee health.

Jennifer Chennells weighs honeybee dietary choice tubes, Oxford Bee Lab (Image credits: Caroline Wood).By assessing the sterol composition of tissue from pupae and adult bees, they were able to see which sterols were present in bee tissues. The researchers say it required delicate work, as individual nurse bees were dissected and their guts separated. 

They used CRISPR-Cas9 gene editing so the yeast would produce these sterols in a sustainable and affordable way. This yeast was selected as it has a high lipid content and has been shown to be food-safe — it is already used to supplement aquaculture feeds.

The yeast biomass was cultured in bioreactors and dried into a powder after harvesting.

“We chose oleaginous yeast Y. lipolytica as the cell factory because it is excellent at making compounds derived from acetyl-CoA, such as lipids and sterols, and because this yeast is safe and easy to scale up,” comments co-author professor Irina Borodina at the NNF Center for Biosustainability, Technical University of Denmark.

“It is used industrially to produce enzymes, omega-3 fatty acids, steviol glycosides as calorie-free sweeteners, pheromones for pest control, and other products.”

Honeybees in food systems

The researchers stress the importance of pollinators like honeybees, which contribute to 70% of global crops. Nutrient deficiencies, climate change, mites, viral diseases, and pesticides pose a significant threat to food security and biodiversity.

Rearing caged honeybees in the Oxford Bee Lab (Image credits: Caroline Wood).Over the last decade, the US reports it has lost 40–50% of its commercial honeybee colonies. Experts warn that the country could lose 60–70% of its colonies by the end of this year.

According to the researchers, their study provides a way to build colony resiliency.

“Honey bees are critically important pollinators for the production of crops such as almonds, apples, and cherries, and so are present in some crop locations in very large numbers, which can put pressure on limited wildflowers. Our engineered supplement could therefore benefit wild bee species by reducing competition for limited pollen supplies,” says co-author Professor Phil Stevenson, RBG Kew and Natural Resources Institute at the University of Greenwich.

Danielle Downey, executive director of honeybee research nonprofit Project Apis m., who was not affiliated with the study, adds: “We rely on honeybees to pollinate one in three bites of our food, yet bees face many stressors.” 

“Good nutrition is one way to improve their resilience to these threats, and in landscapes with dwindling natural forage for bees, a more complete diet supplement could be a game changer. This breakthrough discovery of key phytonutrients that, when included in feed supplements, allow sustained honey bee brood rearing has immense potential to improve outcomes for colony survival and, in turn, the beekeeping businesses we rely on for our food production.”

Finally, the researchers suggest their findings can also open doorways to developing dietary supplements for other pollinators or farmed insects. 

Nutrition Insight previously spoke to the CEO of APIX Biosciences US about how its scientists created a new food source that can sustain honeybee colonies indefinitely without natural pollen.

Last year, a team of Switzerland-based researchers demonstrated that honey bees synthesize nutrients for their native gut microbes.