Researchers discover unique adaptations of fungi associated with bee bread

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Aspergillus flavus is uniquely adapted to survive in bee colonies. Credit: Ling-Hsiu Liao

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Aspergillus flavus is uniquely adapted to survive in bee colonies. Credit: Ling-Hsiu Liao

Previous attempts by honey bee researchers to inventory the fungal diversity in honey bee colonies revealed that Aspergillus flavus is commonly found in hives. In a new study, researchers have discovered that this fungus is uniquely adapted to survive in bee colonies.

The study, “An Aspergillus flavus strain from bee bread of the western honey bee (Apis mellifera) shows adaptations to the distinctive features of the hive environment,” is published in Ecology and evolution.

The western honey bee Apis mellifera stores large amounts of food in the form of bee bread, which is used as the main food source for the hive. The abundant nutritional value of this food source also makes it an attractive target for microorganisms. However, bee bread is sour with little moisture and is infused with the antimicrobial chemical propolis.

Despite the inhospitable nature of bee bread, the microbiome in hives consists of several bacterial and fungal species that are important for the preparation, storage and digestion of honey bee food.

“Most of the research on bee bread has focused on the bacteria, and it’s assumed that the fungi don’t play a big role because the bacteria make it too inhospitable for them,” said Daniel Busch, a student in the Berenbaum (IGOH/ GEGC/GNDP) lab. .

“After speaking with mycologists, I suspected that this was not the case and set out to prove that the fungus was able to live successfully in bee bread.”

In the study, the researchers used three strains of A. flavus: one not found in bee hives, a strain that was isolated from hives in central Illinois, and a pathogenic strain from a honey bee colony that had a stonebrood infection.

They first tested whether the strains showed any differences in their responses to pH and temperature. The latter was addressed because hives are characterized by higher year-round temperatures compared to the outside environment, which is a challenge for many microbes.

Although all strains are able to grow in different temperature ranges, they have apparent differences in growth under different pH conditions. The strain that was isolated from the hives was able to withstand low pH, while the other two could not.

The strains were also tested at different matric potential, which measures how much moisture is available and the response to propolis.

“We saw that the hive strain was able to cope with extreme levels of environmental stress from colony-specific sources,” Bush said. “It was interesting that it could handle propolis, which is thought to have fungicidal properties.”

To better understand how the fungal species associated with the hive were able to adapt, the researchers also sequenced the A. flavus strain and found that it has several genetic mutations that allow it to tolerate the harsh conditions of the beehive environment.

“We believe these are signs that there is a level of adaptation for the fungus that helps it coexist with bees,” Bush said. “We suspect there is some mutual benefit for both organisms, but we haven’t found enough evidence yet.”

The researchers now hope to study how the fungi act on different compositions of bee bread during their life cycle. They hope their work will shed light on how fungicides routinely used to protect beehives will affect these microbes.

More info:
Daniel S. Bush et al, A strain of Aspergillus flavus from bee bread of the western honey bee (Apis mellifera) shows adaptations to distinctive features of the hive environment, Ecology and evolution (2024). DOI: 10.1002/ece3.10918

Log information:
Ecology and evolution

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