Fungal friend or foe: Phenotypic variation of Aspergillus flavus strains within honey bee colonies in the Midwest

Bee bread, a fermented pollen product made by the Western honey bee, Apis mellifera, is the primary protein source for the honey bee colony, particularly the young brood. The fermentation of pollen is microbially mediated, with a variety of bacterial and fungal genera contributing to the conversion of pollen to bee bread. Fungal species within the genus Aspergillus, including A. flavus, A. parasiticus, and A. niger, are commonly found in honey bee-derived bee bread and may be associated with the fermentation of pollen. However, most Aspergillus species are associated with the fungal disease stonebrood among honey bee colonies, as various species produce a potent mycotoxin called aflatoxin. Recently, a single strain of A. flavus (AFBB) was described as atoxigenic (non-aflatoxigenic) and tolerant of stressors associated with the honey bee hive environment – indicating the potential for a mutualistic rather than antagonistic relationship between these two species. To better characterize this potential relationship, I collected bee bread from honey bee colonies in four apiaries across the Midwest, including Illinois, Iowa, Indiana, and Ohio. This study aimed to document the prevalence of a strain of A. flavus that was phenotypically similar to the AFBB strain, which would help to determine if an AFBB-like strain was a common or unique member of the bee bread mycobiome. To accomplish this, I implemented four phenotypic screens to narrow the number of fungal strain isolates to those that were atoxigenic, tolerant of propolis exposure, and identified as A. flavus. Additionally, mating compatibility assays were conducted to deduce if the identified strains were unique. Further, genomic sequencing and de novo genome assembly were used to validate the identification of the strain as A. flavus and identify areas of the genome that may contribute to the strain's phenotype. Through the phenotypic screens, three strains of A. flavus were identified as atoxigenic and tolerant to propolis exposure. Of the three strains, one strain was isolated from a honey bee colony in Indiana, while the other two were isolated from a single honey bee colony in Illinois. Mating compatibility assays determined that each of the three strains were unique strains of A. flavus. Genomic sequencing and de novo genome assembly verified the atoxigenic nature of the strains through the presence of a mutation in the pskA gene, which is associated with aflatoxin production. Meanwhile, exploration of the three genomes provided insight into the three strains’ ability to tolerate propolis exposure, particularly as it relates to the prevalence of cytochrome P450s and genes associated with the metabolism of phenol-containing compounds.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Entomology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Mowery, Samantha Alexis

Contributors dc:contributor

• Berenbaum, May R
• Dolezal, Adam G

• Aspergillus Flavus
• Bee Bread
• Apis Mellifera

Statement dc:rights

• Copyright 2024 Samantha Mowery

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/127260

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F127260