Microbial innovations for disease management in honey bees
Abstract
Arguably the most important insect pollinator, honey bees (Apis mellifera) are threatened by infectious disease, pesticide exposure, and nutritional deficits resulting from habitat loss.
The major goals of this thesis were to advance our understanding of the immune and microbiota factors underpinning synergistic interactions between the threats, and to develop a honey bee-specific probiotic with strain-level functions to alleviate cumulative stress burden.
Drosophila melanogaster was used as a high-throughput discovery platform in molecularly characterizing the effects of candidate probiotic lactobacilli and neonicotinoid-neuroimmune-microbiota mechanisms prior to experimentation in honey bees. Imd pathway activation by lactobacilli was identified to be crucial for mitigating neonicotinoid-induced suppression of Relish/NF-κB signalling, although constitutive overexpression of Rel-68 (active cleavage product) showed no benefit to survival using GAL4/UAS genetic techniques. NOX/DUOX oxidative burst pathways were implicated for their co-modulatory roles but were not directly involved in lactobacilli-mediated resolution of infection susceptibility and/or microbiota dysbiosis.
Next, a pollen patty-based delivery system (BioPatty) was developed to enable honey bee supplementation with three identified probiotic candidates: Lactiplantibacillus plantarum Lp39, Lacticaseibacillus rhamnosus GR-1, and Apilactobacillus kunkeei BR-1 (LX3). The strains were confirmed to be highly viable for a minimum of six days in the BioPatty matrix and could reach their intended hive targets (adult and larval intestinal tracts), with nutrient analyses (AOAC.994.12) demonstrating a near-optimal essential amino acid profile for supporting honey bee health.
Importantly, based on multi-study field trial data and in-vitro rearing experiments, two probiotic functions were validated for the BioPatty including improved pathogen resistance against Paenibacillus larvae (deadly agent of American foulbrood) and microbiota recovery following antibiotic exposure.
Taking a systems-level approach to understanding honey bee microbial ecological networks, a metataxonomic database tool (BEExact) was also developed and validated on ∼234 million short-read 16S rRNA sequences derived from 32 microbiota studies encompassing 50 bee species. In short, BEExact offers a field-wide resource enabling study of unculturable, or yet-to-be cultured, microbial ‘dark matter’ relevant to disease spread amongst the pollinator assemblage.
The collective scope of this work is expansive, and the basic approaches used, in theory, have multitudinous applications broadly relevant to microbial management of terrestrial and aquatic ecosystems.