Comprehension of the age-dependent gut and brain interaction of honey bee workers by integration of multi omics approaches.

Introduction: In honey bees, division of labour is a key feature, with age-related behavioural transitions being closely associated with molecular changes in the brain, gut, and microbiota. Despite evidence of both microbiome and brain changes in honey bees, most studies focus on either aspect or a single method of investigation, limiting our understanding of their interconnected roles in development and task differentiation.

Objectives: In this study, we investigated the molecular changes in the gut and brain in honey bee workers of different ages using (meta-)proteomics and metabolomics to better understand their contribution to behavioural responses and modulation.

Methods: Workers were sampled at seven timepoints throughout their life. Mass spectrometry for (meta-) proteomic and metabolomic of the guts and brains allowed insights into the global structural and functional dynamics of the microbiota, as well as the functional and metabolic alterations in the host gut and brain, and their interactions.

Results: Our results indicate the transport of amino acids between the gut and brain, potentially influencing functional pathways and behavioural phenotypes. We observed a correlation between concentrations of tryptophan and its metabolic products between honey bee brain and gut. This provides evidence regarding gut-brain axis as a way of internal communication for different host mechanisms in honey bees. Microbiota composition changed significantly, with protein numbers increasing significantly in the establishment phase. Proteomic results from both the host and the microbiota reveal that altered metabolic and functional pathway abundances may be due to energy expenditure, task differentiation, and age of onset of foraging.

Conclusion: Overall, our findings are the first to describe the global (meta-)proteomic and metabolomic changes in the honeybee gut and brain throughout a worker's life. This provides new insights toward developing potential biomarkers for evaluation of different functional changes related to various environmental stressors.