Microbial Ecology of the Honey Bee (Apis Mellifera) Alimentary Tract: The Intersection of Diet, Age and Immunity

Abstract

Most animals house symbiotic microorganisms that influence their biology and life history. While microbial symbionts exist in many different capacities and contexts, the intimate association of the honey bee hindgut microbiome with host physiology has drawn attention from numerous fields of study. Of particular interest are the roles the gut microbiota play in disease resistance, individual aging and longevity. Here I explored the honey bee microbiota at both the individual and group level providing insights into the total alimentary tract microbiota as it relates to aging and host health. I found a novel link between diet, gut dysbiosis and reduced longevity. Dysbiosis occurs throughout the alimentary tract highlighting the cohesive nature of gut bacterial symbiosis. Our findings suggest that the early establishment of Snodgrassella alvi in the ileum is associated with healthy worker aging while Frischella perrara and Parasaccharibacter apium establishment is associated with early senescence. Next, I explored how the microbiota changes with worker age and host gene expression. I found that the hindgut microbiota remains relatively stable as workers age regardless of diet or environmental conditions. However, host gene expression and the midgut microbiota differ dramatically with age, and the oldest workers produced a social immune response to control microbial growth throughout the colony, and combat microbial opportunism in the midgut. Next, I manipulated the colony social structure to investigate changes in the gut associated with age and behavioral role. Again, I found little change in the hindgut microbiota, but serendipitously revealed an association of aging host physiology with anatomical changes in midgut tissue. Induced to perform early life behaviors for a second time, the oldest workers all showed the formation of large diverticula indicating a loss of midgut integrity. Collectively, this suggests that opportunistic invaders exploit the aging midgut, as competition with the hindgut microbiome is unsuccessful.