Antibiotic treatment of honey bee colonies alters early gut microbiome assembly and induces persistent dysbiosis in newly emerged workers.

The honey bee worker gut microbiome is assembled during the first days of adult life and, within the first week, matures to a relatively stable state that contributes to host health and behavior. Species composition, spatial distribution in the gut, and temporal species succession patterns all follow predictable and consistent patterns, creating a recognizable healthy worker gut microbiome. Though these quantities change with the age, task, and diet of the host, the mature microbiome is robust to minor disturbances. Mechanisms driving healthy microbiome assembly remain unclear, but abiotic, host-microbe, and microbe-microbe interactions are likely important to this development. Worker microbiomes may be altered to a dysbiotic state through nutritional, pathogen, and antibiotic stressors, increasing individual and colony susceptibility to further injury. Antibiotic use for control of bacterial diseases of larvae has been common beekeeping practice for decades, however, negative effects on the gut microbiota have been shown to decrease survivorship of affected workers and alter task-related behavioral patterns. We examined the succession of the worker gut microbiome across the first three weeks of adulthood in bees treated with the common beekeeper antibiotic tylosin. We found that both microbiome size and structure were significantly altered by tylosin treatment in 1 day old bees, and these effects persisted more than 2 weeks after last treatment application and did not recover to match control microbiomes by 21 days and the time of typical foraging onset. Certain Bifidobacterium and Bombilactobacillus species were strongly depleted by treatment, creating persistent dysbiotic states. These results illustrate early microbiome assembly in the worker gut and the negative effects of tylosin treatment on dynamic microbiome maturation.