Ecological and Evolutionary Relationships between Bees and their Bacterial Gut Microbiota

Abstract

Gut microbial communities exist in the vast majority of animals, and often form complex symbioses with their hosts that affect their host's biology in numerous ways. To date, the majority of studies of these complex interactions have focused on the nutritional benefits provided by the microbiota; however, the natural microbiota can also influence development, immunity, and the metabolism of its host. Apis mellifera, the honey bee, harbors a distinctive bacterial community that is present in individuals from distant locations around the world; however, the basis of the bee-microbiota association is unknown. This dissertation explores properties of the bacterial microbiota within bees, including its persistence of this association, mechanisms of transmission, localization through host ontogeny, and basic metabolic capabilities that define and maintain the symbiotic relationship. Apis and Bombus species (honey and bumble bees) share a distinct bacterial microbiota that is not present in other bees and wasps. Close analysis of the A. mellifera microbiota revealed consistent communities in adult worker gut organs and a general lack of bacteria in larvae. Contact between workers and with hive materials were identified as major routes of transmission for bacterial communities, showing the importance of social behavior in this association. Genomic analysis of a gut bacterium co-sequenced with the Bombus impatiens genome revealed it as a divergent lineage of Gammaproteobacteria, and deletions of conserved metabolic pathways, reduction in genome size, and its low GC content all suggest that the bacterial species has had a long association with its host.