The gut microbiota of social bees is relatively simple and dominated by a core set of taxa that have been reported consistently in individual workers from around the world. Yet, variation remains, and this has been shown to affect host health. We characterised the individual- and regional-scale variation in the honeybee (Apis mellifera) gut microbiota in the North West of England, and asked whether the microbiota was influenced by host genotype or landscape composition. We collected multiple honeybees from 64 colonies, and sequenced the V4 region of the 16S rRNA gene to characterise the mid- and hindgut bacterial communities. We characterised the genotype of each individual honeybee, and also the land cover surrounding each colony. The literature-defined core taxa consistently dominated across the region, despite the varied environments. However, there was variation in the relative abundance of core taxa, and colony membership explained a large proportion of this variation. Individuals from more genetically diverse colonies had more diverse microbiotas, but individual genetic diversity did not influence gut microbial diversity. There was a trend for colonies in more similar landscapes to have more similar microbiota, whilst bees from more urban landscapes had a slightly less diverse microbiota than those from less urban landscapes. Our study provides, to our knowledge, the first demonstration for any species that the gut bacterial communities of individuals can be influenced by the genotypes of other conspecifics in the population. This is particularly important for social organisms, such as honeybees, as colony rather than individual genetic diversity appears to drive gut microbial diversity, a factor related to colony health.

25Symbiotic bacterial communities can protect their hosts from infection by pathogens. Treatment of wild 26 individuals with protective bacteria isolated from hosts can combat the spread of emerging infectious 27 diseases, but it is unclear whether the degree of bacterially-mediated host protection is uniform across 28 multiple isolates of globally-distributed pathogens. Here we use the lethal amphibian fungal pathogen 29Batrachochytrium dendrobatidis as a model to investigate the traits predicting broad-scale in vitro 30 inhibitory capabilities of both individual bacteria and multiple-bacterial consortia. We show that 31 inhibition of multiple pathogen isolates is rare, with no clear phylogenetic signal at the genus level.