Superspreaders have lower gut microbial alpha-diversity and distinct gut microbial composition in a natural rodent population.

The microbiome is well known to drive variation in host states (e.g. behaviour, immunity) that would be expected to modulate the spread of infectious disease-but the role of microbiotal interactions in promoting superspreading is poorly understood. Superspreaders are individuals with a strongly disproportionate contribution to pathogen transmission, and come in two forms. Supershedders transmit infection to more individuals because they shed higher levels of pathogen. Supercontacters transmit infection to more individuals because they have larger numbers of social contacts. We explore associations between the gut microbiota and these two forms of superspreading in a wild rodent model-Bartonella spp. bacteraemia in the field vole (Microtus agrestis). We find evidence that individuals fall into distinct shedding and contacting clusters, and that higher-contacters have lower and more variable gut microbial alpha-diversity than lower-contacters. We also show evidence that both higher-shedders and higher-contacters have distinct gut microbial composition and identify OTUs that are differentially abundant in the gut microbiota of these two classes of individuals when compared to lower-shedders and lower-contacters respectively. We find that the Muribaculaceae are associated with differences in both shedding and contacting, and discuss potential mechanisms by which they may be acting on these host traits.