The tsetse fly obligate mutualist Wigglesworthia morsitans alters gene expression and population density via exogenous nutrient provisioning.

The obligate mutualist Wigglesworthia morsitans provisions nutrients to tsetse flies. The symbiont's response to thiamine (B(1)) supplementation of blood meals, specifically towards the regulation of thiamine biosynthesis and population density, is described. Despite an ancient symbiosis and associated genome tailoring, Wigglesworthia responds to nutrient availability, potentially accommodating a decreased need.