Gut microbiome composition associated with Plasmodium infection in the Eurasian tree sparrow

Recent expansion of microbiome research has uncovered connections between resident microbial communities and blood parasite risk, establishing the potential for microbial disease treatments such as probiotics in the future. However, this field has largely focused on humans and model organisms, leaving much unknown about how microbial communities might directly or indirectly impact parasite infection in wild populations and non-mammals. To contribute to this knowledge base in wild birds, we collected fecal and blood samples from wild Eurasian tree sparrows (Passer montanus) in the United States to test for associations between blood parasite infection and the gut microbiome. We used a widespread molecular approach to test 81 samples from peripheral blood for Plasmodium and Haemoproteus, and we characterized the gut microbiome using fecal samples as a proxy. Neither alpha nor beta diversity significantly varied with detected Plasmodium infection. However, differential abundance analysis highlighted a number of significantly varying bacteria, with the greatest representation within the phyla Proteobacteria and Firmicutes in Plasmodium-infected birds. These differentially abundant taxa offer a starting point for experimental work establishing the relationship between microbial abundance and Plasmodium infection.