Host genotype and infection status interact to shape microbiomes in Daphnia magna
Host bacterial communities (microbiomes) are influenced by a wide range of factors including host genotype and infection status. However, few studies disentangel temporal and host-genotype specific variation in microbiome response to infection across several host tissues. We experimentally exposed the freshwater crustacean Daphnia magna to its fungal parasite Metschnikowia bicuspidata and characterized changes in host bacterial communities associated with the parasite's development within the host. We used 16S rRNA gene sequencing to assess bacterial communities of the host (a) 24 hours ("initial parasite exposure") and 10 days ("successful infection") after exposure to a standard dose of M. bicuspidata spores spores, in host guts, body tissue (excluding guts) and whole individuals. We also investigated whether bacterial community responses to parasite exposure varied by host genotype.Parasite exposure did not immediately alter host gut bacterial communities, but drove host-genotype specific changes in the bacterial community composition of whole individuals. We validated that these changes were not driven by shifts in bacterial communities of culturing medium, due to the addition of the parasite spore solution. Successful infection (i.e. the proliferation of M. bicuspidata spores in the host body) reduced alpha diversity and shifted abundance of dominant bacterial orders in the gut. Moreover, it induced a host genotype.specific changes in body bacterial community composition. Overall, bacterial community responses to parasite exposure and subsequent infection are complex: they occur in a host genotype-dependent manner, differentially at distinct timepoints after parasite exposure and in specific host tissue.