Age-Dependent Increase of Bacterial Loads on Drosophila Surface Benefits the Flies to Combat Fungal Infections

In contrast to the well-recognized physiological importance of gut microbiomes, the composition and function of insect body-surface microbiota are still elusive and highly underexplored. Here we report the use of Drosophila melanogaster as a model for fungal infections and surface microbiome analysis. It was found that the older flies, even with a declined immune efficacy, survived better than the newly eclosed adults when being topically infected with fungal parasites. Our culture-dependent and independent analysis of fly surface microbiomes revealed the substantial increase of bacterial loads along with fly aging. Based on the detected bacterial species, it is suggestive that fly surface microbiotas were mainly assembled from fecal bacteria. In support of the fungal infection results, we found that the dominant bacterial species could effectively inhibit fungal spore germinations. Scanning microscope analysis revealed that fly tarsal segments were largely accumulated with bacterial cells, which could be feasibly dispersed onto different body parts by self-grooming to deter fungal spore germinations. These observations thus unveil a previously unsuspected strategy employed by flies to combat fungal infections in association with the age-dependent immune declines. The findings of this study not only shed lights on the feature and function of Drosophila external microbiomes but will also facilitate future investigations of the insect body-surface microbiotas effecting on insect physiologies.