Heterorhabditis bacteriophora symbiotic and axenic nematodes modify the Drosophila melanogaster larval microbiome

The <i>Drosophila melanogaster</i> microbiome is crucial for regulating physiological processes, including immune system development and function. <i>D. melanogaster</i> offers distinct advantages over vertebrate models, allowing a detailed investigation of host-microbiota interactions and their effects on modulating host defense systems. It is an outstanding model for studying innate immune responses against parasites. Entomopathogenic nematodes (EPNs) activate immune signaling in the fly, leading to immune responses to combat infection. However, the impact of EPN infection on the host larval microbiome remains poorly understood. Therefore, we investigated whether EPN infection affects the <i>D. melanogaster</i> larval microbiome. We infected third-instar <i>D. melanogaster</i> larvae with <i>Heterorhabditis bacteriophora</i> symbiotic nematodes (containing <i>Photorhabdus luminescens</i> bacteria) and axenic nematodes (devoid of symbiotic bacteria). <i>Drosophila melanogaster</i> microbiome analysis revealed statistically significant differences in microbiome composition between uninfected and EPN-infected larvae. Notably, infection with axenic nematodes resulted in 68 unique species, causing a significant shift in the <i>D. melanogaster</i> larval microbiome and an increase in bacterial diversity compared to larvae infected with symbiotic nematodes. This suggests that the absence of the endosymbiont creates ecological niches for unique species and a more diverse microbiome in larvae infected with the axenic nematodes. This research will enhance our understanding of microbial species within the <i>D. melanogaster</i> microbiome that regulate homeostasis during nematode infection. These insights could be beneficial in developing innovative strategies for managing agricultural pests and disease vectors.