Abstract:[Background] At present, there are few studies on how to solve the lethal pathogenicity of harmful fungi to Drosophila melanogaster. The intestinal symbiotic bacteria of Drosophila are one of the current research hotspots, and the study on the interaction between symbiotic bacteria and harmful fungi has attracted widespread attention. [Objective] To assess the competitive interaction between Drosophila symbionts and pathogenic fungi, consequently mitigating the toxicity of fungi to their hosts. [Methods] Fungi were isolated from fly food using PDA medium. The interaction between Drosophila symbionts and pathogenic fungi was examined by means of colony diameter, the number of spores and mycelium branches. The pathogenicity of fungi was examined using Drosophila infection. The germ-free and gnotobiotic flies were established to verify the protection of Drosophila symbionts against fungi. The 2-choice egg-laying apparatus was employed to assay the oviposition selection of D. melanogaster female adults. [Results] A fungus was identified as Phomopsis FY that was detrimental to the survival and development of Drosophila upon infection. Acetobacter orientalis hindered the growth of Phomopsis FY in vitro, and decreased the mortality rate of Phomopsis FY-infected flies in vivo, consequently mitigating the toxicity of Phomopsis FY to the hosts. Additionally, the presence of A. orientalis overrode the avoidance of oviposition on Phomopsis FY-associated substrates. [Conclusion] Phomopsis FY was identified as a conditionally potential Drosophila pathogen. Commensal A. orientalis mitigated the susceptibility of Drosophila to pathogenic fungi, providing insight into the natural interplay between commensal and pathogenic microbial communities that contribute to animal health and pathogenesis.
