Abstract
INTRODUCTION: Autism spectrum disorder (ASD) is a lifelong neurological and developmental disorder that has no cure and is often accompanied by gastrointestinal (GI) issues. The bidirectional communication system known as the gut microbiota-brain axis may help explain how GI dysfunction contributes to neurological symptoms. Loss-of-function mutations in the histone demethylases KDM5A, KDM5B or KDM5C are found in patients with intellectual disability and ASD. Previous studies using a Drosophila Kdm5 loss-of-function (Kdm5 (LOF) ) ASD-like model revealed gut microbial dysbiosis, reduced abundance of Lactiplantibacillus plantarum, and impaired social behavior. While L. plantarum supplementation rescued intestinal abnormalities, it did not restore social behavior. METHODS: Here, we evaluated multiple microbiota-based interventions, including probiotic supplementation with Lactiplantibacillus plantarum, Lactobacillus helveticus, their combination, and fecal microbiota transplantation (FMT), to determine their capacity to modulate gut microbial composition and behavior in Kdm5 (LOF) flies. Gut bacterial abundance was quantified using colony-forming unit (CFU) assays and full-length 16S rRNA gene sequencing. Social behavior was assessed using the social distance assay, while anxiety-like behavior and locomotion were evaluated using the open field test. Gut-specific Kdm5 knockdown was used to assess tissue-specific contributions to microbiota and behavioral phenotypes. RESULTS: Kdm5 deficiency resulted in reduced abundance of culturable Lactobacillus, Acetobacter, and Enterobacter species, accompanied by impaired social behavior. L. plantarum supplementation restored gut microbial abundance in both whole-body Kdm5 (LOF) and gut-specific Kdm5 knockdown models but did not significantly rescue social behavior. In contrast, L. helveticus significantly improved social interaction in Kdm5 (LOF) flies despite minimal effects on gut bacterial abundance, revealing a dissociation between microbial restoration and behavioral outcomes. Gut-specific Kdm5 knockdown phenocopied both microbial and social defects observed in Kdm5 (LOF) mutants. Notably, FMT from healthy donors partially restored Lactobacillus abundance, reshaped gut microbial community structure, and partially improved social behavior in Kdm5 (LOF) recipient flies. CONCLUSIONS: Together, these findings identify Kdm5 as a key regulator of gut microbial viability and social behavior and demonstrate that microbiota-based interventions exert strain- and phenotype-specific effects. Our results reveal that restoration of microbial abundance alone is insufficient to rescue social behavior and highlight the importance of functional host-microbe interactions in gut-brain communication. This work establishes Drosophila as a tractable platform for dissecting epigenetic regulation of microbiota-behavior relationships relevant to ASD and for evaluating targeted probiotic and microbiota-transfer strategies.