Dietary allyl-isothiocyanate affects male triglyceride levels in Drosophila melanogaster without detectable changes in microbiota composition

Allyl-isothiocyanate (AITC), a bioactive compound derived from glucosinolates in cruciferous vegetables, is known for its antimicrobial, anti-inflammatory, and metabolic effects in mammals. However, its in vivo interaction with the gut microbiota and consequent physiological outcomes remain poorly understood. Here, we investigated the impact of dietary AITC on host metabolism and microbiota composition in Drosophila melanogaster, a well-established model for nutritional and metabolic research. Male and female flies were fed a standard diet supplemented with 0.25 mM AITC, with or without antibiotic treatment, for 10 and 30 days. Physiological parameters (body weight, glucose, triglycerides, and survival) were measured, and microbial community profiles were analyzed via 16S rRNA gene amplicon sequencing. AITC supplementation did not significantly affect body weight, glucose content, or survival, regardless of sex or antibiotic co-treatment. However, after 30 days, a significant reduction in triglyceride levels was observed in male flies exposed to AITC (p < 0.05), suggesting a sex-specific metabolic response that persisted under antibiotic treatment. Analysis of the microbiota revealed that the dominant bacterial classes were Alphaproteobacteria, Bacilli, and Gammaproteobacteria, together comprising approximately 77.7% of all detected amplicon sequence variants. AITC did not alter microbial alpha or beta diversity, whereas age and sex significantly influenced community composition. Notably, alpha diversity decreased in older flies. These findings indicate that AITC at the tested concentration does not alter the microbiota in D. melanogaster but may induce sex-dependent effects on lipid metabolism. The absence of clear effects on the microbiota suggests that the observed physiological actions in vivo are not associated with detectable changes in microbiota composition.