Host Gnmt coordinates with Limosilactobacillus reuteri to alleviate ionizing radiation injury via microbiota remodeling and metabolic regulation in Drosophila melanogaster.

Organismal health is dictated by the interplay between host genetics, microbiota, and environmental stressors like ionizing radiation (IR). However, the role of potential metabolic factors, such as Glycine N-methyltransferase (Gnmt), in coordinating this stress response remains largely unexplored. We aimed to investigate whether a candidate host factor, Gnmt, contributes to the radioprotective effects of Limosilactobacillus reuteri (L. reuteri) and to elucidate their coordination in mitigating IR damage. Label-free proteomics identified IR-responsive proteins. Gnmt function was interrogated using genetic manipulation to assess its impact on apoptosis, triacylglycerol (TAG) and free fatty acid (FFA) utilization, and lifespan. Radioprotective effects of two L. reuteri strains (DSM 17938 and ATCC PTA-6475) were evaluated in wild-type and gnmt mutant flies, with microbiota changes analyzed by 16 S rRNA sequencing. Proteomics identified Gnmt as a potential regulator of IR-induced apoptosis and lipid mobilization. Gnmt overexpression extended post-IR lifespan in both sexes. L. reuteri supplementation suppressed IR-induced apoptosis through a pathway that appears Gnmt-independent. However, while strain DSM 17,938 extended lifespan regardless of Gnmt, strain ATCC PTA-6475 required host Gnmt for radioprotection in males. Beta-diversity analysis demonstrated that L. reuteri moved microbial community structures more closely to non-irradiated controls. This involved suppressing potentially opportunistic Enterobacter and promoting commensal Lactobacillus, effects that were largely contingent upon host Gnmt. L. reuteri supplementation improves survival and suppresses apoptosis in irradiated flies. While cellular protection appears Gnmt-independent, systemic microbiota restoration is associated with host Gnmt function. This suggests a dual-track protective mechanism involving both host-Gnmt-coordinated microbiota remodeling and parallel cellular protection pathways.