Metabolomic cues from Salmonella Typhi drive neuroimmune modulations and behavioural adaptation in Caenorhabditis...

Metabolites synthesized by the gut microbial community act as critical mediators in shaping host-pathogen interactions by influencing host immunity, metabolism and behaviour. Previously, S. Typhi infection was reported to induce heritable adaptive avoidance behaviour mediated by dopaminergic signalling and insulin signalling in C. elegans. However, the role of pathogen-derived biomolecules which include metabolites that modulate neuronal function through the gut-brain axis, in regulating these heritable responses remain unexplored. In this study, S. Typhi metabolites were identified as potent modulators capable of inducing infection-like host responses even in the absence of live bacterial infection. Among five extraction methods tested, 80 % methanolic extracted metabolites significantly reduced lifespan (∼41.1 % reduction with p = 0.0409) and induced heritable avoidance response (p < 0.0001) similar to that of whole bacterial infection. LC-MS profiling revealed uniquely enriched and differentially enriched metabolites in S. Typhi M5 extract with 315 metabolites exclusively detected in S. Typhi and several redox-active and neuroactive active metabolites exhibiting higher abundance compared to control E. coli OP50 M5 extract. Pathway enrichment analysis indicated significant enrichment in D-amino acid, galactose, phenylalanine, tyrosine and tryptophan biosynthesis and glutathione metabolism pathways. Consistently, several redox active and neuroactive compounds, such as p-benzoquinone, harmane, and glutathione-related dipeptides, were abundant in S. Typhi metabolome. Exposure to these metabolites disrupted dopaminergic regulation, evidenced by altered DAT-1GFP localization and loss of avoidance behaviour in dat-1 mutants, corroborated by reduced dat-1 and cat-2 expression. Additionally, a significant upregulation of immune-related genes (tol-1, clec-67, skn-1) and activation of the DAF-2/DAF-16 insulin signalling pathway indicated immune activation and host defence responses. Collectively, these findings suggest that S. Typhi derived metabolites can reprogram host neuroimmune signalling through the gut-brain axis, contributing to metabolite-driven adaptive behavioural outcomes in C. elegans.