Gut microbiome species Levilactobacillus brevis regulates reproductive fitness in C. elegans

The human gut microbiome has attracted considerable attention in recent years due to its broad impact on various physiological processes; however, the mechanisms underlying host-microbiota interactions are not fully understood. In particular, direct causal relationships between specific species and host health outcomes remain to be established. Here we examined the effects of human gut microbiome species Levilactobacillus brevis (L. brevis) on host health using C. elegans and found that L. brevis feeding caused significant reproductive dysfunction, including severe egg retention leading to fewer eggs laid, and abnormal egg morphologies. These effects were associated with impaired serotonin signaling in hermaphrodite-specific neurons (HSNs), which regulate egg-laying, while vulval muscle function remained intact. Progeny from L. brevis-fed worms exhibited reduced viability and delayed development, suggesting an overall reduction in C. elegans reproductive fitness. Our findings align with emerging evidence linking gut dysbiosis to reproductive health disorders in humans, and underscore the need to explore specific roles of individual gut microbiota in host health and physiology. Our work also highlights the utility of C. elegans as a model for studying the complex interactions between the microbiome and the host.