Bacterial Cytochrome C Orchestrates Larval Metamorphosis Through Bioelectrical Control of Extracellular Vesicles Biogenesis.

Beyond the well-established roles in biomedical processes, extracellular vesicles (EVs) from Gram-negative bacteria are now identified as potent inducers of larval metamorphosis in marine invertebrates, a critical process for sustaining the health and function of global marine ecosystems. However, the specific inductive molecules within EVs remain largely unknown. Our findings reveal that cytochrome c (CytC), a previously unrecognized chemical signal packaged within EVs, induces larval metamorphosis. CytC maturation is essential for this process, as it enhances the efficiency of electron transfer, thereby supplying the energy required for EV biogenesis and loading with CytC cargo. Molecular docking analysis suggests that bacterial CytC induces the metamorphosis of mussels by binding to Toll-like receptor 4 (TLR4). Notably, a marked rise in CytC gene abundance was observed in the associated bacterial community during larval metamorphosis, which may indicate a programmed enhancement of electrogenic activity within the biofilm microenvironment to support larval developmental transition. Overall, a new paradigm for interkingdom signaling is proposed in this study, wherein CytC serves as a bioelectrical driver of EV biogenesis and a potentially broadly acting inductive signal within EVs for larval metamorphosis in invertebrates.