Transcriptomic and Extracellular Proteomic Analyses Implicate Two-Component Signaling in Medium-Dependent Virulence...

Vibrio mediterranei is an emerging pathogen causing vibriosis outbreaks in marine bivalves, yet the molecular mechanisms by which environmental conditions modulate its virulence remain poorly understood. Here, we combined in vivo infection assays with integrated transcriptomic and extracellular products (ECPs) proteomic analyses to dissect how culture medium composition shapes the virulence of V. mediterranei toward razor clam (Sinonovacula constricta) juveniles. All tested strains caused markedly elevated juvenile mortality when cultured in TCBS medium (up to 98.9%, p < 0.0001), whereas strains grown in 2216E caused low mortality (0-3.3%), and no mortalities were recorded in the bacteria-free seawater control. Comparative ECPs proteomics identified 646 and 399 differentially expressed proteins (DEPs) in DT07 and DT02, respectively, enriched in cell envelope-related processes and in the composition of the extracellular protein fraction, the two-component system (TCS), and oxidative pathways, while transcriptomics revealed 3276 and 2084 differentially expressed genes (DEGs) dominated by carbon and energy metabolism, flagellar assembly, membrane transport, and signal transduction. Cross-omics integration via KEGG Orthology identifiers identified that the TCS (ko02020) was among the most prominent pathways linking the transcriptomic and ECPs proteomic layers, with glnA, pstS, crp, fliC, and tolC detected at both levels. fliC, tolC and crp were consistently detected at both two layers, linking transcriptional reprogramming to extracellular protein abundance. These findings implicated two-component signaling in the increased virulence of V. mediterranei in TCBS medium associated with motility, extracellular abundance, and metabolic adaptation, providing a framework for hypothesis-driven validation linking environmental cues to pathogenic potential in shellfish-associated Vibrios.