A PdhR Regulator Controls Bacterial Motility and Biofilm Formation in Vibrio alginolyticus

Vibrio alginolyticus is a widespread opportunistic marine pathogen. Flagellum-driven motility and biofilm formation are core virulence traits that support environmental survival and host infection and are tightly controlled by diverse transcriptional regulators. Pyruvate dehydrogenase complex regulator (PdhR), a conserved GntR-family transcription factor, regulates pyruvate metabolism in Escherichia coli. However, its physiological function in V. alginolyticus remains unclear. In this study, a pdhR deletion mutant (ΔpdhR) and a complemented strain (C-ΔpdhR) were constructed to investigate the regulatory roles of PdhR. Swimming motility assays and transmission electron microscopy revealed that pdhR deletion markedly impaired motility, indicating that PdhR is required for normal motility. The ΔpdhR mutant exhibited significantly increased biofilm biomass and increased exopolysaccharide (EPS) content but lower extracellular protease activity. RNA sequencing (RNA-seq) analysis identified 1135 differentially expressed genes in ΔpdhR, including downregulated flagellar assembly genes (e.g., fliF, flhA) and upregulated genes encoding outer membrane protein A (OmpA) family proteins and glycosyltransferases. These findings suggest that PdhR is associated with motility and negatively regulates biofilm formation in V. alginolyticus. This study expands our understanding of how a metabolic GntR-type transcription factor coordinates virulence-associated physiological traits in marine opportunistic pathogens.