The multifunctional type VI secretion system of <i>Vibrio parahaemolyticus</i> : from environmental adaptation to interbacterial competition

ABSTRACT Vibrio parahaemolyticus ( V. parahaemolyticus ) is a widespread marine bacterium that has gained prominence as a major seafood-borne pathogen and a primary cause of human gastroenteritis worldwide. The type VI secretion system (T6SS), a highly specialized molecular apparatus that injects effector proteins into competing cells, plays a pivotal role in mediating the pathogenicity, bacterial competitiveness, and environmental adaptability. This review presents an in-depth overview of the T6SS in V. parahaemolyticus , addressing its discovery, molecular architecture, genetic organization, and associated effector proteins. In addition, special attention is given to the functional divergence between T6SS1 and T6SS2, particularly in mediating bacterial antagonism and adaptation to environmental stressors. We further examine the complex regulatory frameworks that control these systems, including environmental signals, surface sensing, quorum sensing, and specific regulators. Understanding these mechanisms advances our knowledge of the survival strategies and pathogenic behaviors of V. parahaemolyticus .