Abstract
Karenia mikimotoi is a harmful algal bloom (HAB) species that poses a significant threat to marine ecosystems due to its hemolytic toxins. This study isolated Vibrio coralliirubri (ACE001), which demonstrated contact-dependent algicidal effects against K. mikimotoi. Chemotaxis assays revealed ACE001's strong attraction to K. mikimotoi cell membranes, indicating the importance of chemotaxis. ACE001 caused a significant decrease in Chlorophyll a and an increase in reactive oxygen species (ROS), indicating oxidative stress. Scanning electron microscopy showed ACE001 adheres to and penetrates K. mikimotoi, leading to cell rupture. Dual RNA-seq revealed suppression of the type VI secretion system (T6SS) and the upregulation of the Sec secretion system, particularly the yidC and secY genes. Mutant strains lacking these genes exhibited reduced algicidal activity. This study provides the evidence of a Vibrio species with algicidal activity against K. mikimotoi, offering insights into its algicidal mechanisms.