Role of Gene in Physiology and Pathogenicity of .

The gene, encoding a lipid A phosphatease, is crucial for lipopolysaccharide (LPS) synthesis in Gram-negative bacteria and plays a critical role in their virulence. This study investigated the role of in , a significant marine pathogen causing gastroenteritis in humans and infections in aquatic animals. We constructed an deletion mutant (Δ) and a complementary strain (CΔ) using homologous recombination. The growth, outer membrane permeability, stress and antibiotic sensitivity, biofilm formation, swarming motility, and virulence of the wild-type (WT), Δ, and CΔ strains were assessed. Additionally, the pathogenicity of Δ was evaluated using shrimp models. The results showed that the gene was successfully deleted and complemented, and its deletion did not impair bacterial growth. However, the Δ strain exhibited an increased outer membrane permeability, reduced resistance to stresses and antibiotics, defective biofilm formation, and a reduced swarming motility. In a co-culture, the Δ strain showed attenuated virulence. In shrimp infected with the Δ strain, the cumulative mortality rate was 22%, significantly lower than the 62% observed in the WT strain. Moreover, the expression levels of immune-related genes in the shrimp hepatopancreas were significantly lower in the Δ group, indicating a significant reduction in infection capability and pathogenicity. These findings indicate that the gene is critical for the virulence of and suggest that is a potential target for therapeutic interventions and vaccine development against infections.