LuxS modulates motility and secretion of extracellular protease in fish pathogen .

can cause infections and diseases in a variety of marine vertebrates and invertebrates, which are harmful to the aquaculture industry. The LuxS quorum-sensing system regulates the expression of virulence factors in a wide variety of pathogenic bacteria. In this study, an in-frame deletion of the gene was constructed to reveal the role of LuxS in the physiology and virulence of . Statistical analysis showed no significant differences in the growth ability, biofilm formation, antibiotic susceptibility, virulence by intraperitoneal injection, and ability of to colonize the spleen and liver of the pearl gentian grouper between the wild-type (WT) and mutant. However, deletion of decreased the secretion of extracellular protease, while increasing swimming and swarming abilities. Simultaneously, a -deleted mutant showed overproduction of lateral flagella, and an intact complemented this defect. Since motility is flagella dependent, 16 flagella biogenesis related genes were selected for further analysis. Based on quantitative real-time reverse transcription-PCR (qRT-PCR), the expression levels of these genes, including the polar flagella genes , , , , , , and and the lateral flagella genes , , , , , , and , were significantly upregulated in the Δ: pMMB207 (Δ) strain as compared with the 345: pMMB207 (WT) and C-Δ strains during the early, mid-exponential, and stationary growth phases. Our results indicate that LuxS plays an important role in controlling motility, flagella biogenesis, and extracellular protease secretion in .