show Abstracthide AbstractThe fish pathogen Aliivibrio salmonicida is the causative agent of the cold-water vibriosis in marine aquacultures. A. salmonicida uses quorum sensing to regulate activities as motility, biofilm formation and adhesion, and processes AinS/R and LuxI/R quorum sensing systems (QS) responsible for the production of eight homoserine lactones (HSLs). By comparing the ainS and luxI mutants to the A. salmonicida wild-type, essential genes regulated by QS signaling were identified suing RNA sequencing. The functional analysis of the differentially expressed genes presented that the most pronounced regulation was involved in bacterial motility and chemotaxis, exopolysaccharide production and surface structures related to adhesion. Moreover, using phenotypical analysis the rugose colony morphology and formed biofilms were disrupted by two highly abundant HSLs, the 3OC6 and 3OHC10. These findings imply that LuxI and AinS synthases have a critical contribution to the QS-dependent regulation on gene expression and the phenotypic traits related to it.