Quorum sensing regulated phenotypes in Aeromonas hydrophila ATCC 7966 deficient in AHL production

The virulence of Aeromonas hydrophila is positively regulated by a quorum sensing (QS) system based on the ahyRI genes. The aim of this study was to evaluate the phenotypic characteristics related to virulence in the A. hydrophila strain ATCC 7966 in order to check if virulence traits are still functioning, despite the absence of a well characterized QS system. As expected, we were not able to detect quorum signaling AHL molecules in A. hydrophila ATCC 7966 by cross-streaking or thin layer chromatography with AHL biosensor strains. Although A. hydrophila ATCC 7966 did not produce AHLs, transcription of the ahyI and ahyR genes was observed by RT-PCR. Phenotypes generally recognized as QS-regulated in A. hydrophila were maintained in ATCC 7966; these phenotypes included proteolytic activity on casein and gelatin and amylolytic, lipolytic, and β-hemolytic activities, as well as the ability to adhere to surfaces and to form biofilms. Moreover, the addition of exogenous AHLs did not induce changes in the evaluated phenotypes. The results suggest that although this strain does not produce AHL as evaluated in this study, it maintains the phenotypes commonly associated with QS in this species indicating that other regulatory mechanisms independent of ahyRI may be in place.