Construction and evaluation of Vibrio alginolyticus ΔclpP mutant, as a safe live attenuated vibriosis vaccine

Vibrio alginolyticus is a common and serious pathogen threatening the progress of coastal aquaculture. ClpP protease has been proved to be closely associated with biofilm formation, stress tolerance, autolysis and virulence in several pathogens. Hence, targeting ClpP may be a potentially viable, attractive option for the preparation of vaccine in preventing vibriosis. In this study, an in-frame deleted mutant strain (Delta clpP) was constructed by allelic exchange mutagenesis to investigate physiological role of clpP in pathogenicity of V. alginolyticus and evaluate its potential as a live attenuated vaccine. The results exhibited that Delta clpP showed no differences in external morphology, growth, swarming motility and ECPase activity. However, Delta clpP represented an increment in biofilm formation, and a decrement in adherence to CIK cells. In addition, virulence of Delta clpP was examined in pearl gentian grouper and was found to be seriously attenuated. Delta clpP induced high antibody titers and provided a valid protection with a relative percent survival value of 83.8% without histopathologic abnormality. Our results indicated Delta clpP showed a great potential to be a live attenuated vaccine.