AUTHOR=Da Fan , Wan Xiaoju , Lin Guixiang , Jian Jichang , Cai Shuanghu 

TITLE=Characterization of fliR-deletion mutant ΔfliR from Vibrio alginolyticus and the evaluation as a live attenuated vaccine

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=Volume 13 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2023.1162299

DOI=10.3389/fcimb.2023.1162299

ISSN=2235-2988

ABSTRACT=Vibrio alginolyticus is the common pathogen affecting various species of marine organisms. It has been demonstrated that FliR is a necessary virulence factor to adhere and infect their hosts for pathogenic bacteria. Frequent disease outbreaks in aquaculture have highlighted the necessity of developing effective vaccines. In the present study, fliR gene of V. alginolyticus was identified as being 783 bp in length, encoding 260 amino acids, and showing significant similarity to homologs of other Vibrio species. The fliR-deletion mutant ΔFliR of V. alginolyticus was successfully constructed, and its biological phenotype analysis showed no significant differences in growth capacity and extracellular enzyme activity compared to the wild-type. However, a substantial reduction of motility ability was detected in ΔFliR. Transcriptomic analysis revealed that the absence of fliR gene is responsible for a significantly decreased expression of flagellar genes, including flaA, flaB, fliS, flhB and fliM. The fliR-deletion mainly affects the related pathways involved in cell motility, membrane transport, signal transduction, carbohydrate metabolism, and amino acid metabolism in V. alginolyticus. The safety and efficacy of ΔFliR as a candidate of live attenuated vaccine were evaluated by intraperitoneal injection in grouper. The results showed ΔFliR hadn’t caused mortality in grouper intraperitoneal injected with the concentration of 1×108 CFU/fish,  survived for 10 d in inoculated fish tissue, showing ΔFliR is safe as the candidate of live attenuated vaccine. The ΔFliR provided the RPS of 67.2% against V. alginolyticus in groupers. The ΔFliR efficiently stimulated antibody production with specific IgM still detected at 42 d post-vaccination, and significantly elevated activities of CAT, SOD, and LDH in the serum. The higher expression levels of immune-related genes were observed in the immune tissues of inoculated grouper compared to the control.