Abstract: Vibrio alginolyticus, a gram-negative bacterium has been described to be among the most common and economically important aquatic pathogen of fish and shellfish. Dihydrolipoamide dehydrogenase （DLDH）is homodimeric flavoproteins that catalyse the NAD⁺ dependent reoxidation of dihydrolipoamide in a number of multienzyme complexes. This enzyme classically involved in energy metabolism. To identify DLDH’s role during infection, dldh gene deletion strain （ZJ03Δdldh）were constructed using the insertion mutation method. With the pRE112 suicide plasmid as the carrier, the Overlap PCR and homologous recombination technology were used to construct the mutant strains. Furthermore, the changes of the physiology and pathogenicity of ZJ03Δdldh mutant strains compared with the strain ZJ03, such as growth, swarming ability, biofilm and LD50 were investigated. The growth curve showed that the mutant grew slowly in lag phase compared to the wild-type strain, and the swarming ability, enzyme activity and biofilm formation of ZJ03Δdldh mutant strains showed significant reduced（P<0.05）. The fish lethal test showed that the virulence of the ZJ03Δdldh mutant strains was 10² times lower than the ZJ03 strain. In conclusion, the ZJ03Δdldh mutant strains were constructed successfully, and this study showed that enzymes classically involved in energy metabolism may play an important role in pathogenic mechanism of V. alginolyticus.

Key words: Vibrio alginolyticus, dldh, mutant, Biological characteristics