Ferric uptake regulator (fur) affects the pathogenicity of Aeromonas veronii TH0426 by regulating flagellar assembly and biofilm formation

Aeromonas veronii has serious implications for food safety and the aquaculture industry. The iron uptake system can effectively regulate the life activities and pathogenicity of microorganisms, and Fur is one of the key proteins. In this experiment, we constructed the Δ fur mutant strain of A. veronii TH0426 using the pRE112 suicide plasmid and the C- fur complementary strain using the pBBR1-MCS generalized host expression plasmid to research the effects of fur gene on the biological function and mechanisms of virulence regulation of TH0426. It was found that when the fur gene was deleted, the polar flagella of TH0426 was disrupted and the biofilm formation ability was significantly reduced, with consequent changes in motility, flagellation-related gene expression, drug resistance, and tolerance. Transcriptome analysis of TH0426 wild-type and Δ fur mutant showed that fur gene could directly or indirectly regulate bacterial flagella assembly, antibiotic resistance, growth and metabolism. In the pathogenic test, compared with the TH0426 wild-type, Δ fur significantly reduced the cytotoxicity to EPC cells at 30 min, 1 h and 2 h, reduced the adhesion and invasion ability to EPC cells by 2.38-fold (P < 0.001), increased LD50 of zebrafish by 58.33-fold (P < 0.001) and decreased bacterial load at 12 h, 24 h, and 48 h. Meanwhile, the result of C- fur was higher than that of Δ fur and lower than that of the TH0426 wild-type in all experiments. In summary, the fur gene is essential for flagellar assembly and biofilm formation and is able to indirectly affect some of the biological properties and animal pathogenicity of TH0426. This research helps to explain the function of the fur gene of the iron uptake system and its role in the pathogenesis of animal.