A comprehensive understanding of the influence and molecular mechanism of exeA on the pathogenicity in Aeromonas hydrophila.

Aeromonas hydrophila is a serious human and animal co-pathogenic bacterium. The type II secretion system (T2SS), a key virulence factor, is vital for the secretion of exotoxins from the bacterium. exeA gene is important for the assembly of the T2SS. However, the role of exeA in the pathogenesis of A. hydrophila is not yet clear. In this study, we constructed a stable A. hydrophila strain with exeA mutation (∆exeA-AH) using homologous recombination. Compared to wild type A. hydrophila (WT-AH), the median lethal doses (LD) significantly increased in ∆exeA-AH. Biological properties of ∆exeA-AH were analyzed to explain the reasons for changes in virulence. The results showed that there was a significant decline in biofilm formation capacity, no significant differences were found in growth ability, hemolytic activity, motility and external structure. In order to further investigate the molecular mechanism of decreased virulence, WT-AH and ∆exeA-AH were subjected to transcriptomic analysis and validated by realtime fluorescence quantitative polymerase chain reaction and western blot. The results showed that the mutation of exeA affected the assembly of T2SS and biofilm formation capacity by decreasing the uptake capacity of iron ions. However, the abilities of T6SS, Sec system, Tat system, signaling peptidase and Lol system were enhanced, hindering further reduction in virulence. In summary, exeA mutation led to a reduction in virulence by impairing the function of T2SS and the ability of biofilm formation but impeded further decline by enhancing T6SS, Sec system, Tat system, signaling peptidase and Lol system.