Comparative analysis of the roles of catalases KatB and KatG in the physiological fitness and pathogenesis of fish pathogen Edwardsiella tarda

Aims: The aim of this study was to reveal functional redundancy and variation of the two catalases KatB and KatG in Edwardsiella tarda. Methods and Results: Genome sequencing of fish pathogen Edw. tarda EIB202 reveals that it contains two genes putatively encoding catalases, katB (ETAE_1368) and katG (ETAE_0889). Under free‐living conditions, single disruption in katB or katG resulted in no growth impairment, whereas double mutation of the two genes led to moderate decrease in growth, indicating that these two catalases were together essential for the physiological fitness by dissipating the endogenous H₂O₂. katG mutant exhibited much more elevated sensitivity to exogenous H₂O₂ than katB mutant did, indicating that KatG was quasi‐essential in detoxifying external reactive oxygen species (ROS) in Edw. tarda EIB202. Further comparative analysis indicated that katB or katG disruption showed different effects on the virulence‐related processes of Edw. tarda such as haemolysin production, bile and serum resistance, as well as the internalization within fish epithelial cells. Moreover, both of the katB and katG mutants exhibited incapacity to replicate in murine macrophage J774 cell model, although the deficiency was seen much severe for ΔkatB/katG mutant. With regard to in vivo virulence, katB and katG mutants displayed delayed lethality and increased LD₅₀ values for zebrafish. Conclusions: KatB and KatG in Edw. tarda serve for the physiological fitness, and pathogenesis related the bacterial survival in macrophage and in vivo of fish. Significance and Impact of the Study: Counteracting ROS for systemic infection, Edw. tarda catalase KatG and KatB merits as potential targets for attenuated live vaccine construction.