The Thioredoxin System in Contributes to Oxidative Stress Tolerance, Motility, and Virulence.

is an important fish pathogen that causes substantial economic losses. In order to understand its pathogenic mechanism, additional new virulence factors need to be identified. The bacterial thioredoxin system is a major disulfide reductase system, but its function is largely unknown in . In this study, we investigated the roles of the thioredoxin system in (named TrxB, TrxA, and TrxC, respectively) by constructing a correspondingly markerless in-frame mutant strain: Δ, Δt, and Δ, respectively. We found that (i) TrxB is confirmed as an intracellular protein, which is different from the prediction made by the Protter illustration; (ii) compared to the wild-type strain, Δ exhibits resistance against HO stress but high sensitivity to thiol-specific diamide stress, while Δ and Δ are moderately sensitive to both HO and diamide conditions; (iii) the deletions of , , and damage 's flagella formation and motility, and plays a decisive role; (iv) deletions of , , and substantially abate bacterial resistance against host serum, especially deletion; (v) and , but not , are involved in bacterial survival and replication in phagocytes; (vi) the thioredoxin system participates in bacterial dissemination in host immune tissues. These findings indicate that the thioredoxin system of plays an important role in stress resistance and virulence, which provides insight into the pathogenic mechanism of .