Edwardsiella ictaluri is a Gram-negative facultative intracellular pathogen causing enteric septicemia in channel catfish. Iron is an essential micronutrient needed for bacterial virulence, and to acquire iron, many Gram-negative bacteria secrete ferric iron chelating siderophores. The ferric hydroxamate uptake (Fhu) system consists of four genes (fhuC, fhuD, fhuB, and fhuA), and is involved in the uptake of hydroxamate type siderophores
across bacterial membranes. However, the Fhu system and its importance in E. ictaluri
virulence have been uninvestigated. Here, we present construction and evaluation of an E. ictaluri DfhuC mutant. The E. ictaluri fhuC gene was deleted in-frame by allelic exchange,
and the mutant’s growth in media and virulence in catfish were determined. Our results indicated that deletion of the E. ictaluri fhuC gene did not affect the growth of E. ictaluri largely in both iron-replete and iron-depleted media. Addition of ferric iron sources into the iron-depleted medium improved the growth of both E. ictaluri DfhuC and wild type
(WT). Catfish mortalities indicated that E. ictaluri DfhuC mutant was attenuated 2.05-fold
compared with the parent strain. The catfish immunized with the E. ictaluri DfhuC mutant showed a high relative percent survival rate (97.50%) after re-challenge with the WT E. ictaluri strain. Taken together, our data indicates that the fhuC gene contributes to E. ictaluri virulence. |
