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Catecholate siderophore esterases Fes, IroD and IroE are required for salmochelins secretion following utilization, but only IroD contributes to virulence of extra‐intestinal pathogenic E scherichia coli
Author(s) -
Caza Mélissa,
Garénaux Amélie,
Lépine François,
Dozois Charles M.
Publication year - 2015
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.13059
Subject(s) - enterobactin , virulence , siderophore , biology , mutant , secretion , microbiology and biotechnology , escherichia coli , salmonella enterica , aerobactin , virulence factor , pathogenic escherichia coli , colicin , intracellular , biochemistry , enterobacteriaceae , gene
Summary Salmochelins are glucosylated forms of enterobactin (enterochelin) and contribute to the virulence of S almonella enterica and some extra‐intestinal pathogenic E scherichia coli ( ExPEC ). Fes, IroD and IroE esterases degrade salmochelins and enterobactin to release iron. We investigated the apparently redundant role of these esterases in virulence and in salmochelin production and utilization of the ExPEC strain χ 7122. The Δ iro D , Δ fes Δ iroD and Δ fes Δ iroD Δ iroE mutants displayed attenuated virulence phenotypes in an avian systemic infection model. Growth of Δ fes Δ iroD and Δ fes Δ iroD Δ iroE mutants was severely reduced in the presence of conalbumin, and although enterobactin was produced, no salmochelins were detected in the culture supernatants of these mutants. Elimination of catecholate synthesis via an entA deletion in a Δ fes Δ iroD Δ iroE restored growth in the presence of conalbumin, but only partially restored the virulence of the strain. Salmochelin production was reestablished by reintroducing active esterases. Intracellular accumulation of cyclic mono‐glucosylated enterobactin was observed in the triple mutant Δ fes Δ iroD Δ iroE , and deletion of fepC , required for catecholate import into the cytoplasm, restored salmochelin detection in supernatants. These results suggest that in the absence of esterases, cyclic salmochelins are synthesized and secreted, but remain cell‐bound after internalization indicating that esterase‐mediated degradation is required for re‐secretion of catecholate siderophore molecules following their utilization.