M. Tolmasky, L. Actis, J. H. Crosa
Jan 1, 1995
Citations
2
Influential Citations
66
Citations
Journal
Molecular Microbiology
Abstract
We have identified and sequenced an hdc gene in the Vibrio anguillarum plasmid pJMl which encodes a histidine decarboxlase enzyme and is an essential component for the biosynthesis of anguibactin. The open reading frame corresponds to a protein of 386 amino acids with a calculated molecular mass of 44 259.69 Da. The amino acid sequence has extensive homology with the pyridoxal‐P‐dependent histidine decarboxylases of Morganella morganii, Klebsiella planticola, and Enterobacter aerogenes. Tn3‐HoHo1 transposition mutagenesis of the hdc gene present in a recombinant clone carrying the entire pJMI Iron uptake region produced two derivatives, one with the lacZ gene in the same orientation as the direction of hdc transcription and the other with the lacZ gene in the opposite orientation. A V. anguillarum strain harbouring one of the mutated derivatives was unable to grow under iron‐limiting conditions and did not produce anguibactin. Therefore, the hdc gene must play a role in the biosynthetic pathway of this siderophore and consequently in conferring the high virulence phenotype to this bacterium. The role of histidine decarboxylase in biosynthesis of anguibactin was confirmed by the fact that growth under iron starvation was restored by addition of histamine to the medium. The presence of anguibactin was also demonstrated in supernatants from cultures of the hdc mutant strains grown under iron starvation with the addition of histamine, further confirming that histamine is a precursor in the biosynthesis of the siderophore. immunoblot analysis of production of β‐galactosidase by V. anguillarum strains carrying the lacZ fusions demonstrated that expression of histidine decarboxylase is not regulated by the iron concentration of the medium.