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J. Biol. Chem., Vol. 277, Issue 4, 2385-2395, January 25, 2002
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From the Under iron limitation, the plant pathogen
Erwinia chrysanthemi produces the catechol-type siderophore
chrysobactin, which acts as a virulence factor. It can also use
enterobactin as a xenosiderophore. We began this work by sequencing the
5'-upstream region of the fct-cbsCEBA operon, which encodes
the ferric chrysobactin receptor and proteins involved in synthesis of
the catechol moiety. We identified a new iron-regulated gene
(cbsH) transcribed divergently relative to the
fct gene, the translated sequence of which is 45.6%
identical to that of Escherichia coli ferric enterobactin esterase. Insertions within this gene interrupt the chrysobactin biosynthetic pathway by exerting a polar effect on a downstream gene
with some sequence identity to the E. coli enterobactin
synthase gene. These mutations had no effect on the ability of the
bacterium to obtain iron from enterobactin, showing that a functional
cbsH gene is not required for iron removal from ferric
enterobactin in E. chrysanthemi. The
cbsH-negative mutants were less able to utilize ferric
chrysobactin, and this effect was not caused by a defect in transport
per se. In a nonpolar cbsH-negative mutant, chrysobactin accumulated intracellularly. These defects were rescued by
the cbsH gene supplied on a plasmid. The amino acid
sequence of the CbsH protein revealed characteristics of the S9 prolyl oligopeptidase family. Ferric chrysobactin hydrolysis was detected in
cell extracts from a cbsH-positive strain that was
inhibited by diisopropyl fluorophosphate. These data are consistent
with the fact that chrysobactin is a
D-lysyl-L-serine derivative. Mössbauer spectroscopy of whole cells at various states of
57Fe-labeled chrysobactin uptake showed that this enzyme is
not required for iron removal from chrysobactin in vivo.
The CbsH protein may therefore be regarded as a peptidase that prevents the bacterial cells from being intracellularly iron-depleted by chrysobactin.
Laboratoire de Pathologie
Végétale, UMR 217 Institut National de la Recherche
Agronomique, Institut National Agronomique Paris-Grignon,
Université Paris 6, 16 rue Claude Bernard, 75231 Paris Cedex 05, France and the ¶ Medical University Lübeck, the
Institute of Physics and the ** Isotope
Laboratory, Ratzeburger Alle 160, D-23538 Lübeck, Germany
The nucleotide sequence(s) reported in this paper has been submitted to the GenBankTM/EBI Data Bank with accession number(s) AF011334.
§ Researcher from CNRS. To whom correspondence should be addressed. Tel.: 33-1-44-08-17-06; Fax: 33-1-44-08-16-31; E-mail: expert@inapg.inra.fr.This article has been cited by other articles:
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