Identification of genes involved in the sequestration of iron in mycobacteria: the ferric exochelin biosynthetic and uptake pathways

Ellen H. Fiss, Shengwei Yu, William R. Jacobs

Research output: Contribution to journalArticle

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Abstract

Mycobacteria produce two siderophores, mycobactin and exochelin. Mycobacterium smegmatis mutants defective in the production of exochelin were isolated using agar medium containing chrome azural S for the sensitive detection of siderophores. Cosmids of genomic libraries from M. smegmatis and Mycobacterium bovis BCG were screened for complementation of the mutation. Subcloning of the complementing M. smegmatis cosmid identified a 4.3 kb fragment required for restoring exochelin biosynthesis. Sequencing of the DNA revealed four open reading frames whose genes were named fxuA. fxuB, fxuC, and fxbA. FxuA, FxuB, and FxuC share amino acid sequence homology with the iron permeases FepG, FepC. and FepD from Escherichia coli. respectively. Deletion analysis identified fxbA as the gene required to restore exochelin biosynthesis in our mutant. Although fxbA does not share amino acid sequence homology with any of the published sequences for siderophore biosynthetic genes, it does show limited homology with the phosphoribosyl‐glycineamide formyltransferases (GAR enzymes) and methionyl‐tRNA formyltransferase over a limited region of the sequence, suggesting that fxbA may code for an enzyme which adds a formyl group in the synthesis of exochelin. A fusion of fxbA with the E. coli lacZ gene demonstrated regulation of gene expression by iron. The ability of M. smegmatis mutants to produce mycobactin in the absence of exochelin supports the hypothesis that exochelin is not a precursor of mycobactin and suggests that the siderophores have independent biosynthetic pathways. In addition, complementation of the M.

Original languageEnglish (US)
Pages (from-to)557-569
Number of pages13
JournalMolecular Microbiology
Volume14
Issue number3
DOIs
StatePublished - Nov 1994

Fingerprint

Biosynthetic Pathways
Mycobacterium
Iron
Mycobacterium smegmatis
Siderophores
Genes
Amino Acid Sequence Homology
Cosmids
Mycobacterium bovis
Phosphoribosylglycinamide Formyltransferase
Hydroxymethyl and Formyl Transferases
Escherichia coli
Lac Operon
Membrane Transport Proteins
Genomic Library
Gene Expression Regulation
Enzymes
exochelins
DNA Sequence Analysis
Open Reading Frames

ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology

Cite this

Identification of genes involved in the sequestration of iron in mycobacteria : the ferric exochelin biosynthetic and uptake pathways. / Fiss, Ellen H.; Yu, Shengwei; Jacobs, William R.

In: Molecular Microbiology, Vol. 14, No. 3, 11.1994, p. 557-569.

Research output: Contribution to journalArticle

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