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A novel streptococcal integrative conjugative element involved in iron acquisition.

Heather Z, Holden MT, Steward KF, Parkhill J, Song L, Challis GL, Robinson C, Davis-Poynter N, Waller AS - Mol. Microbiol. (2008)

Bottom Line: Deletion of eqbA resulted in a small-colony phenotype.Quantification of (55)Fe accumulation and sensitivity to streptonigrin suggested that equibactin is secreted by S. equi and that the eqbH, eqbI and eqbJ genes are required for its associated iron import.In agreement with a structure-based model of equibactin synthesis, supplementation of chemically defined media with salicylate was required for equibactin production.

View Article: PubMed Central - PubMed

Affiliation: Centre for Preventive Medicine, Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk, UK.

ABSTRACT
In this study, we determined the function of a novel non-ribosomal peptide synthetase (NRPS) system carried by a streptococcal integrative conjugative element (ICE), ICESe2. The NRPS shares similarity with the yersiniabactin system found in the high-pathogenicity island of Yersinia sp. and is the first of its kind to be identified in streptococci. We named the NRPS product 'equibactin' and genes of this locus eqbA-N. ICESe2, although absolutely conserved in Streptococcus equi, the causative agent of equine strangles, was absent from all strains of the closely related opportunistic pathogen Streptococcus zooepidemicus. Binding of EqbA, a DtxR-like regulator, to the eqbB promoter was increased in the presence of cations. Deletion of eqbA resulted in a small-colony phenotype. Further deletion of the irp2 homologue eqbE, or the genes eqbH, eqbI and eqbJ encoding a putative ABC transporter, or addition of the iron chelator nitrilotriacetate, reversed this phenotype, implicating iron toxicity. Quantification of (55)Fe accumulation and sensitivity to streptonigrin suggested that equibactin is secreted by S. equi and that the eqbH, eqbI and eqbJ genes are required for its associated iron import. In agreement with a structure-based model of equibactin synthesis, supplementation of chemically defined media with salicylate was required for equibactin production.

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The equibactin locus and predicted functions of the eqb gene products. A. Predicted functions of CDSs in the ICESe2 eqb cluster [IdeR, iron-dependent regulator; Te, type II thioesterase; ppt, 4′-phosphopantetheinyl transferase; A, salicylate-AMP ligase; NRPS, non-ribosomal peptide synthetase; Red, thiazoline reductase; P, permease (component of ABC transporter); ATP, ATPase (component of ABC transporter); ABC, ABC transporter; Re, putative oxidoreductase; α/β, putative α/β hydrolase]. See Table S2 for homology to other NRPS systems and transporters. B. Organization of modules and domains in the Eqb NRPS (ArCP, aryl acid carrier protein; Cy, heterocyclization; A, adenylation; E, epimerization; PCP, peptidyl carrier protein; MT, methyl transferase; Te, type I thioesterase). C. Proposed intermediates in equibactin biosynthesis.
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fig01: The equibactin locus and predicted functions of the eqb gene products. A. Predicted functions of CDSs in the ICESe2 eqb cluster [IdeR, iron-dependent regulator; Te, type II thioesterase; ppt, 4′-phosphopantetheinyl transferase; A, salicylate-AMP ligase; NRPS, non-ribosomal peptide synthetase; Red, thiazoline reductase; P, permease (component of ABC transporter); ATP, ATPase (component of ABC transporter); ABC, ABC transporter; Re, putative oxidoreductase; α/β, putative α/β hydrolase]. See Table S2 for homology to other NRPS systems and transporters. B. Organization of modules and domains in the Eqb NRPS (ArCP, aryl acid carrier protein; Cy, heterocyclization; A, adenylation; E, epimerization; PCP, peptidyl carrier protein; MT, methyl transferase; Te, type I thioesterase). C. Proposed intermediates in equibactin biosynthesis.

Mentions: The ‘cargo’ region between the conjugation and recombination modules that encodes vancomycin resistance in Tn1549 carries transport genes of unknown function in CDTn2/5 and CDSs in ICESe2 with most overall similarity to the NRPS cluster 1 of Clostridium kluyveri, which is proposed to biosynthesize a putative siderophore (Seedorf et al., 2008). Several of the encoded proteins were also similar to the NRPS complex of Yersinia sp. that produces the ferric iron-binding siderophore yersiniabactin. Therefore, we hypothesized that the ICESe2 cargo region which contains the ‘eqb’ gene cluster is responsible for the biosynthesis of a novel thiazoline-containing non-ribosomal peptide that we have tentatively named ‘equibactin’ although it is possible that the product from this NRPS could be identical to previously identified molecules. The eqb cluster contains 14 coding sequences (eqbA–N), the putative functions of which include a DtxR-like repressor (eqbA), non-ribosomal peptide biosynthetic proteins (eqbB–G, eqbMN), a ferric-siderophore-like importer (eqbH–J) and ABC transporters (Fig. 1A).


A novel streptococcal integrative conjugative element involved in iron acquisition.

Heather Z, Holden MT, Steward KF, Parkhill J, Song L, Challis GL, Robinson C, Davis-Poynter N, Waller AS - Mol. Microbiol. (2008)

The equibactin locus and predicted functions of the eqb gene products. A. Predicted functions of CDSs in the ICESe2 eqb cluster [IdeR, iron-dependent regulator; Te, type II thioesterase; ppt, 4′-phosphopantetheinyl transferase; A, salicylate-AMP ligase; NRPS, non-ribosomal peptide synthetase; Red, thiazoline reductase; P, permease (component of ABC transporter); ATP, ATPase (component of ABC transporter); ABC, ABC transporter; Re, putative oxidoreductase; α/β, putative α/β hydrolase]. See Table S2 for homology to other NRPS systems and transporters. B. Organization of modules and domains in the Eqb NRPS (ArCP, aryl acid carrier protein; Cy, heterocyclization; A, adenylation; E, epimerization; PCP, peptidyl carrier protein; MT, methyl transferase; Te, type I thioesterase). C. Proposed intermediates in equibactin biosynthesis.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3672683&req=5

fig01: The equibactin locus and predicted functions of the eqb gene products. A. Predicted functions of CDSs in the ICESe2 eqb cluster [IdeR, iron-dependent regulator; Te, type II thioesterase; ppt, 4′-phosphopantetheinyl transferase; A, salicylate-AMP ligase; NRPS, non-ribosomal peptide synthetase; Red, thiazoline reductase; P, permease (component of ABC transporter); ATP, ATPase (component of ABC transporter); ABC, ABC transporter; Re, putative oxidoreductase; α/β, putative α/β hydrolase]. See Table S2 for homology to other NRPS systems and transporters. B. Organization of modules and domains in the Eqb NRPS (ArCP, aryl acid carrier protein; Cy, heterocyclization; A, adenylation; E, epimerization; PCP, peptidyl carrier protein; MT, methyl transferase; Te, type I thioesterase). C. Proposed intermediates in equibactin biosynthesis.
Mentions: The ‘cargo’ region between the conjugation and recombination modules that encodes vancomycin resistance in Tn1549 carries transport genes of unknown function in CDTn2/5 and CDSs in ICESe2 with most overall similarity to the NRPS cluster 1 of Clostridium kluyveri, which is proposed to biosynthesize a putative siderophore (Seedorf et al., 2008). Several of the encoded proteins were also similar to the NRPS complex of Yersinia sp. that produces the ferric iron-binding siderophore yersiniabactin. Therefore, we hypothesized that the ICESe2 cargo region which contains the ‘eqb’ gene cluster is responsible for the biosynthesis of a novel thiazoline-containing non-ribosomal peptide that we have tentatively named ‘equibactin’ although it is possible that the product from this NRPS could be identical to previously identified molecules. The eqb cluster contains 14 coding sequences (eqbA–N), the putative functions of which include a DtxR-like repressor (eqbA), non-ribosomal peptide biosynthetic proteins (eqbB–G, eqbMN), a ferric-siderophore-like importer (eqbH–J) and ABC transporters (Fig. 1A).

Bottom Line: Deletion of eqbA resulted in a small-colony phenotype.Quantification of (55)Fe accumulation and sensitivity to streptonigrin suggested that equibactin is secreted by S. equi and that the eqbH, eqbI and eqbJ genes are required for its associated iron import.In agreement with a structure-based model of equibactin synthesis, supplementation of chemically defined media with salicylate was required for equibactin production.

View Article: PubMed Central - PubMed

Affiliation: Centre for Preventive Medicine, Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk, UK.

ABSTRACT
In this study, we determined the function of a novel non-ribosomal peptide synthetase (NRPS) system carried by a streptococcal integrative conjugative element (ICE), ICESe2. The NRPS shares similarity with the yersiniabactin system found in the high-pathogenicity island of Yersinia sp. and is the first of its kind to be identified in streptococci. We named the NRPS product 'equibactin' and genes of this locus eqbA-N. ICESe2, although absolutely conserved in Streptococcus equi, the causative agent of equine strangles, was absent from all strains of the closely related opportunistic pathogen Streptococcus zooepidemicus. Binding of EqbA, a DtxR-like regulator, to the eqbB promoter was increased in the presence of cations. Deletion of eqbA resulted in a small-colony phenotype. Further deletion of the irp2 homologue eqbE, or the genes eqbH, eqbI and eqbJ encoding a putative ABC transporter, or addition of the iron chelator nitrilotriacetate, reversed this phenotype, implicating iron toxicity. Quantification of (55)Fe accumulation and sensitivity to streptonigrin suggested that equibactin is secreted by S. equi and that the eqbH, eqbI and eqbJ genes are required for its associated iron import. In agreement with a structure-based model of equibactin synthesis, supplementation of chemically defined media with salicylate was required for equibactin production.

Show MeSH
Related in: MedlinePlus