Biosynthesis of the Iron-Transport Compound Enterochelin: Mutants of
            <i>Escherichia coli</i>
            Unable to Synthesize 2,3-Dihydroxybenzoate

Young, Ian G.; Langman, L; Luke, R. K. J.; Gibson, F.

doi:10.1128/jb.106.1.51-57.1971

Cited by 91 publications

(34 citation statements)

References 26 publications

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“…Second, tonB mutants were isolated in a strain (RK1044) that carried an entA mutation. Young et al (25) had shown that entA mutants were specifically blocked in the pathway leading to the biosynthesis of enterochelin. When B12 transport was examined in entA tonB double mutants, the secondary phase of B,2 transport was still not detectable.…”

Section: Resultsmentioning

confidence: 99%

Transport of vitamin B12 in tonB mutants of Escherichia coli

Bassford¹,

Bradbeer²,

Kadner³

et al. 1976

J Bacteriol

109

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It is known that the tonB mutation in Escherichia coli is responsible for a defect in the transport of iron chelates. These are transported by systems that involve outer membrane components. We found that tonB mutants were also deficient in the secondary, energy-dependent phase of vitamin B12 transport, although the mutants have normal levels ofB12 receptors on their cell surface. In addition, tonB mutants derived from vitamin B12 auxotrophs required elevated levels of B12 for normal growth. Maltose uptake, mediated by another transport system involving an outer membrane component, was unaffected by the tonB mutation.Receptor proteins in the outer membrane of cells ofEscherichia coli and Salmonella typhimurium are intimately involved in the uptake of vitamin B12 and iron chelates. The bfe gene product ofE. coli is an outer membrane protein of 60,000 molecular weight which is obligatory for the cellular adsorption of phage BF23, the three E colicins, and B12 (2,6,14,15). The energy-independent binding of B12 to the bfe product has been shown to be the first step in the transport ofthis vitamin byE. coli. Numerous mutations that affect the uptake of iron chelates are known. According to the available evidence, the tonA product is an 85,000-molecular-weight protein that binds phages Ti, T5, and 480, colicin M, and iron-ferrichrome (1,11,12,23). A separate protein, which may be the product of the feu locus, appears to function as the initial receptor for colicins B and D and for the ferric-enterochelin complex (13, 24). Finally, the uptake of maltose and maltodextrins is facilitated by the function of the product of the lamB gene, the phage lambda receptor (18).Mutations in the tonB locus ofE. coli confer resistance to bacteriophages Ti and 480 and all of the group B colicins (3). In addition, tonB mutants are chromium sensitive (22), resistant to the siderophore antibiotic albomycin (12), hyperexcrete enterochelin (9), and are totally deficient in the uptake of all iron chelates. However, these mutants are still capable of reversibly binding phages Ti and 480, and they retain receptor activity for the colicins and iron chelates (3,11,16). These observations, together with the finding that no outer membrane proteins appear to be missing in tonB mutants (3), suggest that the tonB product is involved in some step of colicin or ferric-entero-chelin uptake subsequent to binding to the receptor.The activities of the uptake systems for a number of amino acids and inorganic phosphate were normal in tonB mutants (8). However, none of these transport systems appears to employ components in the outer membrane. Hence, the effect of alterations in tonB on the function of other transport systems utilizing outer membrane components was investigated. This paper will demonstrate that tonB mutants are totally deficient in the energy-dependent uptake phase of vitamin B12 transport but are unaffected in maltose transport, even at low external concentrations of the substrate. MATERIALS AND METHODSBacterial strains and media. The strains...

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Section: Resultsmentioning

confidence: 99%

Transport of vitamin B12 in tonB mutants of Escherichia coli

Bassford¹,

Bradbeer²,

Kadner³

et al. 1976

J Bacteriol

109

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“…Enterobactin synthetase activity was first analysed using chromatographic fractions obtained from cell extracts which, when combined, produced enterobactin from L-serine, ATP, and DHBA {Bryce and Brot, 1972). A series of enf mutants were isolated which defined the genes entA, entB, entC, entD, entE, entF, and entG, as well as a transport function gene, fep Woodrow ef al.. 1975;Young et al, 1971). Chromatographic fractions from iron-starved cells were mixed with extracts from the ent mutants to reoonstitute enterobactin synthetase activity (Greenwood and Luke, 1976;Greenwood and Luke, 1980;Woodrow ef al., 1979).…”

Section: Discussionmentioning

confidence: 99%

“…The genes specifying enterobactin biosynthesis and transport functions map to minute 13 of the chromosome (Bachmann, 1983), and are expressed coordinately in response to the intracellular iron concentration (Fleming et al, 1983). Enterobactin biosynthesis begins with the conversion of chorismate, an intermediate of aromatic amino acid biosynthesis, to 2,3-dihydroxybenzoate (DHBA) by the activities encoded by entC, entB, and entA (Young et al, 1971). DHBA and L-serine are subsequently converted to enterobactin by the activities ascribed to EntD, EntE, EntF, and EntG Woodrowe^a/., 1975).…”

Section: Introductionmentioning

confidence: 99%

The Escherichia coli enterobactin biosynthesis gene, entD: nucleotide sequence and membrane localization of its protein product

Armstrong

Pettis

Forrester

et al. 1989

Molecular Microbiology

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The nucleotide sequence of the Escherichia coli enterobactin biosynthesis gene entD has been determined. entD specifies a predicted 23579 Dalton protein containing several helical regions, a transmembrane segment and one positively charged domain. The EntD polypeptide was overexpressed and identified in electrophoretic gels as a membrane protein. Although results of conventional membrane fractionation techniques were inconclusive, protease accessibility studies provided evidence that EntD domains are exposed on the inner leaflet of the cytoplasmic membrane. The presence of repetitive extragenic palindromic (REP) sequences within the fepA-entD intercistronic region was confirmed. Lack of a canonical promoter and an iron control region 5' to entD, along with RNA hybridization data, suggest that an iron-regulated transcript contains both fepA and entD.

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“…Wang & Newton (1969) isolated a second mutant, Chr2, which is sensitive to Cr(III) and has an impaired iron uptake. This mutant lacks the complete system to synthesize 2,3-dihydroxybenzoylserine (DHBS), a strong iron chelator that is currently known to be at the basis of the structure of the siderophore enterochelin (Young et al, 1971). As observed for B/rlt, the mutant Chr2 also presented reversion of Cr(III) sensitivity to the wild-type phenotype when iron was added at a high level to the medium.…”

Section: Genes/proteins Involved In Iron Metabolismmentioning

confidence: 98%

Molecular mechanisms of Cr(VI) resistance in bacteria and fungi

et al. 2014

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Hexavalent chromium [Cr(VI)] contamination is one of the main problems of environmental protection because the Cr(VI) is a hazard to human health. The Cr(VI) form is highly toxic, mutagenic, and carcinogenic, and it spreads widely beyond the site of initial contamination because of its mobility. Cr(VI), crossing the cellular membrane via the sulfate uptake pathway, generates active intermediates Cr(V) and/or Cr(IV), free radicals, and Cr(III) as the final product. Cr(III) affects DNA replication, causes mutagenesis, and alters the structure and activity of enzymes, reacting with their carboxyl and thiol groups. To persist in Cr(VI)-contaminated environments, microorganisms must have efficient systems to neutralize the negative effects of this form of chromium. The systems involve detoxification or repair strategies such as Cr(VI) efflux pumps, Cr(VI) reduction to Cr(III), and activation of enzymes involved in the ROS detoxifying processes, repair of DNA lesions, sulfur metabolism, and iron homeostasis. This review provides an overview of the processes involved in bacterial and fungal Cr(VI) resistance that have been identified through 'omics' studies. A comparative analysis of the described molecular mechanisms is offered and compared with the cellular evidences obtained using classical microbiological approaches.

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Biosynthesis of the Iron-Transport Compound Enterochelin: Mutants of Escherichia coli Unable to Synthesize 2,3-Dihydroxybenzoate

Cited by 91 publications

References 26 publications

Transport of vitamin B12 in tonB mutants of Escherichia coli

Transport of vitamin B12 in tonB mutants of Escherichia coli

The Escherichia coli enterobactin biosynthesis gene, entD: nucleotide sequence and membrane localization of its protein product

Molecular mechanisms of Cr(VI) resistance in bacteria and fungi

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