Iron supply to Escherichia coli by synthetic analogs of enterochelin

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Abstract
Synthetic analogs of enterochelin (enterobactin) were tested for their ability to support the growth of E. coli K-12 under Fe-limiting conditions. The cyclic compound MECAM [1,3,5-N,N'',N"-tris-(2,3-dihydroxybenzoyl)-triaminomethylbenzene] and its N-methyl derivative Me3MECAM promoted growth, whereas the 2,3-dihydroxy-5-sulfonyl derivatives MECAMS and Me3 MECAMS were inactive. The same results were obtained with TRIMCAM [1,3,5-tris(2,3-dihydroxybenzoylcarbamido)-benzene] and TRIMCAMS (the 2,3-dihydroxy-5-sulfonyl derivative of TRIMCAM). The sulfonic acid-containing linear compound LICAMS [1,5,10-N,N'',N"-tris(5-sulfo-2,3-dihydroxybenzoyl)-triazadecane] supported growth. LIMCAMC, in which the sulfonyl groups at the 5 position of LICAMS are replaced by carboxyl groups at the 4 position, was inactive. The uptake of the active analogs required for functions specified by the fepB, fesB and tonB genes. Growth promotion of mutants lacking the enterochelin receptor protein in the outer membrane was observed. Only MECAM protected cells against colicin B (which kills cells after entering at the enterochelin uptake sites) and transported Fe3+ at about half the enterochelin rate.

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