Export of the siderophore enterobactin in Escherichia coli: involvement of a 43 kDa membrane exporter

Abstract

Summary The enterobactin system for iron transport in Escherichia coli is well characterized with the exception of the mechanism of enterobactin secretion to the extracellular environment. Escherichia coli membrane protein P43, encoded by ybdA in the chromosomal region of genes involved in enterobactin synthesis, shows strong homology to the 12‐transmembrane segment major facilitator superfamily of export pumps. A P43‐null mutation was created and siderophore nutrition assays, performed with a panel of E. coli strains expressing one or more outer membrane receptors for enterobactin‐related compounds, demonstrated that the P43 mutant was unable to secrete enterobactin efficiently. Products released from the mutant strain were identified with thin‐layer chromatography (TLC) and high‐performance liquid chromatography (HPLC), revealing that the P43 mutant secretes little, if any, enterobactin, but elevated levels of enterobactin breakdown products 2,3‐ dihydroxybenzoylserine (DHBS) monomer, dimer, and trimer. These data establish that P43 is a critical component of the E. coli enterobactin secretion machinery and provides a rationale for the designation of the previous genetic locus ybdA as entS to reflect its relevant biological function.

Genetic organization of an Acinetobacter baumannii chromosomal region harbouring genes related to siderophore biosynthesis and transport

“…This finding is significant in light of the recent report showing that the latter, also known as EntS, is involved in the secretion of enterobactin (Furrer et al, 2002). P45 also showed significant similarity to six P. aeruginosa proteins that belong to the major facilitator superfamily (MFS) class (Borges-Walmsley & Walmsley, 2001;Paulsen et al, 1996) but not to OprM, which is an iron-regulated efflux pump protein that appears to function as the pyoverdin exporter (Poole et al, 1993a, b).…”

“…2, lane 6), encodes a 45 kDa protein highly similar to the E. coli P43 membrane protein (Table 3). The latter, which was recently named EntS, is encoded by the ybdA gene of the E. coli ent operon (Chenault & Earhart, 1991;Shea & McIntosh, 1991) and participates in the secretion of enterobactin (Furrer et al, 2002). The A. baumannii P45 and E. coli P43 proteins contain, with the exception of one, equivalent transmembrane (TM) domains (Fig.…”

A small RNA promotes siderophore production through transcriptional and metabolic remodeling

“…Enterobactin was extracted and visualized according to a previous report (12). Cells were grown in M63, 0.2% glucose, from a 10-fold or 100-fold dilution of an overnight culture in the same media.…”

“…The final assembly of DHB and serine into enterobactin depends on the action of EntD, EntB, EntE, and EntF (11). Once enterobactin has been synthesized, it is transported through the inner membrane by EntS (12) and the outer membrane by TolC (13). Outside the cell, enterobactin will bind to ferric Fe (Fe 3+ ) with an extremely high affinity (14).…”

Potentiation of Antibacterial Activity of the MB-1 Siderophore-Monobactam Conjugate Using an Efflux Pump Inhibitor

“…Among these potentiation-type approaches, we considered the idea that inhibiting endogenous siderophore functionality should circumvent the adaptation phenotype mediated by the competition for iron by native siderophore systems. Siderophore secretion into the extracellular milieu has been shown to be dependent on functional efflux pumps in Gram-negative bacteria (3)(4)(5). In the case of P. aeruginosa, the secretion of newly synthesized pyoverdine is accomplished by the ABC transporter-type efflux system encoded by pvdR, pvdT, and opmQ (6).…”