Signal transfer through three compartments: transcription initiation of the Escherichia coli ferric citrate transport system from the cell surface.

Abstract

Transport of ferric citrate into cells of Escherichia coli K‐12 involves two energy‐coupled transport systems, one across the outer membrane and one across the cytoplasmic membrane. Previously, we have shown that ferric citrate does not have to enter the cytoplasm of E. coli K‐12 to induce transcription of the fec ferric citrate transport genes. Here we demonstrate that ferric citrate uptake into the periplasmic space between the outer and the cytoplasmic membranes is not required for fec gene induction. Rather, FecA and the TonB, ExbB and ExbD proteins are involved in induction of the fec transport genes independent of their role in ferric citrate transport across the outer membrane. The uptake of ferric citrate into the periplasmic space of fecA and tonB mutants via diffusion through the porin channels did not induce transcription of fec transport genes. Point mutants in FecA displayed the constitutive expression of fec transport genes in the absence of ferric citrate but still required TonB, with the exception of one FecA mutant which showed a TonB‐independent induction. The phenotype of the FecA mutants suggests a signal transduction mechanism across three compartments: the outer membrane, the periplasmic space and the cytoplasmic membrane. The signal is triggered upon the interaction of ferric citrate with FecA protein. It is postulated that FecA, TonB, ExbB and ExbD transfer the signal across the outer membrane, while the regulatory protein FecR transmits the signal across the cytoplasmic membrane to FecI in the cytoplasm. FecI serves as a sigma factor which facilitates binding of the RNA polymerase to the fec transport gene promoter upstream of fecA.(ABSTRACT TRUNCATED AT 250 WORDS)

Defined Inactive FecA Derivatives Mutated in Functional Domains of the Outer Membrane Transport and Signaling Protein of Escherichia coli K-12

“…Citrate-mediated 55 Fe 3ϩ transport was determined for E. coli IS1031, which carries a chromosomally encoded FecA R413H mutation that renders cells inactive for citrate-mediated iron transport and exhibits no polar effect on the downstream fecBCDE genes (24,47). IS1031 transformants carried the fecA genes on the medium-copy-number plasmid pT7-7.…”

“…FecA serves as a transport protein for ferric citrate across the outer membrane of Escherichia coli and as a signal receiving and signal transduction protein (4,24,28). Binding of ferric citrate to FecA induces transcription of the ferric citrate transport genes fecABCDE (4,5,7).…”

Signal transduction pathway of TonB-dependent transporters

“…5]. Members of the diverse family of TonBdependent transporters include those for ferric citrate (FecA), ferrichrome (FhuA), ferric enterobactin (FepA), and other organometallic compounds such as vitamin B 12 (BtuB).…”

“…FecI promotes binding of RNA polymerase to the promoter upstream of the ferric citrate import operon, thereby initiating transcription (9,10). Although transport and signaling are ferric citrate-and TonB-dependent processes, these functions are ultimately separable because removing the signaling domain abolishes ferric citrate-mediated transcriptional activation, whereas ferric citrate import remains unaffected (11,12).…”

Identification of differentially expressed genes of Xanthomonas axonopodis pv. citri by representational difference analysis of cDNA

“…Fe is the limiting factor of bacterial growth in planta since micromolar concentrations of iron are necessary to permit bacterial growth and multiplication. The TonB system also mediates the signal transduction from the cellular surface to the cytoplasm, as reported in E. coli and Pseudomonas putida (Harle et al, 1995;Koster et al, 1994). In X. campestris, the genes involved in the uptake of Fe are essential for the induction of a hypersensitive response (Wiggerich and Puhler, 2000).…”