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Background  In the presence of sufficient iron, the  Escherichia coli  protein Fur (Ferric Uptake Regulator) represses genes controlled by the Fur box, a consensus sequence near or within promoters of target genes. De-repression of Fur-controlled genes occurs upon iron deprivation. In the  E. coli  chromosome, there is a bidirectional intercistronic promoter region with two non-overlapping Fur boxes. This region controls Fur-regulated expression of  entCEBAH  in the clockwise direction and  fepB  in the anticlockwise direction.    Results  We cloned the  E. coli  bidirectional  fepB / entC  promoter region into low-copy-number plasmid backbones (pACYC184 and pBR322) along with downstream sequences encoding epitope tags and a multiple cloning site (MCS) compatible with the bacterial adenylate cyclase two-hybrid (BACTH) system. The vector pFCF1 allows for iron-controlled expression of FLAG-tagged proteins, whereas the pFBH1 vector allows for iron-controlled expression of HA-tagged proteins. We showed that  E. coli  knockout strains transformed with pFCF1- entA , pFCF1- entE  and pFBH1- entB  express corresponding proteins with appropriate epitope tags when grown under iron restriction. Furthermore, transformants exhibited positive chrome azurol S (CAS) assay signals under iron deprivation, indicating that the transformants were functional for siderophore biosynthesis. Western blotting and growth studies in rich and iron-depleted media demonstrated that protein expression from these plasmids was under iron control. Finally, we produced the vector pFCF2, a pFCF1 derivative in which a kanamycin resistance ( KanR ) gene was engineered in the direction opposite of the MCS. The  entA  ORF was then subcloned into the pFCF2 MCS. Bidirectional protein expression in an iron-deprived pFCF2- entA  transformant was confirmed using antibiotic selection, CAS assays and growth studies.    Conclusions  The vectors pFCF1, pFCF2, and pFBH1 have been shown to use the  fepB / entC  promoter region to control bidirectional  in trans  expression of epitope-tagged proteins in iron-depleted transformants. In the presence of intracellular iron, protein expression from these constructs was abrogated due to Fur repression. The compatibility of the pFCF1 and pFBH1 backbones allows for iron-controlled expression of multiple epitope-tagged proteins from a single co-transformant.    Electronic supplementary material  The online version of this article (doi:10.1186/s12896-016-0298-1) contains supplementary material, which is available to authorized users.

A novel set of vectors for Fur-controlled protein expression under iron deprivation in Escherichia coli