https://mmbr.asm.org/content/mmbr/47/2/180.full.pdf

Linkage map of Escherichia coli K-12, edition 7.

Nitrate respiration in relation to facultative metabolism in enterobacteria.

A range of bacteria are able to use tetrathionate as a terminal respiratory electron acceptor. Here we report the identification and characterization of the ttrRSBCA locus required for tetrathionate respiration in Salmonella typhimurium LT2a. The ttr genes are located within Salmonella pathogenicity island 2 at centisome 30.5. ttrA, ttrB and ttrC are the tetrathionate reductase structural genes. Sequence analysis suggests that TtrA contains a molybdopterin guanine dinucleotide cofactor and a [4Fe–4S] cluster, that TtrB binds four [4Fe–4S] clusters, and that TtrC is an integral membrane protein containing a quinol oxidation site. TtrA and TtrB are predicted to be anchored by TtrC to the periplasmic face of the cytoplasmic membrane implying a periplasmic site for tetrathionate reduction. It is inferred that the tetrathionate reductase, together with thiosulphate and polysulphide reductases, make up a previously unrecognized class of molybdopterin-dependent enzymes that carry out the reductive cleavage of sulphur–sulphur bonds. Cys-256 in TtrA is proposed to be the amino acid ligand to the molybdopterin cofactor. TtrS and TtrR are the sensor and response regulator components of a two-component regulatory system that is absolutely required for transcription of the ttrBCA operon. Expression of an active tetrathionate reduction system also requires the anoxia-responsive global transcriptional regulator Fnr. The ttrRSBCA gene cluster confers on Escherichia coli the ability to respire with tetrathionate as electron acceptor.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2958.1999.01345.x

The genetic basis of tetrathionate respiration in Salmonella typhimurium.

This map is an update of the edition 9 map by Berlyn et al. (M. K. B. Berlyn, K. B. Low, and K. E. Rudd, p. 1715–1902, in F. C. Neidhardt et al., ed., Escherichia coli and Salmonella: cellular and molecular biology, 2nd ed., vol. 2, 1996). It uses coordinates established by the completed sequence, expressed as 100 minutes for the entire circular map, and adds new genes discovered and established since 1996 and eliminates those shown to correspond to other known genes. The latter are included as synonyms. An alphabetical list of genes showing map location, synonyms, the protein or RNA product of the gene, phenotypes of mutants, and reference citations is provided. In addition to genes known to correspond to gene sequences, other genes, often older, that are described by phenotype and older mapping techniques and that have not been correlated with sequences are included.

/pdf/linkage-map-of-escherichia-coli-k-12-edition-10-the-4xep962ryl.pdf

Linkage Map of Escherichia coli K-12, Edition 10: The Traditional Map

The Tat system is a recently discovered protein export pathway that serves to translocate folded proteins, often containing redox cofactors, across the bacterial cytoplasmic membrane. Here we report that tat strains are associated with a mutant cell septation phenotype, where chains of up to 10 cells are evident. Mutant strains are also hypersensitive to hydrophobic drugs and to lysis by lysozyme in the absence of EDTA, and they leak periplasmic enzymes, characteristics that are consistent with an outer membrane defect. Both phenotypes are similar to those displayed by strains carrying point mutations in the lpxC (envA) gene. The phenotype was not replicated by mutations affecting synthesis and/or activity of all known or predicted Tat substrates. Approximately 20% of all proteins synthesized by Escherichia coli are predicted to be located outside the cytoplasmic compartment. Most proteins destined for export are synthesized with N-terminal signal sequences that direct translocation by the general secretory (Sec) apparatus (17, 21). Secdependent signal sequences lack sequence similarity but have similar overall physical-chemical properties (32). A subset of periplasmic and periplasmically oriented proteins are exported by a mechanism distinct from the Sec pathway (3, 25, 26, 34). Such proteins are synthesized with, or in some cases associate with partner proteins synthesized with, signal sequences harboring the (S/T)RRxFLK “twin-arginine” motif (2). These distinctive signal sequences target substrate proteins to the twin-arginine signal peptide-dependent protein translocase (Tat translocase) which is structurally and mechanistically related to the DpH-dependent protein translocase of plant thylakoid membranes (8, 29). Many Tat-dependent substrate proteins bind redox cofactors and are involved in bacterial energy metabolism. Cofactor acquisition is a cytoplasmic event and is a prerequisite for export, suggesting that proteins are translocated by the Tat apparatus in a folded conformation (22, 25). Minimally the E. coli Tat translocase comprises four probable membrane proteins, encoded by the tatA, tatB, tatC, and tatE genes. The tatA, tatB, and tatC genes are cotranscribed with a fourth gene, tatD, encoding a soluble protein with no discernible role in Tat-dependent protein export (35). TatA, TatB, and TatE are sequence-related proteins, each of which is predicted to comprise a single N-terminal transmembrane a-helix, immediately followed by an amphipathic a-helix at the cytoplasmic side of the membrane (7, 26). TatA and TatE are more than 50% identical at the amino acid level and have overlapping functions in Tat-dependent protein export. Thus, comutation of both tatA and tatE is necessary to observe a complete block in export by the Tat pathway (26). TatB, which is more divergently related to TatA/E (approximately 25% amino acid identity), is a distinct and essential component of the Tat apparatus (27). The tatC gene encodes a highly hydrophobic protein, predicted to contain six membrane-spanning a-helices, which is critical for Tat function (5). In each case, a block in Tat-dependent protein export results in the mislocalization of Tat-dependent substrate proteins to the cytoplasmic compartment. Tat mutant strains are unable to grow anaerobically with either dimethyl sulfoxide or trimethylamine-Noxide as sole terminal electron acceptor, reflecting the failure to correctly localize the terminal reductases. The mutant strains otherwise display no discernible growth phenotype. In this paper, we report that strains lacking genes encoding essential Tat components form chains of up to 10 cells, which appear to be defective in cell separation. Electron microscopy reveals that the phenotype is similar to that of an lpxC (envA) mutant, which has a defect in the synthesis of outer membrane lipid A. Consistent with this, tat mutant strains are hypersensitive to hydrophobic drugs and to lysozyme-induced lysis in the absence of EDTA. We show that this phenotype is not due to the mislocalization of any single Tat substrate protein.

Escherichia coli Strains Blocked in Tat-Dependent Protein Export Exhibit Pleiotropic Defects in the Cell Envelope

We examined the properties of mutants of E. coli which are defective with respect to nitrate reductase activity. chlE::Mu cts and chlG::Mu cts mutants were all chlorate resistant, and the strains that we examined all synthesized nitrate reductase apoenzyme. We concluded that the chlE and chlG loci, like the chlA, chlB, and chlD loci, are involved in the synthesis of insertion of molybdenum cofactor. We identified at least four distinct phenotypic classes of chlC::Tn10 mutants, all of which were fully or partially sensitive to chlorate. Two of these classes may represent lesions in the structural genes for nitrate reductase subunits A and C. Two other classes may be altered in the regulation of the expression of nitrate reductase or other anaerobic enzymes. We propose the mnemonic nar for naming individual genes within the chlC locus.

Nitrate reductase in Escherichia coli K-12: involvement of chlC, chlE, and chlG loci.

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Nitrate reductase in Escherichia coli K-12: involvement of chlC, chlE, and chlG loci.