The respiratory chains of Escherichia coli

Escherichia coli strains carrying the cloned cytochrome d terminal oxidase complex are sensitive to near-UV inactivation

To determine if membrane-bound cytochromes function as endogenous near-UV photosensitizers, strains containing the cloned cydA and cydB genes were tested for near-UV sensitivity. A strain containing both cloned genes overproduced cytochromes b558, b595, and d. Another strain containing only cloned cydB overproduced cytochrome b558. Both cytochrome-overproducing strains were hypersensitive to broad-spectrum near-UV inactivation. The presence of excess cytochromes did not affect sensitivity to far-UV radiation and provided protection against H2O2 inactivation.

Products of Leishmania braziliensis glucose catabolism: release of D-lactate and, under anaerobic conditions, glycerol

Leishmania braziliensis panamensis promastigotes were incubated with glucose as the sole carbon source. About one-fifth of the glucose consumed under aerobic conditions was oxidized to CO2. Nuclear magnetic resonance studies with [1-13C]glucose showed that the other products released were succinate, acetate, alanine, pyruvate, and lactate. Under anaerobic conditions, lactate output increased, glycerol became a major product, and, surprisingly, glucose consumption decreased. Enzymatic assays showed that the lactate formed was D(-)-lactate. The release of alanine during incubation with glucose as the sole carbon source suggested that appreciable proteolysis occurred, consistent with our observation that a large amount of ammonia was released under these conditions. The discoveries that D-lactate is a product of L. braziliensis glucose catabolism, that glycerol is produced under anaerobic conditions, and that the cells exhibit a "reverse" Pasteur effect open the way for detailed studies of the pathways of glucose metabolism and their regulation in this organism.

Molecular cloning and sequencing of the hemD gene of Escherichia coli K-12 and preliminary data on the Uro operon

DNA of plasmid pSAS1002TH (F' ilv+ hemD+ hemC+ cya+) was used to clone the hemD gene of Escherichia coli K-12. Due to poor transformability of the heme-deficient mutants, the restriction fragments of the F' plasmid were first cloned into a mobilizable derivative of pBR322, pSAS1211LP, which was then mobilized into a hemD recA mutant (E. coli SASX419AN). One recombinant plasmid, carrying a HindIII fragment of about 5 kilobases (kb), was shown to complement the hemD mutant and also a cya mutant of E. coli K-12, as well as a hemC mutant of Salmonella typhimurium LT2. Further subcloning of the insert enabled us to locate the hemD gene to a BamHI-PstI fragment (approximately 2.3 kb) which also carried the hemC gene. The hemD gene occupies a region close to the PstI end, since the deletion of a 0.6-kb fragment from this end resulted in loss of the ability to complement the hemD mutation. The use of the promoter-probe vector pK01 and the results of complementation showed that the hemD gene was transcribed under physiological conditions from the same promoter as the hemC gene, the direction of transcription being hemC-hemD. This allows us to define a new polycistronic operon of E. coli K-12, for which we propose the designation Uro operon. Sequencing of the hemD gene showed the presence of an open reading frame (ORF) of 738 nucleotides which could code for a protein with a molecular weight of 27,766, which should correspond to the hemD protein; the ORF starts with the last nucleotide of the hemC gene, the two genes having different reading frames. An ORF of at least 480 base pairs follows the hemD gene after a few nucleotides. The corresponding gene X, the function of which is unknown, might represent a third member of the Uro operon.

Spectral and potentiometric analysis of cytochromes from Bacillus subtilis

Bacillus subtilis cytoplasmic membranes contain several cytochromes which are linked to the respiratory chain. At least six different cytochromes have been separated and identified by ammonium sulphate fractionation and ion-exchange chromatography. They include two terminal oxidases with CO-binding properties and cyanide sensitivity. One of these is an aa3-type cytochrome c oxidase which has characteristic absorption maxima in the reduced-oxidized difference spectrum at 601 nm in the alpha-band and at 443 nm in the Soret band regions. In the alpha-band two separate electron transitions with Em = +205 mV and Em = +335 mV can be discriminated by redox potentiometric titration. The other CO-binding cytochrome c oxidase contains two cytochrome b components with alpha-band maxima at 556 nm and 559 nm. Cytochrome b556 can be reduced by ascorbate and has an Em + +215 mV, whereas cytochrome b559 has an Em = +140 mV. Furthermore a complex consisting of a cytochrome b564 (Em = +140 mV) associated with a cytochrome c554 (Em = +250 mV) was found. This cytochrome c554, which can be reduced by ascorbate, appears to have an asymmetrical alpha-peak and stains for heme-catalyzed peroxidase activity on SDS-containing polyacrylamide gels. A protein with a molecular mass of about 30 kDa is responsible for this activity. A cytochrome b559 (Em = +65 mV) appears to be an essential part of succinate dehydrogenase. Finally a cytochrome c550 component with an apparent mid-point potential of Em = +195 mV has been detected.

Molybdenum effector of fumarate reductase repression and nitrate reductase induction in Escherichia coli

In Escherichia coli the presence of nitrate prevents the utilization of fumarate as an anaerobic electron acceptor. The induction of the narC operon encoding the nitrate reductase is coupled to the repression of the frd operon encoding the fumarate reductase. This coupling is mediated by nitrate as an effector and the narL product as the regulatory protein (S. Iuchi and E. C. C. Lin, Proc. Natl. Acad. Sci. USA 84:3901-3905, 1987). The protein-ligand complex appears to control narC positively but frd negatively. In the present study we found that a molybdenum coeffector acted synergistically with nitrate in the regulation of frd and narC. In chlD mutants believed to be impaired in molybdate transport (or processing), full repression of phi(frd-lac) and full induction of phi(narC-lac) by nitrate did not occur unless the growth medium was directly supplemented with molybdate (1 microM). This requirement was not clearly manifested in wild-type cells, apparently because it was met by the trace quantities of molybdate present as a contaminant in the mineral medium. In chlB mutants, which are known to accumulate the Mo cofactor because of its failure to be inserted as a prosthetic group into proteins such as nitrate reductase, nitrate repression of frd and induction of narC were also intensified by molybdate supplementation. In this case a deficiency of the molybdenum coeffector might have resulted from enhanced feedback inhibition of molybdate transport (or processing) by the elevated level of the unutilized Mo cofactor. In addition, mutations in chlE, which are known to block the synthesis of the organic moiety of the Mo cofactor, lowered the threshold concentration of nitrate (< 1 micromole) necessary for frd repression and narC induction. These changes could be explained simply by the higher intracellular nitrate attainable in cells lacking the ability to destroy the effector.

Regulation of the fdhF gene encoding the selenopolypeptide for benzyl viologen-linked formate dehydrogenase in Escherichia coli

Two classes of mutants defective in benzyl viologen-linked formate dehydrogenase (FDH-BV) activity were isolated from Escherichia coli K12. Class I consisted of four mutants which were specifically devoid of FDH-BV activity. Their mutation mapped between the ssb and melA genes at 92 min on the genome, at a site recently designated fdhF by Pecher et al. (1985). The direction of transcription of gene fdhF was found to be counterclockwise on the E. coli chromosome in one Mudl(Aprlac) fusion mutant. Expression of the lac operon in this mutant was induced by formate and repressed by nitrate, nitrite or trimethylamine N-oxide. It was found to be dependent on the positive control exerted by the fdhA, B and C genes, possibly involved in selenium incorporation, and by an hydB gene affecting the formate hydrogenlyase pathway. Class II, represented by one Mudl(Aprlac) mutant, exhibited no FDH-BV activity and a reduced level of hydrogenase activity. The relevant fdv mutation was shown to be located at 58 min and to affect the expression of fdhF.

Cloning of the cyo locus encoding the cytochrome o terminal oxidase complex of Escherichia coli

The structural genes encoding the cytochrome o terminal oxidase complex (cyo) of Escherichia coli have been subcloned into the multicopy plasmid pBR322 after the Mu-mediated transposition of the gene locus from the bacterial chromosome onto the conjugative R plasmid RP4. Introduction of cyo plasmids into strains (cyo cyd) lacking both terminal oxidases restored the ability of the strains to grow aerobically on nonfermentable substrates. Strains carrying the cyo plasmids produced 5 to 10 times more cytochrome o oxidase than did control strains. The gene products encoded by the cyo plasmids could be immunoprecipitated with monospecific antibodies raised against cytochrome o. The cloned genes will be valuable for studying the structure, function, and regulation of the cytochrome o terminal oxidase complex.

Activation of the lac operon of Escherichia coli by a mutant FNR protein

The FNR protein of E. coli is a transcriptional activator required for the expression of genes involved in anaerobic respiratory pathways. Site-directed mutagenesis was used to alter three amino acids in the recognition helix of the putative DNA-binding domain of FNR, with the aim of changing its specificity to that of the cyclic AMP receptor protein (CRP). In the presence of the mutant protein (FNR-215) expression of the lac operon was activated during anaerobiosis and unaffected by glucose. FNR-215 did not have a uniform effect on the expression of other cAMP-CRP-dependent genes, but the results demonstrate the fundamental similarity between FNR- and CRP-mediated transcriptional activation.

Regulation of Escherichia coli fumarate reductase (frdABCD) operon expression by respiratory electron acceptors and the fnr gene product

The fumarate reductase enzyme complex, encoded by the frdABCD operon, allows Escherichia coli to utilize fumarate as a terminal electron acceptor for anaerobic oxidative phosphorylation. To analyze the expression of fumarate reductase, protein and operon fusions were constructed between the frdA and the lacZ genes and introduced onto the E. coli chromosome at the lambda attachment site. Expression of beta-galactosidase from either fusion was increased 10-fold during anaerobic versus aerobic cell growth, increased an additional 1.5-fold by the presence of fumarate, the substrate, and decreased 23-fold by nitrate, a preferred electron acceptor. The addition of trimethylamine-N-oxide as an electron acceptor did not significantly alter frdA'-'lacZ expression. Control of frd operon expression is therefore exerted at the transcriptional level in response to the availability of the electron acceptors oxygen, fumarate, and nitrate. Anaerobic induction of frdA'-'lacZ expression was impaired in an fnr mutant and was restored when the fnr+ gene was provided in trans, thus establishing that the fnr gene product, Fnr, is responsible for the anaerobic activation of frd operon expression. Nitrate repression of frdA'-'lacZ expression was observed under either aerobic or anaerobic cell growth conditions in both wild-type and fnr mutant strains, demonstrating that the mechanism for nitrate repression is independent of nitrate respiration and oxygen control imparted by Fnr. Studies performed with a fnr'-'lacZ protein fusion confirmed that the fnr gene is expressed both aerobically and anaerobically. A model is proposed for the regulation of frdABCD operon expression in response to the availability of the alternate terminal electron acceptors oxygen, nitrate, and fumarate.

The narL gene product activates the nitrate reductase operon and represses the fumarate reductase and trimethylamine N-oxide reductase operons in Escherichia coli

Escherichia coli, which can utilize O2, nitrate, fumarate, or trimethylamine N-oxide (Me3NO) as terminal electron acceptor, preferentially utilizes the one with the highest redox potential. Thus O2 prevents induction of nitrate, fumarate, and Me3NO reductases, and nitrate curtails the induction of fumarate and Me3NO reductases. Under anaerobic conditions the narL gene product, in the presence of nitrate, is known to activate transcription of the narC operon, which encodes nitrate reductase. This study shows that the same product plays a role in the repression by nitrate of the operons (frd and tor) that encode fumarate and Me3NO reductases. In contrast, the anaerobic repression of ethanol dehydrogenase by nitrate does not require the narL product. Expression of narL does not require the fnr gene product, a pleiotropic activator that is required for full expression of narC, frd, and tor.

Tetrahydrothiophene 1-oxide as an electron acceptor for Escherichia coli

Escherichia coli used tetrahydrothiophene 1-oxide (THTO) as an electron acceptor for anaerobic growth with glycerol as a carbon source; the THTO was reduced to tetrahydrothiophene. Cell extracts also reduced THTO to tetrahydrothiophene in the presence of a variety of electron donors. Chlorate-resistant (chl) mutants (chlA, chlB, chlD, and chlE) were unable to grow with THTO as the electron acceptor. However, growth and THTO reduction by the chlD mutant were restored by high concentrations of molybdate. Similarly, mutants of E. coli that are blocked in the menaquinone (vitamin K2) biosynthetic pathway, i.e., menB, menC, and menD mutants, did not grow with THTO as an electron acceptor. Growth and THTO reduction were restored in these mutants by the presence of appropriate intermediates of the vitamin K biosynthetic pathway.

Identification of the cydC locus required for expression of the functional form of the cytochrome d terminal oxidase complex in Escherichia coli

The aerobic respiratory chain of Escherichia coli contains two terminal oxidases which are differentially regulated. The cytochrome o complex predominates under growth conditions of high aeration, whereas the cytochrome d complex predominates when the oxygen tension is low. Either terminal oxidase will support aerobic growth. The goal of the work presented in this paper was to identify genes required for the expression of the functional form of the cytochrome d complex, other than the genes encoding the polypeptide components of the oxidase complex (cyd locus). A strain lacking the cytochrome o complex (cyo mutant strain) was mutagenized by using a lambda-Mu hybrid hopper bacteriophage, lambda placMu53, which inserts randomly into the chromosome and carries a kanamycin resistance marker. Strains were isolated and examined which were unable to grow aerobically, i.e., which lacked functional cytochrome d complex, and which could not be complemented by introduction of the cyd gene on F-prime episomes. One strain was selected for characterization. The phage insert was mapped to min 18.9 on the genetic linkage map, defining a new genetic locus, cydC. Evidence described in the text suggests that the gene product is probably required for the synthesis of the unique heme d component of the cytochrome d complex.

Involvement of chlA, E, M, and N loci in Escherichia coli molybdopterin biosynthesis

All molybdenum enzymes except nitrogenase contain a common molybdenum cofactor, whose organic moiety is a novel pterin called molybdopterin (MPT). To assist in elucidating the biosynthetic pathway of MPT, two MPT-deficient mutants of Escherichia coli K-12 were isolated. They lacked activities of the molybdenum enzymes nitrate reductase and formate dehydrogenase, did not reconstitute apo nitrate reductase from a Neurospora crassa nit-1 strain, and did not yield form A, a derivative of MPT. By P1 mapping, these two mutations mapped to chlA and chlE, loci previously postulated but never definitely shown to be involved in MPT biosynthesis. The two new mutations are in different genetic complementation groups from previously isolated chlA and chlE mutations and have been designated as chlM and chlN (closely linked to chlA and chlE, respectively). The reported presence of Mo cofactor activity in the chlA1 strain is shown to be due to in vitro synthesis of MPT through complementation between a trypsin-sensitive macromolecule from the chlA1 strain and a low-molecular-weight compound from the nit-l strain.

Reconstitution of pyrroloquinoline quinone-dependent D-glucose oxidase respiratory chain of Escherichia coli with cytochrome o oxidase

D-Glucose dehydrogenase is a pyrroloquinoline quinone-dependent primary dehydrogenase linked to the respiratory chain of a wide variety of bacteria. The enzyme exists in the membranes of Escherichia coli, mainly as an apoenzyme which can be activated by the addition of pyrroloquinoline quinone and magnesium. Thus, membrane vesicles of E. coli can oxidize D-glucose to gluconate and generate an electrochemical proton gradient in the presence of pyrroloquinoline quinone. The D-glucose oxidase-respiratory chain was reconstituted into proteoliposomes, which consisted of two proteins purified from E. coli membranes, D-glucose dehydrogenase and cytochrome o oxidase, and E. coli phospholipids containing ubiquinone 8. The electron transfer rate during D-glucose oxidation and the membrane potential generation in the reconstituted proteoliposomes were almost the same as those observed in the membrane vesicles when pyrroloquinoline quinone was added. The results demonstrate that the quinoprotein, D-glucose dehydrogenase, can reduce ubiquinone 8 directly within phospholipid bilayer and that the D-glucose oxidase system of E. coli has a relatively simple respiratory chain consisting of primary dehydrogenase, ubiquinone 8, and a terminal oxidase.

L-lactate enzyme electrode obtained with immobilized respiratory chain from Escherichia coli and oxygen probe for specific determination of L-lactate in yogurt, wine and blood

An enzyme electrode for L-lactate measurements in various biological media was prepared with an immobilized bacterial respiratory chain fixed to a Clark electrode. The enzymatic film, which was easy to prepare, contained bacteria immobilized in gelatin, tanned with glutaraldehyde. This electrode was sensitive to 0.1 mM L-lactate and could be utilized to 10 mM. The apparent K50 was 5 mM. Less than 8% of the respiration rate with L-lactate was measured with D-lactate and succinate. The competitive inhibitors D-lactate and pyruvate had a K50 of 50 mM. They could be quantitatively measured by inhibition in a range between 5 and 50 mM. It was also possible to discriminate between L-lactate and various metabolites of the respiratory chain: L-malate, succinate, 3-glycero-phosphate or NAD(P)H. Growing E. coli on 1% D-L-lactate as the sole carbon source in minimal medium induced L-lactate respiration tenfold. All other respiratory activities remained below 10% of the activity with L-lactate. A computerized instrument allowed successive measurements every 3 min for more than 10 h with the same enzymatic film. Most of the measured samples required dilution but no clarification or purification. This enzyme electrode may have many applications in basic research (metabolism, enzymology) and applied research (blood, yogurt, juices, wine).

Oxidation of reduced menaquinone by the fumarate reductase complex in Escherichia coli requires the hydrophobic FrdD peptide

Plasmids carrying cloned segments of the frd operon of Escherichia coli have been used in genetic complementation studies to identify two independent mutants defective in the frdD gene, which encodes the hydrophobic FrdD polypeptide of the fumarate reductase complex. Mutations in the frdA and frdB genes have also been mapped by this technique. One of the FrdD peptide mutants, DW109 (frdD-109), showed that fumarate reductase was not as tightly bound to the membrane in this mutant. In addition, the mutation in the FrdD peptide caused an almost total loss of the ability of the enzyme to oxidize either menaquinol-6, a physiological donor for fumarate reduction, or reduced benzyl viologen. However, the mutation did not impair the ability of the membrane-bound fumarate reductase complex to function with succinate as substrate, as evidenced by unchanged turnover numbers for phenazine methosulfate and 2,3-dimethoxy-5-methyl-6-pentyl-1,4-benzoquinone (a quinone analogue) reductase activities. These data establish the essential role of the FrdD polypeptide both in the interaction of the enzyme with reduced menaquinone and thus in anaerobic respiration with fumarate as electron acceptor, and in binding the enzyme to the membrane.

Three classes of Escherichia coli mutants selected for aerobic expression of fumarate reductase

Fumarate reductase (encoded by frd) and succinate dehydrogenase (encoded by sdh) of Escherichia coli are both known to catalyze the interconversion of fumarate and succinate. Fumarate reductase, however, is not inducible aerobically and therefore cannot participate in the dehydrogenation of succinate. Three classes of suppressor mutants, classified as frd oxygen-resistant [frd(Oxr)], constitutive [frd(Con)], and gene amplification [frd(Amp)] mutants, were selected from an sdh strain as pseudorevertants that regained the partial ability to grow aerobically on succinate. All contained increased aerobic levels of fumarate reductase activity. In frd(Oxr) mutants expression of the operon showed increased resistance to aerobic repression. Under anaerobic conditions expression of the operon became less dependent on the fnr+ gene product, a pleiotropic activator protein for genes encoding anaerobic respiratory enzymes. Exogenous fumarate, however, was still required for full induction, and repression by nitrate was undiminished. Thus, aerobic repression and anaerobic nitrate repression appear to involve separate mechanisms. In frd(Con) mutants expression of the operon became highly resistant to aerobic repression. Under anaerobic conditions expression of the operon no longer required the fnr+ gene product or exogenous fumarate and became immune to nitrate repression. In partial diploids bearing an frd(Oxr) or an frd(Con) allele and phi(frd+-lac) there was no mutual regulatory influence between the two genetic loci. Thus, the frd mutations act in cis and hence are probably in the promoter region. In frd(Amp) mutants the frd locus was amplified without significant alteration in the pattern of regulation.

Effects of iron-limitation of Escherichia coli on growth, the respiratory chains and gallium uptake

The effects of iron limitation on growth, the composition and function of the respiratory chains, and gallium uptake in Escherichia coli have been studied. Decreasing the iron concentration in a defined medium using Chelex resin gave lower growth yields in both continuous culture and prolonged batch culture. In the former, iron-limited (entering [Fe] less than or equal to 2.0 microM) cells exhibited diminished respiration rates, respiration-driven proton translocation quotients, and levels of non-haem iron and cytochromes. The cellular concentration of haemoprotein b-590 (a cytochrome alpha 1-like hydroperoxidase) decreased 20-fold on iron limitation, whilst a CO-binding pigment with an absorption maximum in the dithionite-treated form near 500 nm appeared. Gallium(III) (9 microM) added to iron-limited, but not iron-sufficient, cultures diminished growth yields further; cells grown with low entering concentrations of iron took up less gallium than iron-sufficient cells. These results are attributed to the interference by gallium(III) with siderophore-mediated metal uptake. Gallium also stimulated iron uptake and was itself accumulated by iron-sufficient cells, suggesting that gallium(III) also affects the iron transport system(s) of low affinity.

Inhibition of electron transfer and uncoupling effects by emodin and emodinanthrone in Escherichia coli

The anthraquinones emodin (1,3,delta-trihydroxy-6-methylanthraquinone) and emodinanthrone (1,3,8-trihydroxy-6-methylanthrone) inhibited respiration-driven solute transport at micromolar concentrations in membrane vesicles of Escherichia coli. This inhibition was enhanced by Ca ions. The inhibitory action on solute transport is caused by inhibition of electron flow in the respiratory chain, most likely at the level between ubiquinone and cytochrome b, and by dissipation of the proton motive force. The uncoupling action was confirmed by studies on the proton motive force in beef heart cytochrome oxidase proteoliposomes. These two effects on energy transduction in cytoplasmic membranes explain the antibiotic properties of emodin and emodinanthrone.

Anaerobically induced genes of Escherichia coli

A collection of anaerobically induced gene fusions were isolated, and representative isolates were characterized with respect to their regulatory properties, phenotypes, and approximate map locations. Four fusion strains that had defects in the anaerobic metabolism of asparagine or aspartate were found. These fusions were all repressed by alternate electron acceptors, ammonia, and glucose but were induced by other sugars. Several other fusion strains which demonstrated no observable phenotype showed diverse regulatory responses. The anaerobically induced fusions were scattered around the Escherichia coli chromosome more or less at random, suggesting that all the isolates examined were in separate genes.

Bimodal pattern of killing of DNA-repair-defective or anoxically grown Escherichia coli by hydrogen peroxide

Two modes of killing of Escherichia coli K-12 by hydrogen peroxide can be distinguished. Mode-one killing was maximal with hydrogen peroxide at a concentration of 1 to 2 mM. At higher concentrations the killing rate was approximately half maximal and was independent of H2O2 concentration but first order with respect to exposure time. Mode-one killing required active metabolism during the H2O2 challenge, and it resulted in sfiA-independent filamentation of both cells which survived and those which were killed by the challenge. This mode of killing was enhanced in xth, polA, recA, and recB strains and was accelerated in all strains by an unidentified, anoxia-induced cell function. A strain carrying both xth and recA mutations appeared to undergo spontaneous mode-one killing only under aerobic conditions. Mode-one killing appeared to result from DNA damage which normally occurs at a low, nonlethal level during aerobic growth. Mode-two killing occurred at higher doses of H2O2 and exhibited a multihit dependence on both H2O2 concentration and exposure time. Mode-two killing did not require active metabolism, and killed cells did not filament, although survivors demonstrated a dose-dependent growth lag. Strains with DNA-repair defects were not especially susceptible to mode-two killing.

A mutant of Escherichia coli fumarate reductase decoupled from electron transport

The terminal electron-transfer enzyme fumarate reductase of Escherichia coli is a complex iron-sulfur flavoenzyme composed of four nonidentical subunits organized into two domains: FrdA and -B (a membrane-extrinsic catalytic domain) and FrdC and -D (a transmembrane anchor domain). We have identified a mutation within the membrane-intrinsic domain that alters the electron transfer properties of the iron-sulfur and flavin redox centers of the catalytic domain. Functional electron flow from the quinone analog 2,3-dimethyl-1,4-naphthoquinone or from the electron transport chain is impaired. However, the mutant enzyme can be reduced normally by single-electron donors such as the dye benzyl viologen. The mutant phenotype results from a single A----G transition changing His-82, within the second transmembrane alpha-helix of the FrdC anchor sequence, to an arginine. The mutation, physically located within the anchor domain, is manifested by altered catalytic properties, indicating that the intrinsic and extrinsic domains are conformationally connected. These results confirm the important role of the anchor subunits in functional electron transport and have implications for communication between intrinsic and extrinsic domains of membrane proteins.

Oxygen-regulated stimulons of Salmonella typhimurium identified by Mu d(Ap lac) operon fusions

Using the technique of Mu d1(Ap lac)-directed lacZ operon fusions, several oxygen-regulated genetic loci were identified in Salmonella typhimurium. Thirteen anaerobically inducible and six aerobically inducible operon fusions were identified. Based on control by the oxrA and oxrB regulatory loci, the anti-lacZ fusions were grouped into three classes: class I loci were regulated by both oxr loci, class II genes were regulated by oxrA only, and class III loci were not affected by either regulatory locus. Several of the anti-lacZ fusions required growth in complex medium before they exhibited the inducible phenotype. While the expression of some of these loci was repressed when organisms were grown in nitrate, others were stimulated by nitrate. Fusions into the hyd and phs loci were identified among the isolated anti-lacZ fusions. Six oxygen-inducible (oxi) operon fusions were also identified. Two of the oxi loci mapped near oxygen-regulatory loci: oxiC near oxrA and oxiE near oxyR. However, neither fusion appeared to occur within the regulatory locus. The data presented serve to further define the aerobic and anaerobic stimulons of S. typhimurium but indicate additional regulatory circuits above those already defined.

The functional localization of cytochromes b in the respiratory chain of anaerobically grown Proteus mirabilis

The functional localization of the cytochromes b found in anaerobically grown Proteus mirabilis was investigated. From light absorption spectra, scanned during uninhibited and HQNO-inhibited electron transport to various electron acceptors, it was concluded that all cytochromes b function between two HQNO inhibition sites, or more probably in a Q- or b-cycle.

Transcription of the Escherichia coli fumarate reductase genes (frdABCD) and their coordinate regulation by oxygen, nitrate, and fumarate

The fumarate reductase enzyme complex allows Escherichia coli to grow anaerobically with fumarate as a terminal electron acceptor for oxidative phosphorylation when the preferred compounds oxygen and nitrate are not available. We used the pKO promoter test vectors to identify a single promoter for the frdABCD genes which encode fumarate reductase. Expression of galactokinase from the frd promoter-galK operon fusion plasmid was repressed by oxygen and by nitrate and was induced by fumarate, indicating that frd gene expression is regulated at the transcriptional level by these terminal electron acceptors. S1 nuclease analysis, using a single-stranded DNA probe from the frd promoter region and mRNA isolated from a fumarate reductase-induced culture, revealed that the frd mRNA transcript initiates with an adenine residue 93 bases prior to the start of frdA translation. No promoters internal to the frd genes were revealed with the plasmid promoter screening system. S1 nuclease analysis revealed that the frd mRNA terminates in a uridine-rich region centered at 46 bases after the last codon of frdD. A stem and loop structure previously described as the growth rate-dependent attenuator for the linked ampC gene precedes the frd mRNA terminus. This result confirms the proposal that the stem and loop structure serves the dual role of a frd terminator anaerobically and an ampC attenuator aerobically. The four frd genes encoding the subunits of the fumarate reductase complex thus comprise an operon which is regulated at the transcriptional level in response to the cellular availability of the alternate electron acceptors oxygen, nitrate, and fumarate.

Proton translocation coupled to dimethyl sulfoxide reduction in anaerobically grown Escherichia coli HB101

Proton translocation coupled to dimethyl sulfoxide (DMSO) reduction was examined in Escherichia coli HB101 grown anaerobically on glycerol and DMSO. Rapid acidification of the medium was observed when an anaerobic suspension of cells, preincubated with glycerol, was pulsed with DMSO, methionine sulfoxide, nitrate, or trimethylamine N-oxide. The DMSO-induced acidification was sensitive to the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (60 microM) and was inhibited by the quinone analog 2-n-heptyl-4-hydroxy-quinoline-N-oxide (5.6 microM). Neither sodium azide nor potassium cyanide inhibited the DMSO response. An apparent----H+/2e- ratio of 2.9 was obtained for DMSO reduction with glycerol as the reductant. Formate and H2(g), but not lactate, could serve as alternate electron donors for DMSO reduction. Cells grown anaerobically on glycerol and fumarate displayed a similar response to pulses of DMSO, methionine sulfoxide, nitrate, and trimethylamine N-oxide with either glycerol or H2(g) as the electron donor. However, fumarate pulses did not result in acidification of the suspension medium. Proton translocation coupled to DMSO reduction was also demonstrated in membrane vesicles by fluorescence quenching. The addition of DMSO to hydrogen-saturated everted membrane vesicles resulted in a carbonyl cyanide p-trifluoromethoxyphenyl-hydrazone-sensitive fluorescence quenching of quinacrine dihydrochloride. The data indicate that reduction of DMSO by E. coli is catalyzed by an anaerobic electron transport chain, resulting in the formation of a proton motive force.

Dimethyl sulfoxide reductase activity by anaerobically grown Escherichia coli HB101

Escherichia coli grew anaerobically on a minimal medium with glycerol as the carbon and energy source and dimethyl sulfoxide (DMSO) as the terminal electron acceptor. DMSO reductase activity, measured with an artificial electron donor (reduced benzyl viologen), was preferentially associated with the membrane fraction (77 +/- 10% total cellular activity). A Km for DMSO reduction of 170 +/- 60 microM was determined for the membrane-bound activity. Methyl viologen, reduced flavin mononucleotide, and reduced flavin adenine dinucleotide also served as electron donors for DMSO reduction. Methionine sulfoxide, a DMSO analog, could substitute for DMSO in both the growth medium and in the benzyl viologen assay. DMSO reductase activity was present in cells grown anaerobically on DMSO but was repressed by the presence of nitrate or by aerobic growth. Anaerobic growth on DMSO coinduced nitrate, fumarate, and and trimethylamine-N-oxide reductase activities. The requirement of a molybdenum cofactor for DMSO reduction was suggested by the inhibition of growth and a 60% reduction in DMSO reductase activity in the presence of 10 mM sodium tungstate. Furthermore, chlorate-resistant mutants chlA, chlB, chlE, and chlG were unable to grow anaerobically on DMSO. DMSO reduction appears to be under the control of the fnr gene.

The seleno-polypeptide of formic dehydrogenase (formate hydrogen-lyase linked) from Escherichia coli: genetic analysis

The site of integration of phage M mu d (Ap lac) in mutant M9s which leads to deficiency of formic dehydrogenase (benzylviologen-linked) activity was determined. It was shown that the phage had inserted into the gene for the seleno-polypeptide of the enzyme (80 kd) leading to the formation of a truncated peptide (60 kd) still able to incorporate Se. Synthesis of the truncated polypeptide is subject to the same regulatory signals as that of the wild-type enzyme. The formation of the 110 kd seleno-polypeptide, which is a constituent component of the formic dehydrogenase from the formate-nitrate respiratory pathway, is unimpaired in mutant M9s. The location of the gene for the 80 kd seleno-polypeptide was mapped at 92.4 min of the Escherichia coli chromosome.