Isoelectric focusing and crossed immunoelectrophoresis of heme proteins in the Escherichia coli cytoplasmic membrane

Regulation of expression of the cytochrome d terminal oxidase in Escherichia coli is transcriptional

The cytochrome d complex is one of the two terminal oxidases in the aerobic respiratory system of Escherichia coli. This enzyme is not present in cells grown with high levels of dissolved oxygen in the culture medium but accumulates after mid-exponential growth, reaching high levels in stationary-phase cells. In this study, the transcriptional activity of the cyd operon, encoding the two subunits of the enzyme, was examined under a variety of growth conditions. This was accomplished by the use of a chromosomal operon fusion, cyd-lacZ, generated in vivo by a lambda plac-Mu hopper bacteriophage and also by the use of a cyd-lacZ protein fusion created in vitro on a plasmid, transferred onto a lambda transducing phage, and examined as a single-copy lysogen. Transcription of the gene fusions was monitored by determination of beta-galactosidase activity. The data clearly show that cyd is transcriptionally regulated and that induction is observed when the culture reaches a sufficient cell density so as to substantially reduce the steady-state levels of dissolved oxygen. The transcriptional activity is also regulated by other growth conditions, including the carbon source. The turn-on of cyd under semianaerobic conditions does not require the fnr gene product, cyclic AMP, or the cyclic AMP-binding protein.

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.

Purification and characterization of a cell-associated, soluble mannanase from Bacteroides ovatus

Bacteroides ovatus, a human colonic anaerobe, utilizes the galactomannan guar gum as a sole source of carbohydrate. Previously, we found that none of the galactomannan-degrading enzymes were extracellular, and we characterized an outer membrane mannanase which hydrolyzes the backbone of guar gum to produce large fragments. We report here the purification and characterization of a second mannanase from B. ovatus. This enzyme is cell-associated and soluble. Using ion-exchange chromatography, gel filtration, and chromatofocusing steps, we have purified the soluble mannanase to apparent homogeneity. The enzyme has a native molecular weight of 190,000 and a monomeric molecular weight of 61,000. It is distinct from the membrane mannanase not only with respect to cellular location but also with respect to stability and isoelectric point (pI of 6.9 for the membrane mannanase and pI of 4.8 for the soluble mannanase). The soluble mannanase, like the membrane mannanase, hydrolyzed guar gum to produce large fragments rather than monosaccharides. However, if galactosyl side chains were removed from the galactomannan fragments by alpha-galactosidase, both the soluble mannanase and the membrane mannanase could degrade guar gum to monosaccharides. Thus either or both of these two enzymes, working together with alpha-galactosidase, appear to be sufficient for the breakdown of guar gum to the level of monosaccharides.

Succinate dehydrogenase in Rhodopseudomonas sphaeroides: subunit composition and immunocross-reactivity with other related bacteria

Antibodies were raised against the succinate dehydrogenase (SDH) present in the chromatophores of phototrophically grown Rhodopseudomonas sphaeroides. Crossed immunoelectrophoresis experiments indicated that the SDH present in the cytoplasmic membranes of heterotrophically grown R. sphaeroides is probably the same enzyme observed in the chromatophores. The enzyme was extracted by Triton X-100 in a form which consisted of only two subunits (molecular weight, 68,000 and 30,000) and was not associated with a cytochrome b. The antibodies directed against SDH from R. sphaeroides showed no immunocross-reactivity with SDH from phylogenetically related bacterial species, including Rhodopseudomonas capsulata, Paracoccus denitrificans, Rhodopseudomonas palustris, Rhodospirillum rubrum, and Rhodospirillum fulvum.

Oxygen regulation in Salmonella typhimurium

Regulation by oxygen of the peptidase T (pepT) locus of Salmonella typhimurium was studied by measuring beta-galactosidase levels in strains containing a pepT::Mu d1(Apr lac) operon fusion. beta-Galactosidase was induced in anaerobic cultures and late-exponential and stationary-phase aerated cultures. Peptidase T activity also was induced under these growth conditions. pepT+ but not pepT strains will utilize as amino acid sources the tripeptides Leu-Leu-Leu and Leu-Gly-Gly only when grown anaerobically. Mutations at two loci, oxrA and oxrB (oxygen regulation) prevent induction of the pepT locus. The oxrA locus is homologous to the fnr locus of Escherichia coli. We have isolated 12 independent Mu d1 insertions (oxd::Mu d1, oxygen dependent) that show induction of beta-galactosidase in anaerobic cultures and stationary-phase aerated cultures. These insertions fall into nine classes based on map location. All of the oxd::Mu d1 insertions are regulated by oxrA and oxrB and therefore define a global regulon that responds to oxygen limitation.

Purification and characterization of two alpha-galactosidases associated with catabolism of guar gum and other alpha-galactosides by Bacteroides ovatus

When Bacteroides ovatus is grown on guar gum, a galactomannan, it produces alpha-galactosidase I which is different from alpha-galactosidase II which it produces when grown on galactose, melibiose, raffinose, or stachyose. We have purified both of these enzymes to apparent homogeneity. Both enzymes appear to be trimers and have similar pH optima (5.9 to 6.4 for alpha-galactosidase I, 6.3 to 6.5 for alpha-galactosidase II). However, alpha-galactosidase I has a pI of 5.6 and a monomeric molecular weight of 85,000, whereas alpha-galactosidase II has a pI of 6.9 and a monomeric molecular weight of 80,500. alpha-Galactosidase I has a lower affinity for melibiose, raffinose, and stachyose (Km values of 20.8, 98.1, and 8.5 mM, respectively) than does alpha-galactosidase II (Km values of 2.3, 5.9, and 0.3 mM, respectively). Neither enzyme was able to remove galactose residues from intact guar gum, but both were capable of removing galactose residues from guar gum which had been degraded into large fragments by mannanase. The increase in specific activity of alpha-galactosidase which was associated with growth on guar gum was due to an increase in the specific activity of enzyme I. Low, constitutive levels of enzyme II also were produced. By contrast, enzyme II was the only alpha-galactosidase that was detectable in bacteria which had been grown on galactose, melibiose, raffinose, or stachyose.

Isolation and characterization of an Escherichia coli mutant lacking the cytochrome o terminal oxidase

A respiration-deficient mutant of Escherichia coli has been isolated which is unable to grow aerobically on nonfermentable substrates such as succinate and lactate. Spectroscopic and immunological studies showed that this mutant lacks the cytochrome o terminal oxidase of the high aeration branch of the aerobic electron transport chain. This strain carries a mutation in a gene designated cyo which is cotransducible with the acrA locus. Mutations in cyo were obtained by mutagenizing a strain that was cyd and, thus, was lacking the cytochrome d terminal oxidase. Strain RG99, which carries both the cyd- and cyo- alleles, grows normally under anaerobic conditions in the presence of nitrate. Introduction of the cyd+ allele into the strain restores the respiration function of the strain, indicating that the cytochrome o branch of the respiratory chain is dispensable under normal laboratory growth conditions.

The protein composition of the cytoplasmic membrane of aerobically and anaerobically grown Escherichia coli

The protein composition of the cytoplasmic membranes of Escherichia coli, grown aerobically and anaerobically on a glucose minimal medium at pH 7.0, were analyzed by crossed immunoelectrophoresis. Qualitative differences are limited to only two proteins: nitrate reductase (E.C. 1.7.99.4) is absent under aerobic growth conditions, whereas an unidentified protein, with a molecular weight of 81,500 and located at the inner side of the cytoplasmic membrane, is synthesized only in the presence of oxygen. Quantitative differences are observed for many proteins: the ratio of the amount of a specific protein present in cells grown anaerobically and aerobically was, for four proteins, between 0.3 and 1; for 25 proteins, between 1 and 3; and for five proteins, larger than 5.

Immunological analysis of the heme proteins present in aerobically grown Escherichia coli

Immunological methods were used to obtain information about Escherichia coli heme proteins. There is a membrane-bound catalase which consists of a single subunit (as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis) which is also present in the soluble fraction. Antibodies raised against purified, soluble cytochrome b562 showed that this cytochrome is not related to any of the membrane-bound cytochromes, including the b562 component of the cytochrome o complex. Cytochrome b556 is immunologically unrelated to the cytochrome b556 NR associated with the nitrate reductase system. Cytochrome b556 and cytochrome o are not present in a constant ratio in the membrane.

Role of quinones in the branch of the Escherichia coli respiratory chain that terminates in cytochrome o

The role of quinones in the cytochrome o branch of the Escherichia coli respiratory chain was investigated by using mutant strains lacking the cytochrome d terminal oxidase complex. The only cytochromes present were cytochrome b556 and the cytochrome o complex, consisting of cytochrome b555-b562. Mutant strains missing ubiquinone, menaquinone, or both were constructed in the cytochrome d-minus (cyd) background. The steady-state levels of cytochrome b reduction were examined and compared in these strains to assess the effects of the quinone deficiencies. The data clearly show that a ubiquinone deficiency results in a lower level of cytochrome b reduction in the steady state. The data are consistent with a simple model in which ubiquinone is placed on the dehydrogenase side of all the cytochromes in this branch of the respiratory chain. There is no evidence from these experiments for a role of quinones in the respiratory chain at any site besides this one.

Immunological characterization of an Escherichia coli strain which is lacking cytochrome d

The isolated membranes from an Escherichia coli mutant strain which lacks spectroscopically detectable levels of cytochromes d, a1, and b558 also have abnormally low levels of N,N,N',N'-tetramethyl-p-phenylenediamine oxidase activity. In this paper, it is shown that the material previously identified as the N,N,N',N'-tetramethyl-p-phenylenediamine oxidase is, in fact, the two-subunit cytochrome d complex. Antisera directed against the native cytochrome d complex as well as against each of two subunits apparent on sodium dodecyl sulfate-polyacrylamide gels were used to show that the mutant strain lacks both subunits of the cytochrome d complex. Introduction of F-prime F152 into the mutant strain restored the two subunits along with the spectroscopic and enzymatic activity associated with the cytochrome d complex.

Isolation and characterization of an Escherichia coli mutant lacking cytochrome d terminal oxidase

A screening procedure was devised which permitted the isolation of a cytochrome d-deficient mutant by its failure to oxidize the artificial electron donor N,N,N',N'-tetramethyl-p-phenylenediamine. Cytochrome a1 and probably cytochrome b558 were also missing in the mutant. Growth and oxygen uptake rates were similar for both parent and mutant strains. However, the strain lacking cytochrome d had an increased sensitivity to cyanide, indicating that cytochrome d confers some resistance to this respiratory inhibitor. The gene responsible for these phenotypes has been named cyd and maps between tolA and sucB.

Immunochemical relationship of the major outer membrane protein of Rhodopseudomonas sphaeroides 2.4.1 to proteins of other photosynthetic bacteria

Immunoblots of sodium dodecyl sulfate-polyacrylamide gels derived from outer membrane preparations of various strains of Rhodopseudomonas sphaeroides revealed polypeptides which cross-reacted with antibody directed against the major outer membrane protein of R. sphaeroides 2.4.1. Immunochemical quantitation of the major outer membrane protein of strain 2.4.1 showed approximately 5.5 x 10(4) molecules per cell whether cells were grown chemoheterotrophically or photoheterotrophically. Rhodospirillum rubrum outer membranes contained a cross-reactive protein, whereas the outer membranes derived from Rhodopseudomonas capsulata and Paracoccus denitrificans showed no cross-reaction with the antibody prepared against the major outer membrane protein from R. sphaeroides 2.4.1.