Chromosomal location and expression of the structural gene for major outer membrane protein Ia of Escherichia coli K-12 and of the homologous gene of Salmonella typhimurium.

The gene determining the structure of a major outer membrane protein of Escherichia coli, protein Ia, has been located between serC and pyrD, at the min 21 region of the linkage map. This is based on the isolation and characterization of E. coli-Salmonella typhimurium intergeneric hybrids as well as analyses of a mutation (ompF2) affecting the formation of protein Ia. When the serC region of the S. typhimurium chromosome was transduced by phage P1 into E. coli, two classes of transductants were obtained; one produced protein Ia like the parental strain of E. coli, whereas the other produced not protein Ia but a pair of outer membrane proteins structurally related to 35K protein, one of the major outer membrane proteins of S. typhimurium. Furthermore, a strain of S. typhimurium harboring an F' plasmid which carries the ompF region of the E. coli chromosome was found to produce a protein indistinguishable from protein Ia, beside the outer membrane proteins characteristic to the parental Salmonella strain. These results suggest that the structural genes for protein Ia (E. coli) and for 35K protein (S. typhimurium) are homologous to each other and are located at the ompF region of the respective chromosome. The bearing of these findings on the genetic control of protein Ia formation is discussed.     

Behavior of coliphage lambda in hybrids between Escherichia coli and Salmonella

Salmonella typhosa hybrids able to adsorb lambda were obtained by mating S. typhosa recipients with Escherichia coli K-12 donors. After adsorption of wild-type lambda to these S. typhosa hybrids, no plaques or infective centers could be detected. E. coli K-12 gal(+) genes carried by the defective phage lambdadg were transduced to S. typhosa hybrids with HFT lysates derived from E. coli heterogenotes. The lysogenic state which resulted in the S. typhosa hybrids after gal(+) transduction differed from that of E. coli. Ability to produce lambda, initially present, was permanently segregated by transductants of the S. typhosa hybrid. S. typhosa lysogens did not lyse upon treatment for phage induction with mitomycin C, ultraviolet light, or heat in the case of thermoinducible lambda. A further difference in the behavior of lambda in Salmonella hybrids was the absence of zygotic induction of the prophage when transferred from E. coli K-12 donors to S. typhosa. A new lambda mutant class, capable of forming plaques on S. typhosa hybrids refractory to wild-type lambda, was isolated at low frequency by plating lambda on S. typhosa hybrid WR4254. Such mutants have been designated as lambdasx, and a mutant allele of lambdasx was located between the P and Q genes of the lambda chromosome. Plaques were formed also on the S. typhosa hybrid host with a series of lambda(i21) hybrid phages which contain the N gene of phage 21. The significance of these results in terms of Salmonella species as hosts for lambda is discussed.     

Release of a special fraction of the outer membrane from both growing and phage T4-infected Escherichia coli B.

Growing Escherichia coli release envelope material into the medium. Upon infection with T4 phage increased amounts of this material are released and at a greater rate. In order to determine whether both inner and outer membranes are present in this material, and whether the material released by growing cells differs from that released by infected cells, we have examined the protein composition of envelope released by growing and T4-infected E. coli B. Our results show: (a) the protein composition of envelope released from growing or infected cells is similar, (b) the proteins present are representative of the outer membrane, (c) the major outer membrane protein of E. coli B, protein II, is deficient in the released material. We therefore conclude that the envelope material released from growing or infected E. coli represents a special fraction of the outer membrane. This finding is discussed in relation to outer membrane structure and function. In addition, data are presented on the differing outer membrane protein composition of substrains of E. coli B obtained from different laboratories.     

Two-component nature of bacteriophage T4 receptor activity in Escherichia coli K-12.

Escherichia coli bacteriophage T4 uses the lipopolysaccharide of the outer cell envelope membrane as a receptor. Lipopolysaccharide from E. coli K-12 required a major outer membrane protein, polypeptide Ib, for phage inactivation.     

Alterations in the Outer Membrane of the Cell Envelope of Heptose-Deficient Mutants of Escherichia coli

The composition of the cell envelope of a heptose-deficient lipopolysaccharide mutant of Escherichia coli, GR467, was studied after fractionation into its outer and cytoplasmic membrane components by means of sucrose density gradient centrifugation. The outer membrane of GR467 had a lower density than that of its parent strain, CR34. Analysis of the fractionated membranes of GR467 indicated that the phospholipid-to-protein ratio had increased 2.4-fold in the outer membrane. The ratio in the mutant cytoplasmic membrane was also increased, although to a lesser extent. By employing a third parameter, the lipid A content of the outer membrane, it was found that the observed phospholipid-to-protein change in the outer membrane was due predominantly to a decrease in the relative amount of protein. This decrease in protein was particularly significant, since it was concomitant with a 68% decrease in the lipid A recovered in the outer membrane of GR467 relative to the lipid A recovered in the outer membrane of CR34. Similar findings were observed in a second heptose-deficient mutant of E. coli, RC-59. The apparent protein deficiency in GR467 was further studied by subjecting solubilized envelope proteins to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It was found that major envelope proteins which were localized in the outer membrane were greatly diminished in GR467. Two revertants of GR467 with the wild-type amounts of heptose had wild-type relative levels of protein in their outer membranes. A partial heptose revertant had a relative level of protein in its outer membrane between those of the mutant and wild type.     

A component of the side tail fiber of Escherichia coli bacteriophage lambda can functionally replace the receptor-recognizing part of a long tail fiber protein of the unrelated bacteriophage T4.

The distal part of the long tail fiber of Escherichia coli bacteriophage T4 consists of a dimer of protein 37. Dimerization requires the catalytic action of protein 38, which is encoded by T4 and is not present in the virion. It had previously been shown that gene tfa of the otherwise entirely unrelated phage lambda can functionally replace gene 38. Open reading frame (ORF) 314, which encodes a protein that exhibits homology to a COOH-terminal area of protein 37, is located immediately upstream of tfa. The gene was cloned and expressed in E. coli. An antiserum against the corresponding polypeptide showed that it was present in phage lambda. The serum also reacted with the long tail fibers of phage T4 near their free ends. An area of the gene encoding a COOH-terminal region of ORF 314 was recombined, together with tfa, into the genome of T4, thus replacing gene 38 and a part of gene 37 that codes for a COOH-terminal part of protein 37. Such T4-lambda hybrids, unlike T4, required the presence of outer membrane protein OmpC for infection of E. coli B. An ompC missense mutant of E. coli K-12, which was still sensitive to T4, was resistant to these hybrids. We conclude that the ORF 314 protein represents a subunit of the side tail fibers of phage lambda which probably recognize the OmpC protein. ORF 314 was designated stf (side tail fiber). The results also offer an explanation for the very unusual fact that, despite identical genomic organizations, T4 and T2 produce totally different proteins 38. An ancestor of T4 from the T2 lineage may have picked up tfa and stf from a lambdoid phase, thus possibly demonstrating horizontal gene transfer between unrelated phage species.     

Incorporation of phi80 phage into unusual chromosome sites and isolation of a specialized transducing bacteriophage]

The mutant strain KS713 of Escherichia coli K-12 deleted for the normal insertion site and secondary preferable one was obtained. The insertion frequency of phage phi80 into the double deletion strain is reduced about 30-fold with respect to integration into the strain H47 with deletion of the primary phi80 attachment site and about 500-fold relative to integration into wild type Escherichia coli. Analysis of the rare abnormal lysogens of KS 713 strain indicates that there are secondary sites on the chromosome, which are utilized for prophage attachment if insertion at preferable secondary att80-II site is eliminated too. The insertion of phi80 phage into the bfe locus was obtained by the appropriate selection technique. Induced prophage excision from the bfe site was rather efficient and lysates contained phi80 phage particles that could specificically transduce the argH+ gene. Upon transduction into a recipient strain carrying recA, heterogenotes harbouring both the wild-type and the mutant argH genes were isolated. These heterogenotes were used for producing high-frequency transducing lysates.     

Escherichia coli K-12 tolF mutants: alterations in protein composition of the outer membrane.

Outer membrane materials prepared from three independently isolated spontaneous Escherichia coli tolF mutants contained no detectable protein Ia. The loss of this protein was nearly completely compensated for by an increase in other major outer membrane proteins, Ib and II. Thus, the major outer membrane proteins accounted for 40% of the total cell envelope protein in both tol+ and tolF strains. No changes were found in the levels of inner membrane proteins prepared from tolF strains when compared with similar preparations from the tol+ strain. Phage-resistant mutants were selected starting with a tolF strain by using either phage TuIb or phage PA2. These phage-resistant tolF strains contained neither protein Ia nor protein Ib. The mutation leading to the loss of protein Ib in these strains is independent of the tolF mutation and is located near malP on the E. coli genetic map.     

Effects of secA mutations on the synthesis and secretion of proteins in Escherichia coli. Evidence for a major export system for cell envelope proteins

We have followed the synthesis and secretion of a number of periplasmic and outer membrane proteins in three strains of Escherichia coli, a secA amber mutant, a secA temperature-sensitive mutant, and a strain that blocks protein secretion due to a high level of expression of an export-defective hybrid protein between maltose-binding protein and beta-galactosidase (MalE-LacZ). Our results show that after several hours under nonpermissive conditions the specificity and extent of the export blocks in the secA temperature-sensitive mutant and the strain producing the MalE-LacZ hybrid protein are identical, affecting at least four major outer membrane proteins and most but not all periplasmic proteins. The secA gene product, therefore, appears to be an essential component of the major export pathway in E. coli which is used by many envelope proteins independent of whether they are cotranslationally or post-translationally secreted. In contrast, the synthesis of only a subset of these envelope proteins is reduced in the secA amber mutant after shift to the nonpermissive condition. These results indicate that the SecA protein serves roles both in the synthesis and the secretion of certain cell envelope proteins.     

Isolation of an ompC-like outer membrane protein gene from Salmonella typhi

We have isolated the structural gene for an outer membrane protein of Salmonella typhi, from a genomic library constructed in bacteriophage lambda 1059, using the Escherichia coli ompC gene as a heterologous probe. E. coli ompC codes for an outer membrane pore protein (porin) that is induced preferentially at high osmolarity and high temperature. The S. typhi ompC-like gene was subcloned in pBR322 and introduced into E. coli HB101 and into P678-54, a minicell-producing strain. In both strains it expressed a 38.5-kDa protein, which was incorporated into the outer membrane envelope and comigrated with an S. typhi outer membrane protein which was expressed both at low and high osmolarity in vivo.     

Molecular cloning and expression in E. coli of a Salmonella typhi porin gene

Immunoscreening of a Salmonella typhi cosmid library in E. coli allowed the detection of clones producing a 36 kDa porin from S. typhi. The gene is efficiently expressed in an E. coli porin-less mutant and the protein is exported to the outer membrane envelope. Two clones which markedly differ in their level of expression have been isolated.     

Testing the '+2 rule' for lipoprotein sorting in the Escherichia coli cell envelope with a new genetic selection

We report a novel strategy for selecting mutations that mislocalize lipoproteins within the Escherichia coli cell envelope and describe the mutants obtained. A strain carrying a deletion of the chromosomal malE gene, coding for the periplasmic maltose-binding protein (MalE), cannot use maltose unless a wild-type copy of malE is present in trans. Replacement of the natural signal peptide of preMalE by the signal peptide and the first four amino acids of a cytoplasmic membrane-anchored lipoprotein resulted in N-terminal fatty acylation of MalE (lipoMalE) and anchoring to the periplasmic face of the cytoplasmic membrane, where it could still function. When the aspartate at position +2 of this protein was replaced by a serine, lipoMalE was sorted to the outer membrane, where it could not function. Chemical mutagenesis followed by selection for maltose-using mutants resulted in the identification of two classes of mutations. The single class I mutant carried a plasmid-borne mutation that replaced the serine at position +2 by phenylalanine. Systematic substitutions of the amino acid at position +2 revealed that, besides phenylalanine, tryptophan, tyrosine, glycine and proline could all replace classical cytoplasmic membrane lipoprotein sorting signal (aspartate +2). Analysis of known and putative lipoproteins encoded by the E. coli K-12 genome indicated that these amino acids are rarely found at position +2. In the class II mutants, a chromosomal mutation caused small and variable amounts of lipoMalE to remain associated with the cytoplasmic membrane. Similar amounts of another, endogenous outer membrane lipoprotein, NlpD, were also present in the cytoplasmic membrane in these mutants, indicating a minor, general defect in the sorting of outer membrane lipoproteins. Four representative class II mutants analysed were shown not to carry mutations in the lolA or lolB genes, known to be involved in the sorting of lipoproteins to the outer membrane.     

The small viral membrane-associated protein P32 is involved in bacteriophage PRD1 DNA entry

The lipid-containing bacteriophage PRD1 infects a variety of gram-negative cells by injecting its linear double-stranded DNA genome into the host cell cytoplasm, while the protein capsid is left outside. The virus membrane and several structural proteins are involved in phage DNA entry. In this work we identified a new infectivity protein of PRD1. Disruption of gene XXXII resulted in a mutant phenotype defective in phage reproduction. The absence of the protein P32 did not compromise the particle assembly but led to a defect in phage DNA injection. In P32-deficient particles the phage membrane is unable to undergo a structural transformation from a spherical to a tubular form. Since P32(-) particles are able to increase the permeability of the host cell envelope to a degree comparable to that found with wild-type particles, we suggest that the tail-tube formation is needed to eject the DNA from the phage particle rather than to reach the host cell interior.     

Proline 21, a residue within the α-helical domain of ΦX174 lysis protein E, is required for its function in Escherichia coli

ΦX174 lysis protein E-mediated lysis of Escherichia coli is characterized by a protein E-specific fusion of the inner and outer membrane and formation of a transmembrane tunnel structure. In order to understand the fusion process, the topology of protein E within the envelope complex of E. coli was investigated. Proteinase K protection studies showed that, during the time course of protein E-mediated lysis process, more of the fusion protein E-FXa-streptavidin gradually became accessible to the protease at the cell surface. These observations postulate a conformational change in protein E during induction of the lysis process by movement of the C-terminal end of the protein throughout the envelope complex from the inner side to the outer side spanning the entire pore and fusing the inner and outer membranes at distinct areas. The initiation mechanism for such a conformational change could be the cis–trans isomerization of proline residues within α-helical membrane-spanning segments. Conversion of proline 21, presumed to be in the membrane-embedded α-helix of protein E, to alanine, glycine, serine and valine, respectively, resulted in lysis-negative E mutant proteins. Proteinase K accessibility studies using streptavidin as a reporter fused to the P21G mutant protein showed that the C-terminal part of the fusion protein is not translocated to the outer side of the membrane, suggesting that this proline residue is essential for the correct folding of protein E within the cell wall complex of E. coli . Oligomerization of protein P21G-StrpA was not disturbed.     

Genetic and physical studies of lambda transducing bacteriophage carrying the beta subunit gene of the Escherichia coli ribonucleic acid polymerase.

The prophage lambdac1857 was inserted into the bfe gene located near rif (the structural gene for the beta subunit of deoxyribonucleic acid [DNA]-dependent ribonucleic acid polymerase) on the Escherichia coli chromosome. Induced lysates (low-frequency transducing lysates) of such a lysogen contained defective lambda phage particles (lambdadrif+) that can specifically transduce the wild-type rif+ gene. Upon transduction into a recipient strain carrying recA, heterogenotes harboring both the wild-type and the mutant rif genes were isolated. Rec+ derivatives of these heterogenotes produce high-frequency transducing lysates that contain lambdadrif+ and normal active phages at a ratio of 1 to 2. The results of marker rescue experiments and of density determination with several transducing phages indicate that most of the late genes are deleted and replaced by a segment of the chromosomal DNA carrying the bfe-rif region. The length of the chromosomal segment seems to vary between approximately 0.5 and 0.6% of the total bacterial DNA among the three independently isolated lambdadrif+ phages. Electron microscopy of heteroduplex DNA consisting of one strand from lambdadrif+-6 and the other from lambdaimm-21 phages directly confirmed that most of the phage DNA of the "left arm" was replaced by the bacterial DNA. The heteroduplex study also demonstrated that the integration of prophage lambda into the bfe region occurred at the normal cross-over point within the phage attachment site.     

Coevolution of bacteriophage PP01 and Escherichia coli O157:H7 in continuous culture

The interaction between Escherichia coli O157:H7 and its specific bacteriophage PP01 was investigated in chemostat continuous culture. Following the addition of bacteriophage PP01, E. coli O157:H7 cell lysis was observed by over 4 orders of magnitude at a dilution rate of 0.876 h(-1) and by 3 orders of magnitude at a lower dilution rate (0.327 h(-1)). However, the appearance of a series of phage-resistant E. coli isolates, which showed a low efficiency of plating against bacteriophage PP01, led to an increase in the cell concentration in the culture. The colony shape, outer membrane protein expression, and lipopolysaccharide production of each escape mutant were compared. Cessation of major outer membrane protein OmpC production and alteration of lipopolysaccharide composition enabled E. coli O157:H7 to escape PP01 infection. One of the escape mutants of E. coli O157:H7 which formed a mucoid colony (Mu) on Luria-Bertani agar appeared 56 h postincubation at a dilution rate of 0.867 h(-1) and persisted until the end of the experiment (approximately 200 h). Mu mutant cells could coexist with bacteriophage PP01 in batch culture. Concentrations of the Mu cells and bacteriophage PP01 increased together. The appearance of mutant phage, which showed a different host range among the O157:H7 escape mutants than wild-type PP01, was also detected in the chemostat culture. Thus, coevolution of phage and E. coli O157:H7 proceeded as a mutual arms race in chemostat continuous culture.     

Functional Interaction of the tonA/tonB Receptor System in Escherichia coli

Host range mutants of phage T1 (T1h), which productively infected tonB mutants of Escherichia coli, were isolated. The phage mutants were inactivated by isolated outer membranes of E. coli in contrast to the wild-type phage, which only adsorbed reversibly. For the infection process, the tonB function is apparently only required for the irreversible adsorption of the phage T1, but not for the transfer of the phage DNA through the outer membrane and the cytoplasmic membrane of the cell. Mutants of the tonA gene expressing normal amounts of outer membrane receptor proteins were isolated and found to be partially sensitive to phage T5 and resistant to the phages T1 and T1h, colicin M, and albomycin and unable to take up iron as a ferrichrome complex. One tonA mutant remained partially sensitive to T5, colicin M, and albomycin and supported growth of T1h (not of T1) with the same plating efficiency as the parent strain. Only a small region of the tonA receptor protein seems to function for all the very different substrates. A newly isolated host range mutant of T5 (T5h) adsorbed faster to tonA(+) cells than did wild-type T5 and infected tonA missense mutants resistant to wild-type T5. The interplay of the tonA with the tonB function was observed with phage T5 infection, although T5 required only the tonA receptor. Ferrichrome inhibited plaque formation of T5 only when plated on tonB mutants. Adsorption of T5 to cells in liquid medium was influenced by ferrichrome as follows: complete inhibition by 0.1 muM ferrichrome with tonB mutants, not more than 35% inhibition by 1 to 100 muM ferrichrome with the tonB(+) parent strain in the presence of glucose as energy source, and 90% inhibition by 1 muM ferrichrome with partially starved parent cells. We conclude that there exist different functional states of the receptor protein that depend on the energy state of the cell and the tonB function. The latter seems to be required only for translocation processes with outer membrane proteins involved.     

A defined mutation in the protein export gene within the spc ribosomal protein operon of Escherichia coli: isolation and characterization of a new temperature-sensitive secY mutant.

We describe the properties of a temperature-sensitive mutant, ts24, of Escherichia coli. The mutant has a conditional defect in export of periplasmic and outer membrane proteins. At 42 degrees C, precursor forms of these proteins accumulate within the cell where they are protected from digestion by externally added trypsin. The accumulated precursors are secreted and processed very slowly at 42 degrees C. The mutation is complemented by expression of the wild-type secY (or prlA) gene, which has been cloned into a plasmid vector from the promoter-distal part of the spc ribosomal protein operon. The mutant has a single base change in the middle of the secY gene, which would result in the replacement of a glycine residue by aspartic acid in the protein product. These results demonstrate that the gene secY (prlA) is essential for protein translocation across the E. coli cytoplasmic membrane.     

Assembly of outer membrane lipoprotein in an Escherichia coli mutant with a single amino acid replacement within the signal sequence of prolipoprotein.

We have compared the rate of assembly of outer membrane proteins including the lipoprotein in a pair of isogenic mlpA+ (lpp+) and mlpA (lpp) strains by pulse-chase experiments. The rate of assembly of the mutant prolipoprotein into the outer membrane was slightly slower than that of the wild-type lipoprotein. The rate of assembly of protein I and protein H-2 was similar in the wild type and the mutant, whereas the rate of assembly of protein II into the outer membrane was slightly reduced in the mutant strain. The organization of outer membrane was slightly reduced in the mutant strain. The organization of outer membrane proteins in the mutant cells appeared not to be grossly altered, based on the apparent resistance (or susceptibility) of these proteins toward trypsin treatment and their resistance to solubilization by Sarkosyl. Like the wild-type lipoprotein, the mutant prolipoprotein in the outer membrane was resistant to trypsin. On the other hand, the prolipoprotein in the cytoplasmic membrane fraction of the mutant cell envelope was susceptible to trypsin digestion. We conclude from these data that proteolytic cleavage of prolipoprotein is not essential for the translocation and proper assembly of lipoprotein into outer membrane.     

Genetic mapping of tyramine oxidase and arylsulfatase genes and their regulation in intergeneric hybrids of enteric bacteria.

The genes for arylsulfatase (atsA) and tyramine oxidase (tynA) have been mapped in Klebsiella aerogenes by P1 transduction. They are linked to gdhD and trp in the order atsA-tynA-gdhD-trp-pyrF. Complementation analysis using F' episomes from Escherichia coli suggested an analogous location of these genes in E. coli, although arylsulfatase activity was not detected in E. coli. P1 phage and F' episomes were used to create intergeneric hybrid strains of enteric bacteria by transfer of the ats and tyn genes between K. aerogenes, E. coli, and Salmonella typhimurium. Intergeneric transduction of the tynK gene from K. aerogenes to an E. coli restrictionless strain was one to two orders less frequent than that of the leuK gene. The tyramine oxidase of E. coli and S. typhimurium in regulatory activity resemble very closely the enzyme of K. aerogenes. The atsE gene from E. coli was expressed, and latent arylsulfatase protein was formed in K. aerogenes and S typhimurium. The results of tyramine oxidase and arylsulfatase synthesis in intergeneric hybrids of enteric bacteria suggest that the system for regulation of enzyme synthesis is conserved more than the structure or function of enzyme protein during evolution.