Regulation of the OmpA outer membrane protein of Escherichia coli

Serving Two Masters: Effect of Escherichia coli Dual Resistance on Antibiotic Susceptibility

The prevalence of multidrug-resistant bacteria and their increased pathogenicity has led to a growing interest in metallic antimicrobial materials and bacteriophages as potential alternatives to conventional antibiotics. This study examines how resistance to excess iron (III) influences the evolution of bacteriophage resistance in the bacterium Escherichia coli. We utilized experimental evolution in E. coli to test the effect of the evolution of phage T7 resistance on populations resistant to excess iron (III) and populations without excess iron resistance. Phage resistance evolved rapidly in both groups. Dual-resistant (iron (III)/phage) populations were compared to their controls (excess iron (III)-resistant, phage-resistant, no resistance to either) for their performance against each stressor, excess iron (III) and phage; and correlated resistances to excess iron (II), gallium (III), silver (I) and conventional antibiotics. Excess iron (III)/phage-resistant populations demonstrated superior 24 h growth compared to all other populations when exposed to increasing concentrations of iron (II, III), gallium (III), ampicillin, and tetracycline. No differences in 24 h growth were shown between excess iron (III)/phage-resistant and excess iron (III)-resistant populations in chloramphenicol, sulfonamide, and silver (I). The genomic analysis identified selective sweeps in the iron (III) resistant (rpoB, rpoC, yegB, yeaG), phage-resistant (clpX →/→ lon, uvaB, yeaG, fliR, gatT, ypjF, waaC, rpoC, pgi, and yjbH) and iron (III)/phage resistant populations (rcsA, hldE, rpoB, and waaC). E. coli selected for resistance to both excess iron (III) and T7 phage showed some evidence of a synergistic effect on various components of fitness. Dual selection resulted in correlated resistances to ionic metals {iron (II), gallium (III), and silver (I)} and several conventional antibiotics. There is a likelihood that this sort of combination antimicrobial treatment may result in bacterial variants with multiple resistances.

Stress Tolerance and Virulence-Related Roles of Lipopolysaccharide in Burkholderia glumae

The lipopolysaccharide (LPS) composed of lipid A, core, and O-antigen is the fundamental constituent of the outer membrane in gram-negative bacteria. This study was conducted to investigate the roles of LPS in Burkholderia glumae, the phytopathogen causing bacterial panicle blight and seedling rot in rice. To study the roles of the core oligosaccharide (OS) and the O-antigen region, mutant strains targeting the waaC and the wbiFGHI genes were generated. The LPS profile was greatly affected by disruption of the waaC gene and slight reductions were observed in the O-antigen region following wbiFGHI deletions. The results indicated that disruption in the core OS biosynthesis-related gene, waaC, was associated with increased sensitivity to environmental stress conditions including acidic, osmotic, saline, and detergent stress, and to polymyxin B. Moreover, significant impairment in the swimming and swarming motility and attenuation of bacterial virulence to rice were also observed in the waaC-defective mutant. The motility and virulence of O-antigen mutants defective in any gene of the wbiFGHI operon, were not significantly different from the wild-type except in slight decrease in swimming and swarming motility with wbiH deletion. Altogether, the results of present study indicated that the LPS, particularly the core OS region, is required for tolerance to environmental stress and full virulence in B. glumae. To our knowledge, this is the first functional study of LPS in a plant pathogenic Burkholderia sp. and presents a step forward toward full understanding of B. glumae pathogenesis.

Using a Chemical Genetic Screen to Enhance Our Understanding of the Antimicrobial Properties of Gallium against Escherichia coli

The diagnostic and therapeutic agent gallium offers multiple clinical and commercial uses including the treatment of cancer and the localization of tumors, among others. Further, this metal has been proven to be an effective antimicrobial agent against a number of microbes. Despite the latter, the fundamental mechanisms of gallium action have yet to be fully identified and understood. To further the development of this antimicrobial, it is imperative that we understand the mechanisms by which gallium interacts with cells. As a result, we screened the Escherichia coli Keio mutant collection as a means of identifying the genes that are implicated in prolonged gallium toxicity or resistance and mapped their biological processes to their respective cellular system. We discovered that the deletion of genes functioning in response to oxidative stress, DNA or iron–sulfur cluster repair, and nucleotide biosynthesis were sensitive to gallium, while Ga resistance comprised of genes involved in iron/siderophore import, amino acid biosynthesis and cell envelope maintenance. Altogether, our explanations of these findings offer further insight into the mechanisms of gallium toxicity and resistance in E. coli.

Identification of Genes Required for Growth of Escherichia coli MG1655 at Moderately Low pH

The survival of some pathotypes of Escherichia coli in very low pH environments like highly acidic foods and the stomach has been well documented and contributes to their success as foodborne pathogens. In contrast, the ability of E. coli to grow at moderately low pH has received less attention, although this property can be anticipated to be also very important for the safety of mildly acidic foods. Therefore, the objective of this study was to identify cellular functions required for growth of the non-pathogenic strain E. coli MG1655 at low pH. First, the role of the four E. coli amino acid decarboxylase systems, which are the major cellular mechanisms allowing extreme acid survival, was investigated using mutants defective in each of the systems. Only the lysine decarboxylase (CadA) was required for low pH growth. Secondly, a screening of 8544 random transposon insertion mutants resulted in the identification of six genes affecting growth in LB broth acidified to pH 4.50 with HCl. Two of the genes, encoding the transcriptional regulator LeuO and the elongation factor P-β-lysine ligase EpmA, can be linked to CadA production. Two other genes, encoding the diadenosine tetraphosphatase ApaH and the tRNA modification GTPase MnmE, have been previously implicated in the bacterial response to stresses other than low pH. A fifth gene encodes the LPS heptosyltransferase WaaC, and its mutant has a deep rough colony phenotype, which has been linked to reduced acid tolerance in earlier work. Finally, tatC encodes a secA-independent protein translocase that exports a few dozen proteins and thus is likely to have a pleiotropic phenotype. For mnmE, apaH, epmA, and waaC, de novo in frame deletion and genetic complementation confirmed their role in low pH growth, and these deletion mutants were also affected in growth in apple juice and tomato juice. However, the mutants were not affected in survival in gastric simulation medium at pH 2.5, indicating that growth at moderately low pH and survival of extremely low pH depend mostly on different cellular functions.

Characterization of the initial steps in the T7 DNA ejection process

A specialized complex, the tail, is the most common strategy employed by bacterial viruses to deliver their genome without disrupting cell integrity. T7 has a short, non-contractile tail formed by a tubular structure surrounded by fibers. Recent studies showed that incubation of the virus with Escherichia coli lipopolysaccharides (LPS) resulted in complete delivery of the viral genome, demonstrating for the first time that LPS are the T7 receptor. Further screening of the bacterial envelope for proteinaceous compounds that affect T7 ejection showed that porins OmpA and OmpF affect viral particle adsorption and infection kinetics, suggesting that these proteins play a role in the first steps of virus-host interaction. Comparison of the structures before and after ejection showed the conformational changes needed in the tail for genome delivery. Structural similarities between T7 and other viruses belonging to the Podoviridae family suggests that they could also follow a similar DNA ejection mechanism.

Proteomic Analysis of the Mode of Antibacterial Action of Silver Nanoparticles

Silver nanoparticles (nano-Ag) are potent and broad-spectrum antimicrobial agents. In this study, spherical nano-Ag (average diameter = 9.3 nm) particles were synthesized using a borohydride reduction method and the mode of their antibacterial action against E. coli was investigated by proteomic approaches (2-DE and MS identification), conducted in parallel to analyses involving solutions of Ag(+) ions. The proteomic data revealed that a short exposure of E. coli cells to antibacterial concentrations of nano-Ag resulted in an accumulation of envelope protein precursors, indicative of the dissipation of proton motive force. Consistent with these proteomic findings, nano-Ag were shown to destabilize the outer membrane, collapse the plasma membrane potential and deplete the levels of intracellular ATP. The mode of action of nano-Ag was also found to be similar to that of Ag(+) ions (e.g., Dibrov, P. et al, Antimicrob. Agents Chemother. 2002, 46, 2668-2670); however, the effective concentrations of nano-Ag and Ag(+) ions were at nanomolar and micromolar levels, respectively. Nano-Ag appear to be an efficient physicochemical system conferring antimicrobial silver activities.

Mutation in a gene required for lipopolysaccharide and enterobacterial common antigen biosynthesis affects virulence in the plant pathogen Erwinia carotovora subsp. atroseptica

Spontaneous bacteriophage-resistant mutants of the phytopathogen Erwinia carotovora subsp. atroseptica (Eca) SCRI1043 were isolated and, out of 40, two were found to exhibit reduced virulence in planta. One of these mutants, A5/22, showed multiple cell surface defects including alterations in synthesis of outer membrane proteins, lipopolysaccharide (LPS), enterobacterial common antigen (ECA), and flagella. Mutant A5/22 also showed reduced synthesis of the exoenzymes pectate lyase (Pel) and cellulase (Cel), major virulence factors for this pathogen. Genetic analysis revealed the pronounced pleiotropic mutant phenotype to be due to a defect in a single gene (rffG) that, in Escherichia coli, is involved in the production of ECA. We also show that while other enteric bacteria possess duplicate homologues of this gene dedicated separately to synthesis of LPS and ECA, Eca has a single gene.

Linkage map of Escherichia coli K-12, edition 10: the traditional map

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.

The assembly system for the lipopolysaccharide R2 core-type of Escherichia coli is a hybrid of those found in Escherichia coli K-12 and Salmonella enterica. Structure and function of the R2 WaaK and WaaL homologs

In Escherichia coli F632, the 14-kilobase pair chromosomal region located between waaC (formerly rfaC) and waaA (kdtA) contains genes encoding enzymes required for the synthesis of the type R2 core oligosaccharide portion of lipopolysaccharide. Ten of the 13 open reading frames encode predicted products sharing greater than 90% total similarity with homologs in E. coli K-12. However, the products of waaK (rfaK) and waaL (rfaL) each resemble homologs in Salmonella enterica serovar Typhimurium but share little similarity with E. coli K-12. The F632 WaaK and WaaL proteins therefore define differences between the type R2 and K-12 outer core oligosaccharides of E. coli lipopolysaccharides. Based on the chemical structure of the core oligosaccharide of an E. coli F632 waaK::aacC1 mutant and in vitro glycosyltransferase analyses, waaK encodes UDP-N-acetylglucosamine:(glucose) lipopolysaccharide alpha1, 2-N-acetylglucosaminyltransferase. The WaaK enzyme adds a terminal GlcNAc side branch substituent that is crucial for the recognition of core oligosaccharide acceptor by the O-polysaccharide ligase, WaaL. Results of complementation analyses of E. coli K-12 and F632 waaL mutants suggest that structural differences between the WaaL proteins play a role in recognition of, and interaction with, terminal lipopolysaccharide core moieties.

SurA, a periplasmic protein with peptidyl-prolyl isomerase activity, participates in the assembly of outer membrane porins

Little is known about either the process of periplasmic protein folding or how information concerning the folding state in this compartment is communicated. We present evidence that SurA, a periplasmic protein with peptidyl-prolyl isomerase activity, is involved in the maturation and assembly of LamB. LamB is a trimeric outer membrane porin for maltodextrins as well as the bacteriophage lambda receptor in Escherichia coli. We demonstrate that SurA is involved in the conversion of unfolded monomers into a newly identified intermediate in LamB assembly, which behaves as a folded monomer. The absence of SurA blocks the assembly pathway and leads to accumulation of species prior to the folded monomer. These species also accumulate when the stress sigma factor sigmaE is induced by LamB overexpression. We suggest that accumulation of species prior to the generation of folded monomer is a stress signal sensed by sigmaE.

Effect of the local anesthetics phenethyl alcohol and procaine on hns mutants of the acid-induced biodegradative arginine (adi) and lysine (cad) decarboxylases of Escherichia coli

The environmentally responsive biodegradative arginine (adi) and lysine (cad) decarboxylases are maximally induced when Escherichia coli is cultured under acidic, anaerobic conditions in rich medium. Previously, transposon mutagenesis led to the identification of hns (encoding H-NS, a histone-like DNA binding protein) as being a trans-acting regulatory factor of both systems. The hns mutants show depressed expression of adi or cad (i.e., their expression is increased). The effects of the local anesthetics phenethyl alcohol (PEA) and procaine (both environmental perturbants) were investigated with lacZ operon fusions to either adi or cad and their respective hns mutants. These results indicate that wild-type fusion strains are insensitive to either PEA or procaine, but that hns mutants show decreased beta-galactosidase synthesis in the presence of one or both of the local anesthetics. This is the first report of the effect of local anesthetics on hns mutants in this or any other environmentally responsive system.

Role of the rfaG and rfaP genes in determining the lipopolysaccharide core structure and cell surface properties of Escherichia coli K-12

Deletions which removed rfa genes involved in lipopolysaccharide (LPS) core synthesis were constructed in vitro and inserted into the chromosome by linear transformation. The deletion delta rfa1, which removed rfaGPBI, resulted in a truncated LPS core containing two heptose residues but no hexose and a deep rought phenotype including decreased expression of major outer membrane proteins, hypersensitivity to novobiocin, and resistance to phage U3. In addition, delta rfa1 resulted in the loss of flagella and pili and a mucoid colony morphology. Measurement of the synthesis of beta-galactosidase from a cps-lacZ fusion showed that the mucoid phenotype was due to rcsC-dependent induction of colanic acid capsular polysaccharide synthesis. Complementation of delta rfa1 with rfaG+ DNA fragments resulted in a larger core and restored the synthesis of flagella and pili but did not reverse the deep rough phenotype or the induction of cps-lacZ, while complementation with a fragment carrying only rfaP+ reversed the deep rough phenotype but not the loss of flagella and pili. A longer deletion which removed rfaQGPBIJ was also constructed, and complementation studies with this deletion showed that the product of rfaQ was not required for the functions of rfaG and rfaP. Thus, the function of rfaQ remains unknown. Tandem mass spectrometric analysis of LPS core oligosaccharides from complemented delta rfa1 strains indicated that rfaP+ was necessary for the addition of either phosphoryl (P) or pyrophosphorylethanolamine (PPEA) substituents to the heptose I residue, as well as for the partial branch substitution of heptose II by heptose III. The substitution of heptose II is independent of the type of P substituent present on heptose I, and this results in four different core structures. A model is presented which relates the deep rough phenotype to the loss of heptose-linked P and PPEA.

Procaine, a local anesthetic, signals through the EnvZ receptor to change the DNA binding affinity of the transcriptional activator protein OmpR

Local anesthetics are known to reduce the level of OmpF and increase the synthesis of OmpC in the outer membrane of Escherichia coli K-12. It has been shown that the anesthetics procaine and phenethyl alcohol (PEA) act at the transcriptional level for ompF and ompC and that in the case of procaine, its action is dependent on EnvZ, the membrane-bound signal transducer required for ompF and ompC expression. In an effort to further understand how anesthetics regulate ompF and ompC expression, we have analyzed the DNA binding properties of OmpR (the transcriptional activator protein for ompF and ompC genes) from cells treated with procaine or PEA. Treatment of a wild-type cell with either anesthetic converted OmpR from a low-affinity DNA binding form to a high-affinity DNA binding form. The change in DNA binding affinity was correlated with alterations in outer membrane porin profiles and could occur in the absence of protein synthesis. A strain lacking EnvZ was unable to respond to procaine to produce either the shift in the OmpR DNA binding property or cause any change in the outer membrane porin profile. PEA treatment was also dependent on EnvZ for the alteration in the OmpR DNA binding property, but it could induce ompC expression in the absence of EnvZ. Further studies suggest that the amino-terminal region of EnvZ is responsible for the procaine signalling. Our results indicate that procaine and PEA regulate ompF and ompC expression by modifying the DNA binding properties of OmpR through EnvZ signal transduction.

Genetic analysis of lipopolysaccharide core biosynthesis by Escherichia coli K-12: insertion mutagenesis of the rfa locus

Tn10 insertions were selected on the basis of resistance to the lipopolysaccharide (LPS)-specific bacteriophage U3. The majority of these were located in a 2-kilobase region within the rfa locus, a gene cluster of about 18 kb that contains genes for LPS core biosynthesis. The rfa::Tn10 insertions all exhibited a deep rough phenotype that included hypersensitivity to hydrophobic antibiotics, a reduction in major outer membrane proteins, and production of truncated LPS. These mutations were complemented by a Clarke-Carbon plasmid known to complement rfa mutations of Salmonella typhimurium, and analysis of the insert from this plasmid showed that it contained genes for at least six polypeptides which appear to be arranged in the form of a complex operon. Defects in two of these genes were specifically implicated as the cause of the deep rough phenotype. One of these appeared to be rfaG, which encodes a function required for attachment of the first glucose residue to the heptose region of the core. The other gene did not appear to be directly involved in determination of the sugar composition of the core. We speculate that the product of this gene is involved in the attachment of phosphate or phosphorylethanolamine to the core and that it is the lack of one of these substituents which results in the deep rough phenotype.

Mutagenesis by proximity to the recA gene of Escherichia coli

Escherichia coli recA (Prtc) strains, which produce protease constitutive RecA proteins in the absence of DNA-damaging treatments, display an increased frequency of spontaneous mutations. These mutations occurred preferentially in the neighborhood of the recA gene. This cis-like mutagenic effect was observed in the recA, rexAB, phoE and bio genes. The localized mutagenesis can be explained by the ease with which RecA(Prtc) proteins are activated to the protease state, which implies that there should be a relatively high concentration of activated RecA protein near the recA gene, where the protein is synthesized. The unusually high frequency of mutation in the recA gene is a novel example of an overactive gene preferentially turning itself down by mutation.

Low-frequency infection of F- bacteria by transducing particles of filamentous bacteriophages

Filamentous particles containing single-stranded plasmid and bacteriophage DNA are able to infect F- Escherichia coli at frequencies of approximately 10(-6). This infection is dependent on an intact particle and requires the products of the tolQ, tolR, and tolA genes of the bacteria. The addition of CaCl2 can increase the frequency about 100-fold, presumably by increasing the concentration of particles at the bacterial surface.

Translational control of exported proteins that results from OmpC porin overexpression

The regulation of synthesis and export of outer membrane proteins of Escherichia coli was examined by overexpressing ompC in multicopy either from its own promoter or from an inducible promoter in an expression vector. Overexpression of OmpC protein resulted in a nearly complete inhibition of synthesis of the OmpA and LamB outer membrane proteins but had no effect on synthesis of the periplasmic maltose-binding protein. Immunoprecipitation of labeled proteins showed no evidence of accumulation of uncleaved precursor forms of OmpA or maltose-binding protein following induction of OmpC overexpression. The inhibition of OmpA and LamB was tightly coupled to OmpC overexpression and occurred very rapidly, reaching a high level within 2 min after induction. OmpC overexpression did not cause a significant decrease in expression of a LamB-LacZ hybrid protein produced from a lamB-lacZ fusion in which the fusion joint was at the second amino acid of the LamB signal sequence. There was no significant decrease in rate of synthesis of ompA mRNA as measured by filter hybridization of pulse-labeled RNA. These results indicate that the inhibition is at the level of translation. We propose that cells are able to monitor expression of exported proteins by sensing occupancy of some limiting component in the export machinery and use this to regulate translation of these proteins.

Effect of lipopolysaccharide structure on reactivity of antiporin monoclonal antibodies with the bacterial cell surface

We studied the reactivity of 66 anti-Escherichia coli B/r porin monoclonal antibodies (MAbs) with several E. coli and Salmonella typhimurium strains. Western immunoblots showed complete immunological cross-reactivity between E. coli B/r and K-12; among 34 MAbs which recognized porin in immunoblots of denatured outer membranes of E. coli B/r, all reacted with OmpF in denatured outer membranes of E. coli K-12. Extensive reactivity, although less than that for strain B/r (31 of 34 MAbs), occurred for porin from a wild-type isolate, E. coli O8:K27. Only one of the MAbs reacted with porin in denatured outer membranes of S. typhimurium. Even with immunochemical amplification of the Western immunoblot technique, only six MAbs recognized S. typhimurium porin (OmpD), demonstrating that there is significant immunological divergence between the porins of these species. Antibody binding to the bacterial surface, which was analyzed by cytofluorimetry, was strongly influenced by lipopolysaccharide (LPS) structure. An intact O antigen, as in E. coli O8:K27, blocked adsorption of all 20 MAbs in the test panel. rfa+ E. coli K-12, without an O antigen but with an intact LPS core, bound seven MAbs. When assayed against a series of rfa E. coli K-12 mutants, the number of MAbs that recognized porin surface epitopes increased sequentially as the LPS core became shorter. A total of 17 MAbs bound porin in a deep rough rfaD strain. Similar results were obtained with S. typhimurium. None of the anti-E. coli B/r porin MAbs adsorbed to a smooth strain, but three antibodies recognized porin on deep rough (rfaF, rfaE) mutants. These data define six distinct porin surface epitopes that are shielded by LPS from reaction with antibodies.

Bacteriophage K20 requires both the OmpF porin and lipopolysaccharide for receptor function

Mutations which prevent absorption of the bacteriophage K20 to Escherichia coli K-12 were selected by using an altered OmpF protein which confers the ability to grow on maltodextrin in the absence of the LamB maltoporin. The mutations map in the rfa gene cluster and alter the structure of the lipopolysaccharide core.

Role of capsule and O antigen in resistance of Klebsiella pneumoniae to serum bactericidal activity

The ability of Klebsiella pneumoniae strains to resist the bactericidal activity of serum was quantitated. The K. pneumoniae strains tested included mutants lacking the capsular polysaccharide and mutants having a modified lipopolysaccharide structure. The last mutants were obtained as phage-resistant mutants, and their lipopolysaccharide was characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and chemical analysis. Serum-resistant mutants derived from phage-resistant mutants (lipopolysaccharide mutants) were also characterized. Resistance to the bactericidal activity of complement was mediated by the lipopolysaccharide, especially by the O-antigen polysaccharide chains. The capsular polysaccharide seemed not to play any important role in resistance to serum bactericidal activity in this bacterium.

Klebsiella pneumoniae C3 lipopolysaccharide mutants obtained by resistance to bacteriophage FC3-9

Bacteriophage FC3-9 is one of the several bacteriophages of Klebsiella pneumoniae C3 isolated in our laboratory. Mutants resistant to this bacteriophage were isolated and found to be devoid of lipopolysaccharide O antigen, modified in outer-membrane protein composition and sensitive to complement killing (serum-sensitive), unlike the wild-type strain. Serum-resistant mutants were isolated from these strains. They regained the lipopolysaccharide O antigen and the wild-type outer membrane protein composition and became sensitive to bacteriophage FC3-9.

Evidence for specificity at an early step in protein export in Escherichia coli

We previously described mutations in a gene, secB, which have pleiotropic effects on protein export in Escherichia coli. In this paper, we report the isolation of mutants in which the activity of the secB gene was eliminated. Null mutations in secB affected only a subset of exported proteins. Strains carrying these mutations, although unable to grow on L broth plates, were still viable on minimal media. These secB mutations reversed a block in the translation of an exported protein that was caused by the elimination of another component of the secretion machinery, SecA protein. These results suggest that the secB product acts at an early step in the export process and is involved in the export of only a subset of cell envelope proteins.

Lipopolysaccharide-specific bacteriophage for Klebsiella pneumoniae C3

Bacteriophage FC3-1 is one of several specific bacteriophages of Klebsiella pneumoniae C3 isolated in our laboratory. Unlike receptors for other Klebsiella phages, the bacteriophage FC3-1 receptor was shown to be lipopolysaccharide, specifically the polysaccharide fraction (O-antigen and core region). We concluded that capsular polysaccharide, outer membrane proteins, and lipid A were not involved in phage binding. Mutants resistant to this phage were isolated and were found to be devoid of lipopolysaccharide O-antigen by several criteria but to contain capsular material serologically identical to that of the wild type. The polysaccharide fraction was concluded to be the primary phage receptor, indicating that it is available to the phage.

Transformation of Salmonella typhimurium with plasmid DNA: differences between rough and smooth strains

Lipopolysaccharide-defective mutants of Salmonella typhimurium were transformed by plasmid DNA with a Ca2+ treatment method. Only those mutants with an Rc or Rd2 chemotype, due to galE or rfaF mutations, respectively, gave efficiencies greater than 10(5) transformants per microgram of DNA, frequencies 8- to 630-fold higher than with smooth strains or other rough mutants.

Effect of bacteriophage P1 lysogeny on lipopolysaccharide composition and the lambda receptor of Escherichia coli

The outer membrane of Escherichia coli was altered as a consequence of lysogeny by bacteriophages P1 and P1 cmts. The predominant change was a reduction in the size of lipopolysaccharide to a heptose-deficient form. P1 cmts lysogens were still sensitive to several bacteriophages but were resistant to lambda vir. Neither whole cells nor solubilized outer membranes from P1 cmts lysogens were able to inactivate lambda vir, and 32P-labeled lambda vir was unable to adsorb to P1 cmts lysogens. P1 cmts lysogens were also affected in maltose transport. The level of periplasmic maltose-binding protein was reduced somewhat, but there was no significant reduction in the level of the outer membrane lambda receptor (LamB). These membrane abnormalities were all corrected in strains cured of P1 cmts. It is suggested that P1 cmts affects lipopolysaccharide biosynthesis by a phage conversion mechanism and consequently the function of the lambda receptor.

Identification of the dye gene product, mutational loss of which alters envelope protein composition and also affects sex factor F expression in Escherichia coli K-12

The product of the dye gene of Escherichia coli, mapping at 99-100 min, is required for expression of the sex factor F, and also appears to be involved in the regulation of envelope proteins. Mutation of dye thus results in loss of expression of the F-factor ( Fex -), i.e. male sterility, and dye sensitivity (Dyes). We have isolated a plasmid, pRB38 , in which a 6 kb SalI fragment carrying the dye+ gene was cloned into the plasmid pACYC184. This 6 kb SalI fragment also carries two nearby markers, chlG , involved in the synthesis of the molybdenum cofactor, and phoM, required for constitutive expression of alkaline phosphatase. Some of the polypeptides synthesised by pRB38 were identified using the maxi-cell procedure. The product of the dye gene was found to be a polypeptide of Mr = 29,000. Thus derivatives of pRB38 in which the transposon gamma delta was inserted into dye, resulting in a Dyes Fex - phenotype when these plasmids were in a delta dye strain, failed to a produce this polypeptide and in some cases produced a truncated product. Such insertions also resulted in a Chlr and Pho- phenotype when the plasmid was in a delta (dye- chlG -phoM) phoR strain, although complementation tests suggested that the phoM+ and chlG + genes were still intact. Insertions of gamma delta into the promoter distal end of dye did not result in a Dyes Fex - phenotype, although a truncated Dye protein was synthesised, and a Chlr Pho- phenotype was produced. It has been suggested ( Gaffney et al. 1983) that the dye (= sfrA ) gene product is necessary for F-factor expression because it is required for translocation of the F-factor TraJ protein to the outer membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of common virulence plasmids in Yersinia species and their role in the expression of outer membrane proteins

The virulence plasmids pYV019, pYV8081, and pIB1 from Yersinia pestis, Yersinia enterocolitica, and Yersinia pseudotuberculosis, respectively, were characterized by restriction endonuclease analysis. The three plasmids exhibited a region of common DNA previously shown to encode determinants which confer Ca2+ dependence. The plasmids from Y. pestis and Y. pseudotuberculosis were similar throughout their genomes. In contrast, a region of the plasmid from Y. enterocolitica which contained an origin of replication differed from the other two plasmids as determined by DNA homology and replication properties. Plasmid-associated outer membrane proteins from all three species of Yersinia were characterized by polyacrylamide gel electrophoresis. There were no differences in the outer membrane protein profiles between plasmid-containing and homogenic strains lacking the plasmid after growth at 28 degrees C. After growth at 37 degrees C, both Y. enterocolitica and Y. pseudotuberculosis showed at least four major plasmid-associated outer membrane proteins. Y. pestis did not show any discernible changes after growth at 37 degrees C. It was shown by using E. coli minicell analysis that the plasmid DNA from all three species of Yersinia contained the coding capacity for production of the novel outer membrane proteins.

Effect of reduced membrane lipid fluidity on the biosynthesis of lipopolysaccharide of Escherichia coli

A low molecular weight precursor of lipopolysaccharide was accumulated under conditions in which the membrane lipids of a fatty acid auxotroph of Escherichia coli were reduced to a non-fluid state. The lipopolysaccharide precursor was detected, by sodium dodecyl sulfate/polyacrylamide gel electrophoresis and autoradiography, in membranes isolated from cells which were pulse-labeled with N-acetyl-[1-14C]glucosamine. The precursor could be chased into mature lipopolysaccharide by returning the membrane lipids to a normal fluid state. Conversion of the precursor to lipopolysaccharide was inhibited by the presence of potassium cyanide or sodium arsenate. The processing of several outer membrane protein precursors, including the promatrix proteins, was also inhibited under these conditions. Preliminary characterization of the lipopolysaccharide precursor was undertaken.

Regulation of the F conjugation genes studied by hybridization and tra-lacZ fusion

Hybridization experiments and tra-lacZ fusions were used to obtain further insight into the complex series of control systems that affect F conjugation. We confirmed that the regular IncF FinOP control system represses transcription of traJ, and found that the traJ product is required for transcription of traM as well as of the traY-Z operon. The chromosomal sfrA gene product may be required to prevent premature termination of traJ transcription, while the sfrB gene product prevents premature termination at two sites within the traY-Z operon. The FinQ inhibition system determined by several IncI plasmids caused termination at three different sites in the operon, and that of JR66a at one further site. JR66a and R485 strongly inhibit F transfer, but have weak, or no (respectively) effects on transcription: they may inhibit function of one or more transfer gene products.