- Volume 135, Issue 4, 1989
Volume 135, Issue 4, 1989
- Biochemistry
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Factors Influencing the Haematoporphyrin-sensitized Photoinactivation of Candida albicans
More LessPhotosensitizing activity of haematoporphyrin (Hp) on Candida albicans cells is mainly promoted by unbound dye molecules in the bulk aqueous medium. Moreover, the death of photosensitized cells is dependent on the dye concentration, irradiation time, irradiation temperature, and the composition of the growth media. Morphological and biochemical studies indicate that the photoprocess involves an initial limited alteration of the cytoplasmic membrane, which allows the penetration of the dye into the cell with consequent photodamage of intracellular targets. In this respect, the Hp-sensitized photoinactivation of eukaryotic microbial cells differs from that in prokaryotic cells.
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Chemical and Biological Properties of Lipopolysaccharide, Lipid A and Degraded Polysaccharide from Wolinella recta ATCC 33238
Lipopolysaccharide (LPS) was isolated and purified from Wolinella recta ATCC 33238 by the phenol-water procedure and RNAase treatment. The sugar components of the LPS were rhamnose, mannose, glucose, heptose, 2-keto-3-deoxyoctonate (KDO) (3-deoxy-d-mano-octulosonate) and glucosamine. The degraded polysaccharide prepared from LPS by mild acid hydrolysis was fractionated by Sephadex G-50 gel chromatography into three fractions: (1) a high-molecular-mass fraction, eluting just behind the void volume, consisting of a long chain of rhamnose (22 mols per 3 mols of heptose residue) with attached core oligosaccharide; (2) a core oligosaccharide containing heptose, glucose and KDO, substituted with a short side chain of rhamnose; (3) a low-molecular-mass fraction containing KDO and phosphate. The main fatty acids of the lipid A were C12:0′ C14:0′3-OH-C14:0 and 3-OH-C16:0. The biological activities of the LPS were similar to those of Salmonella typhimurium LPS in activation of the clotting enzyme of Limulus amoebocytes, the Schwartzman reaction and mitogenicity for murine lymphocytes, although all the biological activities of lipid A were lower than those of intact LPS.
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Localization and Characterization of Lipolytic Enzymes Produced by Lysobacter enzymogenes
More LessLipolysis by Lysobacter enzymogenes is due to the production of two major extracellular esterases. These were investigated using a turbidimetric assay with Tween 20 as the substrate. One esterase is cell-associated and found in the particulate fraction of cell-free extracts, the other esterase is secreted into the culture medium. In batch culture with 0·8% yeast extract as the medium the particulate esterase was produced mainly during the exponential growth phase and its yield was increased about twofold by the addition of olive oil and other substrates. The supernatant esterase was produced mainly after the exponetial growth phase and was induced six- to tenfold by olive oil. PAGE, combined with activity staining using Tween 20 as the substrate, indicated that the two enzymes have different electrophoretic mobilities. Intact cells expressed 87% of the particulate cell-associated esterase activity. The enzyme was released from cells or from the particulate fraction by incubation with 0·2% Zwittergent 3-14. Tween 20 (2%, v/v) or 1 mM-EDTA released little of the enzyme from whole cells. Separation of the inner and outer membranes of L. enzymogenes showed that the particulate esterase was localized in the outer membrane. Both esterases were very active with Tween 20 as the substrate, but they hydrolysed other compounds at very different rates. The relative activities with Tween 20, p-nitrophenyl palmitate, tributyrin and olive oil were 100, 3, 11 and 0 for the particulate esterase and 100, 73, 0 and 28 for the secreted esterase. In addition to these two extracellular esterases, L. enzymogenes contains a hydrolase in the cytoplasm which is most active with tributyrin.
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- Biotechnology
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Enhanced Secretion of Escherichia coli β-Lactamase by a Spontaneous Erythromycin-resistant Mutant of Bacillus subtilis
More LessAn extracellular-protease-deficient mutant, ME142, was isolated from Bacillus subtilis as a spontaneous erythromycin-resistant (Eryr) clone. This mutant showed conditional sporulation and only sporulated normally in the absence of erythromycin. In the presence of the antibiotic, sporulation was greatly reduced. Production of extracellular proteases by ME142 also exhibited conditional deficiency, possibly due to pleiotropic effects of the sporulation deficiency. The production of protease was 2-10% that of the wild-type level in the presence of erythromycin. ME142 showed poor competence for transformation even in the absence of erythromycin; however, derivatives of ME142 were isolated which had the same Eryr phenotype but which exhibited normal competence. One such mutant, ME162, was used as a host for the secretion of Escherichia coli β-lactamase. The amount of β-lactamase in the culture supernatants of ME162 increased significantly when the cells were cultured with erythromycin, suggesting that proteolysis of the β-lactamase in the supernatants of ME162 was greatly reduced as compared to that in the supernatants of the wild-type strain.
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Transfer and Expression of an Erwinia chrysanthemi Cellulase Gene in Zymomonas mobilis
More LessThe cellulase gene from Erwinia chrysanthemi coding for endoglucanase Z was subcloned into a broad-host-range plasmid pGSS33 in Escherichia coli. The recombinant pNB20 was transferred into Zymomonas mobilis ATCC 10988 by mobilization using the helper plasmid RP4. Plasmid pNB20 was stably maintained in E. coli and Z. mobilis hosts. The endoglucanase gene celZ was expressed efficiently and the level of expression was higher in Z. mobilis than in E. coli. The specific activity of the enzyme was comparable to that of the parent strain of Er. chrysanthemi. The proteins produced by Z. mobilis and Er. chrysanthemi presented identical immunological and electrophoretic properties. Biosynthesis of endoglucanase occurred during the exponential growth phase of Z. mobilis and about 35% of the enzyme was released into the medium in the absence of detectable cell lysis. The endoglucanase appeared to be located in the periplasmic space in Z. mobilis.
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- Development And Structure
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Control of Heterocyst Development in the Cyanobacterium Anabaena cylindrica
More LessThe differentiation of proheterocysts and heterocysts in Anabaena cylindrica was initiated by the removal of NH4Cl from the medium. The development of both proheterocysts and mature heterocysts was inhibited by rifampicin, chloramphenicol and mitomycin C, at final concentrations of 0.2, 4.0 and 1.0 μg ml−1, respectively. However, lower concentrations than these were sufficient to inhibit mature heterocyst development while permitting proheterocyst formation. The presence of rifampicin (0.2 μg ml−1) during the early stages of the induction of differentiation, just prior to the initial visual detection of proheterocysts, led to an increase in the frequency of heterocysts that subsequently developed. To assess the commitment of cells to differentiation, samples of culture were incubated with inhibitors or NH4Cl, or were transferred to darkness, at different times following the initiation of development. Each treatment produced a characteristic commitment time which differed for proheterocysts and mature heterocysts. The data obtained from these experiments have been used to formulate a model for the control of heterocyst development in A. cylindrica, in which DNA replication serves as a timer mechanism for the process.
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Ultrastructure, Serogrouping and Localization of Surface Antigens of Bacteroides intermedius
More LessThe surface ultrastructure of 21 strains of Bacteroides intermedius was investigated by electron microscopy. Rat monoclonal antibodies (mAbs) were used to define serogroups and to detect the location of surface antigens. All 21 isolates had capsules as demonstrated by the use of wet and dry Indian ink stains. Negative staining of whole cells with 1% (w/v) methylamine tungstate showed that all 21 isolates carried clumped peritrichous fibrils with strain dependent morphology, density and length (≤0·75 μm). Fibrils on 11 of 13 fresh clinical isolates were more conspicuously clumped and easily visible, whereas those on 6 of 8 laboratory strains were indistinct and were at the limits of the resolution of the negative staining technique. Staining with ruthenium red (RR), followed by thin sectioning, revealed a dense, amorphous RR staining layer (RRL), up to 24·8 ±3·0 nm thick, adjacent to the outer membrane on all of 15 strains examined. All isolates had a less dense RR staining matrix (RRM) extending away from the RRL. The structure of the RRM varied between strains. Four rat mAbs (37BI6.1, 38BI1, 39BI1.1 and 40BI3.2) were used to serogroup the 21 strains of B. intermedius. Immunonegative staining revealed that the mAbs were not directed against fibrils. Antigens recognized by mAb 37BI6.1 and mAb 39BI1.1 were located on the surfaces of cells, beneath fibrils, and on extracellular vesicles. mAb 38BI1 recognized an antigen which was most accessible on lysed cells, and non-specific binding of mAb 40BI3.2 to grids prevented its localization on the cell surface.
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- Ecology
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Population Dynamics of Scytalidium thermophilum in Mushroom Compost and Stimulatory Effects on Growth Rate and Yield of Agaricus bisporus
Mycelial growth of Agaricus bisporus on sterilized compost is strongly stimulated by pre-incubating the compost with the thermophilic fungus Scytalidium thermophilum. This stimulatory effect is not species specific, for either A. bisporus or S. thermophilum. Normal mushroom compost is almost completely colonized with S. thermophilum. In experimental composts a positive relation was found between the logarithm of mushroom yield of A. bisporusand the density of S. thermophilum. S. thermophilum provides for compost selectivity: it protects against negative effects of compost bacteria on mycelial growth of A. bisporus. S. thermophilum is inactivated by the growth of A. bisporusmycelium.
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- Genetics And Molecular Biology
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Nucleotide Sequence of an OXA-2 β-Lactamase Gene from the R-Plasmid R1767 Derived Plasmid pBP11 and Comparison to Closely Related Resistance Determinants Found in R46 and Tn2603
More LessPlasmid pBP11 contains a sequence homologous to Tn21-like element Tn2410 encoding dihydropteroate synthetase and β-lactamase OXA-2. The nucleotide sequence of a 1·5 kb segment of this region has been determined including the bla gene. It reveals strong sequence homology with the OXA-2 operon of plasmid R46. The implications of an additional 319 bp segment in pBP11 for the different evolution of R46/pKM101 and pBP11 are discussed.
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Nucleotide Sequence of the Bacillus licheniformis Homologue of the Sporulation Locus spoIIA of Bacillus subtilis
More LessThe spoIIA locus of Bacillus licheniformis was cloned into the phage vector 𝜙105J9; selection was based on the ability of the clone to complement mutations in both the first and the last of the spoIIA genes of B. subtilis. The B. licheniformis DNA was subcloned into M13 and sequenced; it includes three genes of identical lengths to those of B. subtilis. The average interspecies difference in nucleotide sequence is 24%; C occurs at the third position of codons 55% more often in the B. licheniformisthan in the B. subtilis sequence. The average difference in predicted amino acid sequence is 11%, but the distribution of these differences is far from random, and there are several long stretches of amino acid sequence that are identical in the two organisms. The distribution of non-conservative amino acid changes between the species is also strikingly non-random; no such changes are found in those regions in which missense mutations are known in B. subtilis. Each species has an open reading frame 5ʹ of the spoIIA gene, but the predicted amino acid sequence, and the distribution of differences between the two species in both nucleotides and predicted amino acids, suggest that these open reading frames are not expressed. Both species have regions 3ʹ of the open reading frames which resemble rhoindependent terminators of transcription, but that in B. licheniformis is longer and could form a more elaborate secondary structure than that in B. subtilis.
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Positive Control of Pseudomonas aeruginosa Amidase Synthesis Is Mediated by a Transcription Anti-termination Mechanism
Robert Drew and Nick LoweThe DNA sequence of the region upstream from the amidase structural gene (amiE) of Pseudomonas aeruginosa indicates that amidase (EC 3.5.1.4) is transcribed from an Escherichia coli-like promoter located 150 bp before the amiE translation initiation codon. The sequence between the promoter and the coding sequence includes a single open reading frame followed by an E. coli-like rho-independent transcription terminator. A deletion within the presumed terminator region which disrupts the potential stem/loop formation leads to high constitutive amidase expression which is independent of the product of the regulator gene (amiR). It is proposed that the catabolic aliphatic amidase of P. aeruginosa is regulated by a transcription anti-termination mechanism. The magnoconstitutive mutant PAC433 has promoter and terminator sequences identical to the wild-type PAC1 but contains a single base pair change in the amiE gene ribosome-binding site.
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Cloning in Escherichia coli of the Enterotoxin Gene from Clostridium perfringens Type A
More LessA 26 bp DNA probe has been constructed with minimal degeneracy to the protein sequence for Clostridium perfringens enterotoxin. The probe has been hybridized against a 6–10 kb chromosomal bank from C. perfringens 8239, prepared as a HindIII partial digest in pHG165. From this survey a clone has been identified containing a 6·8 kb DNA insert with strong hybridization to the probe. Direct plasmid sequencing has identified a translational reading frame within this clone which correlates with the known protein sequence for the type A enterotoxin. DNA sequences 5′ to this open reading frame and containing the putative transcriptional control regions show areas of significant homology with regions upstream from the ATG codon of the tetanus toxin gene.
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Isolation and Characterization of Two Endogenous Phages of Rhodobacter sphaeroides
More LessTwo new temperate bacteriophages for Rhodobacter sphaeroides, designated ϕRsA and ϕRsD, were isolated from a stock of phage ϕRsGl using R. sphaeroides strain DSM 159–2 as the indicator strain. Electron-microscopic examination showed that phage ϕRsA belonged to group B and phage ϕRsD belonged to group A of Bradley’s morphological classification. Phage ϕRsA had a polyhedral head (50 nm in diameter) and a long, flexible, non-contractile tail (250 by 11 nm). Phage ϕRsD also had a polyhedral head (56 nm in diameter) and a sheathed contractile tail (160 by 18 nm). Both phages contained double-stranded DNA with cohesive ends. The size of the ϕRsA genome was about 40 kb and the G + C content was 72·4 mol%. The size of the ϕRsD genome was about 56 kb and the G + C content was approximately 72·6 mol%. Biotinylated DNA probes of phage ϕRsA and of phage ϕRsD hybridized to genomic DNA from R. sphaeroides strains Y and Si 4 but not to DNA from other sources. The host ranges of the two phages were determined using 26 R. sphaeroides strains and six strains of Rhodobacter capsulatus. Phage ϕRsA formed plaques on R. sphaeroides DSM 159–2 only, while phage ϕRsD plaqued on another six strains of R. sphaeroides but not on R. capsulatus.
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The Isolation and Comparison of Cellulase Genes from Two Strains of Ruminococcus albus
More LessEndo-1, 4-β-glucanase genes have been cloned from two strains of Ruminococcus albus recently isolated in this laboratory. Although the strains were phenotypically similar, cross-hybridization studies between them showed significant genetic differences, with only 20% of the genome forming DNA heteroduplexes. Heteroduplexes displayed an average dissociation temperature 9 °C lower than that of the homoduplex. Consistent with this, restriction maps of the two endoglucanase genes showed no similarity, and hybridization work using the endoglucanase genes as probes revealed that neither gene was present in the genome of the other isolate of R. albus. Comparative enzyme characterization showed differences between the enzymes in their response to temperature, pH and substrate preference.
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Cloning and Sequence Analysis of the 10 kDa Antigen Gene of Mycobacterium tuberculosis
More LessThe gene encoding a major protein antigen of Mycobacterium tuberculosis has been cloned and sequenced using oligonucleotide probes derived from the N-terminal sequence of the analogous protein from Mycobacterium bovis BCG. The gene analysis revealed a sequence encoding a protein of 99 amino acid residues, with a molecular mass of 10·7 kDa. Computer prediction suggests that the protein contains three T-cell-determined epitopes (of which one has been demonstrated experimentally) and three B-cell-determined epitopes. The protein sequence was homologous to two prokaryote heat-shock proteins and the gene possessed heat-shock-like promoter sequences upstream of the initiation codon. A hairpin loop identified in the upstream sequence may also be important in regulation of the gene.
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Physical and Genetic Characterization of Chromosomal Copies of the Streptomyces coelicolor Mini-circle
More LessThe two linear, integrated mini-circle copies of Streptomyces coelicolor A3(2) were cloned in Escherichia coli and their positions on the S. coelicolor genetic map were determined. Mini-circle copy A is close to the argA locus, 20 kb upstream of the gyl operon. Mini-circle copy B is close to the cysD locus and is absent from S. coelicolor J1501, which has suffered a chromosomal deletion including mini-circle copy B and possibly associated with the pgl mutation. The mini-circle copies were not involved in any of the several previously identified physical interactions between the plasmid SCP1 and the S. coelicolor chromosome. A new insertion sequence was identified close to the right end of mini-circle copy B in S. coelicolor M145. The free mini-circle of S. coelicolor, when inserted into an attP-deleted derivative of phage ϕC31, actively integrated this phage into the chromosomes of S. coelicolor and S. lividans at preferred and secondary sites. The resulting prophages were stably inherited and remained physically intact. No precise excision of prophages from S. lividans lysogens carrying insertions at preferred or secondary integration sites was detected: instead, free phages were generated by imprecise excisions. These phages allowed the in vivo cloning of segments (> 3 kb in length) of the chromosomal DNA flanking preferred and secondary integration sites. Attempts to delete the preferred integration site by double homologous recombination with a clone carrying flanking DNA sequences and an antibiotic resistance gene were unsuccessful.
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Cloning and Sequence Determination of Six Staphylococcus aureus β-Lactamases and Their Expression in Escherichia coli and Staphylococcus aureus
More LessThe plasmid-encoded β-lactamase genes of six strains of Staphylococcus aureus were cloned and shown to be expressed in Escherichia coli. The cloned genes were re-introduced into S. aureus via a shuttle vector, and expressed β-lactamase. However, clones containing only the small amount of DNA found necessary for expression of ampicillin resistance in E. coli did not express β-lactamase in S.aureus. Much larger pieces of DNA from the original plasmid were necessary to obtain expression in S.aureus. Some of the six strains of S.aureus synthesized β-lactamase constitutively and some released only a small proportion of the enzyme into the medium. Both these characteristics were maintained in the clones so it is concluded that they are features either of the gene itself or of the surrounding DNA. The cloned genes were sequenced and the putative amino acid sequences of the βlactamases were compared. There are several differences between the sequences and in particular one change in the N-terminal region, at a position believed to be especially important for export of proteins from the cell, is thought to have a key effect on whether or not the enzyme is found in the medium.
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Host-Plasmid Interactions in Saccharomyces cerevisiae: Effect of Host Ploidy on Plasmid Stability and Copy Number
More LessThe segregational stability of two chimaeric plasmids has been examined in an isogenic series of haploid, diploid and tetraploid strains of Saccharomyces cerevisiae, constructed by transformation-associated spheroplast fusion. For the highly unstable, ARS-based plasmid YRp7M, a significant increase in its segregational stability was observed with increasing ploidy, while the relatively stable, 2µm-based plasmid pMA3a showed only a small increase in stability in strains of higher ploidy. The copy number of both pMA3a and the endogenous 2m plasmid increased in proportion with the host cell ploidy, while the copy number of TRp7M was increased in the higher ploidy strains but did not correlate with ploidy. These results suggest that the copy numbers of both the 2µm plasmid and a plasmid derived from it are controlled by a nuclear gene and that, in addition, there are 2µm sequences, other than those required for the FLP-mediated recombination system, that play a role in maintaining copy number.
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- Pathogenicity And Medical Microbiology
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Mechanism of Staphylococcal Resistance to Non-oxidative Antimicrobial Action of Neutrophils: Importance of pH and Ionic Strength in Determining the Bactericidal Action of Cathepsin G
More LessThe staphylococcalcidal action of highly purified, enzymically inactive human lysosomal cathepsin G was studied. The bactericidal action of cathepsin G was optimal at pH 7·5 and was inhibited by NaCl; concentrations greater than 0·15 m NaCl completely inhibited killing of Staphylococcus aureus. Under optimal conditions (pH, temperature and NaCl concentration) the ED50 (effective dose) of cathepsin G against S. aureus strain 8325·4 was about 3·1 μg ml−1. Polymeric teichoic acid may serve as a binding site for cathepsin G by promoting electrostatic interactions since a mutant lacking this surface component exhibited enhanced resistance to the lethal action of cathepsin G, compared to the teichoic-acid-positive parental strain. These results suggest that (i) the ability of cathepsin G to kill intraphagosomal staphylococci may be regulated in part by the ionic strength of the environment and the pH of the maturing phagolysosome, and (ii) that strategies which retard acidification of the developing phagolysosome would promote the staphylococcalcidal action of cathepsin G.
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Influence of Iron-limited and Replete Continuous Culture on the Physiology and Virulence of Neisseria gonorrhoeae
More LessNeisseria gonorrhoeae strains P9-2 (PenS) and KW2 (PenR) were grown in chemostats of non-ferrous design at constant growth rate, pH and dissolved oxygen tension. Iron limitation (µmax 0·1 h−1) was imposed by omitting iron salts from the defined medium and titrating increasing concentrations of the non-metabolizable iron chelators ovotransferrin and Desferal, to progressively decrease the growth yield. Metabolic activity during iron limitation was very high, with a q Glc which was 2-or 11-fold greater than during cystine-or glucose-limited growth, respectively. More aspartate and isoleucine were metabolized during cystine-limited growth, while more glutamate, proline and serine were metabolized during glucose-or iron-limited growth. Significant concentrations of alanine or valine were excreted during cystine-or glucose-limited growth, respectively. Iron-limited growth of an initial inoculum of non-piliated, transparent colony-forming (P−O−) gonococci resulted in the selection of 100% piliated bacteria. Initial inocula of P+O− gonococci retained this phenotype for over 100 generations. Iron-limited gonococci were extremely virulent in the guinea-pig subcutaneous chamber model and inocula of even 12 bacteria grew rapidly and persisted. By contrast, cystine-limited (iron-replete) gonococci retained piliation but did not survive in the chambers. Transition from iron-limited to glucose-limited growth resulted in marked loss of piliation but the bacteria remained virulent. Loss of virulence did not correlate with susceptibility to killing by normal human serum, nor with changes in the content or composition of lipooligosaccharide, which contained 2·9, 3·7, 4·3 and 4·8 kDa moieties. Additional proteins were detectable in Sarkosyl-purified outer membranes of iron-limited gonococci but several proteins with molecular masses similar to those described in the literature for iron-restricted gonococci were detectable in cystine-or glucose-limited bacteria.
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