- Volume 141, Issue 8, 1995
Volume 141, Issue 8, 1995
- Biochemistry
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Novel cell-wall teichoic acid from Nocardiopsis albus subsp. albus as a species-specific marker
Cell walls of the three Nocardiopsis albus subsp. albus strains, DSM 43377T, 43378 and 43120 contain structurally identical teichoic acids. The cell wall of each strain has three distinct types of teichoic acids: (1) unsubstituted 3,5-poly(ribitol phosphate), (2) 1,3-poly(glycerol phosphate) partially substituted at C-2 with α-N-acetylglucosamine residues, and (3) 1,5-poly(ribitol phosphate) with each ribitol unit carrying a 2,4-pyruvate ketal group. Types 1 and 3 are reported in prokaryotes for the first time. The structure of the teichoic acids was elucidated by chemical analysis and NMR-spectroscopic methods. Structural identity of the teichoic acids from the three strains belonging to the same species may demonstrate the species-specificity of these polymers.
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Polyol metabolism of Rhodobacter sphaeroides: biochemical characterization of a short-chain sorbitol dehydrogenase
More LessA sorbitol dehydrogenase (SDH; L-iditol: NAD+ 2-oxidoreductase; EC1.1.1.14) was isolated from the phototrophic bacterium Rhodobacter sphaeroides strain M22, a transposon mutant of R. sphaeroides Si4 with the transposon inserted in the mannitol dehydrogenase (MDH) gene. SDH was purified 470-fold to apparent homogeneity by ammonium sulfate precipitation, chromatography on Phenyl-Sepharose, Q-Sepharose and Matrex Gel Red-A, and by gel filtration on Superdex 200. The relative molecular mass (M r) of the native SDH was 61 000 as calculated from its Stokes’ radius (rs = 3.5 nm) and sedimentation coefficient (S 20,w = 4.235). SDS-PAGE resulted in one single band representing a polypeptide with a M r of 29000, indicating that the native protein is a dimer. The isoelectric point of SDH was determined to be pH 4-8. The enzyme was specific for NAD+ and catalysed the oxidation of D-glucitol (sorbitol) to D-fructose, galactitol to D-tagatose and of L-iditol. The apparent K m values were NAD+, 0-06 mM; D-glucitol, 6-2 mM; galactitol, 1-5 mM; NADH, 0-13 mM; D-fructose, 160 mM; and D-tagatose, 13 mM. The pH-optimum of substrate oxidation was 11-0 and that of substrate reduction 6-0-7-2. It was demonstrated that SDH is expressed in the wild-type strain R. sphaeroides Si4 together with MDH during growth on D-glucitol. Forty-four amino acids of the SDH N terminus were sequenced. This sequence exhibited 45-55% identity to the N-terminal sequence of 10 enzymes belonging to the short-chain alcohol dehydrogenase family.
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Hydrophobic properties of the cell surface of Candida albicans: a role in aggregation
More LessThe ability of Candida albicans to aggregate and adhere to biological surfaces is a topic of major biological and medical importance. One factor which has been implicated in such properties is the hydrophobic nature of the cell surface. Two simple spectroscopic techniques are described which permit the rapid determination of this property. The first involves the use of arylnaphthalenesulfonate, the fluorescence emission maximum of which was shown to be a sensitive indicator of dielectric polarity. This was used to identify the hydrophobic characteristics of the cell surface of C. albicans. The second technique involves the use of 90° Rayleigh-Debye light scattering as an indicator of the aggregation state of a fungal suspension. These techniques were then used to compare the surface properties of three different strains of C. albicans and the effects of culture conditions: the hydrophobicity of the strains varied, and galactose-based culture media promoted the greatest degree of cell surface hydrophobicity.
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Powerful methods to establish chromosomal markers in Lactococcus lactis: an analysis of pyrimidine salvage pathway mutants obtained by positive selections
More LessUsing different 5-fluoropyrimidine analogues, positive selection procedures for obtaining mutants blocked in pyrimidine and purine salvage genes of Lactococcus lactis were established. Strains lacking the following enzyme activities due to mutations in the corresponding genes were isolated: uracil phosphoribosyltransferase (upp), uridine/cytidine kinase (udk), pyrimidine nucleoside phosphorylase (pdp), cytidine/deoxycytidine deaminase (cdd), thymidine kinase (tdk) and purine nucleoside phosphorylase (pup). Based on an analysis of the mutants obtained, the pathways by which L. lactis metabolizes uracil and the different pyrimidine nucleosides were verified. The substrate specificities of the different enzymes were determined. It was demonstrated that a single pyrimidine nucleoside phosphorylase accounts for the phosphorolytical cleavage of uridine, deoxyuridine and thymidine, and a single purine nucleoside phosphorylase has activity towards both the ribonucleoside and deoxyribonucleoside derivatives of adenine, guanine and hypoxanthine. No phosphorylase activity towards xanthosine appeared to be present. The selection procedures developed during this work may be employed in establishing markers on the chromosome of many related lactic acid bacteria.
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Regulation of the degradative pathways from 4-toluenesulphonate and 4-toluenecarboxylate to protocatechuate in Comamonas testosteroni T-2
More LessComamonas testosteroni T-2 was grown in salts medium containing intermediates of the established, inducible degradative pathway(s) for 4-toluenesulphonate/4-toluenecarboxylate. The specific activity or, if appropriate, the specific expression of pathway enzymes or their components was constant throughout growth and decreased only slowly in the stationary phase. It was found that the 4-toluenesulphonate methyl-monooxygenase system and 4-sulphobenzyl alcohol dehydrogenase (with 4-sulphobenzaldehyde dehydrogenase) were always co-induced, with similar ratios of their activities during growth with 4-toluenesulphonate, 4-toluenecarboxylate and 4-sulphobenzoate. We presume these enzymes to be co-expressed from one regulatory unit. The ratio of activities of the terephthalate 1,2-dioxygenase system to those of (1R,2S)-dihydroxy-1,4-dicarboxy-3,5-cyclohexadiene dehydrogenase was also constant, and present only during growth with 4-toluenecarboxylate or terephthalate. We presume these two enzymes to be co-expressed from a different regulatory unit. The oxygenase component of 4-sulphobenzoate 3,4-dioxygenase (PSBDOS) was expressed at high levels in most growth conditions examined, the exception being with 4-toluenecarboxylate as carbon source. However, no expression of a specific reductase activity linked to synthesis of the oxygenase of PSBDOS could be detected. The PSBDOS was thus active in vivo solely under conditions where the 4-toluenesulphonate methyl-monooxygenase system was also present, whose reductase is active with the oxygenase of the 4-sulphobenzoate 3,4-dioxygenase system in vitro, and, apparently, in vivo. The synthesis of PSBDOS is thus under the control of a third regulatory unit.
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- Development And Structure
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A pre-induction sporulation gene from Aspergillus nidulans
More LessAsexual sporulation in Aspergillus nidulans is an inducible developmental process controlled by genes that act before and after the inductive stimulus is applied. Genes that act before induction (pre-induction genes) potentially represent functions required for response to induction. This report describes the isolation and characterization of the acoB pre-induction gene which was cloned by complementation of a thermosensitive aconidial mutant followed by gene rescue. Genetic analysis and gene disruption confirmed the identity of the cloned gene. The mRNA of the acoB gene was present in uninduced vegetative hyphae, induced conidiating cultures and in both conidiospores and ascospores. An ORF in the nucleotide sequence of the acoB cDNA specifies a 327-residue protein unrelated to any known peptide sequence. Sequence analysis of the thermosensitive mutant allele, acoB202, revealed that the mutant phenotype is due to a frame-shift mutation that severely truncates the putative ACOB protein. Disruption of the acoB gene also produced a strain that was thermosensitive for conidiation. These properties suggest that acoB may be a gene that is required for sporulation only at elevated temperatures. Hybridization of acoB DNA with DNA from a variety of Aspergillus species showed that homology to this gene is largely restricted to sexually sporulating species that belong to the nidulans group.
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- Environmental Microbiology
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Detection of novel marine methanotrophs using phylogenetic and functional gene probes after methane enrichment
More LessA major limitation of rRNA-targeted group-specific probes is that they may cross-react with organisms of other physiological, or even phylogenetic groups when applied to environmental samples containing unknown sequences. We have exploited the restricted physiology of methane-oxidizing bacteria to assess the specificity and efficiency of probes for this physiological type which target the 16S rRNA or genes involved in methanotroph physiology. Seawater samples were enriched for methanotrophs by addition of methane and essential nutrients. The changes in composition of the bacterial population were monitored by analysis of 16S rRNA gene libraries. Methanotroph group-specific probes failed to give a signal with samples from these enrichments even though a methanol dehydrogenase structural gene was detected. A 16S rDNA sequence that was abundant only after methane addition was recovered and found to show a close phylogenetic relationship to Methylomonas. Organisms containing this sequence were observed in enrichments by in situ hybridization. The combination of enrichment on methane and screening with the broad specificity methanol dehydrogenase probe allowed detection of novel methanotrophs that were not detected with the original suite of methanotroph group-specific probes.
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- Genetics And Molecular Biology
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Activity of mycobacterial promoters during intracellular and extracellular growth
More LesspUS933, a bifunctional Mycobacterium-Escherichia coli translational fusion vector containing an amino-terminally truncated E. coli lacZ reporter gene, was constructed. Derivatives of pUS933, containing the promoter, RBS and start codon of the Mycobacterium bovis BCG hsp60 gene, the Mycobacterium leprae 28 kDa gene and the M. leprae 18 kDa gene were constructed and introduced into E. coli, Mycobacterium smegmatis and M. bovis BCG. -Galactosidase activity was measured for mycobacteria grown in liquid culture. Primerextension analysis was used to determine the transcriptional start point for the 18 kDa promoter in M. smegmatis. Murine macrophages were infected with recombinant BCG containing the pUS933 derivatives and expression levels were examined, by fluorescence microscopy and fluorometry, during intracellular growth of BCG. Both the BCG hsp60 gene promoter and the M. leprae 28 kDa gene promoter gave high levels of -galactosidase expression in all situations examined. In contrast, the M. leprae 18 kDa promoter fragment gave very low levels of expression in M. smegmatis and BCG grown in liquid culture, but in BCG growing within macrophages it was induced to levels almost as high as the other promoters. This indicated that the 18 kDa gene is specifically activated during intracellular growth and may therefore be involved in survival of M. leprae within macrophages. This pattern of regulation may be useful for controlling expression of foreign genes in recombinant BCG strains.
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A new Myxococcus xanthus gene cluster for the biosynthesis of the antibiotic saframycin Mx1 encoding a peptide synthetase
More LessThe gene cluster for the biosynthesis of the heterocyclic quinone antibiotic saframycin Mx1 of Myxococcus xanthus DM504/15 was inactivated and tagged by Tn5 insertions. The tagged genes were cloned in Escherichia coli and used to select overlapping cosmid clones spanning 58 kb of the M. xanthus genome. Gene disruption experiments defined a ≥ 18 kb contiguous DNA region involved in saframycin biosynthesis. Sequencing of part of this region revealed a large ORF containing two 600-amino-acid domains with similarity to peptide synthetase amino-acid-activating sequences, suggesting that saframycin Mx1 is synthesized by a nonribosomal multienzyme complex, similar to other bioactive peptides.
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Isolation of regulatory mutants in photosynthesis gene expression in Rhodobacter sphaeroides 2.4.1 and partial complementation of a PrrB mutant by the HupT histidine-kinase
More LessThe photosynthetic bacterium Rhodobacter sphaeroides responds to the transition from aerobiosis to anaerobic photosynthesis by increasing the expression of the photosynthesis genes. Mutants have been isolated based on their inability, following such a transition, to increase transcription of the puc operon encoding the apoproteins of the light-harvesting complex II. Mutant D5, a representative of one mutant class, described here, although remaining photosynthetically competent, produced only low levels of the photosynthetic spectral complexes. Complementation analysis revealed that either the gene for the photosynthesis response regulator prrA or the gene encoding its cognate sensor kinase, prrB, was capable of rescuing this mutant. However, partial complementation of this mutant was achieved by placing in trans additional copies of other defined genes from the cosmid library of R. sphaeroides. We describe this effect in detail, attributable to the hupT gene, which has been proposed to encode a histidine-kinase for the hydrogen uptake system in Rhodobacter capsulatus. The effect of HupT on the expression of the photosynthesis genes was mediated through PrrA and independent of a functioning hydrogen uptake system. Thus, we raise the possibility that HupT can participate in phosphorylation of the heterologous response regulator PrrA by so-called cross-talk and therefore partially compensate for the defect in the mutant described. The observation of cross-talk, together with the complementation analysis, allowed us to assign the original mutation to the prrB gene; this was confirmed by DNA sequencing. Analysis of cross-talk in the wild-type, prrB and prrA genetic backgrounds suggested that besides kinase activity, PrrB may possess phosphatase activity toward PrrA. We also report the cloning, organization and structure of some of the hup genes from R. sphaeroides and construction of a Hup- strain.
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cAMP-cAMP receptor protein complex: five binding sites in the control region of the Escherichia coli mannitol operon
More LessThe control region of the mannitol (mtl) operon of Escherchia coli has been shown to contain five cAMP receptor protein (CRP) binding sequences, the most yet reported for any operon. A DNA fragment encompassing the entire mtl operon regulatory region was generated by PCR, and the binding of the cAMP-CRP complex was studied. Using restrictional analysis to separate, delineate and destroy the various putative CRP binding sites, all five sites were shown to be functional for CRP binding in vitro. Four of these sites bound the cAMP-CRP complex with high affinity while the fifth site (the most distal relative to the transcriptional start site) bound the complex with lower affinity. Simultaneous binding of cAMP-CRP complexes to several of these sites was demonstrated. The results serve to identify and define five dissimilar CRP binding sites in a single operon of E. coli. A model for mtl operon transcriptional initiation and repression complexes is presented.
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Multidrug resistance in Klebsiella pneumoniae: a novel gene, ramA, confers a multidrug resistance phenotype in Escherichia coli
More LessSpontaneous multidrug-resistant (Mdr) mutants of Klebsiella pneumoniae strain ECL8 arose at a frequency of 2-2 ° 10-8 and showed increased resistance to a range of unrelated antibiotics, including chloramphenicol, tetracycline, nalidixic acid, ampicillin, norfloxacin, trimethoprim and puromycin. A chromosomal fragment from one such mutant was cloned, and found to confer an Mdr phenotype on Escherichia coli K12 cells that was essentially identical to that of the K. pneumoniae mutant. Almost complete loss of the OmpF porin in the E. coli transformant, and of the corresponding porin in the K. pneumoniae mutant, was observed. The presence of the Mdr mutation in K. pneumoniae or the cloned K. pneumoniae ramA (resistance antibiotic multiple) locus in E. coli also resulted in active efflux of tetracycline, and increased active efflux of chloramphenicol. After transformation of a ramA plasmid into E. coli, expression of chloramphenicol resistance occurred later than expression of resistance to tetracycline, puromycin, trimethoprim and nalidixic acid. The ramA gene was localized and sequenced. It encodes a putative positive transcriptional activator that is weakly related to the E. coli MarA and SoxS proteins. A ramA gene was also found to be present in an Enterobacter cloacae fragment that has previously been shown to confer an Mdr phenotype, and it appears that ramA, rather than the romA gene identified in that study, is responsible for multidrug resistance. The ramA gene from the wild-type K. pneumoniae was identical to that of the mutant strain and also conferred an Mdr phenotype on E. coli, indicating that the mutation responsible for Mdr in K. pneumoniae had not been cloned.
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The bldA-encoded tRNA is poorly expressed in the bldi mutant of Streptomyces coelicolor A3(2)
More LessThe bldA gene, encoding a leucyl tRNA recognizing the UUA codon, is expressed at significantly lower levels in the bldii mutant, Streptomyces coelicolor J703, than in the parent S. coelicolor A3(2). Expression of a TTA-containing reporter gene was reduced in the bldi mutant, as was the mature, 87 nucleotide, form of the bldA-encoded tRNA. This reduced level of the tRNA was also seen when the bldA gene was introduced on a high-copy-number plasmid into the bldi mutant, suggesting that maximal bldA expression may require a bldii-dependent promoter.
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Topological analysis of the lysine-specific permease of Escherichia coli
More LessEscherichia coli accumulates lysine via two systems, one specific for lysine (LysP) and a second inhibited by arginine or ornithine (LAO). The lysP gene encodes a polypeptide of 489 residues. A topological analysis of the LysP protein was performed using gene fusions. Random in-frame fusions of the lysP gene with the lacZ or blaM genes were generated. Site-directed mutagenesis was also used to generate additional blaM fusions at specific locations in the lysP gene. Two methods were used to alleviate the problem of lethal expression of some lysP::blaM fusions. First, ternary fusions were constructed in which the arsD gene was fused at the 5' end of the lysP gene and the blaM gene fused at specific sites within the lysP gene. In these plasmids lysP expression was controlled by the ars promoter. Secondly, an E. coli strain with a pcnB mutation was used with some fusions to maintain the plasmids at a reduced copy number. From analysis of 30 gene fusions, a topological model of the LysP protein is proposed in which the protein has 12 membrane-spanning regions, with the N- and C-termini in the cytosol.
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- Pathogenicity And Medical Microbiology
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A 46 kDa integral membrane protein from Mycobacterium leprae resembles a number of bacterial and mammalian membrane transport proteins
In this paper we describe the nucleotide sequence of a 3·4 kbp region of the Mycobacterium leprae genome. This region contains an open reading frame of 1290 bp with a coding capacity for a protein of 46179 Da, designated the 38L protein. Using antibodies against part of the 38L protein, we were able to demonstrate that the 38L protein is present in the membrane protein fraction of M. leprae. The 38L protein showed significant matches with a number of integral membrane proteins involved in the transport of small molecules through the cellular membrane. Among these are a human and a murine protein involved in melanin biosynthesis. The 38L protein might play a role in the hypopigmentation observed in leprosy patients.
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Immune reactions to Bacteroides fragilis populations with three different types of capsule in a model of infection
More LessThe survival and growth of populations of the obligately anaerobic pathogenic bacterium Bacteroides fragilis enriched for large capsules (LCs), small capsules (SCs) or an electron-dense layer (EDL; non-capsulate by light microscopy) were examined in a mouse model of infection over a minimum period of 20 d. Chambers which allowed the influx of leukocytes, but not the efflux of bacteria, were implanted in the mouse peritoneal cavity. The LC and EDL populations consistently attained viable cell densities of the order of 10-10 c.f.u. ml-1 within 24 h, whereas the SC population did not. However, after 3 d, all three bacterial populations maintained total viable numbers of 10-109 c.f.u. ml-1 within the chambers. LC expression was selected against within 24 h in the model, the populations becoming non-capsulate by light microscopy, whereas in the SC population expression of the SC was retained by approximately 90% of the population. The EDL population remained non-capsulate by light microscopy throughout. Lymphocytes infiltrated the chambers to an equal extent for all three B. fragilis populations and at approximately 1000 times higher concentration than chambers which contained only quarter-strength Ringer's solution. The presence of neutrophils within the chambers did not cause a decrease in the total viable bacterial count. Each population elicited antibodies specific for outer-membrane proteins and polysaccharide, as detected by immunoblotting, which cross-reacted with the other populations. Differences were observed in the immunogenicity of the outer-membrane proteins within the three populations. Neutrophils were initially the predominant cell type in the chambers, but as the total leukocyte count increased with incubation time, neutrophils were outnumbered by other leukocytes. Flow cytometric investigations indicated that by day 7 the majority of these leukocytes were B-cells. Bearing in mind the constraints of this model system, it appears that all three populations of B. fragilis have the potential for in vivo growth and that each elicits an immune reaction.
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Cholera toxin (CTX) genetic element in Vibrio cholerae O139
PFGE analysis of the Notl-and Sfil-digested genome of Vibrio cholerae O139 strains isolated from different epidemic regions of India showed that all the strains are of clonal origin and the genome size is about 2·2 Mb. An analysis of the electrophoretic profiles of the genome of O139 strains, the RFLP of the cholera toxin (ctx) gene and Southern blot hybridization of Notl-digested genomes of classical, El Tor and 0139 with a Notl-linking clone of classical strain 569B, suggest that these strains closely resemble V. cholerae 01 biotype El Tor, but are widely different from the classical 01 vibrios. Using restriction enzymes which cleave a single site in either the core region or in the direct repeat sequence (RS) of the CTX genetic element, it has been shown that the genome of most of the O139 strains has two copies of the ctx gene in tandem connected by two RSs. The chromosomal location of the CTX genetic element in the 0139 strain is the same as that reported for El Tor vibrios. The organization of the virulence gene cassettes in different O139 strains shows genetic heterogeneity in the population. Whilst most of the epidemic strains have two copies of the CTX genetic element, in some strains the number of elements has been amplified and in at least one strain a single copy of the element has been deleted.
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Reduction of exogenous ferric iron by a surface-associated ferric reductase of Listeria spp
More LessThe reduction of exogenous ferric iron by Listeria monocytogenes, a Gram-positive food-borne pathogen, was investigated. Using an assay incorporating the ferrous iron chelator ferrozine, we showed that intact cells of L. monocytogenes, when exposed to ferric iron, were able to rapidly reduce and solubilize the iron to the ferrous form. Reduction occurred only after direct contact between the bacteria and the iron source. A number of different ferric iron chelates, including transferrin and lactoferrin-bound iron, haemoglobin, ferritin, and iron complexed to siderophores, could be reduced. The ferric reductase activity was expressed by both reference strains and clinical isolates of L. monocytogenes and by all other species of Listeria, although significant quantitative differences were observed. In L. monocytogenes, the expression of ferric reductase was not affected by the growth phase of the bacteria nor by the presence or absence of iron in the growth medium. However, expression was greatly reduced in bacteria grown anaerobically and when cultured in media of reduced pH. In addition, bacteria grown at a cold temperature displayed greater ferric reductase activity than cells grown at higher temperatures. A surface-associated ferric reductase system may be one component of a general iron scavenging mechanism which can be used by Listeria growing in a variety of environments.
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Attenuated typhoid vaccine Salmonella typhi Ty21a: fingerprinting and quality control
More LessLive attenuated vaccines, developed with molecular genetical techniques, require new approaches for their quality control. To develop novel quality control tests that enhanced and extended existing procedures, the attenuated vaccine strain Salmonella typhi Ty21a and its parent strain Ty2 were characterized by pulsed-field gel electrophoresis (PFGE) and direct nucleotide sequence analysis. Mutant and parent strains were distinguished using fingerprints generated by the resolution on PFGE of chromosomal DNA digested with each of the enzymes Sfil, Spel or Xbal. These fingerprints were stable through multiple in vitro passages of the vaccine strain and were identical from one batch of vaccine to another. It was also possible to distinguish between the mutant and parent strains by direct nucleotide sequence analysis of the galE gene. This analysis identified two base changes in the gene from strain Ty21a: a single base deletion causing a frameshift that would result in a truncated gene product, accounting for the galE phenotype; and a transition that eliminated an Alul restriction site. The consequent change in the Alul fingerprint of the galE gene in strain Ty21a provided a rapid, PCR-based alternative to the use of differential media or biochemical assays for the identification of the vaccine strain.
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Anti-Candida activity of a novel killer toxin from the yeast Williopsis mrakii
More LessA screening of putative killer yeast strains showed that spore-forming ascomycetous yeasts of the genera Pichia and Williopsis displayed the broadest range of activity against sensitive strains of Candida spp. and Saccharomyces cerevisiae. Williopsis mrakii (NCYC 500) showed extensive anti-Candida activity against strains isolated from clinical specimens. W. mrakii killer factor was produced in minimal media as a function of growth and its activity reached constant levels as cells entered stationary phase. The proteinaceous killer toxin was found to be unstable outwith a specific range of temperature and pH (above 30 °C and pH 4°0), and further analysis showed that the active toxin molecule was an acidic polypeptide with a relative molecular mass between 1°8-5°0 kDa. At critical concentrations the killer factor exerted a greater effect on stationary phase cells of Candida than cells from an exponential phase of growth. At low concentrations, the killer toxin produced a fungistatic effect on sensitive yeasts but at higher concentrations there was evidence to suggest that membrane damage accounted for the zymocidal effects of the killer factor. The cidal nature of the toxin was reflected in a rapid decrease in sensitive cell viability. Findings presented suggest that W. mrakii killer toxin has potential as a novel antimycotic agent in combatting medically important strains of Candida.
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