- Volume 145, Issue 8, 1999
Volume 145, Issue 8, 1999
- Genetics And Molecular Biology
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Analysis of the ColE1 stability determinant Rcd
More LessMultimer formation is an important cause of instability for many multicopy plasmids. Plasmid ColE1 is maintained stably because multimers are converted to monomers by Xer-mediated site-specific recombination at the cer site. However, multimer resolution is not the whole story; inactivation of a promoter (P cer ) within cer causes plasmid instability even though recombination is unaffected. The promoter directs the synthesis of a short transcript (Rcd) which is proposed to delay the division of multimer-containing cells. Mapping of the 5′ terminus of Rcd confirms that transcription initiates from P cer The 3′ terminus shows considerable heterogeneity, consistent with a primary transcript of 95 nt being degraded via intermediates of 79 and 70 nt. Secondary structure predictions for Rcd are presented. Of four mutations which abolish Rcd-mediated growth inhibition, one reduces the activity of P cer while the other three map to the rcd coding sequence and reduce the steady-state level of the transcript. RNA folding analysis suggests that these three mutant transcripts adopt a common secondary structure in which the major stem-loop differs from that of wild-type Rcd. A survey of 24 cer-like multimer resolution sites revealed six which contain P cer like sequences. The putative transcripts from these sites have similar predicted secondary structures to Rcd and contain a highly conserved 15 base sequence. To test the hypothesis that Rcd acts as an anti-sense RNA, interacting with its target gene(s) through the 15 nt sequence, we used DNA hybridization and sequence analysis to find matches to this sequence in the Escherichia coli chromosome. Our failure to find plausible anti-sense targets has led to the suggestion that Rcd may interact directly with a protein target.
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A novel approach for the construction of a Campylobacter mutant library
Given the lack of functional transposons for use in Campylobacter spp., an alternative method of insertional mutagenesis using natural transformation was developed. High efficiencies of transformation were only obtained with species-specific DNA. This feature was a key element in the construction of mutant libraries of this bacterium. A chromosomal library of Campylobacter jejuni 81116 DNA was made in shuttle vector pUOA18. Next, a kanamycin-resistance (KmR) cassette was ligated into the inserts of the plasmids. C. jejuni 81116 was then transformed with the resulting products to allow homologous recombination between genomic fragments present in the shuttle vector and the chromosome. Transformants were pooled and chromosomal DNA from these transformants was used to retransform C. jejuni 81116. This resulted in transformants containing the KmR cassette in the chromosome but lacking the vector. In order to evaluate this approach for the construction of a mutant bank, the KmR insertional mutants were screened for loss of motility. Partial characterization of 11 non-motile mutants indicated that the inserted genes are involved in motility. Four mutants had the KmR cassette inserted in genes involved in flagella biosynthesis, namely flaA/B, neuB and flgK, and produced incomplete or no flagella. Four mutants had the KmR cassette inserted in genes possibly involved in flagella motor function: pflA, fliM and orf1 downstream of the fliN gene. Three mutants had the KmR cassette inserted in genes that are homologous to genes encoding hypothetical proteins of Helicobacter pylori.
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Genetic analysis of the GcvA binding site in the gcvA control region
More LessThe GcvA protein both activates and represses the gcv operon and negatively regulates its own transcription. GcvA binds to three sites in the gcv control region and to one site in the gcvA control region; each of these binding sites contains the conserved 5bp DNA sequence 5′-CTAAT-3′. This report describes the role this DNA sequence plays in autoregulation and expression of gcvA. Through single base-pair mutations, the importance of three of these five basepairs in the autoregulation of gcvA expression is shown. Two of the gcvA control region mutations described cause a gcvA::lacZ fusion to be overexpressed at 9-24 times the wild-type level. The increase in expression is due in part to a complete loss of autoregulation and in part to a GcvA-independent mechanism. One of the mutants was shown by Western blot analysis to increase the intracellular concentration of GcvA. This high level of gcvA expression subsequently causes the loss of purine-mediated repression of a gcvT::lacZ fusion. However, overexpression of gcvR re-established purine-mediated repression of the gcvT::lacZ fusion, supporting the model for gcv regulation that suggests the need for a relatively constant GcvA to GcvR ratio for appropriate regulation of gcv expression in response to glycine and purine availability.
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A multidomain xylanase from a Bacillus sp. with a region homologous to thermostabilizing domains of thermophilic enzymes
More LessThe gene xynC encoding xylanase C from Bacillus sp. BP-23 was cloned and expressed in Escherichia coli. The nucleotide sequence of a 3538 bp DNA fragment containing xynC gene was determined, revealing an open reading frame of 3258 bp that encodes a protein of 120567 Da. A comparison of the deduced amino acid sequence of xylanase C with known β-glycanase sequences showed that the encoded enzyme is a modular protein containing three different domains. The central region of the enzyme is the catalytic domain, which shows high homology to family 10 xylanases. A domain homologous to family IX cellulose-binding domains is located in the C-terminal region of xylanase C, whilst the N-terminal region of the enzyme shows homology to thermostabilizing domains found in several thermophilic enzymes. Xylanase C showed an activity profile similar to that of enzymes from mesophilic microorganisms. Maximum activity was found at 45°C, and the enzyme was only stable at 55°C or lower temperatures. Xylotetraose, xylotriose, xylobiose and xylose were the main products from birchwood xylan hydrolysis, whilst the enzyme showed increasing activity on xylo-oligosaccharides of increasing length, indicating that the cloned enzyme is an endoxylanase. A deletion derivative of xylanase C, lacking the region homologous to thermostabilizing domains, was constructed. The truncated enzyme showed a lower optimum temperature for activity than the full-length enzyme, 35°C instead of 45°C, and a reduced thermal stability that resulted in a complete inactivation of the enzyme after 2 h incubation at 55°C.
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- Genomics
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Transcription of genes near the sspE locus of the Bacillus subtilis genome
More LessThe yfhP, yfhQ (mutY homologue), yfhS and yfhR (oxidoreductase homologue) genes, which are located upstream of the sspE locus, have been identified in the Bacillus subtilis genome. Transcriptional analysis showed that yfhP, yfhQ and yfhR are transcribed during the exponential growth phase, and sspE is monocistronically transcribed in the late sporulation phase and co-transcribed with yfhQ and/or yfhR during exponential growth. However, SspE was not translated during this period. Northern blot and primer extension analyses indicated that yfhS is transcribed by E·E during sporulation. No significant difference between wild-type and yfhS mutant strains was found in the rate of sporulation or germination, the heat tolerance of spores or the transcription of the sspE locus during sporulation. The transcription of the yfhP and yfhQ-yfhR-sspE loci increased 2.5- and 5.3-fold in a yfhP-deficient strain compared to the wild-type strain at t -2 (2 h before initiation of sporulation). In addition, transcription corresponding to the yfhR-sspE loci increased more than twofold with maximum values observed at t -15. These results suggest that YfhP may act as a negative regulator for the transcription of yfhQ, yfhR, sspE and yfhP.
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- Pathogenicity And Medical Microbiology
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Tracking adhesion factors in Staphylococcus caprae strains responsible for human bone infections following implantation of orthopaedic material
Ten Staphylococcus caprae strains isolated from four patients and responsible for bone infections following implantation of orthopaedic material were compared to four S. caprae strains collected from milk samples of healthy goats. The following characteristics were investigated: SmaI patterns, hybridization patterns with pBA2 (ribotypes), slime production, adhesion to matrix proteins (fibrinogen, fibronectin, collagen) and the staphylococcal adhesion genes (fnbA, clfA, cna, atlE, ica, fbe). None of the characteristics enabled us to distinguish the human strains from the goat strains. Slime was occasionally produced by S. caprae strains but all of them carried nucleotide sequences hybridizing at low stringency with the following genes: atIE encoding a S. epidermidis autolysin binding vitronectin and responsible for the primary adhesion to polystyrene, ica operon involved in the biosynthesis of a S. epidermidis extracellular polysaccharide, and the part of cIfA encoding the serine-aspartate repeated region of a S. aureus cell-wall fibrinogen-binding protein.
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Helicobacter pylori VacA cytotoxin associated with the bacteria increases epithelial permeability independently of its vacuolating activity
Polarized epithelial monolayers of Madin-Darby canine kidney (MDCK) cells were used to study the pathogenicity of Helicobacter pylori, with an emphasis on the effect of VacA. The adherence of H. pylori to MDCK monolayers resulted in a decrease in trans-epithelial resistance (TER) across the cell monolayer. Isogenic vacA mutants did not lower the TER, demonstrating that the effect is strictly linked to the action of the toxin. A similar effect was observed with all VacA-producing strains, including those producing m2 toxins that are inactive in the vacuolating assay. In contrast to that seen with purified toxin, TER decrease was not enhanced by acid pH, which may indicate that the toxin associated to the bacterial surface is possibly in a monomeric state and therefore does not require a pH-induced conformation to be active. These data raise the possibility that one role of VacA in ulcerogenesis may consist of increasing the paracellular permeability of the gastric epithelium.
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Characterization of apxlVA, a new RTX determinant of Actinobacillus pleuropneumoniae
A fourth type of RTX determinant was identified in Actinobacillus pleuropneumoniae and was designated apxlVA. When expressed in Escherichia coli, recombinant ApxlVA showed a weak haemolytic activity and cohaemolytic synergy with the sphingomyelinase (beta-toxin) of Staphylococcus aureus. These activities required the presence of an additional gene, ORF1, that is located immediately upstream of apxlVA. The apxlVA gene product could not be detected in A. pleuropneumoniae cultures grown under various conditions in vitro; however, pigs experimentally infected with A. pleuropneumoniae serotypes 1, 5 and 7 started to produce antibodies that reacted with recombinant ApxlVA 14 d post-infection, indicating that apxlVA is expressed in vivo. In addition, sera from pigs naturally and experimentally infected with any of the serotypes all reacted with recombinant ApxlVA. The apxlVA gene from the serotype 1 A. pleuropneumoniae type strain Shope 4074T encodes a protein with a predicted molecular mass of 202 kDa which has typical features of RTX proteins including hydrophobic domains in the N-terminal half and 24 glycine-rich nonapeptides in the C-terminal half that bind Ca2+. The glycine-rich nonapeptides are arranged in a modular structure and there is some variability in the number of modules in the ApxIVA proteins of different serotypes of A. pleuropneumoniae. The deduced amino acid sequences of the ApxlVA proteins have significant similarity with the Neisseria meningitidis iron-regulated RTX proteins FrpA and FrpC, and to a much lesser extent with other RTX proteins. The apxlVA gene could be detected in all A. pleuropneumoniae serotypes and seems to be species-specific. Although the precise role of this new RTX determinant in pathogenesis of porcine pleuropneumonia needs to be determined, apxlVA is the first in vivo induced toxin gene that has been described in A. pleuropneumoniae.
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- Physiology And Growth
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Growth inhibition of Clostridium cellulolyticum by an inefficiently regulated carbon flow
More LessCarbon flow in Clostridium cellulolyticum was investigated either in batch or continuous culture using a synthetic medium with cellobiose as the sole source of carbon and energy. Previous experiments carried out using a complex growth medium led to the conclusion that the carbon flow was stopped by intracellular NADH. In this study, results showed that cells cultured in a synthetic medium were better able to control electron flow since the NADH/NAD+ ratios were in the range 0.3-0.7, whereas a ratio as high as 57 was previously found in cells cultured on a complex medium. Furthermore, a specific rate of cellobiose consumption of 2.13 mmol (g cells)-1 h-1 was observed on synthetic medium whereas the highest value obtained on complex medium was 0.68 mmol (g cells)-1 h-1. When C. cellulolyticum was grown in continuous culture and cellobiose in the feed medium was increased from 5.84 to 17.57 mM in stepwise fashion, there was an increase in cellobiose utilization without growth inhibition. In contrast, when the reactor was fed directly with 14.62 mM cellobiose, residual cellobiose was observed (4.24 mM) and growth was limited. These data indicate that C. cellulolyticum is not able to optimize its growth and carbon flow in response to a sudden increase in the concentration of growth substrate cellobiose. This interpretation was confirmed (i) by the study of cellobiose batch fermentation where it was demonstrated that growth inhibition was not due to nutritional limitation or inhibition by fermentation products but was associated with carbon excess and (ii) by the growth of C. cellulolyticum in dialysis culture where no growth inhibition was observed due to the limitation of carbon flow by the low rate of cellobiose diffusion through the dialysis tubing.
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Restoration of inositol prototrophy in the fission yeast Schizosaccharomyces pombe
More LessThe biosynthesis of inositol requires only two enzymes, inositol-1-phosphate synthase (encoded by INO1) and an inositol monophosphatase, but the regulation of inositol biosynthesis is under multiple controls and is exquisitely regulated. In the budding yeast Saccharomyces cerevisiae, mutations in any of 26 different genes lead to inositol auxotrophy. The fission yeast Schizosaccharomyces pombe, however, is a natural inositol auxotroph. An investigation has been initiated to examine the possible reasons that might have led to inositol auxotrophy in Sch. pombe. Complementation with a genomic library of an inositol prototrophic yeast indicated that a Pichia pastoris INO1 gene alone could confer inositol prototrophy to Sch. pombe and that the gene was absent in Sch. pombe. To investigate possible reasons for the loss of INO1 gene in Sch. pombe, an attempt was made to disrupt inositol homeostasis in Sch. pombe by overproduction of intracellular inositol, but this did not lead to any discernible adverse effects. The sources of inositol in the natural environment of Sch. pombe were also examined. As the natural environment of Sch. pombe contains significant amounts of phytic acid (inositol hexaphosphate), an investigation was carried out and it was discovered that Sch. pombe can utilize phytic acid as a source of inositol under very specific conditions.
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Secretion of FK506/FK520 and rapamycin by Streptomyces inhibits the growth of competing Saccharomyces cerevisiae and Cryptococcus neoformans
More LessFK506 and rapamycin are immunosuppressants that inhibit signalling cascades required for T-cell activation, yet both are natural products of Streptomyces that live in the soil. FK506 and rapamycin also have potent antimicrobial activity against yeast and pathogenic fungi, suggesting a natural role in inhibiting growth of competing micro-organisms. The immunosuppressive and antimicrobial activities of FK506 and rapamycin are mediated by binding to the FKBP12 prolyl isomerase and the resulting FKBP12/FK506 and FKBP12/rapamycin complexes inhibit conserved protein targets, either the phosphatase calcineurin or the TOR (target of rapamycin) kinases, respectively. Streptomyces sp., ‘Streptomyces hygroscopicus subsp. ascomyceticus’ and Streptomyces hygroscopicus, which produce FK506, FK520 (also known as ascomycin, a C21 ethyl derivative of FK506) and rapamycin, respectively, produced toxins that inhibited the growth of competing cells of the yeast Saccharomyces cerevisiae and the pathogenic fungus Cryptococcus neoformans. Yeast and fungal mutants lacking FKBP12 or expressing dominant drug-resistant calcineurin or TOR mutants were resistant to FK506 and rapamycin, and to the toxins produced by Streptomyces. Streptomyces strains with mutations in the FK506 or rapamycin biosynthetic enzymes were impaired in toxin production. Finally, the toxins secreted by ‘S. hygroscopicus subsp. ascomyceticus’ and S. hygroscopicus promoted formation of FKBP12/calcineurin and FKBP12/TOR complexes in a two-hybrid assay and mutations that rendered calcineurin or TOR drug-resistant prevented interaction. These observations support the hypothesis that Streptomyces evolved to secrete FK506, FK520 and rapamycin as toxins to inhibit the growth of competing yeast and fungi.
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A comparison of the kinetics of plasmid transfer in the conjugation systems encoded by the F plasmid from Escherichia coli and plasmid pCF10 from Enterococcus faecalis
More LessQuantitative measurements of horizontal DNA transfer are critical if one wishes to address questions relating to ecology, evolution and the safe use of recombinant bacteria. Traditionally, the efficiency of a conjugation system has been described by its transfer frequency. However, transfer frequencies can be determined in many ways and may be sensitive to physical, chemical and biological conditions. In this study the authors have used the mechanistic similarity between bacterial conjugation and simple enzyme catalysis in order to calculate the maximal conjugation rate (V max) and the recipient concentration (K m) at which the conjugation rate is half its maximal value, for two different conjugation systems: the F plasmid from Escherichia coli and plasmid pCF10 from Enterococcus faecalis. The results are compared with the data obtained from the aggregation-mediated conjugation system encoded on pXO16 from Bacillus thuringiensis. The conjugation systems analysed are fundamentally different; however, they have some characteristics in common: they are able to sustain conjugative transfer in liquid medium and the transfer efficiencies are very high. Conjugation encoded by the F plasmid in E. coli involves the formation of small aggregates (2-20 cells), established by sex pili, and the plasmid's maximal conjugation rate was estimated to be approximately 0·15 transconjugants per donor per minute. Pheromone-induced conjugation in Ent. faecalis, which involves the formation of large aggregates, was found to proceed at a maximal conjugation rate of 0·29 transconjugants per donor per minute. Also, the K m value differed significantly between these conjugation systems; this may reflect the inherent differences in mating pair formation and transfer mechanisms. In these conjugation systems, the donors underwent a ‘recovery period’ between rounds of conjugative transfer and newly formed transconjugants required a period of about 40-80 min to mature into proficient donors.
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- Plant-Microbe Interactions
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Spore surface glycoproteins of Colletotrichum lindemuthianum are recognized by a monoclonal antibody which inhibits adhesion to polystyrene
Conidia (spores) of Colletotrichum lindemuthianum, a fungal plant pathogen causing bean anthracnose, adhere to the aerial parts of host plants to initiate the infection process. These spores possess a fibrillar' spore coat' as well as a cell wall. In a previous study a mAb, UB20, was raised that recognized glycoproteins on the spore surface. In this study UB20 was used to localize and characterize these glycoproteins and to investigate their possible role in adhesion. Glycoproteins recognized by UB20 were concentrated on the outer surface of the spore coat and, to a lesser extent, at the plasma membrane/cell wall interface. Extraction of spores with hot water or 0-2% SDS resulted in removal of the spore coat. Western blotting with UB20 showed that a relatively small number of glycoproteins were extracted by these procedures, including a major component at 110 kDa. Biotinylation of carbohydrate moieties, together with cell fractionation, confirmed that these glycoproteins were exposed at the surface of the spores. In adhesion assays, < 90% of ungerminated conidia attached to polystyrene Petri dishes within 30 min. UB20 IgG at low concentrations inhibited attachment in an antigen-specific manner. This suggests that the glycoproteins recognized by this mAb may function in the initial rapid attachment of conidia to hydrophobic substrata. Polystyrene microspheres bound selectively to the 110 kDa glycoprotein in Western blots, providing further evidence that this component could mediate interactions with hydrophobic substrata.
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Isolation of the gene encoding an immunodominant membrane protein of the apple proliferation phytoplasma, and expression and characterization of the gene product
An immunodominant membrane protein (IMP) of the apple proliferation (AP) phytoplasma was detected in preparations from AP-diseased periwinkle plants using monoclonal and polyclonal antibodies to the AP agent. Following isolation from Western blots and partial sequencing, degenerate oligonucleotides derived from the IMP sequence were used as probes to identify a DNA fragment containing the ORF encoding the IMP. Complete sequencing and subsequent analysis of the cloned DNA fragment revealed the presence of two ORFs, predicted to encode proteins with molecular masses of 25 kDa (P-318A) and 19 kDa (P-318B). Whilst database searches failed to assign a possible function to P-318A, analysis of P-318B predicted an amphiphilic membrane protein with a positively charged N-terminal portion, followed by a hydrophobic segment forming an α-helix, and a hydrophilic C-terminal part located outside of the cell. The amphiphilic nature of P-318B was confirmed by its solubility in Triton X-114. The gene encoding P-318B was expressed in Escherichia coli and the resulting protein was used to immunize rabbits. The antiserum obtained reacted specifically with P-318B. The same protein was also detected by an antiserum raised against antigen preparations from APdiseased plants. The P-318B antiserum did not react with antigen preparations from plants infected with the closely related pear decline phytoplasma. However, in Southern hybridization studies, the gene encoding the IMP hybridized to genomic fragments of the pear decline and European stone fruit yellows phytoplasmas. It also showed significant sequence similarity to a gene encoding an antigenic membrane protein of the sweet potato witches' broom phytoplasma, but not to a gene encoding a major immunogenic membrane protein of an aster yellows group phytoplasma. Since it appears that most phytoplasmas possess a major immunogenic membrane protein which may have a function in pathogenesis, this work may be a basis for further studies on fundamental aspects of host-pathogen interactions. It also describes a new approach to obtain suitable immunogens to produce specific antibodies for detection and characterization of the non-culturable phytoplasmas.
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Erwinia carotovora DsbA mutants: evidence for a periplasmic-stress signal transduction system affecting transcription of genes encoding secreted proteins
More LessThe dsbA genes, which encode major periplasmic disulfide-bond-forming proteins, were isolated from Erwinia carotovora subsp. carotovora (Ecc) and Erwinia carotovora subsp. atroseptica (Eca), and the dsbC gene, encoding another periplasmic disulfide oxidoreductase was isolated from Ecc. All three genes were sequenced and mutants deficient in these genes were created by marker exchange mutagenesis. The Ecc mutants were severely affected in activity and secretion of pectate lyase, probably due to the absence of functional PelC, which is predicted to require disulfide bond formation to achieve its correct conformation prior to secretion across the outer membrane. Similarly, endopolygalacturonase, also predicted to possess disulfide bonds, displayed reduced activity. The major Ecc cellulase (CeIV) does not contain cysteine residues and was still secreted in dsbA-deficient strains. This observation demonstrated unequivocally that the localization and activity of the individual components of the Out apparatus are independent of disulfide bond formation. Surprisingly, cellulase activity was shown to be increased ~ two- to threefold in the DsbA mutant. This phenomenon resulted from transcriptional up-regulation of cel/V gene expression. In contrast, transcription of both pe/C and peh were down-regulated in dsbA-deficient strains when compared to the wild-type. Protease (Prt) activity and secretion were unaffected in the Ecc dsbA mutant. Prt activity was considerably reduced in the double dsbA dsbC mutant. However Prt was secreted normally in this strain. The Eca dsbA mutant was found to be non-motile, suggesting that disulfide bond formation is essential for motility in this strain. All of the dsb mutants showed reduced tissue maceration in planta. These results suggest that a feedback regulation system operates in Ecc. In this system, defects in periplasmic disulfide bond formation act as a signal which is relayed to the transcription machinery regulating gene expression in diverse ways.
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Isolation of an extracellular protease gene of Erwinia carotovora subsp. carotovora strain SCC3193 by transposon mutagenesis and the role of protease in phytopathogenicity
More LessUsing mini-Tn5CmR:: gusA, a transposon that allows transcriptional fusions to a promoterless β-glucuronidase gene, a mutant of Erwinia carotovora subsp. carotovora SCC3193 deficient in extracellular protease production and soft-rot pathogenicity in plants was isolated. The mutant, designated SCC6004, produced normal levels of pectate lyase, polygalacturonase and cellulase. The region of the transposon insertion was partially sequenced to permit the design of specific oligonucleotide primers to amplify a 2·7 kb Clal fragment from E. carotovora subsp. carotovora SCC3193. The DNA sequence of the cloned fragment contained two complete and one partial ORFs. One of the complete ORFs (ORF1) was designated prtW and encodes a secreted protease. The deduced amino acid sequence of PrtW showed a high overall identity of 60-66% to the previously described Erwinia chrysanthemi proteases, but no homology to other proteases isolated from different E. carotovora strains. Downstream from ORF1, a further complete ORF (ORF2) and a partial ORF (ORF3) were found, with deduced peptide sequences that have significant similarity to the Inh and PrtD proteins, respectively, from E. chysanthemi, which are involved in protease secretion. Gene fusion to the gusA reporter was employed to characterize the regulation of prtW. The prtW gene was found to be strongly induced in the presence of plant extracts. The mutant exhibited reduced virulence, suggesting that PrtW enhances the ability of strain SCC3193 to macerate plant tissue.
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- Systematics And Evolution
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Phylogenetic analysis and rapid identification of Candida dubliniensis based on analysis of ACT1 intron and exon sequences
More LessThe phylogenetic position of Candida dubliniensis has previously been established on the basis of the sequence of rRNA genes. In order to confirm the relationship between C. dubliniensis and other yeast species, particularly Candida albicans, using non-rRNA gene sequences the ACT1 gene was chosen for analysis. Three overlapping fragments that together span the entire C. dubliniensis ACT1 gene (CdACT1) were amplified from a recombinant phage isolated from a genomic DNA λ library using PCR. These were cloned and used to determine the contiguous sequence of the gene. Analysis of the sequence data revealed the presence of a 1131 bp ORF interrupted by a single 632 bp intron at the 5′ extremity of the gene. Comparison of the CdACT1 sequence with the C. albicans homologue (CaACT1) revealed that although the exons are 97.9% identical the introns are only 83.4% identical. Phylogenetic trees generated using ACT1 exon and intron sequences from a range of yeast species unequivocally confirmed the phylogenetic position of C. dubliniensis as a unique taxon within the genus Candida. Analysis of the ACT1-associated intron sequences from 10 epidemiologically unrelated C. dubliniensis isolates from disparate geographical locations showed a very low level of intraspecies sequence variation. In order to develop an accurate and rapid method to identify C. dubliniensis from primary isolation plates the significant divergence between the C. dubliniensis and C. albicans ACT1 intron sequences was exploited by designing C. dubliniensis-specific PCR primers. Using a rapid boiling method to produce template DNA directly from colonies from primary isolation plates in 10 min, these primers were used in a blind test with 122 isolates of C. dubliniensis, 53 isolates of C. albicans, 10 isolates of C. stellatoidea and representative isolates of other clinically relevant Candida and other yeast species. Only the C. dubliniensis isolates yielded the C. dubliniensis-specific 288 bp amplimer. Use of this technique on colonies suspected to be C. dubliniensis allows their correct identification as C. dubliniensis in as little as 4 h.
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Volume 16 (1957)
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Volume 15 (1956)
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Volume 14 (1956)
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Volume 13 (1955)
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Volume 12 (1955)
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Volume 11 (1954)
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Volume 10 (1954)
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Volume 9 (1953)
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Volume 8 (1953)
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Volume 7 (1952)
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Volume 6 (1952)
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Volume 5 (1951)
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Volume 4 (1950)
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Volume 3 (1949)
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Volume 2 (1948)
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Volume 1 (1947)