雷氏普罗威登斯菌青霉素G酰化酶基因在大肠杆菌中的克隆与表达

利用PCR和分子克隆技术从雷氏普罗威登斯菌（Prouidencia rettgeri)(ATCC29944)的基因组DNA中获得一个青霉素G酰化酶（penicillinGacylase,PGA)基因并将其装入表达质粒pET24a。携带有重组质粒pETPGA的Escherichia coli基因工程菌BL21（DE3）/pETPGA实现了PGA的高效表达,对发酵条件的研究表明基因工程菌在24℃,添加5g/L甘油条件下以1.0mmol/LIPTG诱导1.5h酶活力即达到993.4U/L,比野生菌酶活力（15U/L）提高了66倍。     

Analysis of altered protein expression patterns of Chlamydia pneumoniae by an integrated proteome-works system

We have identified, analyzed, and quantified differential protein expression profile of five C. pneumoniae proteins, Adk (adenylate kinase), AhpC (thiol-specific antioxidant), CrpA (15 KD cysteine rich protein), Map (methionine aminopeptidae), and Cpn0710 (hypothetical protein) under normal versus persistent growth conditions induced by interferon-gamma, at different time intervals of their replicative cycle by successfully employing the latest proteomic analysis tool, PDQuest 2-D analysis software. We have also determined that this software represents a reliable analytical tool for mapping protein expression patterns in C. pneumoniae.     

The galU gene expression in Streptococcus pneumoniae

Bacillus subtilis possesses carbon-flux regulating histidine protein (Crh), a paralog of the histidine protein (HPr) of the phosphotransferase system (PTS). Like HPr, Crh becomes (de)phosphorylated in vitro at residue Ser46 by the metabolite-controlled HPr kinase/phosphorylase HPrK/P. Depending on its phosphorylation state, Crh exerts regulatory functions in connection with carbohydrate metabolism. So far, knowledge on phosphorylation of Crh in vivo has been limited and derived from indirect evidence. Here, we studied the dynamics of Crh phosphorylation directly by non-denaturing gel electrophoresis followed by Western analysis. The results confirm that HPrK/P is the single kinase catalyzing phosphorylation of Crh in vivo. Accordingly, phosphorylation of Crh is triggered by the carbon source as observed previously for HPr, but with some differences. Phosphorylation of both proteins occurred during exponential growth and disappeared upon exhaustion of the carbon source. During exponential growth, ~80% of the Crh molecules were phosphorylated when cells utilized a preferred carbon source. The reverse distribution, i.e. around 20% of Crh molecules phosphorylated, was obtained upon utilization of less favorable substrates. This clear-cut classification of the substrates into two groups has not previously been observed for HPr(Ser)~P formation. The likely reason for this difference is the additional PTS-dependent phosphorylation of HPr at His15, which limits accumulation of HPr(Ser)~P.     

Regulation of tryptophan synthase gene expression in Chlamydia trachomatis

We previously reported that Chlamydia trachomatis expresses the genes encoding tryptophan synthase (trpA and trpB). The results presented here indicate that C. trachomatis also expresses the tryptophan repressor gene (trpR). The complement of genes regulated by tryptophan levels in C. trachomatis is limited to trpBA and trpR. trp gene expression was repressed if chlamydiae-infected HeLa cells were cultured the presence of tryptophan and induced if grown in tryptophan-depleted medium or in the presence of IFN-gamma. Furthermore, expression of the trp genes in strains which encode a functional tryptophan synthase is repressed when infected cells are cultured in the presence of the tryptophan precursor indole. Results from experiments with cycloheximide, an inhibitor of eukaryotic protein synthesis, indicate that in addition to the absolute size of the intracellular tryptophan pool, host competition for available tryptophan plays a key role in regulating expression of the trp genes. The tryptophan analogue, 5-fluorotryptophan, repressed trp gene expression and induced the formation of aberrant organisms of C. trachomatis. The growth-inhibitory properties of 5-fluorotryptophan could be reversed with exogenous tryptophan but not indole. In total, our results indicate that the ability to regulate trp gene expression in response to tryptophan availability is advantageous for the intracellular survival of this organism. Furthermore, the fact that C. trachomatis has retained the capacity to respond to tryptophan limitation supports the view that the in vivo antichlamydial effect of IFN-gamma is via the induction of the tryptophan-degrading enzyme, indoleamine 2,3-dioxygenase.     

Chlamydia pneumoniae respiratory infections in Taiwan

To understand the epidemiology of Chlamydia pneumoniae acute infections in Taiwan, we collected 116 paired and 244 single sera from patients suspected of C. pneumoniae infection and conducted microimmunofluorescence test. Eighty-three patients (83/360, 23%) met the diagnostic criteria of current C. pneumoniae infection. The C. pneumoniae infections were significantly higher in men than in women (P< or =0.0001) and were most frequent in the group of 40-49 year-olds, and the people older than 70 years old. C. pneumoniae infection often occurred in the late autumn lasting to the cold winter and in the transition period between the spring and summer.     

Intrastrain and interstrain genetic variation within a paralogous gene family in Chlamydia pneumoniae

Background

Chlamydia pneumoniae causes human respiratory diseases and has recently been associated with atherosclerosis. Analysis of the three recently published C. pneumoniae genomes has led to the identification of a new gene family (the Cpn 1054 family) that consists of 11 predicted genes and gene fragments. Each member encodes a polypeptide with a hydrophobic domain characteristic of proteins localized to the inclusion membrane.

Results

Comparative analysis of this gene family within the published genome sequences provided evidence that multiple levels of genetic variation are evident within this single collection of paralogous genes. Frameshift mutations are found that result in both truncated gene products and pseudogenes that vary among isolates. Several genes in this family contain polycytosine (polyC) tracts either upstream or within the terminal 5' end of the predicted coding sequence. The length of the polyC stretch varies between paralogous genes and within single genes in the three genomes. Sequence analysis of genomic DNA from a collection of 12 C. pneumoniae clinical isolates was used to determine the extent of the variation in the Cpn 1054 gene family.

Conclusions

These studies demonstrate that sequence variability is present both among strains and within strains at several of the loci. In particular, changes in the length of the polyC tract associated with the different Cpn 1054 gene family members are common within each tested C. pneumoniae isolate. The variability identified within this newly described gene family may modulate either phase or antigenic variation and subsequent physiologic diversity within a C. pneumoniae population.     

Tissue-specific Salmonella Typhimurium gene expression during persistence in pigs

Salmonellosis caused by Salmonella Typhimurium is one of the most important bacterial zoonotic diseases. The bacterium persists in pigs resulting in asymptomatic 'carrier pigs', generating a major source for Salmonella contamination of pork. Until now, very little is known concerning the mechanisms used by Salmonella Typhimurium during persistence in pigs. Using in vivo expression technology (IVET), a promoter-trap method based on ΔpurA attenuation of the parent strain, we identified 37 Salmonella Typhimurium genes that were expressed 3 weeks post oral inoculation in the tonsils, ileum and ileocaecal lymph nodes of pigs. Several genes were expressed in all three analyzed organs, while other genes were only expressed in one or two organs. Subsequently, the identified IVET transformants were pooled and reintroduced in pigs to detect tissue-specific gene expression patterns. We found that efp and rpoZ were specifically expressed in the ileocaecal lymph nodes during Salmonella peristence in pigs. Furthermore, we compared the persistence ability of substitution mutants for the IVET-identified genes sifB and STM4067 to that of the wild type in a mixed infection model. The ΔSTM4067::kanR was significantly attenuated in the ileum contents, caecum and caecum contents and faeces of pigs 3 weeks post inoculation, while deletion of the SPI-2 effector gene sifB did not affect Salmonella Typhimurium persistence. Although our list of identified genes is not exhaustive, we found that efp and rpoZ were specifically expressed in the ileocaecal lymph nodes of pigs and we identified STM4067 as a factor involved in Salmonella persistence in pigs. To our knowledge, our study is the first to identify Salmonella Typhimurium genes expressed during persistence in pigs.     

Ultrastructure of Chlamydia pneumoniae in cell culture

The electron microscopic appearance of Chlamydia pneumoniae elementary bodies with pear-shaped, loose outer membrane has been suggested as one criterion of its classification as a new chlamydial species. The study of the original strain TW 183 in LCL 929 and HL cells and a low-passage isolate of Kajaani-6 isolate in HL cells revealed spherical compact elementary bodies common to other chlamydia.     

Differential expression of Pmp10 in cell culture infected with Chlamydia pneumoniae CWL029

The complete genome of Chlamydia pneumoniae contains a total of 21 genes encoding polymorphic membrane proteins (Pmp). From this large Pmp family three genes, pmp8, pmp10 and pmp11, were cloned and antibodies against recombinant full-length Pmp proteins were produced. Indirect immunofluorescence microscopy of HEp-2 cells infected with C. pneumoniae CWL029 was performed with the Pmp antibodies in combination with a Chlamydia-specific anti-lipopolysaccharide (LPS) antibody. This double staining technique clearly showed that expression of Pmp10 was differential. Additional double staining with monoclonal antibodies to the surface of C. pneumoniae elementary bodies and the anti-LPS antibody resulted in identification of seven monoclonal antibodies that reacted identically to the Pmp10 antibody indicating that Pmp10 is an immunodominant protein. Finally, the molecular mechanism responsible for differential expression is suggested to be variation in the guanine residues in the polyG tract of pmp10.     

Molecular cloning of the penicillin G acylase gene from Arthrobacter viscosus

Penicillin G acylase was purified from the cultured filtrate of Arthrobacter viscosus 8895GU and was found to consist of two distinct subunits with apparent molecular weights of 24,000 (alpha) and 60,000 (beta). The partial N-terminal amino acid sequences of the alpha and beta subunits were determined with a protein gas phase sequencer, and a 29-base oligonucleotide corresponding to the partial amino acid sequence of the alpha subunit was synthesized. An Escherichia coli transformant having the penicillin G acylase gene was isolated from an A. viscosus gene library by hybridization with the 29-base probe. The resulting positive clone was further screened by the Serratia marcescens overlay technique. E. coli carrying a plasmid designated pHYM-1 was found to produce penicillin G acylase in the cells. This plasmid had an 8.0-kilobase pair DNA fragment inserted in the EcoRI site of pACYC184.     

Continuous penicillin G hydrolysis in an electro-membrane reactor with immobilized penicillin G acylase

Penicillin G (2%, w/v in phosphate buffer, pH 8) was hydrolysed in a flow-through, miniature electro-membrane reactor with the penicillin G acylase immobilized in 5% (w/v) polyacrylamide (diam. 10 mm, thickness 2.6 mm, enzyme activity 24 U ml^–1). The conversion of penicillin G increased from 0.15 to almost 0.5 when the electric current applied to the reactor was changed from –600 to +600 A/m² with a substrate residency of 1 h. Symbols and abbreviations c _j ^p & concentration of component j in product stream (M) c _j ^s & concentration of component j in substrate stream (M) c _s ^o & substrate concentration at reactor inlet (M) C _j ^p=c _j ^p/c _S ⁰ & scaled concentration of component j in product stream C _j ^s=c _j ^s/c _S ⁰ & scaled concentration of component j in substrate stream i & electric current density (A/m²) j & reaction component, j P, Q or S P & main reaction product (6-aminopenicillanic acid) PGA & penicillin G acylase Q & side reaction product (phenylacetic acid) S & substrate (penicillin G) Y _s=C _P ^s+C _P ^p & substrate conversion & mean residence time of substrate and product streams in reactor (h) =C _Q ^s+C _Q ^p+C _S ^s+C _S ^s & check-sum of scaled concentrations =C _P ^p/(C _P ^s+C _P ^p) & separation factor of 6-aminopenicillanic acid (0 1)     

Enhancing enzymatic activity of penicillin G acylase by coexpressing pcm gene

Penicillin G acylase (PGA; E.C. 3.5.1.11) is an important enzyme which has broad applications in industries of β-lactim antibiotics production. In this study, a promising PGA gene from Alcaligenes faecalis (afpga) and another pcm gene encoding protein isoaspartate methyltransferase (PIMT) were constructed into pET43.1a⁽⁺⁾ and pET28a⁽⁺⁾, respectively. The recombinant plasmids pETAFPGA and pETPCM were transformed into the same host cell Escherichia coli BL21 (DE3). Results suggested that the two plasmids could peacefully exist in the host cell and the two genes could be efficiently expressed after induction. The product of pcm gene could function as a helper molecule for enzyme AFPGA. PIMT increased the enzymatic activities in supernatant of ferment broth (1.6 folds) and cell lysate (1.8 folds), while it did not significantly affect the expression level of penicillin G acylase.     

Cloning, expression, and characterization of uracil-DNA glycosylase of Chlamydia pneumoniae in Escherichia coli

A uracil-DNA glycosylase gene was cloned from Chlamydia pneumoniae AR39 and expressed in E. coli strains BL21 (DE3) and BL21 (DE3) pLysS. After purification by Ni-NTA His x Bind Resin and DEAE Sepharose Fast Flow column chromatography, recombinant CpUDG with a specific activity of 1,000,000 U/mg was obtained. The enzymatic activity of the purified CpUDG protein was further characterized using oligodeoxyribonucleotides carrying uracil bases as substrates. The base opposite to uracil in double strand DNAs affected uracil removal efficiencies in the order: U/- > U/T > U/C > U/G > U/A. Free uracil and abasic sites (AP site) could inhibit the reaction. The optimal temperature and pH for uracil removal by CpUDG were 37 degrees C and pH 8.0, respectively. Site-directed mutagenesis studies indicated that amino acids D77, H200, and A205 were important for the catalytic activity of CpUDG. Together, these data suggest that CpUDG is a member of the UDG family-I protein. This is the first report on cloning, expression, and characterization of Chlamydia uracil-DNA glycosylase.     

Genome sequences of Chlamydia trachomatis MoPn and Chlamydia pneumoniae AR39

The genome sequences of Chlamydia trachomatis mouse pneumonitis (MoPn) strain Nigg (1 069 412 nt) and Chlamydia pneumoniae strain AR39 (1 229 853 nt) were determined using a random shotgun strategy. The MoPn genome exhibited a general conservation of gene order and content with the previously sequenced C.trachomatis serovar D. Differences between C.trachomatis strains were focused on an ~50 kb ‘plasticity zone’ near the termination origins. In this region MoPn contained three copies of a novel gene encoding a >3000 amino acid toxin homologous to a predicted toxin from Escherichia coli 0157:H7 but had apparently lost the tryptophan biosyntheis genes found in serovar D in this region. The C.pneumoniae AR39 chromosome was >99.9% identical to the previously sequenced C.pneumoniae CWL029 genome, however, comparative analysis identified an invertible DNA segment upstream of the uridine kinase gene which was in different orientations in the two genomes. AR39 also contained a novel 4524 nt circular single-stranded (ss)DNA bacteriophage, the first time a virus has been reported infecting C.pneumoniae. Although the chlamydial genomes were highly conserved, there were intriguing differences in key nucleotide salvage pathways: C.pneumoniae has a uridine kinase gene for dUTP production, MoPn has a uracil phosphororibosyl transferase, while C.trachomatis serovar D contains neither gene. Chromosomal comparison revealed that there had been multiple large inversion events since the species divergence of C.trachomatis and C.pneumoniae, apparently oriented around the axis of the origin of replication and the termination region. The striking synteny of the Chlamydia genomes and prevalence of tandemly duplicated genes are evidence of minimal chromosome rearrangement and foreign gene uptake, presumably owing to the ecological isolation of the obligate intracellular parasites. In the absence of genetic analysis, comparative genomics will continue to provide insight into the virulence mechanisms of these important human pathogens.     

<Emphasis Type="Italic">Chlamydia trachomatis</Emphasis>responds to heat shock,penicillin induced persistence,and IFN-gamma persistence by altering levels of the extracytoplasmic stress response protease HtrA

Background  

Chlamydia trachomatis, an obligate intracellular human pathogen, is the most prevalent bacterial sexually transmitted infection worldwide and a leading cause of preventable blindness. HtrA is a virulence and stress response periplasmic serine protease and molecular chaperone found in many bacteria. Recombinant purified C. trachomatis HtrA has been previously shown to have both activities. This investigation examined the physiological role of Chlamydia trachomatis HtrA.