Biochemical and molecular analysis of phospholipase C and phospholipase D activity in mycobacteria

Resurgence of mycobacterial infections in the United States has led to an intense effort to identify potential virulence determinants in the genus Mycobacterium, particularly ones that would be associated with the more virulent species (e.g., Mycobacterium tuberculosis). Thin-layer chromatography (TLC) using radiolabeled phosphatidylcholine and sphingomyelin as substrates indicated that cell extracts of M. tuberculosis contain both phospholipase C (PLC) and phospholipase D (PLD) activities. In contrast, only PLD activity was detected in cell extracts of M. smegmatis. Neither activity was detected in cell-free culture supernatants from these organisms. We and others recently identified two open reading frames in M. tuberculosis with the potential to encode proteins which are highly homologous to the nonhemolytic (PlcN) and hemolytic (PlcH) phospholipase C enzymes of Pseudomonas aeruginosa. In contrast to the plc genes in P. aeruginosa, which are considerably distal to each other (min 34 and 64 on the chromosome), the mycobacterial genes, designated mpcA and mpcB, are tandemly arranged in the same relative orientation and separated by only 191 bp. Both the mpcA and the mpcB genes were individually cloned in M. smegmatis, and PLC activity was expressed from each gene in this organism. Hybridization experiments using the mpcA and the mpcB genes as probes under conditions of moderate stringency identified sequences homologous to these genes in M. bovis, M. bovis BCG, and M. marinum but not in several other Mycobacterium species, including M. smegmatis, M. avium, and M. intracellulare. TLC analysis using radiolabeled substrates indicated that M. bovis and M. marinum cell extracts contain PLC and PLD activities, but only PLD activity was detected in M. bovis BCG cell extracts. Sphingomyelinase activity was also detected in whole-cell extracts of M. tuberculosis, M. marinum, M. bovis, and M. bovis BCG, but this activity was not detected in extracts of M. smegmatis. Sphingomyelinase activity was detected in cell extracts from M. smegmatis harboring either recombinant mpcA or mpcB. These data indicate that PLC and sphingomyelinase activities are associated with the most virulent mycobacterial species, while PLD activity was detected in both virulent and saprophytic strains.

Role of Pseudomonas aeruginosa lipase in inflammatory mediator release from human inflammatory effector cells (platelets, granulocytes, and monocytes

Previously, we have shown that Pseudomonas aeruginosa lipase and phospholipase C (PLC), two extracellular lipolytic enzymes, interact with each other during 12-hydroxyeicosatetraenoic acid (HETE) generation from human platelets. In this regard. the addition of purified P. aeruginosa lipase to PLC-containing crude P. aeruginosa culture supernatants enhances the generation of the chemotactically active 12-HETE from human platelets. Therefore, we analyzed the interaction of purified P. aeruginosa lipase and purified hemolytic P. aeruginosa PLC with regard to inflammatory mediator release from human platelets, neutrophilic and basophilic granulocytes, and monocytes. Purified P. aeruginosa PLC, but not purified lipase by itself, induced 12-HETE generation from human platelets, the generation of leukotriene B4 (LTB4) and oxygen metabolites, enzyme release from human neutrophils, and histamine release from basophils but diminished interleukin-8 (IL-8) release from human monocytes in a dose-dependent manner. The addition of purified lipase enhanced PLC-induced 12-HETE and LTB4 generation, did not influence enzyme, histamine, or IL-8 release, but diminished the PLC-induced chemiluminescent response. Similar results were obtained when the hemolytic PLC from Clostridium perfringens was used instead of P. aeruginosa PLC. For further comparison, we used the well-defined calcium ionophore A23187 and phorbol-12-myristate-13-acetate (PMA) as stimuli. Lipase enhanced calcium ionophore-induced LTB4 generation and beta-glucuronidase release but reduced calcium ionophore-induced and PMA-induced chemiluminescence. In parallel, we analyzed the role of lipase in a crude P. aeruginosa culture supernatant containing PLC and lipase. Lipase activity in the P. aeruginosa culture supernatant was inhibited by treatment with the lipase-specific inhibitor hexadecylsulfonyl fluoride, leaving the activity of PLC unaffected. The capacity of "lipase-inactivated culture supernatant" to induce 12-HETE and LTB4 generation was diminished by 50 to 100%. Our results suggest that the simultaneous secretion of lipase and PLC by P. aeruginosa residing in an infected host may result in severe pathological effects which cannot be explained by the sole action of the individual virulence factor on inflammatory effector cells.

Isolation and characterization of a Pseudomonas aeruginosa gene, ptxR, which positively regulates exotoxin A production

Exotoxin A production in Pseudomonas aeruginosa is a complicated and highly regulated process that involves several genes. In this report, we describe the isolation of a new toxA regulatory gene (ptxR) which affects exotoxin A production in P. aeruginosa. In an iron-deficient medium, the presence of a plasmid carrying ptxR in P. aeruginosa PAO1 resulted in a four-to fivefold increase in exotoxin A synthesis. No effect was observed on the levels of elastase, phospholipase C, exoenzyme S, and alkaline protease. Using subcloning and complementation experiments, ptxR was localized to a 2.1 kb Kpnl-Bg/II fragment. Nucleotide sequence analysis revealed the presence of an open reading frame which encodes a 34.97 kDa protein (PtxR). The size of the predicted PtxR compares closely with the 34 kDa PtxR that was synthesized in Escherichia coli using the T7 expression system. The deduced amino acid sequence of PtxR is homologous to that of several members of the LysR family of transcriptional activators. The amino-terminus region of PtxR contains a putative helix-turn-helix DNA-binding motif. Specific ptxR-deletion mutants in P. aeruginosa strains PAO1 and PA103 were constructed. In comparison with their parent strains, both mutants showed a significant reduction in the level of exotoxin A activity. However, upon extensive subculturing, the level of exotoxin A produced by the PAO1::ptxR mutant was similar to that of PAO1. Transcriptional studies, using both toxA-lacZ fusion and RNA analysis, confirmed that ptxR increases toxA and regA transcription. These results suggest that ptxR regulates (through regA) exotoxin A production at the transcriptional level.

Ferric uptake regulator (Fur) mutants of Pseudomonas aeruginosa demonstrate defective siderophore-mediated iron uptake, altered aerobic growth, and decreased superoxide dismutase and catalase activities

Pseudomonas aeruginosa is considered a strict aerobe that possesses several enzymes important in the disposal of toxic oxygen reduction products including iron- and manganese-cofactored superoxide dismutase and catalase. At present, the nature of the regulation of these enzymes in P. aeruginosa Is not understood. To address these issues, we used two mutants called A4 and C6 which express altered Fur (named for ferric uptake regulation) proteins and constitutively produce the siderophores pyochelin and pyoverdin. Both mutants required a significant lag phase prior to log-phase aerobic growth, but this lag was not as apparent when the organisms were grown under microaerobic conditions. The addition of iron salts to mutant A4 and, to a greater extent, C6 cultures allowed for an increased growth rate under both conditions relative to that of bacteria without added iron. Increased manganese superoxide dismutase (Mn-SOD) and decreased catalase activities were also apparent in the mutants, although the second catalase, KatB, was detected in cell extracts of each fur mutant. Iron deprivation by the addition of the iron chelator 2,2'-dipyridyl to wild-type bacteria produced an increase in Mn-SOD activity and a decrease in total catalase activity, similar to the fur mutant phenotype. Purified wild-type Fur bound more avidly than mutant Fur to a PCR product containing two palindromic 19-bp "iron box" regions controlling expression of an operon containing the sodA gene that encodes Mn-SOD. All mutants were defective in both ferripyochelin- and ferripyoverdin-mediated iron uptake. Two mutants of strain PAO1, defective in pyoverdin but not pyochelin biosynthesis, produced increased Mn-SOD activity. Sensitivity to both the redox-cycling agent paraquat and hydrogen peroxide was greater in each mutant than in the wild-type strain. In summary, the results indicate that mutations in the P. aeruginosa fur locus affect aerobic growth and SOD and catalase activities in P. aeruginosa. We postulate that reduced siderophore-mediated iron uptake, especially that by pyoverdin, may be one possible mechanism contributing to such effect.

Gene repression by the ferric uptake regulator in Pseudomonas aeruginosa: cycle selection of iron-regulated genes

The expression of at least 24 distinct genes of Pseudomonas aeruginosa PAO1 is under direct control of the "ferric uptake regulator" (Fur). Novel targets of the Fur protein were isolated in a powerful SELEX (systematic evolution of ligands by exponential enrichment)-like cycle selection consisting of in vitro DNA-Fur interaction, binding to anti-Fur antibody, purification on protein G, and PCR amplification. DNA fragments obtained after at least three exponential enrichment cycles were cloned and subjected to DNA mobility-shift assays and DNase I footprint analyses to verify the specific interaction with the Fur protein in vitro. Iron-dependent expression of the corresponding genes in vivo was monitored by RNase protection analysis. In total, 20 different DNA fragments were identified which represent actual Pseudomonas iron-regulated genes (PIGs). While four PIGs are identical to already known genes (pfeR, pvdS, tonB, and fumC, respectively), 16 PIGs represent previously unknown genes. Homology studies of the putative proteins encoded by the PIGs allowed us to speculate about their possible function. Two PIG products were highly similar to siderophore receptors from various species, and three PIG products were significantly homologous to alternative sigma factors. Furthermore, homologs of the Escherichia coli ORF1-tolQ, nuoA, stringent starvation protein Ssp, and of a two-component regulatory system similar to the Pseudomonas syringae LemA sensor kinase were identified. The putative gene products of seven additional PIGs did not show significant homologies to any known proteins. The PIGs were mapped on the P.aeruginosa chromosome. Their possible role in iron metabolism and virulence of P. aeruginosa is discussed.

Comparative usefulness of ribotyping, exotoxin A genotyping, and SalI restriction fragment length polymorphism analysis for Pseudomonas aeruginosa lineage assessment

Ribotyping, exotoxin A genotyping (EAGP), and restriction fragment length polymorphism (RFLP) analysis of total DNA with SalI (SalI RFLP) were compared for intraspecies discrimination of 93 Pseudomonas aeruginosa isolates. Type-ability of all methods was 100% and the results of typing with each method remained unchanged during laboratory manipulation. Clonal groups defined with each molecular method were largely coincident and, in those cases where inconsistencies were detected, isolates were analyzed by transverse alternating field gel electrophoresis (TAFE) and arbitrarily primed polymerase chain reaction (AP-PCR). SalI RFLP analysis was highly discriminative so as to distinguish unrelated isolates of close lineage. However, it was not a good method to identify isolates of unrelated lineage because SalI RFLP appeared to be subjected to convergent evolution. The index of discrimination suggested by Hunter and Gaston was determined to assess the discriminatory power of the molecular methods utilized either alone or in several combinations. Combined use of ribotyping and SalI RFLP analysis reached the highest index of discrimination (0.982) and proved to be a very valuable tool for epidemiological differentiation of P. aeruginosa isolates.

Role of the ferric uptake regulator of Pseudomonas aeruginosa in the regulation of siderophores and exotoxin A expression: purification and activity on iron-regulated promoters

The cloned Pseudomonas aeruginosa fur (ferric uptake regulator) gene was overexpressed in P. aeruginosa by using a T7 expression system, and the Fur protein (PA-Fur) was purified by using a combination of ion-exchange chromatography and metal affinity chromatography. The DNA binding activity of the PA-Fur protein was confirmed by gel mobility shift assays and DNase I footprints of the synthetic DNA fragment GATAAT GATAATCATTATC, representing a perfect "Fur box". In addition, it was shown that PA-Fur is capable of binding to promoter and operator determinants of the tightly iron-regulated Escherichia coli fepA-fes enterobactin gene system. The activity of PA-Fur on the promoters of iron-regulated genes involved in the production of two siderophores, pyochelin and pyoverdin, and in the expression of exotoxin A was investigated. Data indicating that the promoters of the pchR gene, encoding a transcriptional activator for pyochelin synthesis, and of the pvdS gene, encoding a positive regulator for pyoverdin production, are specifically recognized by Fur-Fe(II) are presented, suggesting that PA-Fur represses expression of pchR and pvdS during growth in an iron-replete environment. However, neither the promoter region of the gene encoding exotoxin A (toxA) nor the promoters of the regAB operon, required for toxA expression, interacted with high concentrations of purified PA-Fur. These data indicate that iron regulation of exotoxin A production involves additional factors which may ultimately be under the control of PA-Fur.

Cloning and characterization of the katB gene of Pseudomonas aeruginosa encoding a hydrogen peroxide-inducible catalase: purification of KatB, cellular localization, and demonstration that it is essential for optimal resistance to hydrogen peroxide

Pseudomonas aeruginosa is an obligate aerobe that is virtually ubiquitous in the environment. During aerobic respiration, the metabolism of dioxygen can lead to the production of reactive oxygen intermediates, one of which includes hydrogen peroxide. To counteract the potentially toxic effects of this compound, P. aeruginosa possesses two heme-containing catalases which detoxify hydrogen peroxide. In this study, we have cloned katB, encoding one catalase gene of P. aeruginosa. The gene was cloned on a 5.4-kb EcoRI fragment and is composed of 1,539 bp, encoding 513 amino acids. The amino acid sequence of the P. aeruginosa katB was approximately 65% identical to that of a catalase from a related species, Pseudomonas syringae. The katB gene was mapped to the 71- to 75-min region of the P. aeruginosa chromosome, the identical region which harbors both sodA and sodB genes encoding both manganese and iron superoxide dismutases. When cloned into a catalase-deficient mutant of Escherichia coli (UM255), the recombinant P. aeruginosa KatB was expressed (229 U/mg) and afforded this strain resistance to hydrogen peroxide nearly equivalent to that of the wild-type E. coli strain (HB101). The KatB protein was purified to homogeneity and determined to be a tetramer of approximately 228 kDa, which was in good agreement with the predicted protein size derived from the translated katB gene. Interestingly, KatB was not produced during the normal P. aeruginosa growth cycle, and catalase activity was greater in nonmucoid than in mucoid, alginate-producing organisms. When exposed to hydrogen peroxide and, to a greater extent, paraquat, total catalase activity was elevated 7- to 16-fold, respectively. In addition, an increase in KatB activity caused a marked increase in resistance to hydrogen peroxide. KatB was localized to the cytoplasm, while KatA, the "housekeeping" enzyme, was detected in both cytoplasmic and periplasmic extracts. A P. aeruginosa katB mutant demonstrated 50% greater sensitivity to hydrogen peroxide than wild-type bacteria, suggesting that KatB is essential for optimal resistance of P. aeroginosa to exogenous hydrogen peroxide.

Rapid and sensitive method for evaluating Pseudomonas aeruginosa virulence factors during corneal infections in mice

A murine corneal scratch model has been used extensively to study various aspects of the pathogenesis of Pseudomonas aeruginosa, a common etiologic agent of corneal infections. This model uses mild inhalation anesthetics which keep the animals immobile for a relatively short time and promote the interaction between the infecting organisms and the corneal wound. Under these circumstances, only a small number of P. aeruginosa isolates delivered at inocula of > 10(7) CFU are infectious. We determined that this model is useful for studying other P. aeruginosa strains given at lower doses if injectable anesthetics are administered prior to infection to keep the animals immobile for 15 to 30 min. Under these conditions, eight clinical isolates of P. aeruginosa tested at doses of 10(8) CFU per eye induced corneal perforation and/or phthisis in C3H/HeN mice. The 50% infective doses of several strains were between 3 x 10(2) and 1 x 10(5) CFU per mouse eye. When this modified anesthetic procedure was used to evaluate the roles of different P. aeruginosa virulence factors in eye infections, pathology was not observed when eyes were inoculated with 10(8) CFU of strains deficient in production of a complete lipopolysaccharide or the RpoN sigma factor. A strain with a point mutation in the fur gene, involved in production of iron-regulated factors, showed decreased virulence, while a mutant deficient in both hemolytic and nonhemolytic phospholipase C was fully virulent. By modifying the anesthesia procedure, the corneal scratch model allows rapid evaluations of the roles of P. aeruginosa virulence factors in corneal infections.

A new extracellular protein of Pseudomonas aeruginosa PA103 regulated by regA

The expression of exotoxin A (ExoA) from Pseudomonas aeruginosa is influenced by iron and is under the control of the regulatory gene regA. To test whether regA plays a role in the expression of other iron-regulated proteins a RegA- mutant was constructed by insertional mutagenesis. The polypeptide pattern of this mutant (PA103R) was compared with the parental strain (PA103) and a trans-complemented strain PA103R(pREX18) after growth of the strains in conditions containing low or high concentrations of iron. An iron-regulated 42 kDa protein (RRP) was identified and purified from the culture supernatant of PA103 and PA103R(pREX18) which was missing in PA103R. Database analysis of the N-terminal sequence of this regA-regulated protein (RRP) revealed no similarity to other proteins. Preliminary investigations into the function of RRP revealed that it has no proteolytic or cytotoxic activity. Using two-dimensional electrophoretic analysis of whole cells, a technique which allowed separation of over 600 polypeptides, we were unable to identify any other iron-regulated protein whose expression was regulated by regA.

Cloning and characterization of the Pseudomonas aeruginosa sodA and sodB genes encoding manganese- and iron-cofactored superoxide dismutase: demonstration of increased manganese superoxide dismutase activity in alginate-producing bacteria

Pseudomonas aeruginosa is a strict aerobe which is likely exposed to oxygen reduction products including superoxide and hydrogen peroxide during the metabolism of molecular oxygen. To counterbalance the potentially hazardous effects of elevated endogenous levels of superoxide, most aerobic organisms possess one or more superoxide dismutases or compounds capable of scavenging superoxide. We have previously shown that P. aeruginosa possesses both an iron- and a manganese-cofactored superoxide dismutase (D. J. Hassett, L. Charniga, K. A. Bean, D. E. Ohman, and M. S. Cohen, Infect. Immun. 60:328-336, 1992). In this study, the genes encoding manganese (sodA)- and iron (sodB)- cofactored superoxide dismutase were cloned by using a cosmid library of P. aeruginosa FRD which complemented an Escherichia coli (JI132) strain devoid of superoxide dismutase activity. The sodA and sodB genes of P. aeruginosa, when cloned into a high-copy-number vector (pKS-), partially restored the aerobic growth rate defect, characteristic of the Sod- strain, to that of the wild type (AB1157) when grown in Luria broth. The nucleotide sequences of sodA and sodB have open reading frames of 612 and 579 bp that encode dimeric proteins of 22.9 and 21.2 kDa, respectively. These data were also supported by the results of in vitro expression studies. The deduced amino acid sequence of the P. aeruginosa manganese and iron superoxide dismutase revealed approximately 50 and 67% similarity with manganese and iron superoxide dismutases from E. coli, respectively. There was also remarkable similarity with iron and manganese superoxide dismutases from other phyla. The mRNA start site of sodB was mapped to 174 bp upstream of the ATG codon. A likely promoter with similarity to the -10 and -35 consensus sequence of E. coli was observed upstream of the ATG start codon of sodB. Regions sequenced 519 bp upstream of the sodA electrophoresis, sodA gene revealed no such promoter, suggesting an alternative mode of control for sodA. By transverse field electrophoresis, sodA and sodB were mapped to the 71- to 75-min region on the P. aeruginosa PAO1 chromosome. Strikingly, mucoid alginate-producing bacteria generated greater levels of manganese superoxide dismutase than nonmucoid revertants, suggesting that mucoid P. aeruginosa is responding to oxidative stress and/or changes in the redox status of the cell.

Alveolar epithelial injury and pleural empyema in acute P. aeruginosa pneumonia in anesthetized rabbits

We developed an experimental model of acute Pseudomonas aeruginosa pneumonia in anesthetized ventilated rabbits to determine whether bacterial-induced injury to the alveolar epithelium would occur and the effect of the injury on the pleural space. Dose-response studies established that 10(9) colony-forming units of P. aeruginosa (wild-type strain, PAO-1) were required to injure the epithelial barrier and to cause pleural empyema with exudative pleural effusions that contained both the instilled alveolar protein tracer and P. aeruginosa. We explored the mechanisms of P. aeruginosa-induced lung and pleural injury by using three isogenic bacterial strains to compare several extracellular virulence products. PAO-S21, which carries an insertion mutation in a regulatory gene that prevents the production of exoenzyme S, resulted in no lung or pleural injury. PAO-R1, which carries a deletion in a regulatory gene that controls the production of elastase and alkaline protease, caused the same degree of lung and pleural injury as PAO-1 did. Instillation of PLC-SRN, which has both structural genes encoding phospholipase C activity deleted, resulted in a moderate reduction in alveolar epithelial injury. Although other products may be involved, exoenzyme S and phospholipase C are important in mediating injury to the alveolar epithelial barrier in acute P. aeruginosa pneumonia in rabbits.

Coordinate regulation of siderophore and exotoxin A production: molecular cloning and sequencing of the Pseudomonas aeruginosa fur gene

A 5.9-kb DNA fragment was cloned from Pseudomonas aeruginosa PA103 by its ability to functionally complement a fur mutation in Escherichia coli. A fur null mutant E. coli strain that contains multiple copies of the 5.9-kb DNA fragment produces a 15-kDa protein which cross-reacts with a polyclonal anti-E. coli Fur serum. Sequencing of a subclone of the 5.9-kb DNA fragment identified an open reading frame predicted to encode a protein 53% identical to E. coli Fur and 49% identical to Vibrio cholerae Fur and Yersinia pestis Fur. While there is extensive homology among these Fur proteins, Fur from P. aeruginosa differs markedly at its carboxy terminus from all of the other Fur proteins. It has been proposed that this region is a metal-binding domain in E. coli Fur. A positive selection procedure involving the isolation of manganese-resistant mutants was used to isolate mutants of strain PA103 that produce altered Fur proteins. These manganese-resistant Fur mutants constitutively produce siderophores and exotoxin A when grown in concentrations of iron that normally repress their production. A multicopy plasmid carrying the P. aeruginosa fur gene restores manganese susceptibility and wild-type regulation of exotoxin A and siderophore production in these Fur mutants.

Osmoprotectants and phosphate regulate expression of phospholipase C in Pseudomonas aeruginosa

Phospholipase C has been increasingly recognized as a significant virulence determinant in the pathogenesis of Gram-negative and Gram-positive infections. Pseudomonas aeruginosa carries two, non-tandem genes encoding phospholipase C (PLC) activity. One PLC (PLC-H) haemolyses human and sheep erythrocytes while the other is not haemolytic for these kinds of red blood cells. It was previously determined that the synthesis of both PLCs is regulated by inorganic phosphate (Pi), but little else was known regarding the regulation of these potentially important virulence determinants of P. aeruginosa. In this report, data are presented demonstrating that both PLC genes are regulated at the transcriptional level by Pi and by a P. aeruginosa homologue of the positive regulator of genes in the Pi regulon of Escherichia coli, i.e. PhoB. In addition to Pi, it is also shown in this report that the synthesis of both PLC-H and PLC-N is induced by compounds which are not only derived from the substrate product of both enzymes, i.e. phosphorylcholine, but are also known osmoprotectants in eukaryotic and prokaryotic cells. The osmoprotective derivatives of phosphorylcholine which induce the synthesis of PLC in P. aeruginosa include choline, glycine betaine, and dimethylglycine, but not sarcosine (monomethylglycine) or glycine. By constructing mutants which are deficient in the production of each separate PLC and in the production of PhoB it was determined that induction of PLC-H by the osmoprotective compounds is independent of Pi concentration and PhoB, while induction of PLC-N by these compounds requires Pi-deficient conditions and PhoB.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of toxA and regA by the Escherichia coli fur gene and identification of a Fur homologue in Pseudomonas aeruginosa PA103 and PA01

A multicopy plasmid containing the Escherichia coli fur gene was introduced into Pseudomonas aeruginosa strain PA103C. This strain contains a toxA-lacZ fusion integrated into its chromosome at the toxA locus. Beta-galactosidase synthesis in this strain is regulated by iron, as is seen for exotoxin A production. Beta-galactosidase synthesis and exotoxin A production in PA103C containing multiple copies of E. coli fur was still repressed in low iron conditions. The transcription of regA, a positive regulator of toxA, was also found to be inhibited by multiple copies of the E. coli fur gene. In addition, the ability of PA103C containing multiple copies of E. coli fur to produce protease was greatly reduced relative to PA103C containing a vector control. A polyclonal rabbit serum containing antibodies that recognize E. coli Fur was used to screen whole-cell extracts from Vibrio cholerae, Shigella flexneri, Salmonella typhimurium and Pseudomonas aeruginosa. All strains tested expressed a protein that was specifically recognized by the anti-Fur serum. These results and those described above suggest that Fur structure and function are conserved in a variety of distinct bacterial genera and that at least some of these different genera use this regulatory protein to control genes encoding virulence factors.

Physical mapping of virulence-associated genes in Pseudomonas aeruginosa by transverse alternating-field electrophoresis

The relative chromosomal locations of 20 virulence-associated genes in four clinical isolates of Pseudomonas aeruginosa were investigated by using transverse alternating-field electrophoresis. Each strain had a characteristic restriction pattern when digested with either SpeI or DraI and electrophoresed with 15-s pulses. All four strains had restriction fragments that hybridized with each of the gene probes used, although there were variations in fragment size. An SpeI physical map constructed by Ratnaningsih et al. (E. Ratnaningsih, S. Dharmsthiti, V. Krishnapillai, A. Morgan, M. Sinclair, and B. W. Holloway, J. Gen. Microbiol. 136:2351-2357, 1990) for one of these strains, PAO1, was used to identify the location of 11 previously unmapped genes. The physical locations of the remaining genes were found to be consistent with their genetically mapped loci. Whereas phospholipase C and alginate structural and regulatory genes were associated in three separate clusters in the early, middle, and late regions of the chromosome, no virulence cluster was identified. Our data suggest that the pathogenicity of P. aeruginosa results from the gradual acquisition of genes encoding various virulence determinants.

Pseudomonas aeruginosa LasB mutant constructed by insertional mutagenesis reveals elastolytic activity due to alkaline proteinase and the LasA fragment

The extracellularly secreted endopeptidase elastase (LasB) is regarded as an important virulence factor of Pseudomonas aeruginosa. It has also been implicated in the processing of LasA which enhances elastolytic activity of LasB. In order to investigate the role of LasB in virulence and LasA processing, a LasB-negative mutant, PAO1E, was constructed by insertional mutagenesis of the LasB structural gene, lasB, in P. aeruginosa PAO. An internal 636 bp lasB fragment of the plasmid pRB1803 was ligated into a derivative of the mobilization vector pSUP201-1. The resulting plasmid, pBRMOB-LasB, was transformed into Escherichia coli and transferred by filter matings to the LasB-positive P. aeruginosa strain, PAO1. Plasmid integration in the lasB site of the chromosome was confirmed by Southern blot analysis. Radioimmunoassay and immunoblotting of PAO1E supernatant fluids yielded no detectable LasB (less than 1 ng ml-1 LasB). The absence of LasB in PAO1E was further proven by the inability of its culture supernatant fluid to cleave transferrin or rabbit immunoglobulin G (IgG) after a 72 h incubation. The residual proteolytic activity of PAO1E culture supernatant fluid was attributed to alkaline proteinase (Apr), since it was totally inhibited by specific antibodies against Apr. Residual elastolytic activity in culture supernatant fluid of PAO1E was due to the LasA fragment and to the combined action of the LasA fragment with Apr on elastin. The sizes of purified LasA from PAO1 and PAO1E were identical (22 kDa). These results show that, besides LasB and the LasA fragment, Apr may also act on elastin in the presence of the LasA fragment and that the proteolytic processing of LasA in P. aeruginosa is independent of LasB.

DNA fingerprinting by pulsed field gel electrophoresis and ribotyping to distinguish Pseudomonas cepacia isolates from a nosocomial outbreak

We typed 40 isolates of Pseudomonas cepacia obtained from patients involved in a single outbreak using pulsed field gel electrophoresis and ribotyping. All isolates from the majority of the patients, 16 of 18 (89%), were included in a single group. These typing methods should aid in the clarification of the epidemiology of infection with P. cepacia.

Molecular analysis of hemolytic and phospholipase C activities of Pseudomonas cepacia

By using a gene-specific fragment from the hemolytic phospholipase C (PLC) gene of Pseudomonas aeruginosa as a probe and data from Southern hybridizations under reduced stringency conditions, we cloned a 4.2-kb restriction fragment from a beta-hemolytic Pseudomonas cepacia strain which expressed hemolytic and PLC activities in Escherichia coli under the control of the lac promoter. It was found, by using a T7 phage promoter-directed expression system, that this DNA fragment carries at least two genes. One gene which shares significant DNA homology with both PLC genes from P. aeruginosa encodes a 72-kDa protein, while the other gene encodes a 22-kDa protein. When both genes on the 4.2-kb fragment were expressed from the T7 promoter in the same cell, hemolytic and PLC activities could be detected in the cell lysate. In contrast, when each individual gene was expressed in different cells or when lysates containing the translated products of each separate gene were mixed, neither hemolytic activity nor PLC activity could be detected. Clinical and environmental isolates of P. cepacia were examined for beta-hemolytic activity, PLC activity, sphingomyelinase activity, and reactivity in Southern hybridizations with a probe from P. cepacia which is specific for the larger gene which encodes the 72-kDa protein. There were considerable differences in the ability of the different strains to express hemolytic and PLC activities, and the results of Southern DNA-DNA hybridizations of the genomic DNAs of these strains revealed considerable differences in the probe-reactive fragments between high- and medium-stringency conditions as well as remarkable variation in size and number of probe-reactive fragments among different strains. Analysis of the genomic DNAs from hemolytic and nonhemolytic variants of an individual strain (PC-69) by agarose gel electrophoresis. Southern hybridization, and transverse alternating pulsed field gel electrophoresis suggests that the conversion of the hemolytic phenotype to the nonhemolytic phenotype is associated with either the loss of a large plasmid (greater than 200 kb) or a large deletion of the chromosome of P. cepacia PC-69.

Molecular comparison of a nonhemolytic and a hemolytic phospholipase C from Pseudomonas aeruginosa

Pseudomonas aeruginosa produces two secreted phospholipase C (PLC) enzymes. The expression of both PLCs is regulated by Pi. One of the PLCs is hemolytic, and one is nonhemolytic. Low-stringency hybridization studies suggested that the genes encoding these two PLCs shared DNA homology. This information was used to clone plcN, the gene encoding the 77-kilodalton nonhemolytic PLC, PLC-N. A fragment of plcN was used to mutate the chromosomal copy of plcN by the generation of a gene interruption mutation. This mutant produces 55% less total PLC activity than the wild type, confirming the successful cloning of plcN. plcN was sequenced and encodes a protein which is 40% identical to the hemolytic PLC (PLC-H). The majority of the homology lies within the NH2 two-thirds of the proteins, while the remaining third of the amino acid sequence of the two proteins shows very little homology. Both PLCs hydrolyze phosphatidylcholine; however, each enzyme has a distinct substrate specificity. PLC-H hydrolyzes sphingomyelin in addition to phosphatidylcholine, whereas PLC-N is active on phosphatidylserine as well as phosphatidylcholine. These studies suggest structure-function relationships between PLC activity and hemolysis.

Nucleotide sequence of the Pseudomonas aeruginosa phoB gene, the regulatory gene for the phosphate regulon

The nucleotide sequence of Pseudomonas aeruginosa phoB was determined. The sequence data suggest that the PhoB polypeptide consists of 229 amino acid residues and has a predicted molecular weight of 25,708. In the regulatory region of the gene, a very well conserved phosphate box was found. The sequence data also predicted the presence of an open reading frame downstream of phoB, which could be phoR. The deduced amino acid sequence of phoB was significantly homologous to that of the Escherichia coli phoB gene product and to those of several known procaryotic transcriptional regulators such as PhoP, OmpR, VirG, Dye, NtrC, and AlgR.

Decreased pulmonary vasoreactivity in an animal model of chronic Pseudomonas pneumonia

Chronic pulmonary infection/colonization caused by Pseudomonas aeruginosa accounts for much of the morbidity and mortality in cystic fibrosis (CF). The effect of chronic pulmonary P. aeruginosa infection on the pulmonary circulation has not been studied. Therefore, we investigated the effect of chronic P. aeruginosa infection on pulmonary hemodynamics in a rat model. Two groups of rats were inoculated with either agar beads containing 1.0 x 10(4) colony-forming units of P. aeruginosa (infected) or an equal volume of sterile beads alone (control). In vivo, pulmonary vasoreactivity measured as the percent change in total pulmonary resistance during hypoxia was decreased at 1 wk (22 +/- 7% versus 57 +/- 3%), 2 wk (29 +/- 5% versus 73 +/- 17%), 3 wk (41 +/- 8% versus 77 +/- 14%), and 6 to 9 wk (23 +/- 10 versus 53 +/- 7; p less than 0.05 all time points; mean +/- SEM) postinoculation in infected animals when compared with that in time-matched control animals. At 6 to 9 wk postinoculation, pulmonary artery pressure was significantly elevated in infected rats (25.8 +/- 1.6 versus 21.0 +/- 1.0 mm Hg; p less than 0.05) when compared with that in control animals. Histopathologic findings were characterized by bronchiectasis as well as by chronic bronchial, parenchymal, and perivascular inflammation at all time points in infected animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Possible insertion sequences in a mosaic genome organization upstream of the exotoxin A gene in Pseudomonas aeruginosa

Nucleotide sequence and Southern hybridization data revealed a mosaic genome organization in a region that extends several thousand base pairs upstream of the exotoxin A (toxA) gene in Pseudomonas aeruginosa. An interstrain comparison of DNA in this region showed a pattern of alternating segments of homologous and nonhomologous sequences. Two nonhomologous elements, approximately 1 kilobase pair upstream of the gene in strains PA103 and Ps388, were characterized in more detail. The sequence elements, denoted IS-PA-1 and IS-PA-2 for the different strains, are about 1,000 and 785 base pairs long, respectively, and have 5-base-pair direct repeats at their boundaries, consistent with their being DNA insertion sequences. The distribution of these elements in 34 different strains was determined. IS-PA-1 was found in a single copy upstream of toxA in half of the strains and was found in two copies in four of the strains. Some strains contained neither element, and one strain carried both. The genome of another strain, WR5, which lacks toxA, was shown to contain a 350-base-pair region that was highly homologous to DNA sequences located just upstream of toxA in other strains. The WR5 genome lacked several kilobase pairs of DNA that was found both upstream and downstream of this homologous region in the other strains.

Genetic mapping of the structural gene for phospholipase C of Pseudomonas aeruginosa PAO

An insertion mutation constructed by gene replacement methods was used to map the gene corresponding to the hemolytic phospholipase C (plcS gene) in Pseudomonas aeruginosa PAO1 by R68.45-mediated conjugation. plcS mapped approximately at 67 min on the 75-min chromosomal map (B. W. Holloway, K. O'Hoy, and H. Matsumoto, p. 213-221, in S. J. O'Brien, ed., Genetic Maps 1987, vol. 4, 1987), between the markers pur-67 and pru-375 and considerably distal to the regulatory genes plcA and plcB, which are located at approximately 12 min.