Studies of phospholipase C (heat-labile hemolysin) in Pseudomonas aeruginosa

Sphingosine induction of the Pseudomonas aeruginosa hemolytic phospholipase C/sphingomyelinase (PlcH)

Hemolytic phospholipase C, PlcH, is an important virulence factor for Pseudomonas aeruginosa. PlcH preferentially hydrolyzes sphingomyelin and phosphatidylcholine, and this hydrolysis activity drives tissue damage and inflammation and interferes with the oxidative burst of immune cells. Among other contributors, transcription of plcH was previously shown to be induced by phosphate starvation via PhoB and the choline metabolite, glycine betaine, via GbdR. Here, we show that sphingosine can induce plcH transcription and result in secreted PlcH enzyme activity. This induction is dependent on the sphingosine-sensing transcriptional regulator SphR. The SphR induction of plcH occurs from the promoter for the gene upstream of plcH that encodes the neutral ceramidase, CerN, and transcriptional readthrough of the cerN transcription terminator. Evidence for these conclusions came from mutation of the SphR binding site in the cerN promoter, mutation of the cerN terminator, enhancement of cerN termination by adding the rrnB terminator, and reverse transcriptase PCR (RT-PCR) showing that the intergenic region between cerN and plcH is made as RNA during sphingosine, but not choline, induction. We also observed that, like glycine betaine induction, sphingosine induction of plcH is under catabolite repression control, which likely explains why such induction was not seen in other studies using sphingosine in rich media. The addition of sphingosine as a novel inducer for PlcH points to the regulation of plcH transcription as a site for the integration of multiple host-derived signals.

IMPORTANCE

PlcH is a secreted phospholipase C/sphingomyelinase that is important for the virulence of Pseudomonas aeruginosa. Here, we show that sphingosine, which presents itself or as a product of P. aeruginosa sphingomyelinase and ceramidase activity, leads to the induction of plcH transcription. This transcriptional induction occurs from the promoter of the upstream ceramidase gene generating a conditional operon. The transcript on which plcH resides, therefore, is different depending on which host molecule or condition leads to induction, and this may have implications for PlcH post-transcriptional regulation. This work also adds to our understanding of P. aeruginosa with host-derived sphingolipids.

A Bacterial Quorum Sensing Regulated Protease Inhibits Host Immune Responses by Cleaving Death Domains of Innate Immune Adaptors

Innate immune adaptor proteins are critical components of the innate immune system that propagate pro-inflammatory responses from their upstream receptors, and lead to pathogen clearance from the host. Bacterial pathogens have developed strategies to survive inside host cells without triggering the innate immune surveillance in ways that are still not fully understood. Here, it is reported that Pseudomonas aeruginosa induces its quorum sensing mechanism after macrophage engulfment. Further investigation of its secretome identified a quorum sensing regulated product, LasB, is responsible for innate immune suppression depending on the MyD88-mediated signaling. Moreover, it is showed that this specific type of pathogen-mediated innate immune suppression is due to the enzymatic digestion of the death domains of the innate immune adaptors, mainly MyD88, and attributed to LasB's large substrate binding groove. Lastly, it is demonstrated that the secretion of LasB from P. aeruginosa directly contributed to MyD88 degradation within macrophages. Hence, it is discovered an example of bacterial quorum sensing-regulated cellular innate immune suppression by direct cleavage of immune adaptors.

Phospholipase C: underrated players in microbial infections

During bacterial infections, one or more virulence factors are required to support the survival, growth, and colonization of the pathogen within the host, leading to the symptomatic characteristic of the disease. The outcome of bacterial infections is determined by several factors from both host as well as pathogen origin. Proteins and enzymes involved in cellular signaling are important players in determining the outcome of host-pathogen interactions. phospholipase C (PLCs) participate in cellular signaling and regulation by virtue of their ability to hydrolyze membrane phospholipids into di-acyl-glycerol (DAG) and inositol triphosphate (IP3), which further causes the activation of other signaling pathways involved in various processes, including immune response. A total of 13 PLC isoforms are known so far, differing in their structure, regulation, and tissue-specific distribution. Different PLC isoforms have been implicated in various diseases, including cancer and infectious diseases; however, their roles in infectious diseases are not clearly understood. Many studies have suggested the prominent roles of both host and pathogen-derived PLCs during infections. PLCs have also been shown to contribute towards disease pathogenesis and the onset of disease symptoms. In this review, we have discussed the contribution of PLCs as a determinant of the outcome of host-pathogen interaction and pathogenesis during bacterial infections of human importance.

Pseudomonas aeruginosa: pathogenesis, virulence factors, antibiotic resistance, interaction with host, technology advances and emerging therapeutics

Pseudomonas aeruginosa (P. aeruginosa) is a Gram-negative opportunistic pathogen that infects patients with cystic fibrosis, burn wounds, immunodeficiency, chronic obstructive pulmonary disorder (COPD), cancer, and severe infection requiring ventilation, such as COVID-19. P. aeruginosa is also a widely-used model bacterium for all biological areas. In addition to continued, intense efforts in understanding bacterial pathogenesis of P. aeruginosa including virulence factors (LPS, quorum sensing, two-component systems, 6 type secretion systems, outer membrane vesicles (OMVs), CRISPR-Cas and their regulation), rapid progress has been made in further studying host-pathogen interaction, particularly host immune networks involving autophagy, inflammasome, non-coding RNAs, cGAS, etc. Furthermore, numerous technologic advances, such as bioinformatics, metabolomics, scRNA-seq, nanoparticles, drug screening, and phage therapy, have been used to improve our understanding of P. aeruginosa pathogenesis and host defense. Nevertheless, much remains to be uncovered about interactions between P. aeruginosa and host immune responses, including mechanisms of drug resistance by known or unannotated bacterial virulence factors as well as mammalian cell signaling pathways. The widespread use of antibiotics and the slow development of effective antimicrobials present daunting challenges and necessitate new theoretical and practical platforms to screen and develop mechanism-tested novel drugs to treat intractable infections, especially those caused by multi-drug resistance strains. Benefited from has advancing in research tools and technology, dissecting this pathogen's feature has entered into molecular and mechanistic details as well as dynamic and holistic views. Herein, we comprehensively review the progress and discuss the current status of P. aeruginosa biophysical traits, behaviors, virulence factors, invasive regulators, and host defense patterns against its infection, which point out new directions for future investigation and add to the design of novel and/or alternative therapeutics to combat this clinically significant pathogen.

Microbial biosurfactant research: time to improve the rigour in the reporting of synthesis, functional characterization and process development

The demand for microbially produced surface-active compounds for use in industrial processes and products is increasing. As such, there has been a comparable increase in the number of publications relating to the characterization of novel surface-active compounds: novel producers of already characterized surface-active compounds and production processes for the generation of these compounds. Leading researchers in the field have identified that many of these studies utilize techniques are not precise and accurate enough, so some published conclusions might not be justified. Such studies lacking robust experimental evidence generated by validated techniques and standard operating procedures are detrimental to the field of microbially produced surface-active compound research. In this publication, we have critically reviewed a wide range of techniques utilized in the characterization of surface-active compounds from microbial sources: identification of surface-active compound producing microorganisms and functional testing of resultant surface-active compounds. We have also reviewed the experimental evidence required for process development to take these compounds out of the laboratory and into industrial application. We devised this review as a guide to both researchers and the peer-reviewed process to improve the stringency of future studies and publications within this field of science.

Galleria mellonella larvae fat body disruption (Lepidoptera: Pyralidae) caused by the venom of Habrobracon brevicornis (Hymenoptera: Braconidae)

The ability of Habrobracon brevicornis venom to elevate the nutritional suitability of a host by affecting the host larvae fat body condition was studied. To understand whether H. brevicornis crude venom impacts the host biochemical profile, the concentrations of total lipids and main sugars in the host larvae lymph were analyzed. All measurements were carried out during the first 3 days after envenomation. A significant increase in the lipid level was fixed only on the second day after envenomation. A significant increase in the total trehalose count was detected during all 3 days, while a significant increase in glucose concentration was noted only on the first day. Well-observed disruptions were fixed in thin and semithin sections of the G. mellonella larval fat body starting from the second day after envenomation. Significant increases in both phospholipase A₂ and C enzyme activity as well as acid proteases were detected in the wax moth fat body after envenomation during all experimental times. At the same time, imbalances in the antioxidant system, including changes in the activities of superoxide dismutase, peroxidases, catalase, and glutathione-S-transferase, were detected. The reliable increase in the expression of the gene encoding Hsp70 was fixed both for 24 and 48 h after envenomation, while a reliable increase in the expression of the gene encoding inhibitor of apoptosis protein was detected only 24 h after wax moth larvae envenomation. Considering the absence of DNA fragmentation, the imbalance in the "ROS/antioxidants" system, and the increased activity of phospholipases and acid proteases in the fat body cells from envenomated wax moth larvae, we can hypothesize that the fat body disruption occurs in a necrotic manner. The results of the work expand the knowledge about the biochemical aspects of interaction between ectoparasitoids and their hosts.

Cancer Microbiome; Opportunities and Challenges

BACKGROUND

Microbe-host association has emerged as a modulator in modern medicine. Cancer and its associated host microbes are collectively referred to as the cancer microbiome. The cancer microbiome is complex, and many aspects remain unclear including metabolic plasticity, microenvironment remodeling, cellular communications, and unique signatures within the host, all of which have a vital role in homeostasis and pathogenesis of host physiology. However, the role of the microbiome in cancer initiation, progression, and therapy is still poorly understood and remains to be explored.

OBJECTIVE

The objective of this review is to elucidate the role of the microbiome in cancer metabolism and the tumor microenvironment. It also focuses on the importance of therapeutic opportunities and challenges in the manipulation of the cancer microbiome.

METHODS

A literature search was conducted on the role of the microbiome in cancer initiation, progression, and therapy.

CONCLUSION

The tumor microenvironment and cancer metabolism are significant in host-microbiome interactions. The microbiome can modulate standard cancer therapies like chemotherapy and immunotherapy. Microbiome transplantation has also been demonstrated as an effective therapy against cancer. Furthermore, the modulation of the microbiome also has potential clinical outcomes in modern medicine.

The microbiome in urological diseases

Due to the rapid development of next-generation sequencing, it has become possible to obtain information on the sequences of all genes in a specific microbiome. The detection of bacteria in patients with no urinary tract infections indicated that the dogma that “urine is sterile” was false, leading to active research regarding the roles of the urinary microbiome in the human urinary tract. Here, we present a review of the current literature regarding the role of the microbiome in urology.

Emerging roles of ECM remodeling processes in cancer

Extracellular matrix (ECM) plays a central and dynamic role in the creation of tumor microenvironment. Herein we discuss the emerging biophysical and biochemical aspects of ECM buildup and proteolysis in cancer niche formation. Dysregulated ECM remodeling by cancer cells facilitate irreversible proteolysis and crosslinking, which in turn influence cell signaling, micro environmental cues, angiogenesis and tissue biomechanics. Further, we introduce the emerging roles of cancer microbiome in aberrant tumor ECM remodeling and membrane bound nano-sized vesicles called exosomes in creation of distant pre-metastatic niches. A detailed molecular and biophysical understanding of the ECM morphologies and its components such as key enzymes, structural and signaling molecules are critical in identifying the next generation of therapeutic and diagnostic targets in cancer.

Development, Optimization, and Validation of a High Throughput Screening Assay for Identification of Tat and Type II Secretion Inhibitors of Pseudomonas aeruginosa

Antibiotics are becoming less effective in treatment of infections caused by multidrug-resistant Pseudomonas aeruginosa. Antimicrobial therapies based on the inhibition of specific virulence-related traits, as opposed to growth inhibitors, constitute an innovative and appealing approach to tackle the threat of P. aeruginosa infections. The twin-arginine translocation (Tat) pathway plays an important role in the pathogenesis of P. aeruginosa, and constitutes a promising target for the development of anti-pseudomonal drugs. In this study we developed and optimized a whole-cell, one-well assay, based on native phospholipase C activity, to identify compounds active against the Tat system. Statistical robustness, sensitivity and consequently suitability for high-throughput screening (HTS) were confirmed by a dry run/pre-screening test scoring a Z′ of 0.82 and a signal-to-noise ratio of 49. Using this assay, we evaluated ca. 40,000 molecules and identified 59 initial hits as possible Tat inhibitors. Since phospholipase C is exported into the periplasm by Tat, and subsequently translocated across the outer membrane by the type II secretion system (T2SS), our assay could also identify T2SS inhibitors. To validate our hits and discriminate between compounds that inhibited either Tat or T2SS, two separate counter assays were developed and optimized. Finally, three Tat inhibitors and one T2SS inhibitor were confirmed by means of dose-response analysis and additional counter and confirming assays. Although none of the identified inhibitors was suitable as a lead compound for drug development, this study validates our assay as a simple, efficient, and HTS compatible method for the identification of Tat and T2SS inhibitors.

Detection of Pseudomonas aeruginosa biomarkers from thermally injured mice in situ using imaging mass spectrometry

Monitoring patients with burn wounds for infection is standard practice because failure to rapidly and specifically identify a pathogen can result in poor clinical outcomes, including death. Therefore, a method that facilitates detection and identification of pathogens in situ within minutes of biopsy would be a significant benefit to clinicians. Mass spectrometry is rapidly becoming a standard tool in clinical settings, capable of identifying specific pathogens from complex samples. Imaging mass spectrometry (IMS) expands the information content by enabling spatial resolution of biomarkers in tissue samples as in histology, without the need for specific stains/antibodies. Herein, a murine model of thermal injury was used to study infection of burn tissue by Pseudomonas aeruginosa. This is the first use of IMS to detect P. aeruginosa infection in situ from thermally injured tissue. Multiple molecular features could be spatially resolved to infected or uninfected tissue. This demonstrates the potential use of IMS in a clinical setting to aid doctors in identifying both presence and species of pathogens in tissue.

In vitro study of virulence potential of Acinetobacter baumannii outer membrane vesicles

Acinetobacter baumannii has emerged as an important opportunistic pathogen mostly causing nosocomial infections. The virulence factors of this important pathogen are largely unknown. Outer membrane vesicles (OMV) are naturally secreted by many gram negative and gram positive bacteria. These vesicles contain outer membrane proteins, lipids, periplasmic proteins, DNA and RNA. Their role in intracellular and intercellular signaling, transfer of virulence factors and eliciting immune response in host cells has been established in many pathogens. In this study, we investigated OMVs from three multi-drug resistant (MDR) clinical isolates and a non-MDR reference strain of A. baumannii for virulence potential. A. baumannii OMVs showed phospholipase C, hemolytic and leukotoxic activities. We found large variations in virulence potential between OMVs of MDR clinical isolates and non-MDR reference strain. These effector molecules were concentrated in OMVs than whole cell bacterial culture and cell-free supernatant. OMV-mediated phospholipase, hemolytic and leucotoxic activities may have a key role in pathogenicity of A. baumannii infection and may be future targets for therapeutic and preventive strategies. This is, to the best of our knowledge, the first report showing virulence potential of A. baumannii OMVs.

Hyperbiofilm phenotype of Pseudomonas aeruginosa defective for the PlcB and PlcN secreted phospholipases

Biofilms are dense communities of bacteria enmeshed in a protective extracellular matrix composed mainly of exopolysaccharides, extracellular DNA, proteins, and outer membrane vesicles (OMVs). Given the role of biofilms in antibiotic-tolerant and chronic infections, novel strategies are needed to block, disperse, or degrade biofilms. Enzymes that degrade the biofilm matrix are a promising new therapy. We screened mutants in many of the enzymes secreted by the type II secretion system (T2SS) and determined that the T2SS, and specifically phospholipases, play a role in biofilm formation. Mutations in the xcp secretion system and in the plcB and plcN phospholipases all resulted in hyperbiofilm phenotypes. PlcB has activity against many phospholipids, including the common bacterial membrane lipid phosphatidylethanolamine, and may degrade cell membrane debris or OMVs in the biofilm matrix. Exogenous phospholipase was shown to reduce aggregation and biofilm formation, suggesting its potential role as a novel enzymatic treatment to dissolve biofilms.

The secretome of Acinetobacter baumannii ATCC 17978 type II secretion system reveals a novel plasmid encoded phospholipase that could be implicated in lung colonization

Acinetobacter baumannii infections are compounded with a striking lack of treatment options. In many Gram-negative bacteria, secreted proteins play an important early role in avoiding host defences. Typically, these proteins are targeted to the external environment or into host cells using dedicated transport systems. Despite the fact that medically relevant species of Acinetobacter possess a type II secretion system (T2SS), only recently, its significance as an important pathway for delivering virulence factors has gained attention. Using in silico analysis to characterize the genetic determinants of the T2SS, which are found clustered in other organisms, in Acinetobacter species, they appear to have a unique genetic organization and are distributed throughout the genome. When compared to other T2SS orthologs, individual components of the T2SS apparatus showed the highest similarity to those of Pseudomonas aeruginosa. A mutant of Acinetobacter baumannii strain ATCC 17978 lacking the secretin component of the T2SS (ΔgspD), together with a trans-complemented mutant, were tested in a series of in vitro and in vivo assays to determine the role of T2SS in pathogenicity. The ΔgspD mutant displayed decreased lipolytic activity, associated with attenuated colonization ability in a murine pneumonia model. These phenotypes are linked to LipAN, a novel plasmid-encoded phospholipase, identified through mass spectroscopy as a T2SS substrate. Recombinant LipAN showed specific phospholipase activity in vitro. Proteomics on the T2-dependent secretome of ATCC 17978 strain revealed its potential dedication to the secretion of a number of lipolytic enzymes, among others which could contribute to its virulence. This study highlights the role of T2SS as an active contributor to the virulence of A. baumannii potentially through secretion of a newly identified phospholipase.

The interplay of extracellular matrix and microbiome in urothelial bladder cancer

Many pathological changes in solid tumours are caused by the accumulation of genetic mutations and epigenetic molecular alterations. In addition, tumour progression is profoundly influenced by the environment surrounding the transformed cells. The interplay between tumour cells and their microenvironment has been recognized as one of the key determinants of cancer development and is being extensively investigated. Data suggest that both the extracellular matrix and the microbiota represent microenvironments that contribute to the onset and progression of tumours. Through the introduction of omics technologies and pyrosequencing analyses, a detailed investigation of these two microenvironments is now possible. In urological research, assessment of their dysregulation has become increasingly important to provide diagnostic, prognostic and predictive biomarkers for urothelial bladder cancer. Understanding the roles of the extracellular matrix and microbiota, two key components of the urothelial mucosa, in the sequelae of pathogenic events that occur in the development and progression of urothelial carcinomas will be important to overcome the shortcomings in current bladder cancer treatment strategies.

VENOM FROM THE ECTOPARASITIC WASP Habrobracon hebetor ACTIVATES CALCIUM-DEPENDENT DEGRADATION OF Galleria mellonella LARVAL HEMOCYTES

Ectoparasitoids inject venom into hemolymph during oviposition. We determined the influence of envenomation by the parasitoid, Habrobracon hebetor, on the hemocytes of its larval host, Galleria mellonella. An increase in both intracellular Са(2+) content and phospholipase C activity of the host hemocytes was recorded during 2 days following envenomation by the parasitoid. The decreased hemocyte viability was detected 1, 2, and 24 h after the envenomation. Injecting of the crude venom (final protein concentration 3 μg/ml) into the G. mellonella larvae led to the reduced hemocyte adhesion. The larval envenomation caused a decrease in transmembrane potential of the hemocytes. These findings document the suppression of hemocytic immune effectors in the parasitized host larvae.

Serum influences the expression of Pseudomonas aeruginosa quorum-sensing genes and QS-controlled virulence genes during early and late stages of growth

In response to diverse environmental stimuli at different infection sites, Pseudomonas aeruginosa, a serious nosocomial pathogen, coordinates the production of different virulence factors through a complicated network of the hierarchical quorum-sensing (QS) systems including the las, rhl, and the 2-alkyl-4-quinolone-related QS systems. We recently showed that at early stages of growth serum alters the expression of numerous P. aeruginosa genes. In this study, we utilized transcriptional analysis and enzyme assays to examine the effect of serum on the QS and QS-controlled virulence factors during early and late phases of growth of the P. aeruginosa strain PAO1. At early phase, serum repressed the transcription of lasI, rhlI, and pqsA but not lasR or rhlR. However, at late phase, serum enhanced the expression of all QS genes. Serum produced a similar effect on the synthesis of the autoinducers 3OC₁₂-HSL, C₄-HSL, and HHQ/PQS. Additionally, serum repressed the expression of several QS-controlled genes in the early phase, but enhanced them in the late phase. Furthermore, serum influenced the expression of different QS-positive (vqsR, gacA, and vfr) as well as QS-negative (rpoN, qscR, mvaT, and rsmA) regulatory genes at either early or late phases of growth. However, with the exception of PAOΔvfr, we detected comparable levels of lasI/lasR expression in PAO1 and PAO1 mutants defective in these regulatory genes. At late stationary phase, serum failed to enhance lasI/lasR expression in PAOΔvfr. These results suggest that depending on the phase of growth, serum differentially influenced the expression of P. aeruginosa QS and QS-controlled virulence genes. In late phase, serum enhanced the expression of las genes through vfr.

Effect of phosphatidylcholine on the level expression of plc genes of Aspergillus fumigatus by real time PCR method and investigation of these genes using bioinformatics analysis

BACKGROUND AND OBJECTIVES

Phosphlipases are a group of enzymes that breakdown phosphatidylcholine (phospholipids) molecules producing second products. These produced products have a divers role in the cell like signal transduction and digestion in humans. In this research the effect of phosphatidylcholine on the expression of plc genes of A. fumigatus was studied. The plc genes of this fungus were also interrogated using bioinformatics studies.

MATERIALS AND METHODS

Real-time PCR was performed to study the expression of plc genes and these genes were interrogated using bioinformatics studies.

RESULTS

There was more significant expression for all three plc genes when A. fumigatus was grown on the presence of phosphatidylcholine in the medium. The sequence of plc genes of A. fumigatus was also interrogated using bioinformatics analysis and their relationship with the other microorganisms was investigated.

CONCLUSION

Real-time PCR revealed that afplc1, afplc2 and afplc3 were up-regulated in the presence of phosphatidylcholine. In this study we suggest either the plc's of A. fumigatus were present in an ancestral genome and have become lost in some lineages, or that they have been acquired from other organisms by horizontal gene transfer. We also found that plc's of this fungus appeared to be more closely related to the plant plc's than the bacterial plc's.

Deciphering the multifactorial nature of Acinetobacter baumannii pathogenicity

BACKGROUND

Acinetobacter baumannii is an emerging bacterial pathogen that causes a broad array of infections, particularly in hospitalized patients. Many studies have focused on the epidemiology and antibiotic resistance of A. baumannii, but little is currently known with respect to its virulence potential.

METHODOLOGY/PRINCIPAL FINDINGS

The aim of this work was to analyze a number of virulence-related traits of four A. baumannii strains of different origin and clinical impact for which complete genome sequences were available, in order to tentatively identify novel determinants of A. baumannii pathogenicity. Clinical strains showed comparable virulence in the Galleria mellonella model of infection, irrespective of their status as outbreak or sporadic strains, whereas a non-human isolate was avirulent. A combined approach of genomic and phenotypic analyses led to the identification of several virulence factors, including exoproducts with hemolytic, phospholipase, protease and iron-chelating activities, as well as a number of multifactorial phenotypes, such as biofilm formation, surface motility and stress resistance, which were differentially expressed and could play a role in A. baumannii pathogenicity.

CONCLUSION/SIGNIFICANCE

This work provides evidence of the multifactorial nature of A. baumannii virulence. While A. baumannii clinical isolates could represent a selected population of strains adapted to infect the human host, subpopulations of highly genotypically and phenotypically diverse A. baumannii strains may exist outside the hospital environment, whose relevance and distribution deserve further investigation.

Recent progress on phospholipases: different sources, assay methods, industrial potential and pathogenicity

Significant studies on phospholipases optimization, characterization, physiological role and industrial potential have been conducted worldwide. Some of them have been directed for biotechnological advances such as gene discovery and functional enhancement by protein engineering. Others reported phospholipases as virulence factor and major cause of pathophysiological effects. A general overview on phospholipase is needed for the identification of new reliable and efficient phospholipase, which would be potentially used in number of industrial and medical applications. Phospholipases catalyse the hydrolysis of one or more ester and phosphodiester bonds of glycerophospholipids. They vary in site of action on phospholipid which can be used industrially for modification/production of new phospholipids. Catalytically active phospholipase mainly use phosphatidylcholine as major substrate, but they can also show specificity with other phospholipids. Several accurate phospholipase assay methods are known, but a rapid and reliable method for high-throughput screening is still a challenge for efficient supply of superior phospholipases and their practical applications. Major application of phospholipase is in industries like oil refinery, health food manufacturing, dairy, cosmetics etc. All types of phospholipases can be involved as virulence factor. They can also be used as diagnostic markers for microbial infection. The importance of phospholipase in virulence is proven and inhibitors of the enzyme can be used as candidate for preventing the associated disease.

Lipid hydrolizing enzymes in virulence: Mycobacterium tuberculosis as a model system

This review is focused on the virulent traits of lipolytic enzymes from bacteria with special emphasis on Mycobacterium tuberculosis. In vivo, triacylglycerols in the form of inclusion bodies are present in tubercle bacilli in the lungs. This pathogenic bacterium possesses a lipase gene (Lip) family, which is expressed and differentially regulated under a variety of in vitro conditions. Not much research work has been carried out on these lipolytic enzymes. A better understanding of lipolytic enzymes in mycobacteria would lead to develop new strategies for tuberculosis treatment. The present review highlights the recent work done in the field of mycobacterium lipolytic enzymes and their involvement in the virulence and pathogenicity.

Comparative analysis of extracellular enzymes and virulence exhibited by Burkholderia pseudomallei from different sources

To evaluate the potential role of extracellular proteins in the pathogenicity and virulence of Burkholderia pseudomallei, the activities of several enzymes in the culture filtrates of nine clinical and six environmental isolates were investigated in vitro and in vivo in ICR strain of mice. The production of protease, phosphatase, phospholipase C, superoxide dismutase, catalase and peroxidase were detected in the culture filtrates of all the 15 isolates at different time points of growth 4-24h. Over time, activity of each enzyme at each time point varied. Profile of secretion was similar among the 15 isolates irrespective of source, that is clinical or environmental. Catalase, phosphatase and phospholipase C were found to be increased in 60-100% of the isolates post-passage in mice. In vivo inoculation studies in ICR mice demonstrated a wide difference in their ability to cause bacteraemia, splenic or external abscesses and mortality rate ranged from few days to several weeks.

Control of Pseudomonas aeruginosa in the lung requires the recognition of either lipopolysaccharide or flagellin

Acute lung infection due to Pseudomonas aeruginosa is an increasingly serious problem that results in high mortality especially in the compromised host. In this study, we set out to ascertain what components of the TLR system are most important for innate immunity to this microorganism. We previously demonstrated that TLR2,4-/- mice were not hypersusceptible to infection by a wild-type P. aeruginosa strain. However, we now find that mice lacking both TLR2 and TLR4 (TLR2,4-/- mice) are hypersusceptible to infection following challenge with a P. aeruginosa mutant devoid of flagellin production. We demonstrate that this hypersusceptibility is largely due to a lack of innate defense by the host that fails to control bacterial replication in the lung. Further evidence that a response to flagellin is a key factor in the failure of TLR2,4-/- mice to control the infection with the mutant strain was obtained by demonstrating that the intrapulmonary administration of flagellin over a 18 h period following infection, saved 100% of TLR2,4-/- mice from death. We conclude that the interactions of either TLR4 with LPS or TLR5 with flagellin can effectively defend the lung from P. aeruginosa infection and the absence of a response by both results in hypersusceptibility to this infection.

Resistance and virulence of Pseudomonas aeruginosa clinical strains overproducing the MexCD-OprJ efflux pump

Since their initial description 2 decades ago, MexCD-OprJ-overproducing efflux mutants of Pseudomonas aeruginosa (also called nfxB mutants) have rarely been described in the clinical setting. Screening of 110 nonreplicate clinical isolates showing moderate resistance to ciprofloxacin (MIC from 0.5 microg/ml to 4 microg/ml) yielded only four mutants (3.6%) of that type harboring various alterations in the repressor gene nfxB. MexCD-OprJ upregulation correlated with an increased resistance to ciprofloxacin, cefepime, and chloramphenicol in most of the clinical strains, concomitant with a higher susceptibility to ticarcillin, aztreonam, imipenem, and aminoglycosides. Evidence was obtained that this increased susceptibility to aminoglycosides results from the impaired activity of efflux pump MexXY-OprM. Furthermore, MexCD-OprJ upregulation was found to impair bacterial growth and to have a strain-specific, variable impact on rhamnolipid, elastase, phospholipase C, and pyocyanin production. Review of patient files indicated that the four nfxB mutants were responsible for confirmed cases of infection and emerged during long-term therapy with ciprofloxacin. Taken together, these data show that, while rather infrequent among P. aeruginosa strains with low-level resistance to ciprofloxacin, MexCD-OprJ-overproducing mutants may be isolated after single therapy with fluoroquinolones and may be pathogenic.

Role of lipase in Burkholderia cepacia complex (Bcc) invasion of lung epithelial cells

The Burkholderia cepacia complex (Bcc) is a group of ten closely related species associated with life-threatening infection in cystic fibrosis (CF). These bacteria are highly antibiotic resistant, with some strains transmissible, and in a subgroup of patients, they can cause a rapid and fatal necrotising pneumonia. The Bcc organisms produce a range of exoproducts with virulence potential, including exopolysaccharide, proteases and lipases. Many members of the Bcc are also capable of epithelial cell invasion, although the mechanism(s) involved are poorly understood. This study investigates a role for Bcc lipase in epithelial cell invasion by Bcc strains. Lipase activity was measured in eight species of the Bcc. Strains that produced high levels of lipase were predominantly from the B. multivorans and B. cenocepacia species. Pre-treatment of two epithelial cell lines with Bcc lipase significantly increased invasion by two B. multivorans strains and one B. cenocepacia strain and did not affect either plasma membrane or tight junction integrity. Inhibition of Bcc lipase production by the lipase inhibitor Orlistat significantly decreased invasion by both B. multivorans and B. cenocepacia strains in a concentration-dependent manner. This study demonstrates the extent of lipase production across the Bcc and establishes a potential role for lipase in Bcc epithelial cell invasion.

Identification of an IS6110 insertion site in plcD, the unique phospholipase C gene of Mycobacterium bovis

The IS6110 repetitive element is present in multiple copies in most Mycobacterium tuberculosis complex bacteria, except for Mycobacterium bovis strains, which usually contain a single copy of IS6110 located on a 1·9 kb PvuII fragment of the direct repeat region. IS6110 transposition can disrupt coding regions and is a major force of genomic variation. In a previous work it was demonstrated that phospholipase C genes are preferential loci for IS6110 transposition in M. tuberculosis clinical strains. Bacterial phospholipase C enzymes participate in pathogenic mechanisms used by different organisms, and have been implicated in intracellular survival, cytolysis and cell-to-cell spread. Four phospholipase C genes (plcA, plcB, plcC and plcD) were detected in the genomes of M. tuberculosis, Mycobacterium africanum, Mycobacterium microti and ‘Mycobacterium canettii’. M. bovis and the vaccine strain M. bovis Bacillus Calmette–Guérin contain only the plcD gene. In the present work, the existence of IS6110 insertions within plcD, the unique phospholipase C gene of M. bovis, has been investigated by PCR, Southern blot hybridization and sequencing analysis. In 18 (7·3 %) of 245 isolates analysed, the plcD gene was interrupted by the insertion of one copy of IS6110, which in all cases was transposed in the same orientation and at the same position, 1 972 894, relative to the genome of M. bovis AF2122/97. These 18 isolates were distributed in 6 different spoligotype patterns and contained 4 to 8 IS6110 copies. In contrast, strains showing an intact plcD gene contained one (87 %), two (9·4 %) or three (2·4 %) IS6110 copies, and only a single isolate (1·2 %) had four IS6110 copies. The implications of plcD gene disruption in M. bovis have not been fully investigated, but no differences in the organ distribution of the disease were detected when animals infected with strains from the same spoligotype patterns bearing plcD : : IS6110 and intact plcD were compared.

Virulence of Pseudomonas aeruginosa Cells Surviving Photodynamic Treatment with Toluidine Blue

We report results of a study carried out to investigate photodynamic effect of Touildine blue (TBO) on virulent factors secreted by Pseudomonas aeruginosa. Viability of MCF-7 cells incubated with culture supernatants of bacteria photosensitized with TBO (experimental) was found to be higher than that for MCF-7 cells incubated with culture supernatants of bacterial cells treated either with TBO in dark (control II) or not receiving any treatment (neither TBO nor light (control I)). Furthermore, whereas MCF-7 cells incubated with supernatants of bacteria, control I and II, showed significant morphological alterations, no such changes were observed in MCF-7 cells incubated with supernatant of experimental cells. The activities of phospholipase C and proteases, virulent factors of P. aeruginosa, were also found to decrease on photosensitization. These results suggest that the potency of virulent factors is reduced in cells surviving photodynamic treatment with TBO and this may have implication in treatment of infections caused by P. aeruginosa.

Analysis of genetic polymorphisms affecting the four phospholipase C (plc) genes in Mycobacterium tuberculosis complex clinical isolates

The Mycobacterium tuberculosis genome contains four highly related genes which present significant similarity to Pseudomonas aeruginosa genes encoding phospholipase C enzymes. Three of these genes, plcA, plcB and plcC, are organized in tandem (locus plcABC). The fourth gene, plcD, is located in a different region. This study investigates variations in plcABC and plcD genes in clinical isolates of M. tuberculosis, Mycobacterium africanum and ‘Mycobacterium canettii’. Genetic polymorphisms were examined by PCR, Southern blot hybridization, sequence analysis and RT-PCR. Seven M. tuberculosis isolates contain insertions of IS6110 elements within plcA, plcC or plcD. In 19 of 25 M. tuberculosis isolates examined, genomic deletions were identified, resulting in loss of parts of genes or complete genes from the plcABC and/or plcD loci. Partial plcD deletion was observed in one M. africanum isolate. In each case, deletions were associated with the presence of a copy of the IS6110 element and in all occurrences IS6110 was transposed in the same orientation. A mechanism of deletion resulting from homologous recombination of two copies of IS6110 was recognized in a group of genetically related M. tuberculosis isolates. Five M. tuberculosis isolates presented major polymorphisms in the plcABC and plcD regions, along with loss of expression competence that affected all four plc genes. Phospholipase C is a well-known bacterial virulence factor. The precise role of phospholipase C in the pathogenicity of M. tuberculosis is unknown, but considering the potential importance that the plc genes may have in the virulence of the tubercle bacillus, the study of isolates cultured from patients with active tuberculosis bearing genetic variations affecting these genes may provide insights into the significance of phospholipase C enzymes for tuberculosis pathogenicity.

Pseudomonas aeruginosa and cystic fibrosis: correlation between exoenzyme production and patient's clinical state

In this study, we investigated the correlation between the production by Pseudomonas aeruginosa isolates of four exoenzymes (protease, elastase, neuraminidase, and phospholipase C (PLC)) and the clinical state of cystic fibrosis (CF) patients. We studied 212 P. aeruginosa isolates from 22 CF patients chronically infected with this bacterium. Patients were classified into three clinical groups according to a modified Shwachman-Kulczycki-Khaw (SKK) scoring system. The production of enzymes by isolates from patients in the three populations was analyzed and compared using four statistical tests: chi-square, Mann-Whitney U, principal component analysis, and discriminant analysis. Isolates from patients with excellent or good clinical status (group I, SKK score >/=71) had higher elastase and neuraminidase activities than isolates from the other patients. In contrast, PLC activity, a common characteristic of CF isolates, was higher in isolates from patients with poor or weak clinical status (group III, SKK score </=55). PLC also appeared to be the best parameter for differentiating between groups I and III. Enzyme production was highly variable in group II isolates (SKK score, 56-70). Our results suggest that P. aeruginosa isolates from patients with good clinical status produce large amounts of neuraminidase, and that PLC production may be involved in the decrease in pulmonary function.

Reduced virulence of a hfq mutant of Pseudomonas aeruginosa O1

The Sm-like protein Hfq has been implicated in the regulation of sigmaS-dependent and sigmaS-independent genes in E. coli and in the regulation of virulence factors in both, Yersinia enterocolitica and Brucella abortus. Here, we have studied the effect of Hfq on virulence and stress response of Pseudomonas aeruginosa (PAO1). We have constructed a PAO1hfq- mutant and a PAO1hfq-rpoS- double mutant to permit distinction between direct and indirect effects of Hfq. When compared to the wild-type and the rpoS- strains, the hfq knock out strain showed a reduced growth rate and was unable to utilize glucose as a sole carbon source. Elastase activity was 80% reduced in the hfq- mutant when compared to the wild-type or the rpoS- strain, whereas alginate production seemed to be solely affected by sigmaS. The production of catalase and pyocyanin was shown to be affected in an additive manner by both, Hfq and sigmaS. Moreover, twitching and swarming mediated by typeIV pili was shown to be impaired in the hfq- mutant. When compared to PAO1 wild-type and the rpoS- mutant, the hfq- mutant decreased virulence in Galleria mellonella by a factor of 1 x 10(4) and 5 x 10(3), respectively. Likewise, when compared to wild-type, the PAO1hfq- mutant was significantly attenuated in virulence when administered intraperitoneally in mice. These results strongly suggest that Hfq is a global regulator of PAO1 virulence and stress response which is not exclusively due to its role in stimulating the synthesis of sigmaS.

Phosphatidylinositol-specific phospholipase C activity in Lactobacillus rhamnosus with capacity to translocate

Phosphatidylinositol-specific phospholipase C (PI-PLC) activity was investigated in 25 different lactic acid bacteria (LAB) strains belonging to the genera Lactobacillus, Weisella, and Enterococcus. PI-PLC activity was detected in 44% of the strains studied in culture medium without carbon source. From the PI-PLC positive strains, Lactobacillus rhamnosus ATCC 7469 was selected for translocation studies. Healthy mice were orally administered with a daily dose of 2.0 x 10(9) of viable L. rhamnosus suspension. Viable bacteria were detected in liver and spleen of mice fed with LAB for 7 days. Bacterial colonies isolated from liver were biochemically characterized, and further subjected to randomly amplified polymorphic DNA. Amplification patterns of five strains displayed identical profiles to L. rhamnosus. PI-PLC activity was determined in the strains recovered from liver.

Evidence for the expression of native Mycobacterium tuberculosis phospholipase C: recognition by immune sera and detection of promoter activity

The genome of Mycobacterium tuberculosis H37Rv contains three contiguous genes (plc-a, plc-b and plc-c) which are similar to the Pseudomonas aeruginosa phospholipase C (PLC) genes. Expression of mycobacterial PLC-a and PLC-b in E. coli and M. smegmatis has been reported, whereas expression of the native proteins in M. tuberculosis H37Rv has not been demonstrated. The objective of the present study was to demonstrate that native PLC-a is expressed in M. tuberculosis H37Rv. Sera from mice immunized with recombinant PLC-a expressed in E. coli were used in immunoblots to evaluate PLC-a expression. The immune serum recognized a 49-kDa protein in immunoblots against M. tuberculosis extracts. No bands were visible in M. tuberculosis culture supernatants or extracts from M. avium, M. bovis and M. smegmatis. A 550-bp DNA fragment upstream of plc-a was cloned in the pJEM12 vector and the existence of a functional promoter was evaluated by detection of beta-galactosidase activity. beta-Galactosidase activity was detected in M. smegmatis transformed with recombinant pJEM12 grown in vitro and inside macrophages. The putative promoter was active both in vitro and in vivo, suggesting that expression is constitutive. In conclusion, expression of non-secreted native PLC-a was demonstrated in M. tuberculosis.

Potential role of phospholipases in virulence and fungal pathogenesis

Microbial pathogens use a number of genetic strategies to invade the host and cause infection. These common themes are found throughout microbial systems. Secretion of enzymes, such as phospholipase, has been proposed as one of these themes that are used by bacteria, parasites, and pathogenic fungi. The role of extracellular phospholipase as a potential virulence factor in pathogenic fungi, including Candida albicans, Cryptococcus neoformans, and Aspergillus, has gained credence recently. In this review, data implicating phospholipase as a virulence factor in C. albicans, Candida glabrata, C. neoformans, and A. fumigatus are presented. A detailed description of the molecular and biochemical approaches used to more definitively delineate the role of phospholipase in the virulence of C. albicans is also covered. These approaches resulted in cloning of three genes encoding candidal phospholipases (caPLP1, caPLB2, and PLD). By using targeted gene disruption, C. albicans null mutants that failed to secrete phospholipase B, encoded by caPLB1, were constructed. When these isogenic strain pairs were tested in two clinically relevant murine models of candidiasis, deletion of caPLB1 was shown to lead to attenuation of candidal virulence. Importantly, immunogold electron microscopy studies showed that C. albicans secretes this enzyme during the infectious process. These data indicate that phospholipase B is essential for candidal virulence. Although the mechanism(s) through which phospholipase modulates fungal virulence is still under investigations, early data suggest that direct host cell damage and lysis are the main mechanisms contributing to fungal virulence. Since the importance of phospholipases in fungal virulence is already known, the next challenge will be to utilize these lytic enzymes as therapeutic and diagnostic targets.

Potential role of phospholipases in virulence and fungal pathogenesis

Microbial pathogens use a number of genetic strategies to invade the host and cause infection. These common themes are found throughout microbial systems. Secretion of enzymes, such as phospholipase, has been proposed as one of these themes that are used by bacteria, parasites, and pathogenic fungi. The role of extracellular phospholipase as a potential virulence factor in pathogenic fungi, including Candida albicans, Cryptococcus neoformans, and Aspergillus, has gained credence recently. In this review, data implicating phospholipase as a virulence factor in C. albicans, Candida glabrata, C. neoformans, and A. fumigatus are presented. A detailed description of the molecular and biochemical approaches used to more definitively delineate the role of phospholipase in the virulence of C. albicans is also covered. These approaches resulted in cloning of three genes encoding candidal phospholipases (caPLP1, caPLB2, and PLD). By using targeted gene disruption, C. albicans null mutants that failed to secrete phospholipase B, encoded by caPLB1, were constructed. When these isogenic strain pairs were tested in two clinically relevant murine models of candidiasis, deletion of caPLB1 was shown to lead to attenuation of candidal virulence. Importantly, immunogold electron microscopy studies showed that C. albicans secretes this enzyme during the infectious process. These data indicate that phospholipase B is essential for candidal virulence. Although the mechanism(s) through which phospholipase modulates fungal virulence is still under investigations, early data suggest that direct host cell damage and lysis are the main mechanisms contributing to fungal virulence. Since the importance of phospholipases in fungal virulence is already known, the next challenge will be to utilize these lytic enzymes as therapeutic and diagnostic targets.

Pseudomonas aeruginosa from patients with cystic fibrosis affects function of pulmonary surfactant

Patients with cystic fibrosis are severely affected by an infection with Pseudomonas aeruginosa, a microbe known to synthesize phospholipase C. This study was designed to determine whether that enzyme would affect the function of pulmonary surfactant phospholipids. Mucoid and nonmucoid strains of P. aeruginosa, freshly obtained from patients with cystic fibrosis, were cultured for 12 h on agar plates. The bacteria were suspended in saline solution and then pelleted by centrifugation. The supernatant was used to dilute the surfactant preparation, calf lung surfactant extract, from 35 to 2 mg/mL. Surfactant function, before and after incubation, was examined with a capillary surfactometer, an instrument specifically developed for an evaluation of the ability of surfactant to maintain patency of a narrow glass tube, simulating a terminal conducting airway. Phospholipid hydrolysis was also evaluated biochemically by determining the total content of phospholipids in surfactant before and after incubation. In five experiments, the lipids were separated with thin-layer chromatography, and the phosphorus content was determined in the diacylphosphatidylcholine band before and after incubation for 6, 24, and 48 h. Capillary openness and phospholipid concentration decreased as enzyme concentration and time of incubation increased (p<0.0001). Linear regression showed a significant correlation between time of capillary openness and phospholipid concentration (r = 0.957; p<0.0001). Calf lung surfactant extract hydrolysis was catalyzed by extracts of the bacteria, particularly the nonmucoid, analogous to the catalysis observed with phospholipase C. Surfactant hydrolysis catalyzed by enzymes from P. aeruginosa might severely affect surfactant function provided enzyme concentration is high and time of incubation is long.

Evaluation of Mycobacterium tuberculosis genes involved in resistance to killing by human macrophages

A coinfection assay was developed to examine Mycobacterium tuberculosis genes suspected to be involved in resistance to killing by human macrophages. THP-1 macrophages were infected with a mixture of equal numbers of recombinant Mycobacterium smegmatis LR222 bacteria expressing an M. tuberculosis gene and wild-type M. smegmatis LR222 bacteria expressing the xylE gene. At various times after infection, the infected macrophages were lysed and the bacteria were plated. The resulting colonies were sprayed with catechol to determine the number of recombinant colonies and the number of xylE-expressing colonies. M. smegmatis bacteria expressing the M. tuberculosis glutamine synthetase A (glnA) gene or open reading frame Rv2962c or Rv2958c demonstrated significantly increased survival rates in THP-1 macrophages relative to those of xylE-expressing bacteria. M. smegmatis bacteria expressing M. tuberculosis genes for phospholipase C (plcA and plcB) or for high temperature requirement A (htrA) did not.

Contribution of quorum sensing to the virulence of Pseudomonas aeruginosa in burn wound infections

The Pseudomonas aeruginosa quorum-sensing systems, las and rhl, control the production of numerous virulence factors. In this study, we have used the burned-mouse model to examine the contribution of quorum-sensing systems to the pathogenesis of P. aeruginosa infections in burn wounds. Different quorum-sensing mutants of P. aeruginosa PAO1 that were defective in the lasR, lasI, or rhlI gene or both the lasI and rhlI genes were utilized. The following parameters of the P. aeruginosa infection were examined: (i) lethality to the burned mouse, (ii) dissemination of the P. aeruginosa strain within the body of the infected mouse (by determining the numbers of CFU of P. aeruginosa within the liver and spleen), and (iii) spread of the P. aeruginosa strain within the burned skin (by determining the numbers of CFU of P. aeruginosa at the inoculation site and at a site about 15 mm from the inoculation site [distant site]). In comparison with that of PAO1, the in vivo virulence of lasI, lasR, and rhlI mutants was significantly reduced. However, the most significant reduction in in vivo virulence was seen with the lasI rhlI mutant. The numbers of CFU that were recovered from the livers, spleens, and skin of mice infected with different mutants were significantly lower than those of PAO1. At 8 and 16 h post burn infection, comparable numbers of CFU of PAO1 and lasI and rhlI mutants were obtained from both the inoculation and distant sites of the burned skin of infected mice. In contrast, CFU of the lasR mutant and the lasI rhlI double mutant were recovered only from the inoculation site of infected mice at 8 and 16 h post burn infection. The ability of a plasmid carrying either the lasI or rhlI gene or the lasI and rhlI genes to complement the defect of the lasI rhlI double mutant was also examined. The presence of any of these plasmids within the lasI rhlI double mutant significantly enhanced its in vivo virulence, as well as its ability to spread within the burned skin. These results suggest that the quorum-sensing systems play an important role in the horizontal spread of P. aeruginosa within burned skin and in the dissemination of P. aeruginosa within the bodies of burned-and-infected mice and contributed to the overall virulence of P. aeruginosa in this animal model.

Cloning and characterization of a nonhemolytic phospholipase C gene from Burkholderia pseudomallei

We cloned and characterized a phosphatidylcholine-hydrolyzing phospholipase C (PC-PLC) gene from Burkholderia pseudomallei. DNA sequence analysis of the gene indicated an open reading frame coding for 700 amino acids with a 34-amino-acid signal peptide. When cleaved, this yields a secreted 73-kDa mature protein. The deduced amino acid sequence exhibited 48% similarity to that of a nonhemolytic PLC from Pseudomonas aeruginosa. The expressed PC-PLC was heat stable, nonhemolytic for sheep erythrocytes, and active between pH 2 and 8. Western blot analysis with sera from melioidosis patients indicated that they produced immunoglobulin M antibodies against this PC-PLC protein.

Amino acid substitutions in PilD, a bifunctional enzyme of Pseudomonas aeruginosa. Effect on leader peptidase and N-methyltransferase activities in vitro and in vivo

Subunits of type IV pili and a subset of proteins of the type II extracellular protein secretion apparatus undergo two consecutive post-translational modifications: leader peptide cleavage, followed by methylation of the newly created N-terminal amino acid. These two reactions are carried out by a single bifunctional enzyme encoded in Pseudomonas aeruginosa by the pilD gene. Properties of PilD mutants at positions Gly95 and/or Lys96 which were differentially affected in leader peptidase and N-methyltransferase function were characterized. None of the single amino acid substitutions showed a significant alteration in their ability to cleave the prepilin leader peptide; however, two double mutants did exhibit a modest reduction in the efficiency of cleavage. In contrast, a significant decrease of N-methyltransferase activity was detected in PilD having substitutions at Gly95. Mutants with substitutions at position Lys96 showed a variable effect on N-methyltransferase activity with an apparent requirement for any charged amino acid at this position. Absence of N-methyltransferase activity did not appear to interfere with the ability of P. aeruginosa to assemble functional pili. Moreover, pilin monomers isolated from P. aeruginosa expressing PilD with Gly95 substitutions were not methylated. Although complete methylation does not appear to be absolutely required for pilus assembly in P. aeruginosa, this modification may be important for pilus function in its natural habitat.

Osmoprotectant-dependent expression of plcH, encoding the hemolytic phospholipase C, is subject to novel catabolite repression control in Pseudomonas aeruginosa PAO1

Expression of the hemolytic phospholipase C (PlcH) of Pseudomonas aeruginosa is induced under phosphate starvation conditions or in the presence of the osmoprotectants choline and glycine betaine. Because choline and glycine betaine may serve as carbon and energy sources in addition to conferring osmoprotection to P. aeruginosa, it seemed possible that induction of plcH is subject to catabolite repression control (CRC) by tricarboxylic cycle intermediates such as succinate. Total phospholipase (PLC) activity in osmoprotectant-induced cultures of P. aeruginosa PAO1 supplemented with 20 mM succinate was three- to fourfold lower than the levels in cultures supplemented with the non-catabolite-repressive substrate lactate. Analyses of osmoprotectant-dependent plcH expression in a derivative of strain PAO1 containing a plcH::lacZ operon fusion showed that (i) succinate prevented induction of plcH expression by osmoprotectants; and (ii) addition of succinate reduced or shut down further expression of plcH in osmoprotectant-induced bacteria, while cultures supplemented with lactate had little or no change in plcH expression. RNase protection analysis confirmed that repression of plcH occurs at the transcriptional level. However, a P. aeruginosa mutant decoupled in CRC exhibited a phenotype similar to that of the wild-type strain (PAO1) with respect to succinate-dependent repression of plcH expression. Osmoprotectant-induced total PLC activities, levels of expression of plcH measured with the same plcH::lacZ fusion, and levels of plcH transcription in a CRC-deficient strain reflected those seen in strain PAO1. This indicates that CRC of plcH functions by a distinct mechanism which differs from that regulating the glucose or mannitol catabolic pathway. A strain carrying a mutation in vfr, which encodes the Escherichia coli Crp homolog in P. aeruginosa, still exhibited a wild-type phenotype with respect to osmoprotectant-dependent expression and CRC of plcH. These data indicate that there is a novel CRC system that regulates the expression of plcH in P. aeruginosa.

PlcR1 and PlcR2 are putative calcium-binding proteins required for secretion of the hemolytic phospholipase C of Pseudomonas aeruginosa

The plcHR operon of Pseudomonas aeruginosa includes the structural gene for the hemolytic phospholipase C,plcH (previously known as plcS), and two overlapping, in-phase, genes designated plcR1 and plcR2. Hemolytic and phospholipase C (PLC) activities produced by Escherichia coli and P. aeruginosa T7 expression systems were measured in strains carrying both plcH and plcR genes and in strains carrying each gene separately. When plcH was expressed by itself in the E. coli T7 system, the area of the hemolytic zone on blood agar was less than twice the area of growth. By contrast, when plcR was coexpressed with plcH in this system, the area of the hemolytic zone was approximately 10 times that of the area of the growth on blood agar. Native polyacrylamide gel electrophoretic analyses of PlcH activity expressed in either the E. coli or the P. aeruginosa T7 system carrying plcH alone, or along with the plcR genes, suggest that PlcR either posttranslationally alters the physical or biochemical nature of PlcH or releases PlcH from a complex in the cell so that it can be secreted. The hypothesis that PlcR is involved in the secretion of PlcH is supported by the observation that the ratio of extracellular to cell-associated PlcH activity produced by P. aeruginosa strains containing an in-frame deletion in the chromosomal plcR genes is significantly reduced in comparison with this ratio seen with the wild-type parental strain. This defect in the secretion of PlcH can be complemented by the plcR genes in trans. Additional data suggest that PlcR does not directly affect the secretion of the nonhemolytic phospholipase C (PlcN). PlcR is highly similar to a calcium-binding protein (CAB) from Streptomyces erythraeus. PlcR and CAB contain typical motifs (EF hands) characteristic of eucaryotic calcium-binding proteins, including calmodulin. P. aeruginosa naturally produces membrane vesicles (MVs) containing extracellular proteins including PLC. MVs from the PAO1WT strain contained at least 10-fold more PLC specific activity than those isolated from a strain carrying a deletion of plcR (PAO1 deltaR). Immunogold electron microscopy of PAO1WT and PAO1 deltaR whole cells revealed a distribution of PlcH in these strains consistent with the hypothesis that PlcR is required for the secretion of PlcH.

Characterization of elastase-deficient clinical isolates of Pseudomonas aeruginosa

Elastase production in Pseudomonas aeruginosa is regulated by the lasR, lasI, rhlR, and rhlI genes. Recently, we have analyzed several clinical isolates of P. aeruginosa for the production of elastase and other extracellular virulence factors. Four of these isolates (CIT1, CIW5, CIW7, and CIW8) produced no elastolytic activity. We have characterized these isolates with respect to their elastase-deficient phenotype. Elastase was detected by immunoblotting experiments using elastase-specific antiserum. We also determined the presence of IasB and IasR mRNAs by Northern (RNA) blot hybridization experiments using lasB and lasR internal probes, respectively. None of the four elastase-deficient strains produced either the elastase protein or the lasB mRNA. Complementation experiments (using plasmids carrying either the lasB or the lasR gene) were conducted to determine if the isolates carry defective lasB or lasR genes. The presence of either a lasB or a lasR plasmid in CIW7 and CIW8 resulted in the production of very low levels of elastase and lasB mRNA. Neither elastase nor lasB mRNA was detected in CIT1 and CIW5 carrying the lasB plasmid. The presence of the lasR plasmid in CIT1 and CIW5 resulted in the production of lasB mRNA and elastase protein in CIW5 only. All elastase-deficient strains produced detectable levels of lasR mRNA which were enhanced in the presence of the lasR plasmid. The Pseudomonas autoinducer (which is encoded by lasI) was also produced by all strains. CIT1 produced both hemolysin and alkaline protease but was defective in pyocyanin production. These results suggest that (i) CIT1 may contain a defect in a lasB-regulatory gene, (ii) CIW5 carries a defect within lasR, and (iii) the defect in isolates CIW7 and CIW8 affects the efficiency of lasB transcription.

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.

A species-specific nucleotide sequence of Mycobacterium tuberculosis encodes a protein that exhibits hemolytic activity when expressed in Escherichia coli

Species-specific proteins may be implicated in the unique pathogenic mechanisms characteristic of Mycobacterium tuberculosis. In previous studies, a 3.0-kb species-specific DNA fragment of M. tuberculosis was identified (C. A. Parra, L. P. Londoño, P. del Portillo, and M. E. Patarroyo, Immun. 59:3411-3417, 1991). The nucleotide sequence of this 3.0-kb fragment has been obtained. This sequence was shown to contain two open reading frames (ORFs) whose putative gene products share 68.9% identity between each other. The major ORF shows 57.8% similarity with PLC-N and 53.2% similarity with PLC-H, two phospholipase C enzymes from Pseudomonas aeruginosa. The major ORF was amplified by PCR and cloned into the pGEX-5T expression vector. Cell extracts of Escherichia coli overexpressing this glutathione S-transferase fusion protein were shown to produce beta-hemolysis suggestive of phospholipase activity. Since phospholipase C enzymes have been reported as virulence factors of P. aeruginosa and also of the intracellular pathogen Listeria monocytogenes, it is possible that the proteins identified in this study could also play a role in sustaining tuberculosis infection in humans.