The Pseudomonas aeruginosa proteome during anaerobic growth

Calprotectin elicits aberrant iron starvation responses in Pseudomonas aeruginosa under anaerobic conditions

Pseudomonas aeruginosa is an opportunistic pathogen that uses several mechanisms to survive in the iron-limiting host environment. The innate immune protein calprotectin (CP) sequesters ferrous iron [Fe(II)], among other divalent transition metal ions, to limit its availability to pathogens. CP levels are increased in individuals with cystic fibrosis (CF), a hereditary disease that leads to chronic pulmonary infection by P. aeruginosa. We previously showed that aerobic CP treatment of P. aeruginosa induces a multi-metal starvation response that alters expression of several virulence properties. However, the CF lung is a hypoxic environment due to the growth of P. aeruginosa in dense biofilms. Here, we report that anaerobic CP treatment of P. aeruginosa induces many processes associated with an aerobic iron starvation response, including decreased phenazine production and increased expression of the PrrF small regulatory RNAs (sRNAs). However, the iron starvation response elicited by CP in anaerobic conditions shows characteristics that are distinct from responses observed in aerobic growth, including a lack of siderophore production and increased induction of genes for the FeoAB Fe(II) and Phu heme uptake systems. Also distinct from aerobic conditions, CP treatment induces expression of genes for predicted manganese transporters MntH1 and MntH2 during anaerobic growth while eliciting a less robust zinc starvation response compared to aerobic conditions. Induction of mntH2 is dependent on the PrrF sRNAs, suggesting a novel example of metal regulatory cross-talk. Thus, anaerobic CP treatment results in a multi-metal starvation response with key distinctions from aerobic conditions, revealing differences in P. aeruginosa metal homeostasis during anaerobic growth.IMPORTANCEIron is critical for most microbial pathogens, and the innate immune system sequesters this metal to limit microbial growth. Pathogens must overcome iron sequestration to survive during infection. For many pathogens, iron homeostasis has primarily been studied in aerobic conditions. Nevertheless, some host environments are hypoxic, including chronic lung infection sites in individuals with cystic fibrosis (CF). Here, we use the innate immune protein calprotectin, which sequesters divalent metal ions including Fe(II), to study the anaerobic iron starvation response of a common CF lung pathogen, Pseudomonas aeruginosa. We report several distinctions of this response during anaerobiosis, highlighting the importance of carefully considering the host environment when investigating the role of nutritional immunity in host-pathogen interactions.

The secondary metabolite hydrogen cyanide protects Pseudomonas aeruginosa against sodium hypochlorite-induced oxidative stress

The high pathogenicity of Pseudomonas aeruginosa is attributed to the production of many virulence factors and its resistance to several antimicrobials. Among them, sodium hypochlorite (NaOCl) is a widely used disinfectant due to its strong antimicrobial effect. However, bacteria develop many mechanisms to survive the damage caused by this agent. Therefore, this study aimed to identify novel mechanisms employed by P. aeruginosa to resist oxidative stress induced by the strong oxidizing agent NaOCl. We analyzed the growth of the P. aeruginosa mutants ΔkatA, ΔkatE, ΔahpC, ΔahpF, ΔmsrA at 1 μg/mL NaOCl, and showed that these known H2O2 resistance mechanisms are also important for the survival of P. aeruginosa under NaOCl stress. We then conducted a screening of the P. aeruginosa PA14 transposon insertion mutant library and identified 48 mutants with increased susceptibility toward NaOCl. Among them were 10 mutants with a disrupted nrdJa, bvlR, hcnA, orn, sucC, cysZ, nuoJ, PA4166, opmQ, or thiC gene, which also exhibited a significant growth defect in the presence of NaOCl. We focussed our follow-up experiments (i.e., growth analyzes and kill-kinetics) on mutants with defect in the synthesis of the secondary metabolite hydrogen cyanide (HCN). We showed that HCN produced by P. aeruginosa contributes to its resistance toward NaOCl as it acts as a scavenger molecule, quenching the toxic effects of NaOCl.

A novel ruthenium-silver based antimicrobial potentiates aminoglycoside activity against Pseudomonas aeruginosa

The rapid dissemination of antibiotic resistance combined with the decline in the discovery of novel antibiotics represents a major challenge for infectious disease control that can only be mitigated by investments in novel treatment strategies. Alternative antimicrobials, including silver, have regained interest due to their diverse mechanisms of inhibiting microbial growth. One such example is AGXX, a broad-spectrum antimicrobial that produces highly cytotoxic reactive oxygen species (ROS) to inflict extensive macromolecular damage. Due to the connections identified between ROS production and antibiotic lethality, we hypothesized that AGXX could potentially increase the activity of conventional antibiotics. Using the gram-negative pathogen Pseudomonas aeruginosa, we screened possible synergistic effects of AGXX on several antibiotic classes. We found that the combination of AGXX and aminoglycosides tested at sublethal concentrations led to a rapid exponential decrease in bacterial survival and restored the sensitivity of a kanamycin-resistant strain. ROS production contributes significantly to the bactericidal effects of AGXX/aminoglycoside treatments, which is dependent on oxygen availability and can be reduced by the addition of ROS scavengers. Additionally, P. aeruginosa strains deficient in ROS detoxifying/repair genes were more susceptible to AGXX/aminoglycoside treatment. We further demonstrate that this synergistic interaction was associated with a significant increase in outer and inner membrane permeability, resulting in increased antibiotic influx. Our study also revealed that AGXX/aminoglycoside-mediated killing requires an active proton motive force across the bacterial membrane. Overall, our findings provide an understanding of cellular targets that could be inhibited to increase the activity of conventional antimicrobials. IMPORTANCE The emergence of drug-resistant bacteria coupled with the decline in antibiotic development highlights the need for novel alternatives. Thus, new strategies aimed at repurposing conventional antibiotics have gained significant interest. The necessity of these interventions is evident especially in gram-negative pathogens as they are particularly difficult to treat due to their outer membrane. This study highlights the effectiveness of the antimicrobial AGXX in potentiating aminoglycoside activities against P. aeruginosa. The combination of AGXX and aminoglycosides not only reduces bacterial survival rapidly but also significantly re-sensitizes aminoglycoside-resistant P. aeruginosa strains. In combination with gentamicin, AGXX induces increased endogenous oxidative stress, membrane damage, and iron-sulfur cluster disruption. These findings emphasize AGXX's potential as a route of antibiotic adjuvant development and shed light on potential targets to enhance aminoglycoside activity.

MoaB1 Homologs Contribute to Biofilm Formation and Motility by Pseudomonas aeruginosa and Escherichia coli

moaB homologs, encoding the molybdopterin biosynthetic protein B1, have been reported to be expressed under anoxic conditions and during biofilm growth in various microorganisms; however, little is known about MoaB's function. Here, we demonstrate that in Pseudomonas aeruginosa, MoaB1 (PA3915) contributes to biofilm-related phenotypes. Specifically, moaB1 expression is induced in biofilms, and insertional inactivation of moaB1 reduced biofilm biomass accumulation and pyocyanin production while enhancing swarming motility, and pyoverdine abundance without affecting attachment, swimming motility, or c-di-GMP levels. Inactivation of the highly conserved E. coli homolog of moaB1, moaBEc, likewise coincided with reduced biofilm biomass accumulation. In turn, heterologous expression of moaBEc restored biofilm formation and swarming motility by the P. aeruginosa moaB1 mutant to wild-type levels. Moreover, MoaB1 was found to interact with other conserved biofilm-associated proteins, PA2184 and PA2146, as well as the sensor-kinase SagS. However, despite the interaction, MoaB1 failed to restore SagS-dependent expression of brlR encoding the transcriptional regulator BrlR, and inactivation of moaB1 or moaBEc had no effect on the antibiotic susceptibility phenotype of biofilms formed by P. aeruginosa and E. coli, respectively. While our findings did not establish a link between MoaB1 and molybdenum cofactor biosynthesis, they suggest that MoaB1 homologs contribute to biofilm-associated phenotypes across species boundaries, possibly hinting at the existence of a previously undescribed conserved biofilm pathway. IMPORTANCE Proteins contributing to the biogenesis of molybdenum cofactors have been characterized; however, the role of the molybdopterin biosynthetic protein B1 (MoaB1) has remained elusive, and solid evidence to support its role in biosynthesis of molybdenum cofactor is lacking. Here, we demonstrate that, in Pseudomonas aeruginosa, MoaB1 (PA3915) contributes to biofilm-related phenotypes in a manner that does not support a role of MoaB1 in the biosynthesis of molybdenum cofactors.

A Review of Pseudomonas aeruginosa Metallophores: Pyoverdine, Pyochelin and Pseudopaline

P. aeruginosa is a common Gram-negative bacterium found in nature that causes severe infections in humans. As a result of its natural resistance to antibiotics and the ability of biofilm formation, the infection with this pathogen can be therapeutic challenging. During infection, P. aeruginosa produces secondary metabolites such as metallophores that play an important role in their virulence. Metallophores are metal ions chelating molecules secreted by bacteria, thus allowing them to survive in the host under metal scarce conditions. Pyoverdine, pyochelin and pseudopaline are the three metallophores secreted by P. aeruginosa. Pyoverdines are the primary siderophores that acquire iron from the surrounding medium. These molecules scavenge and transport iron to the bacterium intracellular compartment. Pyochelin is another siderophore produced by this bacterium, but in lower quantities and its affinity for iron is less than that of pyoverdine. The third metallophore, pseudopaline, is an opine narrow spectrum ion chelator that enables P. aeruginosa to uptake zinc in particular but can transport nickel and cobalt as well. This review describes all the aspects related to these three metallophore, including their main features, biosynthesis process, secretion and uptake when loaded by metals, in addition to the genetic regulation responsible for their synthesis and secretion.

Main Metabolites of Pseudomonas aeruginosa: A Study of Electrochemical Properties

Pseudomonas aeruginosa is a ubiquitously distributed soil and water bacterium and is considered an opportunistic pathogen in hospitals. In cystic fibrosis patients, for example, infections with P. aeruginosa can be severe and often lead to chronic or even fatal pneumonia. Therefore, rapid detection and further identification are of major importance in hospital hygiene and infection control. This work shows the electrochemical properties of five P. aeruginosa key metabolites considering their potential use as specific signaling agents in an electrochemical sensor system. The pure solutes of pyocyanin (PYO), Pseudomonas quinolone signal (PQS), pyochelin (PCH), 2-heptyl-4-hydroxyquinoline (HHQ), and 2-heptyl-4-hydroxyquinoline N-oxide (HQNO) were analyzed by different electrochemical techniques (cyclic and square wave voltammetry) and measured using a Gamry Reference 600+ potentiostat. Screen-printed electrodes (DropSens DRP110; carbon working and counter, silver reference electrode) were used to determine signal specificities, detection limits, as well as pH dependencies of the substances. All of the compounds were electrochemically inducible with well-separated oxidation and/or reduction peaks at specific peak potentials relative to the reference electrode. Additionally, all analytes exhibited linear concentration dependency in ranges classically reported in the literature. The demonstration of these properties is a promising step toward direct multiplexed detection of P. aeruginosa in environmental and clinical samples and thus, can make a significant contribution to public health and safety.

Comparative Proteomics Reveals the Anaerobic Lifestyle of Meat-Spoiling Pseudomonas Species

The ability of certain Pseudomonas (P.) species to grow or persist in anoxic habitats by either denitrification, acetate fermentation, or arginine fermentation has been described in several studies as a special property. Previously, we had isolated strains belonging to the species P. lundensis, P. weihenstephanensis, and P. fragi from anoxic modified atmosphere packaged (MAP) minced beef and further proved their anaerobic growth in vitro on agar plates. This follow-up study investigated the anaerobic growth of two strains per respective species in situ on inoculated chicken breast filet under 100% N₂ modified atmosphere. We were able to prove anaerobic growth of all six strains on chicken breast filet with cell division rates of 0.2–0.8/day. Furthermore, we characterized the anaerobic metabolic lifestyle of these Pseudomonas strains by comparative proteomics, upon their cultivation in meat simulation media, which were constantly gassed with either air or 100% N₂ atmospheres. From these proteomic predictions, and respective complementation by physiological experiments, we conclude that the Pseudomonas strains P. fragi, P. weihenstephanensis, P. lundensis exhibit a similar anaerobic lifestyle and employ arginine fermentation via the arginine deiminase (ADI) pathway to grow anaerobically also on MAP meats. Furthermore, glucose fermentation to ethanol via the ED-pathway is predicted to enable long term survival but no true growth, while respiratory growth with nitrate as alternative electron acceptor or glucose fermentation to acetate could be excluded due to absence of essential genes. The citric acid cycle is partially bypassed by the glyoxylate shunt, functioning as the gluconeogenetic route without production of NADH₂ under carbon limiting conditions as e.g., in packaged meats. Triggered by an altered redox balance, we also detected upregulation of enzymes involved in protein folding as well as disulfide bonds isomerization under anoxic conditions as a counteracting mechanism to reduce protein misfolding. Hence, this study reveals the mechanisms enabling anaerobic grow and persistence of common meat-spoiling Pseudomonas species, and further complements the hitherto limited knowledge of the anaerobic lifestyle of Pseudomonas species in general.

A metabolic and physiological design study of Pseudomonas putida KT2440 capable of anaerobic respiration

BACKGROUND

Pseudomonas putida KT2440 is a metabolically versatile, HV1-certified, genetically accessible, and thus interesting microbial chassis for biotechnological applications. However, its obligate aerobic nature hampers production of oxygen sensitive products and drives up costs in large scale fermentation. The inability to perform anaerobic fermentation has been attributed to insufficient ATP production and an inability to produce pyrimidines under these conditions. Addressing these bottlenecks enabled growth under micro-oxic conditions but does not lead to growth or survival under anoxic conditions.

RESULTS

Here, a data-driven approach was used to develop a rational design for a P. putida KT2440 derivative strain capable of anaerobic respiration. To come to the design, data derived from a genome comparison of 1628 Pseudomonas strains was combined with genome-scale metabolic modelling simulations and a transcriptome dataset of 47 samples representing 14 environmental conditions from the facultative anaerobe Pseudomonas aeruginosa.

CONCLUSIONS

The results indicate that the implementation of anaerobic respiration in P. putida KT2440 would require at least 49 additional genes of known function, at least 8 genes encoding proteins of unknown function, and 3 externally added vitamins.

Evaluation of the Biodegradation Efficiency of Four Various Types of Plastics by Pseudomonas aeruginosa Isolated from the Gut Extract of Superworms

Plastic waste worldwide is becoming a serious pollution problem for the planet. Various physical and chemical methods have been tested in attempts to remove plastic dumps. However, these have usually resulted in secondary pollution issues. Recently, the biodegradation of plastic by fungal and bacterial strains has been spotlighted as a promising solution to remove plastic wastes without generating secondary pollution. We have previously reported that a Pseudomonas aeruginosa strain isolated from the gut of a superworm is capable of biodegrading polystyrene (PS) and polyphenylene sulfide (PPS). Herein, we demonstrate the extraordinary biodegradative power of P. aeruginosa in efficiently depolymerizing four different types of plastics: PS, PPS, polyethylene (PE) and polypropylene (PP). We further compared biodegradation rates for these four plastic types and found that PE was biodegraded fastest, whereas the biodegradation of PP was the slowest. Moreover, the growth rates of P. aeruginosa were not always proportional to biodegradation rates, suggesting that the rate of bacterial growth could be influenced by the composition and properties of intermediate molecules produced during plastic biodegradation, and these may supply useful cellular precursors and energy. In conclusion, an initial screening system to select the most suitable bacterial strain to biodegrade certain types of plastic is particularly important and may be necessary to solve plastic waste problems both presently and in the future.

The O2-independent pathway of ubiquinone biosynthesis is essential for denitrification in Pseudomonas aeruginosa

Many proteobacteria, such as Escherichia coli, contain two main types of quinones: benzoquinones, represented by ubiquinone (UQ) and naphthoquinones, such as menaquinone (MK), and dimethyl-menaquinone (DMK). MK and DMK function predominantly in anaerobic respiratory chains, whereas UQ is the major electron carrier in the reduction of dioxygen. However, this division of labor is probably not very strict. Indeed, a pathway that produces UQ under anaerobic conditions in an UbiU-, UbiV-, and UbiT-dependent manner has been discovered recently in E. coli Its physiological relevance is not yet understood, because MK and DMK are also present in E. coli Here, we established that UQ9 is the major quinone of Pseudomonas aeruginosa and is required for growth under anaerobic respiration (i.e. denitrification). We demonstrate that the ORFs PA3911, PA3912, and PA3913, which are homologs of the E. coli ubiT, ubiV, and ubiU genes, respectively, are essential for UQ9 biosynthesis and, thus, for denitrification in P. aeruginosa These three genes here are called ubiTPa , ubiVPa , and ubiUPa We show that UbiVPa accommodates an iron-sulfur [4Fe-4S] cluster. Moreover, we report that UbiUPa and UbiTPa can bind UQ and that the isoprenoid tail of UQ is the structural determinant required for recognition by these two Ubi proteins. Since the denitrification metabolism of P. aeruginosa is believed to be important for the pathogenicity of this bacterium in individuals with cystic fibrosis, our results highlight that the O2-independent UQ biosynthetic pathway may represent a target for antibiotics development to manage P. aeruginosa infections.

Virulence and Pathogenicity Properties of Aggregatibacter actinomycetemcomitans

Aggregatibacter actinomycetemcomitans is a periodontal pathogen colonizing the oral cavity of a large proportion of the human population. It is equipped with several potent virulence factors that can cause cell death and induce or evade inflammation. Because of the large genetic diversity within the species, both harmless and highly virulent genotypes of the bacterium have emerged. The oral condition and age, as well as the geographic origin of the individual, influence the risk to be colonized by a virulent genotype of the bacterium. In the present review, the virulence and pathogenicity properties of A. actinomycetemcomitans will be addressed.

First Insights Into Bacterial Gastrointestinal Tract Communities of the Eurasian Beaver (Castor fiber)

The Eurasian or European beaver (Castor fiber) is the second-largest living rodent after the capybara. It is a semi-aquatic animal known for building dams and lodges. They strictly feed on lignocellulose-rich plants and correspondingly harbor cellulolytic microbial communities in their digestive tract. In this study, the bacterial community composition, diversity, and functional profile of different gut compartments ranging from stomach to colon have been explored. A total of 277 bacterial operational taxonomic units (OTUs) at species level were obtained from the gut systems of two males (juvenile and subadult) and one subadult female beaver. In general, cecum and colon are dominated by Firmicutes and Actinobacteria. High abundance of Bacteroidetes was observed only in male juvenile beaver cecum and colon, suggesting that the bacterial composition changes with age. Within the cecum and colon, members of known cellulase-producing bacterial taxa including the families Ruminococcaceae, Lachnospiraceae, and Clostridiaceae 1 were detected. The presence of putative genes encoding cellulolytic and carbohydrate-degrading enzymes indicated also the degradation of recalcitrant plant material in both gut compartments. The bacterial community in the gut systems of the Eurasian beaver differed from that of the North American beaver. Higher abundance of Actinobacteria and lower abundances of Bacteroidetes were recorded in the Eurasian beaver. Similar differences were obtained to bacterial communities of termites and herbivorous animals such as bovine. The data presented in this study provides the first insight into bacterial communities in the gut system of the Eurasian beaver.

Glutathione Activates Type III Secretion System Through Vfr in Pseudomonas aeruginosa

Glutathione (GSH) is the most abundant antioxidant in all living organisms. Previously, we have shown that a deletion mutant in the glutathione synthetase gene (ΔgshB) decreases the expression of type III secretion system (T3SS) genes of Pseudomonas aeruginosa. However, the mechanism remains elusive. In this study, a comprehensive transcriptomic analysis of the GSH-deficient mutant ΔgshAΔgshB was used to elucidate the role of GSH in the pathogenesis of P. aeruginosa. The data show that the expression of genes in T3SS, type VI secretion system (T6SS) and some regulatory genes were impaired. ΔgshAΔgshB was attenuated in a mouse model of acute pneumonia, swimming and swarming motilities, and biofilm formation. Under T3SS inducing conditions, GSH enhanced the expression of T3SS in both wild-type PAO1 and ΔgshAΔgshB, but not in Δvfr. Genetic complementation of Δvfr restored the ability of GSH to induce the expression of T3SS genes. Site-directed mutagenesis based substitution of cysteine residues with alanine in Vfr protein abolished the induction of T3SS genes by GSH, confirming that GSH regulates T3SS genes through Vfr. Exposure to H₂O₂ decreased free thiol content on Vfr, indicating that the protein was sensitive to redox modification. Importantly, GSH restored the oxidized Vfr to reduced state. Collectively, these results suggest that GSH serves as an intracellular redox signal sensed by Vfr to upregulate T3SS expression in P. aeruginosa. Our work provides new insights into the role of GSH in P. aeruginosa pathogenesis.

Recent Applications of Diazirines in Chemical Proteomics

The elucidation of substrate-protein interactions is an important component of the drug development process. Due to the complexity of native cellular environments, elucidating these fundamental biochemical interactions remains challenging. Photoaffinity labeling (PAL) is a versatile technique that can provide insight into ligand-target interactions. By judicious modification of substrates with a photoreactive group, PAL creates a covalent crosslink between a substrate and its biological target following UV-irradiation. Among the commonly employed photoreactive groups, diazirines have emerged as the gold standard. In this Minireview, recent developments in the field of diazirine-based photoaffinity labeling will be discussed, with emphasis being placed on their applications in chemical proteomic studies.

A phosphatidic acid-binding protein is important for lipid homeostasis and adaptation to anaerobic biofilm conditions in Pseudomonas aeruginosa

A quantitative Pseudomonas aeruginosa proteomics approach revealed increased abundance of the so-far uncharacterized protein PA3911 in anaerobic biofilms grown under conditions of the cystic fibrosis lung. Physiological relevance of ORF PA3911 was demonstrated, inter alia, using phenotype microarray experiments. The mutant strain showed increased susceptibility in the presence of antimicrobials (minocycline, nafcillin, oxacillin, chloramphenicol and thiamphenicol), enhanced twitching motility and significantly impaired biofilm formation. PA3911 is a soluble, cytoplasmic protein in P. aeruginosa. In protein–lipid overlay experiments, purified PA3911 bound specifically to phosphatidic acid (PA), the central hub of phospholipid metabolism. Structure-guided site-directed mutagenesis was used to explore the proposed ligand-binding cavity of PA3911. Protein variants of Leu56, Leu58, Val69 and Leu114 were shown to impair PA interaction. A comparative shotgun lipidomics approach demonstrated a multifaceted response of P. aeruginosa to anaerobic conditions at the lipid head group and fatty acid level. Lipid homeostasis in the PA3911 mutant strain was imbalanced with respect to lysophosphatidylcholine, phosphatidylcholine and diacylglycerol under anaerobic and/or aerobic conditions. The impact of the newly identified PA-binding protein on lipid homeostasis and the related macroscopic phenotypes of P. aeruginosa are discussed.

Promysalin Elicits Species-Selective Inhibition of Pseudomonas aeruginosa by Targeting Succinate Dehydrogenase

Natural products have served as an inspiration to scientists both for their complex three-dimensional architecture and exquisite biological activity. Promysalin is one such Pseudomonad secondary metabolite that exhibits narrow-spectrum antibacterial activity, originally isolated from the rhizosphere. We herein utilize affinity-based protein profiling (AfBPP) to identify succinate dehydrogenase (Sdh) as the biological target of the natural product. The target was further validated in silico, in vitro, in vivo, and through the selection, and sequencing, of a resistant mutant. Succinate dehydrogenase plays an essential role in primary metabolism of Pseudomonas aeruginosa as the only enzyme that is involved both in the tricarboxylic acid cycle (TCA) and in respiration via the electron transport chain. These findings add credence to other studies that suggest that the TCA cycle is an understudied target in the development of novel therapeutics to combat P. aeruginosa, a significant pathogen in clinical settings.

A single point mutation in class III ribonucleotide reductase promoter renders Pseudomonas aeruginosa PAO1 inefficient for anaerobic growth and infection

Pseudomonas aeruginosa strain PAO1 has become the reference strain in many laboratories. One enzyme that is essential for its cell division is the ribonucleotide reductase (RNR) enzyme that supplies the deoxynucleotides required for DNA synthesis and repair. P. aeruginosa is one of the few microorganisms that encodes three different RNR classes (Ia, II and III) in its genome, enabling it to grow and adapt to diverse environmental conditions, including during infection. In this work, we demonstrate that a lack of RNR activity induces cell elongation in P. aeruginosa PAO1. Moreover, RNR gene expression during anaerobiosis differs among P. aeruginosa strains, with class III highly expressed in P. aeruginosa clinical isolates relative to the laboratory P. aeruginosa PAO1 strain. A single point mutation was identified in the P. aeruginosa PAO1 strain class III RNR promoter region that disrupts its anaerobic transcription by the Dnr regulator. An engineered strain that induces the class III RNR expression allows P. aeruginosa PAO1 anaerobic growth and increases its virulence to resemble that of clinical strains. Our results demonstrate that P. aeruginosa PAO1 is adapted to laboratory conditions and is not the best reference strain for anaerobic or infection studies.

Pseudomonas aeruginosa Exhibits Deficient Biofilm Formation in the Absence of Class II and III Ribonucleotide Reductases Due to Hindered Anaerobic Growth

Chronic lung infections by the ubiquitous and extremely adaptable opportunistic pathogen Pseudomonas aeruginosa correlate with the formation of a biofilm, where bacteria grow in association with an extracellular matrix and display a wide range of changes in gene expression and metabolism. This leads to increased resistance to physical stress and antibiotic therapies, while enhancing cell-to-cell communication. Oxygen diffusion through the complex biofilm structure generates an oxygen concentration gradient, leading to the appearance of anaerobic microenvironments. Ribonucleotide reductases (RNRs) are a family of highly sophisticated enzymes responsible for the synthesis of the deoxyribonucleotides, and they constitute the only de novo pathway for the formation of the building blocks needed for DNA synthesis and repair. P. aeruginosa is one of the few bacteria encoding all three known RNR classes (Ia, II, and III). Class Ia RNRs are oxygen dependent, class II are oxygen independent, and class III are oxygen sensitive. A tight control of RNR activity is essential for anaerobic growth and therefore for biofilm development. In this work we explored the role of the different RNR classes in biofilm formation under aerobic and anaerobic initial conditions and using static and continuous-flow biofilm models. We demonstrated the importance of class II and III RNR for proper cell division in biofilm development and maturation. We also determined that these classes are transcriptionally induced during biofilm formation and under anaerobic conditions. The molecular mechanism of their anaerobic regulation was also studied, finding that the Anr/Dnr system is responsible for class II RNR induction. These data can be integrated with previous knowledge about biofilms in a model where these structures are understood as a set of layers determined by oxygen concentration and contain cells with different RNR expression profiles, bringing us a step closer to the understanding of this complex growth pattern, essential for P. aeruginosa chronic infections.

RNASeq Based Transcriptional Profiling of Pseudomonas aeruginosa PA14 after Short- and Long-Term Anoxic Cultivation in Synthetic Cystic Fibrosis Sputum Medium

The opportunistic human pathogen Pseudomonas aeruginosa can thrive under microaerophilic to anaerobic conditions in the lungs of cystic fibrosis patients. RNA_Seq based comparative RNA profiling of the clinical isolate PA14 cultured in synthetic cystic fibrosis medium was performed after planktonic growth (OD₆₀₀ = 2.0; P), 30 min after shift to anaerobiosis (A-30) and after anaerobic biofilm growth for 96h (B-96) with the aim to reveal differentially regulated functions impacting on sustained anoxic biofilm formation as well as on tolerance towards different antibiotics. Most notably, functions involved in sulfur metabolism were found to be up-regulated in B-96 cells when compared to A-30 cells. Based on the transcriptome studies a set of transposon mutants were screened, which revealed novel functions involved in anoxic biofilm growth.In addition, these studies revealed a decreased and an increased abundance of the oprD and the mexCD-oprJ operon transcripts, respectively, in B-96 cells, which may explain their increased tolerance towards meropenem and to antibiotics that are expelled by the MexCD-OprD efflux pump. The OprI protein has been implicated as a target for cationic antimicrobial peptides, such as SMAP-29. The transcriptome and subsequent Northern-blot analyses showed that the abundance of the oprI transcript encoding the OprI protein is strongly decreased in B-96 cells. However, follow up studies revealed that the susceptibility of a constructed PA14ΔoprI mutant towards SMAP-29 was indistinguishable from the parental wild-type strain, which questions OprI as a target for this antimicrobial peptide in strain PA14.

Essential O2-responsive genes of Pseudomonas aeruginosa and their network revealed by integrating dynamic data from inverted conditions

Identification of the gene network through which Pseudomonas aeruginosa PAO1 (PA) adapts to altered oxygen-availability environments is essential for a better understanding of stress responses and pathogenicity of PA. We performed high-time-resolution (HTR) transcriptome analyses of PA in a continuous cultivation system during the transition from high oxygen tension to low oxygen tension (HLOT) and the reversed transition from low to high oxygen tension (LHOT). From those genes responsive to both transient conditions, we identified 85 essential oxygen-availability responsive genes (EORGs), including the expected ones (arcDABC) encoding enzymes for arginine fermentation. We then constructed the regulatory network for the EORGs of PA by integrating information from binding motif searching, literature and HTR data. Notably, our results show that only the sub-networks controlled by the well-known oxygen-responsive transcription factors show a very high consistency between the inferred network and literature knowledge, e.g. 87.5% and 83.3% of the obtained sub-network controlled by the anaerobic regulator (ANR) and a quorum sensing regulator RhIR, respectively. These results not only reveal stringent EORGs of PA and their transcription regulatory network, but also highlight that achieving a high accuracy of the inferred regulatory network might be feasible only for the apparently affected regulators under the given conditions but not for all the expressed regulators on a genome scale.

Synthesis and antibacterial activity of a new derivative of the Meldrun acid: 2,2-dimethyl-5-(4H-1,2,4-triazol-4-ylaminomethylene)-1,3-dioxane-4,6-dione (C9H10N4O4)

The discovery of new substances with proven antimicrobial activity is the current study goal of various researchers. Usage of synthetic products has grown considerably in the past few years due to processing agility, and capability of going through previous chemical modifications in order to enhance its biological activity. Widespread careless use of antimicrobials has made the number of resistant microorganisms rise significantly, thus demanding more efficient drugs to fight them. One of these synthetic candidates for this purpose is the substance 2,2-Dimethyl-5-(4H-1,2,4-triazol-4-ylaminomethylene)-1,3-dioxane-4,6-dione (C9H10N4O4), aminomethylene derivative from Meldrum's acid. This substance, alone and in association with common antibiotics, were evaluated in vitro for antimicrobial activity, and had their minimum inhibitory concentration (MIC) towards Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 10536 and Pseudomonas aeruginosa ATCC 15442, as well as multiresistant strains Escherichia coli 27, Staphylococcus aureus 358 and Pseudomonas aeruginosa 03 determined. The antimicrobial modulation action tests of the aminoglycosides with C9H10N4O4 were performed according to the microdilution method, and resulted in observation of a positive synergic effect.

Microcolony formation by the opportunistic pathogen Pseudomonas aeruginosa requires pyruvate and pyruvate fermentation

A hallmark of the biofilm architecture is the presence of microcolonies. However, little is known about the underlying mechanisms governing microcolony formation. In the pathogen Pseudomonas aeruginosa, microcolony formation is dependent on the two-component regulator MifR, with mifR mutant biofilms exhibiting an overall thin structure lacking microcolonies, and overexpression of mifR resulting in hyper-microcolony formation. Using global transcriptomic and proteomic approaches, we demonstrate that microcolony formation is associated with stressful, oxygen-limiting but electron-rich conditions, as indicated by the activation of stress response mechanisms and anaerobic and fermentative processes, in particular pyruvate fermentation. Inactivation of genes involved in pyruvate utilization including uspK, acnA and ldhA abrogated microcolony formation in a manner similar to mifR inactivation. Moreover, depletion of pyruvate from the growth medium impaired biofilm and microcolony formation, while addition of pyruvate significantly increased microcolony formation. Addition of pyruvate to or expression of mifR in lactate dehydrogenase (ldhA) mutant biofilms did not restore microcolony formation, while addition of pyruvate partly restored microcolony formation in mifR mutant biofilms. In contrast, expression of ldhA in mifR::Mar fully restored microcolony formation by this mutant strain. Our findings indicate the fermentative utilization of pyruvate to be a microcolony-specific adaptation of the P. aeruginosa biofilm environment.

A theoretical and experimental proteome map of Pseudomonas aeruginosa PAO1

A total proteome map of the Pseudomonas aeruginosa PAO1 proteome is presented, generated by a combination of two-dimensional gel electrophoresis and protein identification by mass spectrometry. In total, 1128 spots were visualized, and 181 protein spots were characterized, corresponding to 159 different protein entries. In particular, protein chaperones and enzymes important in energy conversion and amino acid biosynthesis were identified. Spot analysis always resulted in the identification of a single protein, suggesting sufficient spot resolution, although the same protein may be detected in two or more neighboring spots, possibly indicating posttranslational modifications. Comparison to the theoretical proteome revealed an underrepresentation of membrane proteins, though the identified proteins cover all predicted subcellular localizations and all functional classes. These data provide a basis for subsequent comparative studies of the biology and metabolism of P. aeruginosa, aimed at unraveling global regulatory networks.

Comparisons of Two Proteomic Analyses of Non-Mucoid and Mucoid Pseudomonas aeruginosa Clinical Isolates from a Cystic Fibrosis Patient

Pseudomonas aeruginosa chronically infects the lungs of cystic fibrosis (CF) patients. The conditions in the CF lung appear to select for P. aeruginosa with advantageous phenotypes for chronic infection. However, the mechanisms that allow the establishment of this chronic infection have not been fully characterized. We have previously reported the transcriptional analysis of two CF isolates strains 383 and 2192. Strain 2192 is a mucoid, alginate overproducing strain whereas strain 383 is non-mucoid. Mucoid strains are associated with chronic infection of the CF lung and non-mucoid strains are the typical initially infecting isolates. To elucidate novel differences between these two strains, we employed two methods of shotgun proteomics: isobaric tags for relative and absolute quantitation (iTRAQ) and two-dimensional gel electrophoresis (2-DE). iTRAQ compares the amount of protein between samples and relies on protein abundance, while 2-DE gel electrophoresis depends on selection of separated protein spots. For both these methods, mass spectrometry was then used to identify proteins differentially expressed between the two strains. The compilation of these two proteomic methods along with Western blot analysis revealed proteins of the HSI-I operon of the type 6 secretion system, showed increased expression in 383 compared to 2192, confirming the our previous transcriptional analysis. Proteomic analysis of other proteins did not fully correlate with the transcriptome but other differentially expressed proteins are discussed. Also, differences were noted between the results obtained for the two proteomic techniques. These shotgun proteomic analyses identified proteins that had been predicted only through gene identification; we now refer to these as "proteins of unknown functions" since their existence has now been established however their functional characterization remains to be elucidated.

Implications of the inability of Listeria monocytogenes EGD-e to grow anaerobically due to a deletion in the class III NrdD ribonucleotide reductase for its use as a model laboratory strain

Listeria monocytogenes is a Gram-positive facultative intracellular bacterium that causes life-threatening diseases in humans. It grows and survives in environments of low oxygen tension and under conditions of strict anaerobiosis. Oxygen-limiting conditions may be an important factor in determining its pathogenicity. L. monocytogenes serovar 1/2a strain EGD-e has been employed intensively to elucidate the mechanisms of intracellular multiplication and virulence. Listeria possesses genes encoding class I aerobic and class III anaerobic ribonucleotide reductases (RNRs). The class III RNR consists of a catalytic subunit NrdD and an activase NrdG. Surprisingly, L. monocytogenes EGD-e, but not other L. monocytogenes strains or other listerial species, is unable to grow under strict anaerobic conditions. Inspection of listerial NrdD amino acid sequences revealed a six-amino acid deletion in the C-terminal portion of the EGD-e protein, next to the essential glycyl radical domain. Nevertheless, L. monocytogenes EGD-e can grow under microaerophilic conditions due to the recruitment of residual class Ia RNR activity. A three-dimensional (3D) model based on the structure of bacteriophage T4 NrdD identified the location of the deletion, which appears in a highly conserved part of the NrdD RNR structure, in the α/β barrel domain near the glycyl radical domain. The deleted KITPFE region is essential either for interactions with the NrdG activase or, indirectly, for the stability of the glycyl radical loop. Given that L. monocytogenes EGD-e lacks a functional anaerobic RNR, the present findings are relevant to the interpretation of studies of pathogenesis with this strain specifically, in particular under conditions of low oxygen tension.

Anaerobic adaptation in Pseudomonas aeruginosa: definition of the Anr and Dnr regulons

The anaerobic metabolism of the opportunistic pathogen Pseudomonas aeruginosa is important for growth and biofilm formation during persistent infections. The two Fnr-type transcription factors Anr and Dnr regulate different parts of the underlying network in response to oxygen tension and NO. Little is known about all members of the Anr and Dnr regulons and the mediated immediate response to oxygen depletion. Comprehensive transcriptome and bioinformatics analyses in combination with a limited proteome analyses were used for the investigation of the P. aeruginosa response to an immediate oxygen depletion and for definition of the corresponding Anr and Dnr regulons. We observed at first the activation of fermentative pathways for immediate energy generation followed by induction of alternative respiratory chains. A solid position weight matrix model was deduced from the experimentally identified Anr boxes and used for identification of 170 putative Anr boxes in potential P. aeruginosa promoter regions. The combination with the experimental data unambiguously identified 130 new members for the Anr and Dnr regulons. The basis for the understanding of two regulons of P. aeruginosa central to biofilm formation and infection is now defined.

Comparative microarray analysis reveals that the core biofilm-associated transcriptome of Pseudomonas aeruginosa comprises relatively few genes

Pseudomonas aeruginosa is a model organism for the study of intercellular communication and biofilm formation. As such, P. aeruginosa has been the subject of several microarray analyses comparing gene expression in biofilms and planktonic cultures. In the current work, we carried out a meta-analysis of these data sets to try and identify genes that are generically associated with biofilm formation in all of the conditions examined. Although the total number of transcripts modulated in the biofilms was large within the individual studies, the overlap between the data sets was small. Indeed, only five transcripts were upregulated and six transcripts were downregulated by more than twofold in the three data sets analysed. However, when the threshold modulation was relaxed to less than twofold, the overlap between the data sets increased, revealing a set of transcripts common to all of the studies. Transcriptional fusions and quantitative real-time PCR were used to independently confirm a selection of the observed modulations. Notably, we found that the expression profile of genes encoding the catabolic pathways for branched chain and aromatic amino acids was altered in biofilms, and that these alterations correlated with the onset of anaerobic growth. These findings were confirmed by quantitative amino acid analysis of culture supernatants. A mutant in one of the genes that we identified showed diminished biofilm formation in an attachment assay. The relatively small number of common biofilm-specific endpoint transcripts throws doubt on the suggestion that biofim formation proceeds through a pre-determined developmental pathway.

Proteomics of bacterial pathogens: Pseudomonas aeruginosa infections in cystic fibrosis - a case study

Technology development in the high throughput sciences of genomics, transcriptomics and proteomics, has been driven by bacteriological research. These organisms are excellent models for testing new methodology due to their comparatively small genome size, the relative ease of culturing large amounts of material, and the inherent biomedical, environmental and biotechnological interest in their underlying biology. Techniques developed in prokaryotes have since become applicable to higher organisms and human disease, opening vast research opportunities for understanding complex molecular processes. Pseudomonas aeruginosa is an excellent example of a microbe with fascinating properties suitable for stretching the boundaries of technology, and with underlying biology that remains poorly understood. P. aeruginosa is an opportunistic pathogen in humans and contains one of the largest genetic capabilities for a single-celled organism (approximately 5500 genes), which allows it to encode a wide variety of surface-associated and secreted virulence factors, as well as adapt to harsh environments, forming resistance to an array of antibacterial agents. While it is a major threat as a nosocomial pathogen, and particularly in the immunocompromised, it is also the most significant cause of mortality in patients suffering from the genetic disorder, cystic fibrosis. This review examines the role of proteomics in gaining a better understanding of the molecular basis of P. aeruginosa infection and persistence in the lungs of cystic fibrosis patients.

Protein families reflect the metabolic diversity of organisms and provide support for functional prediction

Comparative genomics has shown that protein families vary significantly within and across organisms in both number and functional composition. In the present work, we tested how the diversity at the family level reflects biological differences among organisms and contributes to their unique characteristics. For this purpose, we collected sequence-similar proteins of three selected families from model bacteria: Escherichia coli, Bacillus subtilis, and Pseudomonas aeruginosa. Protein relationships were identified using a phylogenomic approach to connect the functional diversity of enzymes to the metabolic capabilities of these organisms. All protein families studied have distinct functional compositions across the selected bacteria as supported by our Bayesian analysis. Some conserved functional features among family members included a shared reaction mechanism, cofactor usage, and/or ligand specificity. Many observations of the presence/absence of protein functions matched current knowledge of the physiology and biochemistry of the bacteria. In some cases, new functional predictions were made to family members previously uncharacterized. We believe that genome comparisons at the protein family level would also be useful in predicting metabolic diversity for organisms that are relatively unknown or currently uncultured in the laboratory.

Biofilms and type III secretion are not mutually exclusive in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that causes acute and chronic infections in immunocompromised individuals. It is also a model organism for bacterial biofilm formation. Acute infections are often associated with planktonic or free-floating cells, high virulence and fast growth. Conversely, chronic infections are often associated with the biofilm mode of growth, low virulence and slow growth that resembles that of planktonic cells in stationary phase. Biofilm formation and type III secretion have been shown to be reciprocally regulated, and it has been suggested that factors related to acute infection may be incompatible with biofilm formation. In a previous proteomic study of the interrelationships between planktonic cells, colonies and continuously grown biofilms, we showed that biofilms under the growth conditions applied are more similar to planktonic cells in exponential phase than to those in stationary phase. In the current study, we investigated how these conditions influence the production of virulence factors using a transcriptomic approach. Our results show that biofilms express the type III secretion system, whereas planktonic cells do not. This was confirmed by the detection of PcrV in the cellular and secreted fractions of biofilms, but not in those of planktonic cells. We also detected the type III effector proteins ExoS and ExoT in the biofilm effluent, but not in the supernatants of planktonic cells. Biofilm formation and type III secretion are therefore not mutually exclusive in P. aeruginosa, and biofilms could play a more active role in virulence than previously thought.

Pseudomonas aeruginosa PAO1 pyocin production affects population dynamics within mixed-culture biofilms

Transcriptomic and phenotypic studies showed that pyocins are produced in Pseudomonas aeruginosa PAO1 aerobic and anaerobic biofilms. Pyocin activity was found to be high in slow-growing anaerobic biofilms but transient in aerobic biofilms. Biofilm coculture of strain PAO1 and a pyocin-sensitive isolate showed that pyocin production had a significant impact on bacterial population dynamics, particularly under anaerobic conditions.

Dynamic proteome changes of Shigella flexneri 2a during transition from exponential growth to stationary phase

Shigella flexneri is an infectious pathogen that causes dysentery to human, which remains a serious threat to public health, particularly in developing countries. In this study, the global protein expression patterns of S. flexneri during transition from exponential growth to stationary phase in vitro were analyzed by using 2-D PAGE combined with MALDI-TOF MS. In a time-course experiment with five time points, the relative abundance of 49 protein spots varied significantly. Interestingly, a putative outer membrane protein YciD (OmpW) was almost not detected in the exponential growth phase but became one of the most abundant proteins in the whole stationary-phase proteome. Some proteins regulated by the global regulator FNR were also significantly induced (such as AnsB, AspA, FrdAB, and KatG) or repressed (such as AceEF, OmpX, SodA, and SucAB) during the growth phase transition. These proteins may be the key effectors of the bacterial cell cycle or play important roles in the cellular maintenance and stress responses. Our expression profile data provide valuable information for the study of bacterial physiology and form the basis for future proteomic analyses of this pathogen.

Local and global regulators linking anaerobiosis to cupA fimbrial gene expression in Pseudomonas aeruginosa

The cupA gene cluster of Pseudomonas aeruginosa encodes components and assembly factors of a putative fimbrial structure that enable this opportunistic pathogen to form biofilms on abiotic surfaces. In P. aeruginosa the control of cupA gene expression is complex, with the H-NS-like MvaT protein functioning to repress phase-variable (on/off) expression of the operon. Here we identify four positive regulators of cupA gene expression, including three unusual regulators encoded by the cgrABC genes and Anr, a global regulator of anaerobic gene expression. We show that the cupA genes are expressed in a phase-variable manner under anaerobic conditions and that the cgr genes are essential for this expression. We show further that cgr gene expression is negatively controlled by MvaT and positively controlled by Anr and anaerobiosis. Expression of the cupA genes therefore appears to involve a regulatory cascade in which anaerobiosis, signaled through Anr, stimulates expression of the cgr genes, resulting in a concomitant increase in cupA gene expression. Our findings thus provide mechanistic insight into the regulation of cupA gene expression and identify anaerobiosis as an inducer of phase-variable cupA gene expression, raising the possibility that phase-variable expression of fimbrial genes important for biofilm formation may occur in P. aeruginosa persisting in the largely anaerobic environment of the cystic fibrosis host lung.

Two-pronged survival strategy for the major cystic fibrosis pathogen, Pseudomonas aeruginosa, lacking the capacity to degrade nitric oxide during anaerobic respiration

Protection from NO gas, a toxic byproduct of anaerobic respiration in Pseudomonas aeruginosa, is mediated by nitric oxide (NO) reductase (NOR), the norCB gene product. Nevertheless, a norCB mutant that accumulated approximately 13.6 microM NO paradoxically survived anaerobic growth. Transcription of genes encoding nitrate and nitrite reductases, the enzymes responsible for NO production, was reduced >50- and 2.5-fold in the norCB mutant. This was due, in part, to a predicted compromise of the [4Fe-4S](2+) cluster in the anaerobic regulator ANR by physiological NO levels, resulting in an inability to bind to its cognate promoter DNA sequences. Remarkably, two O(2)-dependent dioxygenases, homogentisate-1,2-dioxygenase (HmgA) and 4-hydroxyphenylpyruvate dioxygenase (Hpd), were derepressed in the norCB mutant. Electron paramagnetic resonance studies showed that HmgA and Hpd bound NO avidly, and helped protect the norCB mutant in anaerobic biofilms. These data suggest that protection of a P. aeruginosa norCB mutant against anaerobic NO toxicity occurs by both control of NO supply and reassignment of metabolic enzymes to the task of NO sequestration.

Growth phenotypes of Pseudomonas aeruginosa lasR mutants adapted to the airways of cystic fibrosis patients

The opportunistic pathogen Pseudomonas aeruginosa undergoes genetic change during chronic airway infection of cystic fibrosis (CF) patients. One common change is a mutation inactivating lasR, which encodes a transcriptional regulator that responds to a homoserine lactone signal to activate expression of acute virulence factors. Colonies of lasR mutants visibly accumulated the iridescent intercellular signal 4-hydroxy-2-heptylquinoline. Using this colony phenotype, we identified P. aeruginosa lasR mutants that emerged in the airway of a CF patient early during chronic infection, and during growth in the laboratory on a rich medium. The lasR loss-of-function mutations in these strains conferred a growth advantage with particular carbon and nitrogen sources, including amino acids, in part due to increased expression of the catabolic pathway regulator CbrB. This growth phenotype could contribute to selection of lasR mutants both on rich medium and within the CF airway, supporting a key role for bacterial metabolic adaptation during chronic infection. Inactivation of lasR also resulted in increased beta-lactamase activity that increased tolerance to ceftazidime, a widely used beta-lactam antibiotic. Loss of LasR function may represent a marker of an early stage in chronic infection of the CF airway with clinical implications for antibiotic resistance and disease progression.

Proteome analysis ofRickettsia felis highlights the expression profile of intracellular bacteria

The proteome of Rickettsia felis, an obligate intracellular bacterium responsible for spotted fever, was analyzed using two complementary proteomic approaches: 2-DE coupled with MALDI-TOF, and SDS-PAGE with nanoLC-MS/MS. This strategy allowed identification of 165 proteins and helped to answer some questions raised by the genome sequence of this bacterium. We successfully identified potential virulence factors including two putative adhesins, four proteins of the type IV secretion system, four Sca autotransporters, four components of ABC transporters, some R. felis-specific proteins, and one antitoxin of the toxin-antitoxin system. Notably, the antitoxin was the first to be identified in intracellular bacteria. Only one protein containing rickettsia palindromic repeats was found, whereas none of the split genes, transposases, or tetratricopeptide/ankyrin repeats were detectably expressed. Comparison of the protein expression profiles of R. felis and 23 other bacterial species according to functional categories showed that intracellular bacteria express more proteins related to translation, especially ribosomal proteins. However, the remaining bacteria express more proteins related to energy production and carbohydrate/amino acid metabolism. In conclusion, this study reveals R. felis virulence factor expression and highlights the unique protein expression profile of intracellular bacteria.

Anaerobic culture conditions favor biofilm-like phenotypes inPseudomonas aeruginosaisolates from patients with cystic fibrosis

Pseudomonas aeruginosa causes chronic infections in the lungs of cystic fibrosis (CF) individuals and remains the leading cause of morbidity and mortality associated with the disease. Biofilm growth and phenotypic diversification are factors thought to contribute to this organism's persistence. Most studies have focused on laboratory isolates such as strain PAO1, and there are relatively few reports characterizing the properties of CF strains, especially under decreased oxygen conditions such as occur in the CF lung. This study compared the phenotypic and functional properties of P. aeruginosa from chronically infected CF adults with those of strain PAO1 and other clinical non-CF isolates under aerobic and anaerobic culture conditions. The CF isolates overall displayed a reduced ability to form biofilms in standard in vitro short-term models. They also grew more slowly in culture, and exhibited decreased adherence to glass and decreased motilities (swimming, swarming and twitching). All of these characteristics were markedly accentuated by anaerobic growth conditions. Moreover, the CF strain phenotypes were not readily reversed by culture manipulations designed to encourage planktonic growth. The CF strains were thus inherently different from strain PAO1 and most of the other non-CF clinical P. aeruginosa isolates tested. In vitro models used to research CF isolate biofilm growth need to take the above properties of these strains into account.

Identification of Pseudomonas aeruginosa genes involved in virulence and anaerobic growth

Pseudomonas aeruginosa is a gram-negative, opportunistic pathogen and a significant cause of acute and chronic infections in patients with compromised host defenses. Evidence suggests that within infections P. aeruginosa encounters oxygen limitation and exists in microbial aggregates known as biofilms. However, there is little information that describes genes involved in anaerobic growth of P. aeruginosa and their association with virulence of this pathogen. To identify genes required for anaerobic growth, random transposon (Tn) mutagenesis was used to screen for mutants that demonstrated the inability to grow anaerobically using nitrate as a terminal electron acceptor. Of approximately 35,000 mutants screened, 57 mutants were found to exhibit no growth anaerobically using nitrate. Identification of the genes disrupted by the Tn revealed 24 distinct loci required for anaerobic growth on nitrate, including several genes not previously associated with anaerobic growth of P. aeruginosa. Several of these mutants were capable of growing anaerobically using nitrite and/or arginine, while five mutants were unable to grow anaerobically under any of the conditions tested. Three mutants were markedly attenuated in virulence in the lettuce model of P. aeruginosa infection. These studies have identified novel genes important for anaerobic growth and demonstrate that anaerobic metabolism influences virulence of P. aeruginosa.