Genetics of O-antigen biosynthesis in Pseudomonas aeruginosa

Synthesis of Oligosaccharide Components of the Outer Core Domain of P. aeruginosa Lipopolysaccharide Using a Multifunctional Hydroquinone-Derived Reducing-End Capping Group

The synthesis of a trisaccharide (common to glycoform I and II) and a tetrasaccharide (common to glycoform I) from the outer core domain of Pseudomonas aeruginosa lipopolysaccharide (LPS) using a novel hydroquinone-based reducing-end capping group is reported. This multifunctional capping group was utilized as purification handle and was stable toward many common transformations in oligosaccharide synthesis. The access to outer-core LPS antigens with a TBDPS-protected hydroquinone (TPH) at the reducing end will be useful for glycan array and therapeutic glycoconjugate synthesis.

Structure of the Bacillus anthracis dTDP-l-rhamnose biosynthetic pathway enzyme: dTDP-α-d-glucose 4,6-dehydratase, RfbB

Many bacteria require l-rhamnose as a key cell wall component. This sugar is transferred to the cell wall using an activated donor dTDP-l-rhamnose, which is produced by the dTDP-l-rhamnose biosynthetic pathway. We determined the crystal structure of the second enzyme of this pathway dTDP-α-d-glucose 4,6-dehydratase (RfbB) from Bacillus anthracis. Interestingly, RfbB only crystallized in the presence of the third enzyme of the pathway RfbC; however, RfbC was not present in the crystal. Our work represents the first complete structural characterization of the four proteins of this pathway in a single Gram-positive bacterium.

Heparinase Is Essential for Pseudomonas aeruginosa Virulence during Thermal Injury and Infection

The opportunistic pathogen Pseudomonas aeruginosa is a major cause of sepsis in severely burned patients. If it is not eradicated from the wound, it translocates to the bloodstream, causing sepsis, multiorgan failure, and death. We recently described the P. aeruginosa heparinase-encoding gene, hepP, whose expression was significantly enhanced when P. aeruginosa strain UCBPP_PA14 (PA14) was grown in whole blood from severely burned patients. Further analysis demonstrated that hepP contributed to the in vivo virulence of PA14 in the Caenorhabditis elegans model. In this study, we utilized the murine model of thermal injury to examine the contribution of hepP to the pathogenesis of P. aeruginosa during burn wound infection. Mutation of hepP reduced the rate of mortality from 100% for mice infected with PA14 to 7% for mice infected with PA14::hepP While comparable numbers of PA14 and PA14::hepP bacteria were recovered from infected skin, only PA14 was recovered from the livers and spleens of infected mice. Despite its inability to spread systemically, PA14::hepP formed perivascular cuffs around the blood vessels within the skin of the thermally injured/infected mice. Intraperitoneal inoculation of the thermally injured mice, bypassing the need for translocation, produced similar results. The rate of mortality for mice infected with PA14::hepP was 0%, whereas it was 66% for mice infected with PA14. As before, only PA14 was recovered from the livers and spleens of infected mice. These results suggest that hepP plays a crucial role in the pathogenesis of PA14 during burn wound infection, most likely by contributing to PA14 survival in the bloodstream of the thermally injured mouse during sepsis.

The O-specific polysaccharide lyase from the phage LKA1 tailspike reduces Pseudomonas virulence

Pseudomonas phage LKA1 of the subfamily Autographivirinae encodes a tailspike protein (LKA1gp49) which binds and cleaves B-band LPS (O-specific antigen, OSA) of Pseudomonas aeruginosa PAO1. The crystal structure of LKA1gp49 catalytic domain consists of a beta-helix, an insertion domain and a C-terminal discoidin-like domain. The putative substrate binding and processing site is located on the face of the beta-helix whereas the C-terminal domain is likely involved in carbohydrates binding. NMR spectroscopy and mass spectrometry analyses of degraded LPS (OSA) fragments show an O5 serotype-specific polysaccharide lyase specificity. LKA1gp49 reduces virulence in an in vivo Galleria mellonella infection model and sensitizes P. aeruginosa to serum complement activity. This enzyme causes biofilm degradation and does not affect the activity of ciprofloxacin and gentamicin. This is the first comprehensive report on LPS-degrading lyase derived from a Pseudomonas phage. Biological properties reveal a potential towards its applications in antimicrobial design and as a microbiological or biotechnological tool.

Genome Comparison of Pseudomonas fluorescens UM270 with Related Fluorescent Strains Unveils Genes Involved in Rhizosphere Competence and Colonization

Pseudomonas fluorescens UM270 is a rhizosphere-colonizing bacterium that produces multiple diffusible and volatile compounds involved in plant growth-promoting activities. Strain UM270 exhibits excellent biocontrol capacities against diverse fungal pathogens.In a previous study, the general UM270 genome characteristics were published. Here, we report a deeper analysis of its gene content and compare it to other P. fluorescens strains to unveil the genetic elements that might explain UM270's great colonizing and plant growth-promoting capabilities. Our analyses found high variation in genome size and gene content among the eight Pseudomonas genomes analyzed (strains UM270, Pf0-1, A506, F113, SBW25, PICF-7, UK4 and UW4). A core genome of 3,039 coding DNA sequences (CDSs) was determined, with 599 CDSs present only in the UM270 genome. From these unique UM270 genes, a set of 192 CDSs was found to be involved in signaling, rhizosphere colonization and competence, highlighted as important traits to achieve an effective biocontrol and plant growth promotion.

Specific surface glycan decorations enable antimicrobial peptide resistance in plant-beneficial pseudomonads with insect-pathogenic properties

Some plant-beneficial pseudomonads can invade and kill pest insects in addition to their ability to protect plants from phytopathogens. We explored the genetic basis of O-polysaccharide (O-PS, O-antigen) biosynthesis in the representative insecticidal strains Pseudomonas protegens CHA0 and Pseudomonas chlororaphis PCL1391 and investigated its role in insect pathogenicity. Both strains produce two distinct forms of O-PS, but differ in the organization of their O-PS biosynthesis clusters. Biosynthesis of the dominant O-PS in both strains depends on a gene cluster similar to the O-specific antigen (OSA) cluster of Pseudomonas aeruginosa. In CHA0 and other P. protegens strains, the OSA cluster is extensively reduced and new clusters were acquired, resulting in high diversity of O-PS structures, possibly reflecting adaptation to different hosts. CHA0 mutants lacking the short OSA form of O-PS were significantly impaired in insect virulence in Galleria injection and Plutella feeding assays. CHA0, PCL1391, and other insecticidal pseudomonads exhibited high resistance to antimicrobial peptides, including cecropins that are central to insect immune defense. Resistance of both model strains depended on the dominant OSA-type O-PS. Our results suggest that O-antigen is essential for successful insect infection and illustrate, for the first time, its importance in resistance of Pseudomonas to antimicrobial peptides.

The salicylidene acylhydrazide INP0341 attenuates Pseudomonas aeruginosa virulence in vitro and in vivo

Pseudomonas aeruginosa is an opportunistic pathogen that can be very hard to treat because of high resistance to different antibiotics and alternative treatment regimens are greatly needed. An alternative or a complement to traditional antibiotic is to inhibit virulence of the bacteria. The salicylidene acylhydrazide, INP0341, belongs to a class of compounds that has previously been shown to inhibit virulence in a number of Gram-negative bacteria. In this study, the virulence blocking effect of INP0341 on P. aeruginosa was studied in vitro and in vivo. Two important and closely related virulence system were examined, the type III secretion system (T3SS) that translocates virulence effectors into the cytosol of the host cell to evade immune defense and facilitate colonization and the flagella system, needed for motility and biofilm formation. INP0341 was shown to inhibit expression and secretion of the T3SS toxin exoenzyme S (ExoS) and to prevent bacterial motility on agar plates and biofilm formation. In addition, INP0341 showed an increased survival of P. aeruginosa-infected mice. In conclusion, INP0341 attenuates P. aeruginosa virulence.

Biology, Mechanism, and Structure of Enzymes in the α-d-Phosphohexomutase Superfamily

Enzymes in the α-d-phosphohexomutases superfamily catalyze the reversible conversion of phosphosugars, such as glucose 1-phosphate and glucose 6-phosphate. These reactions are fundamental to primary metabolism across the kingdoms of life and are required for a myriad of cellular processes, ranging from exopolysaccharide production to protein glycosylation. The subject of extensive mechanistic characterization during the latter half of the 20th century, these enzymes have recently benefitted from biophysical characterization, including X-ray crystallography, NMR, and hydrogen-deuterium exchange studies. This work has provided new insights into the unique catalytic mechanism of the superfamily, shed light on the molecular determinants of ligand recognition, and revealed the evolutionary conservation of conformational flexibility. Novel associations with inherited metabolic disease and the pathogenesis of bacterial infections have emerged, spurring renewed interest in the long-appreciated functional roles of these enzymes.

Cyclic-di-GMP regulates lipopolysaccharide modification and contributes to Pseudomonas aeruginosa immune evasion

Pseudomonas aeruginosa is a Gram-negative bacterial pathogen associated with acute and chronic infections. The universal c-di-GMP second messenger is instrumental in the switch from a motile lifestyle to resilient biofilm as in the cystic fibrosis lung. The SadC diguanylate cyclase is associated with this patho-adaptive transition. Here we identified an unrecognized SadC partner, WarA, which we show is a methyltransferase in complex with a putative kinase WarB. We established that WarA binds to c-di-GMP, which potentiates its methyltransferase activity. Together, WarA and WarB have structural similarities with the bi-functional Escherichia coli LPS O antigen regulator WbdD. Strikingly, WarA influences P. aeruginosa O antigen modal distribution and interacts with the LPS biogenesis machinery. LPS is known to modulate the immune response in the host, and by using a zebrafish infection model, we implicate WarA in the ability of P. aeruginosa to evade detection by the host.

Conjugative type IVb pilus recognizes lipopolysaccharide of recipient cells to initiate PAPI-1 pathogenicity island transfer in Pseudomonas aeruginosa

Background

Pseudomonas aeruginosa pathogenicity island 1 (PAPI-1) is one of the largest genomic islands of this important opportunistic human pathogen. Previous studies have shown that PAPI-1 encodes several putative virulence factors, including a major regulator of biofilm formation and antibiotic-resistance traits. PAPI-1 is horizontally transferable into recipient strains lacking this island via conjugation mediated by the specialized type IV pilus. The PAPI-1 encodes a cluster of ten genes associated with the synthesis and assembly of the type IV pilus. The PAPI-1 acquisition mechanism is currently not well understood.

Results

In this study, we performed a series of conjugation experiments and identified determinants of PAPI-1 acquisition by analyzing transfer efficiency between the donor and a series of mutant recipient strains. Our data show that common polysaccharide antigen (CPA) lipopolysaccharide (LPS), a homopolymer of D-rhamnose, is required for initiating PAPI-1 transfer, suggesting that this structure acts as a receptor for conjugative type IV pilus in recipient strains. These results were substantiated by experimental evidence from PAPI-1 transfer assay experiments, in which outer membrane or LPS preparations from well-defined LPS mutants were added to the transfer mix to assess the role of P. aeruginosa LPS in PAPI-1 transfer and in vitro binding experiments between pilin fusion protein GST-pilV2’ and immobilized LPS molecules were performed. Our data also showed that P. aeruginosa strains that had already acquired a copy of PAPI-1 were unable to import additional copies of the island, and that such strains produced proportionally lower amounts of CPA LPS compared to the strains lacking PAPI-1.

Conclusions

These results suggest that a PAPI-1 exclusion mechanism exists in P. aeruginosa that might serve to regulate the avoidance of uncontrolled expansions of the bacterial genome.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-017-0943-4) contains supplementary material, which is available to authorized users.

Review: Conserved and variable structural features in the lipopolysaccharide of Pseudomonas aeruginosa

The review is devoted to recent progress in the structural elucidation of the lipopolysaccharide of the bacterium Pseudomonas aeruginosa, including O-antigen biological repeats, core oligosaccharide, and lipid A. Data on biosynthesis, genetics and serology of the lipopolysaccharide isolated from various P. aeruginosa O-serogroups are discussed in relation to the chemical structures.

Identification of Novel Genomic Islands in Liverpool Epidemic Strain of Pseudomonas aeruginosa Using Segmentation and Clustering

Pseudomonas aeruginosa is an opportunistic pathogen implicated in a myriad of infections and a leading pathogen responsible for mortality in patients with cystic fibrosis (CF). Horizontal transfers of genes among the microorganisms living within CF patients have led to highly virulent and multi-drug resistant strains such as the Liverpool epidemic strain of P. aeruginosa, namely the LESB58 strain that has the propensity to acquire virulence and antibiotic resistance genes. Often these genes are acquired in large clusters, referred to as "genomic islands (GIs)." To decipher GIs and understand their contributions to the evolution of virulence and antibiotic resistance in P. aeruginosa LESB58, we utilized a recursive segmentation and clustering procedure, presented here as a genome-mining tool, "GEMINI." GEMINI was validated on experimentally verified islands in the LESB58 strain before examining its potential to decipher novel islands. Of the 6062 genes in P. aeruginosa LESB58, 596 genes were identified to be resident on 20 GIs of which 12 have not been previously reported. Comparative genomics provided evidence in support of our novel predictions. Furthermore, GEMINI unraveled the mosaic structure of islands that are composed of segments of likely different evolutionary origins, and demonstrated its ability to identify potential strain biomarkers. These newly found islands likely have contributed to the hyper-virulence and multidrug resistance of the Liverpool epidemic strain of P. aeruginosa.

Transcriptome analysis of Pseudomonas aeruginosa PAO1 grown at both body and elevated temperatures

Functional genomics research can give us valuable insights into bacterial gene function. RNA Sequencing (RNA-seq) can generate information on transcript abundance in bacteria following abiotic stress treatments. In this study, we used the RNA-seq technique to study the transcriptomes of the opportunistic nosocomial pathogen Pseudomonas aeruginosa PAO1 following heat shock. Samples were grown at both the human body temperature (37 °C) and an arbitrarily-selected temperature of 46 °C. In this work using RNA-seq, we identified 133 genes that are differentially expressed at 46 °C compared to the human body temperature. Our work identifies some key P. aeruginosa PAO1 genes whose products have importance in both environmental adaptation as well as in vivo infection in febrile hosts. More importantly, our transcriptomic results show that many genes are only expressed when subjected to heat shock. Because the RNA-seq can generate high throughput gene expression profiles, our work reveals many unanticipated genes with further work to be done exploring such genes products.

Lipopolysaccharide transport to the cell surface: biosynthesis and extraction from the inner membrane

The cell surface of most Gram-negative bacteria is covered with lipopolysaccharide (LPS). The network of charges and sugars provided by the dense packing of LPS molecules in the outer leaflet of the outer membrane interferes with the entry of hydrophobic compounds into the cell, including many antibiotics. In addition, LPS can be recognized by the immune system and plays a crucial role in many interactions between bacteria and their animal hosts. LPS is synthesized in the inner membrane of Gram-negative bacteria, so it must be transported across their cell envelope to assemble at the cell surface. Over the past two decades, much of the research on LPS biogenesis has focused on the discovery and understanding of Lpt, a multi-protein complex that spans the cell envelope and functions to transport LPS from the inner membrane to the outer membrane. This paper focuses on the early steps of the transport of LPS by the Lpt machinery: the extraction of LPS from the inner membrane. The accompanying paper (May JM, Sherman DJ, Simpson BW, Ruiz N, Kahne D. 2015 Phil. Trans. R. Soc. B 370, 20150027. (doi:10.1098/rstb.2015.0027)) describes the subsequent steps as LPS travels through the periplasm and the outer membrane to its final destination at the cell surface.

Genetic Evidence for O-Specific Antigen as Receptor of Pseudomonas aeruginosa Phage K8 and Its Genomic Analysis

Phage therapy requires the comprehensive understanding of the mechanisms underlying the host-phage interactions. In this work, to identify the genes related to Pseudomonas aeruginosa phage K8 receptor synthesis, 16 phage-resistant mutants were selected from a Tn5G transposon mutant library of strain PAK. The disrupted genetic loci were identified and they were related to O-specific antigen (OSA) synthesis, including gene wbpR, ssg, wbpV, wbpO, and Y880_RS05480, which encoded a putative O-antigen polymerase Wzy. The Lipopolysaccharide profile of the Y880_RS05480 mutant was analyzed and shown to lack the O-antigen. Therefore, the data from characterization of Y880_RS05480 by TMHMM and SDS-PAGE silver staining analysis suggest that this locus might encode Wzy. The complete phage K8 genome was characterized as 93879 bp in length and contained identical 1188-bp terminal direct repeats. Comparative genomic analysis showed that phage K8 was highly homologous to members of the genus PaP1-like phages. On the basis of our genetic findings, OSA of P. aeruginosa PAK is proven to be the receptor of phage K8. The highly conserved structural proteins among the genetic closely related phages suggest that they may recognize the same receptor.

Pseudolysogeny and sequential mutations build multiresistance to virulent bacteriophages in Pseudomonas aeruginosa

Coevolution between bacteriophages (phages) and their prey is the result of mutualistic interactions. Here, we show that pseudolysogeny is a frequent outcome of infection by virulent phages of Pseudomonas aeruginosa and that selection of resistant bacterial mutants is favoured by continuous production of phages. We investigated the frequency and characteristics of P. aeruginosa strain PAO1 variants resisting infection by different combinations of virulent phages belonging to four genera. The frequency of resistant bacteria was 10- 5 for single phage infection and 10- 6 for infections with combinations of two or four phages. The genome of 27 variants was sequenced and the comparison with the genome of the parental PAO1 strain allowed the identification of point mutations or small indels. Four additional variants were characterized by a candidate gene approach. In total, 27 independent mutations were observed affecting 14 genes and a regulatory region. The mutations affected genes involved in biosynthesis of type IV pilus, alginate, LPS and O-antigen. Half of the variants possessed changes in homopolymer tracts responsible for frameshift mutations and these phase variation mutants were shown to be unstable. Eleven double mutants were detected. The presence of free phage DNA was observed in association with exclusion of superinfection in half of the variants and no chromosomal mutation could be found in three of them. Upon further growth of these pseudolysogens, some variants with new chromosomal mutations were recovered, presumably due to continuous evolutionary pressure.

Bacterial membrane vesicles, an overlooked environmental colloid: Biology, environmental perspectives and applications

Phospholipid vesicles play important roles in biological systems. Bacteria are one of the most abundant organisms on Earth, and bacterial membrane vesicles (MVs) were first observed 50 years ago. Many bacteria release MVs to the environment that mainly consist of the cell membrane and typically range from 20 to 400 nm in size. Bacterial MVs are involved in several biological functions, such as delivery of cargo, virulence and gene transfer. MVs can be isolated from laboratory culture and directly from the environment, indicating their high abundance in and impact on ecosystems. Many colloidal particles in the environment ranging in size from 1 nm to 1 μm have been reported but not characterized at the molecular level, and MVs remain to be explored. Hence, MVs can be considered terra incognita in environmental colloid research. Although MV biogenesis and biological roles are yet to be fully understood, the accumulation of knowledge has opened new avenues for their applications. Via genetic engineering, the MV yield can be greatly increased, and the components of MVs can be tailored. Recent studies have demonstrated that MVs have promising potential for applications such as drug delivery systems and nanobiocatalysts. For instance, MV vaccines have been extensively studied and have already been approved in Europe. Recent MV studies have evoked great interest in the fields of biology and biotechnology, but fundamental questions, such as their transport in the environment or physicochemical features of MVs, remain to be addressed. In this review, we present the current understanding of bacterial MVs and environmental perspectives and further introduce their applications.

Characterization of the Pseudomonas aeruginosa Glycoside Hydrolase PslG Reveals That Its Levels Are Critical for Psl Polysaccharide Biosynthesis and Biofilm Formation

A key component of colonization, biofilm formation, and protection of the opportunistic human pathogen Pseudomonas aeruginosa is the biosynthesis of the exopolysaccharide Psl. Composed of a pentameric repeating unit of mannose, glucose, and rhamnose, the biosynthesis of Psl is proposed to occur via a Wzx/Wzy-dependent mechanism. Previous genetic studies have shown that the putative glycoside hydrolase PslG is essential for Psl biosynthesis. To understand the function of this protein, the apo-structure of the periplasmic domain of PslG (PslG(31-442)) and its complex with mannose were determined to 2.0 and 1.9 Å resolution, respectively. Despite a domain architecture and positioning of catalytic residues similar to those of other family 39 glycoside hydrolases, PslG(31-442) exhibits a unique 32-Å-long active site groove that is distinct from other structurally characterized family members. PslG formed a complex with two mannose monosaccharides in this groove, consistent with binding data obtained from intrinsic tryptophan fluorescence. PslG was able to catalyze the hydrolysis of surface-associated Psl, and this activity was abolished in a E165Q/E276Q double catalytic variant. Surprisingly, P. aeruginosa variants with these chromosomal mutations as well as a pslG deletion mutant were still capable of forming Psl biofilms. However, overexpression of PslG in a pslG deletion background impaired biofilm formation and resulted in less surface-associated Psl, suggesting that regulation of this enzyme is important during polysaccharide biosynthesis.

Pel is a cationic exopolysaccharide that cross-links extracellular DNA in the Pseudomonas aeruginosa biofilm matrix

Biofilm formation is a complex, ordered process. In the opportunistic pathogen Pseudomonas aeruginosa, Psl and Pel exopolysaccharides and extracellular DNA (eDNA) serve as structural components of the biofilm matrix. Despite intensive study, Pel's chemical structure and spatial localization within mature biofilms remain unknown. Using specialized carbohydrate chemical analyses, we unexpectedly found that Pel is a positively charged exopolysaccharide composed of partially acetylated 1→4 glycosidic linkages of N-acetylgalactosamine and N-acetylglucosamine. Guided by the knowledge of Pel's sugar composition, we developed a tool for the direct visualization of Pel in biofilms by combining Pel-specific Wisteria floribunda lectin staining with confocal microscopy. The results indicate that Pel cross-links eDNA in the biofilm stalk via ionic interactions. Our data demonstrate that the cationic charge of Pel is distinct from that of other known P. aeruginosa exopolysaccharides and is instrumental in its ability to interact with other key biofilm matrix components.

Proteomic profiling of lysine acetylation in Pseudomonas aeruginosa reveals the diversity of acetylated proteins

Protein lysine acetylation is a reversible and highly regulated post-translational modification with the well demonstrated physiological relevance in eukaryotes. Recently, its important role in the regulation of metabolic processes in bacteria was highlighted. Here, we reported the lysine acetylproteome of Pseudomonas aeruginosa using a proteomic approach. We identified 430 unique peptides corresponding to 320 acetylated proteins. In addition to the proteins involved in various metabolic pathways, several enzymes contributing to the lipopolysaccharides biosynthesis were characterized as acetylated. This data set illustrated the abundance and the diversity of acetylated lysine proteins in P. aeruginosa and opens opportunities to explore the role of the acetylation in the bacterial physiology.

Biosynthesis of the Common Polysaccharide Antigen of Pseudomonas aeruginosa PAO1: Characterization and Role of GDP-D-Rhamnose:GlcNAc/GalNAc-Diphosphate-Lipid α1,3-D-Rhamnosyltransferase WbpZ

The opportunistic pathogen Pseudomonas aeruginosa produces two major cell surface lipopolysaccharides, characterized by distinct O antigens, called common polysaccharide antigen (CPA) and O-specific antigen (OSA). CPA contains a polymer of D-rhamnose (D-Rha) in α1-2 and α1-3 linkages. Three putative glycosyltransferase genes, wbpX, wbpY, and wbpZ, are part of the CPA biosynthesis cluster. To characterize the enzymatic function of the wbpZ gene product, we chemically synthesized the donor substrate GDP-D-Rha and enzymatically synthesized GDP-D-[(3)H]Rha. Using nuclear magnetic resonance (NMR) spectroscopy, we showed that WbpZ transferred one D-Rha residue from GDP-D-Rha in α1-3 linkage to both GlcNAc- and GalNAc-diphosphate-lipid acceptor substrates. WbpZ is also capable of transferring D-mannose (D-Man) to these acceptors. Therefore, WbpZ has a relaxed specificity with respect to both acceptor and donor substrates. The diphosphate group of the acceptor, however, is required for activity. WbpZ does not require divalent metal ion for activity and exhibits an unusually high pH optimum of 9. WbpZ from PAO1 is therefore a GDP-D-Rha:GlcNAc/GalNAc-diphosphate-lipid α1,3-D-rhamnosyltransferase that has significant activity of GDP-D-Man:GlcNAc/GalNAc-diphosphate-lipid α1,3-D-mannosyltransferase. We used site-directed mutagenesis to replace the Asp residues of the two DXD motifs with Ala. Neither of the mutant constructs of wbpZ (D172A or D254A) could be used to rescue CPA biosynthesis in the ΔwbpZ knockout mutant in a complementation assay. This suggested that D172 and D254 are essential for WbpZ function. This work is the first detailed characterization study of a D-Rha-transferase and a critical step in the development of CPA synthesis inhibitors.

IMPORTANCE

This is the first characterization of a D-rhamnosyltransferase and shows that it is essential in Pseudomonas aeruginosa for the synthesis of the common polysaccharide antigen.

A multivariate approach to correlate bacterial surface properties to biofilm formation by lipopolysaccharide mutants of Pseudomonas aeruginosa

Bacterial biofilms are involved in various medical infections and for this reason it is of great importance to better understand the process of biofilm formation in order to eradicate or mitigate it. It is a very complex process and a large range of variables have been suggested to influence biofilm formation. However, their internal importance is still not well understood. In the present study, a range of surface properties of Pseudomonas aeruginosa lipopolysaccharide mutants were studied in relation to biofilm formation measured in different kinds of multi-well plates and growth conditions in order to better understand the complexity of biofilm formation. Multivariate analysis was used to simultaneously evaluate the role of a range of physiochemical parameters under different conditions. Our results suggest the presence of serum inhibited biofilm formation due to changes in twitching motility. From the multivariate analysis it was observed that the most important parameters, positively correlated to biofilm formation on two types of plates, were high hydrophobicity, near neutral zeta potential and motility. Negative correlation was observed with cell aggregation, as well as formation of outer membrane vesicles and exopolysaccharides. This work shows that the complexity of biofilm formation can be better understood using a multivariate approach that can interpret and rank the importance of different factors being present simultaneously under several different environmental conditions, enabling a better understanding of this complex process.

Pseudomonas aeruginosa isolates from dental unit waterlines can be divided in two distinct groups, including one displaying phenotypes similar to isolates from cystic fibrosis patients

Pseudomonas aeruginosa displays broad genetic diversity, giving it an astonishing capacity to adapt to a variety of environments and to infect a wide range of hosts. While many P. aeruginosa isolates of various origins have been analyzed, isolates from cystic fibrosis (CF) patients have received the most attention. Less is known about the genetic and phenotypic diversity of P. aeruginosa isolates that colonize other environments where flourishing biofilms can be found. In the present study, 29 P. aeruginosa isolates from dental unit waterlines and CF patients were collected and their genetic and phenotypes profiles were compared to determine whether environmental and clinical isolates are related. The isolates were first classified using the random amplified polymorphic DNA method. This made it possible to distribute the isolates into one clinical cluster and two environmental clusters. The isolates in the environmental cluster that were genetically closer to the clinical cluster also displayed phenotypes similar to the clinical isolates. The isolates from the second environmental cluster displayed opposite phenotypes, particularly an increased capacity to form biofilms. The isolates in this cluster were also the only ones harboring genes that encoded specific epimerases involved in the synthesis of lipopolysaccharides, which could explain their increased ability to form biofilms. In conclusion, the isolates from the dental unit waterlines could be distributed into two clusters, with some of the environmental isolates resembled the clinical isolates.

A recombinant horseshoe crab plasma lectin recognizes specific pathogen-associated molecular patterns of bacteria through rhamnose

Horseshoe crab is an ancient marine arthropod that, in the absence of a vertebrate-like immune system, relies solely on innate immune responses by defense molecules found in hemolymph plasma and granular hemocytes for host defense. A plasma lectin isolated from the hemolymph of Taiwanese Tachypleus tridentatus recognizes bacteria and lipopolysaccharides (LPSs), yet its structure and mechanism of action remain unclear, largely because of limited availability of horseshoe crabs and the lack of a heterogeneous expression system. In this study, we have successfully expressed and purified a soluble and functional recombinant horseshoe crab plasma lectin (rHPL) in an Escherichia coli system. Interestingly, rHPL bound not only to bacteria and LPSs like the native HPL but also to selective medically important pathogens isolated from clinical specimens, such as Gram-negative Pseudomonas aeruginosa and Klebsiella pneumoniae and Gram-positive Streptococcus pneumoniae serotypes. The binding was demonstrated to occur through a specific molecular interaction with rhamnose in pathogen-associated molecular patterns (PAMPs) on the bacterial surface. Additionally, rHPL inhibited the growth of P. aeruginosa PAO1 in a concentration-dependent manner. The results suggest that a specific protein-glycan interaction between rHPL and rhamnosyl residue may further facilitate development of novel diagnostic and therapeutic strategies for microbial pathogens.

Deciphering the genome repertoire of Pseudomonas sp. M1 toward β-myrcene biotransformation

Pseudomonas sp. M1 is able to mineralize several unusual substrates of natural and xenobiotic origin, contributing to its competence to thrive in different ecological niches. In this work, the genome of M1 strain was resequenced by Illumina MiSeq to refine the quality of a published draft by resolving the majority of repeat-rich regions. In silico genome analysis led to the prediction of metabolic pathways involved in biotransformation of several unusual substrates (e.g., plant-derived volatiles), providing clues on the genomic complement required for such biodegrading/biotransformation functionalities. Pseudomonas sp. M1 exhibits a particular sensory and biotransformation/biocatalysis potential toward β-myrcene, a terpene vastly used in industries worldwide. Therefore, the genomic responsiveness of M1 strain toward β-myrcene was investigated, using an RNA sequencing approach. M1 cells challenged with β-myrcene(compared with cells grown in lactate) undergo an extensive alteration of the transcriptome expression profile, including 1,873 genes evidencing at least 1.5-fold of altered expression (627 upregulated and 1,246 downregulated), toward β-myrcene-imposed molecular adaptation and cellular specialization. A thorough data analysis identified a novel 28-kb genomic island, whose expression was strongly stimulated in β-myrcene-supplemented medium, that is essential for β-myrcene catabolism. This island includes β-myrcene-induced genes whose products are putatively involved in 1) substrate sensing, 2) gene expression regulation, and 3) β-myrcene oxidation and bioconversion of β-myrcene derivatives into central metabolism intermediates. In general, this locus does not show high homology with sequences available in databases and seems to have evolved through the assembly of several functional blocks acquired from different bacteria, probably, at different evolutionary stages.

Genome-wide patterns of recombination in the opportunistic human pathogen Pseudomonas aeruginosa

The bacterium Pseudomonas aeruginosa is a significant cause of acute nosocomial infections as well as chronic respiratory infections in patients with cystic fibrosis (CF). Recent reports of the intercontinental spread of a CF-specific epidemic strain, combined with high intrinsic levels of antibiotic resistance, have made this opportunistic pathogen an important public health concern. Strain-specific differences correlate with variation in clinical outcomes of infected CF patients, increasing the urgency to understand the evolutionary origin of genetic factors conferring important phenotypes that enable infection, virulence, or resistance. Here, we describe the genome-wide patterns of homologous and nonhomologous recombination in P. aeruginosa, and the extent to which the genomes are affected by these diversity-generating processes. Based on whole-genome sequence data from 32 clinical isolates of P. aeruginosa, we examined the rate and distribution of recombination along the genome, and its effect on the reconstruction of phylogenetic relationships. Multiple lines of evidence suggested that recombination was common and usually involves short stretches of DNA (200-300 bp). Although mutation was the main source of nucleotide diversity, the import of polymorphisms by homologous recombination contributed nearly as much. We also identified the genomic regions with frequent recombination, and the specific sequences of recombinant origin within epidemic strains. The functional characteristics of the genes contained therein were examined for potential associations with a pathogenic lifestyle or adaptation to the CF lung environment. A common link between many of the high-recombination genes was their functional affiliation with the cell wall, suggesting that the products of recombination may be maintained by selection for variation in cell-surface molecules that allows for evasion of the host immune system.

Expression of antisense small RNAs in response to stress in Pseudomonas aeruginosa

BACKGROUND

RNA sequencing technologies reveal that bacteria express RNA molecules other than mRNA, rRNA or tRNA. During the last years genome-wide bacterial transcriptomes have been shown to comprise intergenic RNA, antisense RNA, and untranslated regions, all capable of performing diverse regulatory functions.

RESULTS

In this study we used RNA-seq to identify 232 antisense RNAs (asRNAs) in the opportunistic pathogen Pseudomonas aeruginosa grown under 13 different conditions. The conditions studied include exponential and stationary growth as well as osmotic, oxidative and antibiotic stress. We found a significant overrepresentation of asRNAs that are transcribed opposite to genes involved in cell division and in cell wall, lipopolysaccharide (LPS), and capsule biosynthesis, most likely reflecting the conditions used in this study. A substantial number of asRNAs significantly changed their expression under osmotic, oxidative and antibiotic stress, suggesting that asRNAs may play regulatory roles during these conditions. We also made a comparison between the asRNAs detected in this study in P. aeruginosa PAO1 with the asRNAs detected in two previous studies in P. aeruginosa PA14, and found that the extent of overlap between the studies is very limited.

CONCLUSIONS

RNA-seq experiments are revealing hundreds of novel transcripts in all bacterial genomes investigated. The comparison between independent studies that used RNA-seq to detect novel asRNAs in P. aeruginosa shows that the overlap between the results reported is very narrow. It is necessary to address how reproducibility of these kind of studies should be reported in order to avoid misleading conclusions when comparing data generated by non-identical methods.

Coordination of swarming motility, biosurfactant synthesis, and biofilm matrix exopolysaccharide production in Pseudomonas aeruginosa

Biofilm formation is a complex process in which many factors are involved. Bacterial swarming motility and exopolysaccharides both contribute to biofilm formation, yet it is unclear how bacteria coordinate swarming motility and exopolysaccharide production. Psl and Pel are two key biofilm matrix exopolysaccharides in Pseudomonas aeruginosa. This opportunistic pathogen has three types of motility, swimming, twitching, and swarming. In this study, we found that elevated Psl and/or Pel production reduced the swarming motility of P. aeruginosa but had little effect on swimming and twitching. The reduction was due to decreased rhamnolipid production with no relation to the transcription of rhlAB, two key genes involved in the biosynthesis of rhamnolipids. Rhamnolipid-negative rhlR and rhlAB mutants synthesized more Psl, whereas exopolysaccharide-deficient strains exhibited a hyperswarming phenotype. These results suggest that competition for common sugar precursors catalyzed by AlgC could be a tactic for P. aeruginosa to balance the synthesis of exopolysaccharides and rhamnolipids and to control bacterial motility and biofilm formation inversely because the biosynthesis of rhamnolipids, Psl, and Pel requires AlgC to provide the sugar precursors and an additional algC gene enhances the biosynthesis of Psl and rhamnolipids. In addition, our data indicate that the increase in RhlI/RhlR expression attenuated Psl production. This implied that the quorum-sensing signals could regulate exopolysaccharide biosynthesis indirectly in bacterial communities. In summary, this study represents a mechanism that bacteria utilize to coordinate swarming motility, biosurfactant synthesis, and biofilm matrix exopolysaccharide production, which is critical for biofilm formation and bacterial survival in the environment.

Effect of algae and plant lectins on planktonic growth and biofilm formation in clinically relevant bacteria and yeasts

This study aimed to evaluate the abilities of plant and algae lectins to inhibit planktonic growth and biofilm formation in bacteria and yeasts. Initially, ten lectins were tested on Staphylococcus epidermidis, Staphylococcus aureus, Klebsiella oxytoca, Pseudomonas aeruginosa, Candida albicans, and C. tropicalis at concentrations of 31.25 to 250 μg/mL. The lectins from Cratylia floribunda (CFL), Vatairea macrocarpa (VML), Bauhinia bauhinioides (BBL), Bryothamnion seaforthii (BSL), and Hypnea musciformis (HML) showed activities against at least one microorganism. Biofilm formation in the presence of the lectins was also evaluated; after 24 h of incubation with the lectins, the biofilms were analyzed by quantifying the biomass (by crystal violet staining) and by enumerating the viable cells (colony-forming units). The lectins reduced the biofilm biomass and/or the number of viable cells to differing degrees depending on the microorganism tested, demonstrating the different characteristics of the lectins. These findings indicate that the lectins tested in this study may be natural alternative antimicrobial agents; however, further studies are required to better elucidate the functional use of these proteins.

Sensor domain of histidine kinase KinB of Pseudomonas: a helix-swapped dimer

The overproduction of polysaccharide alginate is responsible for the formation of mucus in the lungs of cystic fibrosis patients. Histidine kinase KinB of the KinB-AlgB two-component system in Pseudomonas aeruginosa acts as a negative regulator of alginate biosynthesis. The modular architecture of KinB is similar to other histidine kinases. However, its periplasmic signal sensor domain is unique and is found only in the Pseudomonas genus. Here, we present the first crystal structures of the KinB sensor domain. The domain is a dimer in solution, and in the crystal it shows an atypical dimer of a helix-swapped four-helix bundle. A positively charged cavity is formed on the dimer interface and involves several strictly conserved residues, including Arg-60. A phosphate anion is bound asymmetrically in one of the structures. In silico docking identified several monophosphorylated sugars, including β-D-fructose 6-phosphate and β-D-mannose 6-phosphate, a precursor and an intermediate of alginate synthesis, respectively, as potential KinB ligands. Ligand binding was confirmed experimentally. Conformational transition from a symmetric to an asymmetric structure and decreasing dimer stability caused by ligand binding may be a part of the signal transduction mechanism of the KinB-AlgB two-component system.

Pseudomonas aeruginosa serotypes in nosocomial pneumonia: prevalence and clinical outcomes

INTRODUCTION

Pseudomonas aeruginosa frequently causes nosocomial pneumonia and is associated with poor outcome. The purpose of this study was to assess the prevalence and clinical outcome of nosocomial pneumonia caused by serotype-specific P. aeruginosa in critically ill patients under appropriate antimicrobial therapy management.

METHODS

A retrospective, non-interventional epidemiological multicenter cohort study involving 143 patients with confirmed nosocomial pneumonia caused by P. aeruginosa. Patients were analyzed for a period of 30 days from time of nosocomial pneumonia onset. Fourteen patients fulfilling the same criteria from a phase IIa studyconducted at the same time/centers were included in the prevalence calculations but not in the clinical outcome analysis.

RESULTS

The prevalence of serotypes was: O6 (29%), O11 (23%), O10 (10%), O2 (9%), and O1 (8%). Serotypes with a prevalence of less than 5% were found in 13% of patients, 8% were classified as not typeable. Across all serotypes, 19% mortality, 70% clinical resolution, 11% clinical continuation, and 5% clinical recurrence were recorded. Age and higher APACHE II (Acute Physiology and Chronic Health Evaluation II) were predictive risk factors associated with probability of death and lower clinical resolution for P. aeruginosa nosocomial pneumonia. Mortality tends to be higher with O1 (40%) and lower with O2 (0%); clinical resolution tends to be better with O2 (82%) compared to other serotypes. Persisting pneumonia with O6 and O11 was, respectively, 8% and 21%; clinical resolution with O6 and O11 was, respectively, 75% and 57%.

CONCLUSIONS

In P. aeruginosa nosocomial pneumonia, the most prevalent serotypes were O6 and O11. Further studies including larger group sizes are needed to correlate clinical outcome with virulence factors of P. aeruginosa in patients with nosocomial pneumonia caused by various serotypes; and to compare O6 and O11, the two serotypes most frequently encountered in critically ill patients.

Virulence Properties of Rough and Smooth Strains ofVibrio choleraeO1

A comparative study was carried out to see the differences in pathogenicity of rough and smooth strains. A total of 10 strains including 5 each of rough and smooth strains of Vibrio cholerae O1 were tested and found positive for toxin production by enzyme-linked immunosorbent assay (ELISA) in Richardson's and AKI media. All the smooth and rough strains, except one, showed a titre of 1: 10 and 1: 100 in Richardson's and AKI media, respectively. Both types of strains produced enterotoxin in rabbit ileal loop (RIL). The differences in multiplication abilities of smooth and rough strains in RIL were statistically significant (P <0.05). However, these differences in multiplying abilities did not influence the adherence potential or enterotoxin production as there was no significant difference (P >0.05) between these properties. This study demonstrated that the rough strains are equally pathogenic and as important as smooth strains.

Determination of the quaternary structure of a bacterial ATP-binding cassette (ABC) transporter in living cells

Pseudomonas aeruginosa is a pathogenic Gram-negative bacterium that affects patients with cystic fibrosis and immunocompromised individuals. This bacterium coexpresses two unique forms of lipopolysaccharides (LPSs) on its surface, the A- and B-band LPS, which are among the main virulence factors that contribute to its pathogenicity. The polysaccharides in A-band LPSs are synthesized in the cytoplasm and translocated into the periplasm via an ATP-binding cassette (ABC) transporter consisting of a transmembrane protein, Wzm, and a cytoplasmic nucleotide-binding protein, Wzt. Most of the biochemical studies of A-band PSs in Pseudomonas aeruginosa are focused on the stages of the synthesis and ligation of PS, leaving the export stage involving the ABC transporter mostly unexplored. This difficulty is compounded by the fact that the subunit composition and structure of this bi-component ABC transporter are still unknown. Here we propose a simple but powerful method, based on Förster Resonance Energy Transfer (FRET) and optical micro-spectroscopy technology, to probe the structure of dynamic (as opposed to static) protein complexes in living cells. We use this method to determine the association stoichiometry and quaternary structure of the Wzm-Wzt complex in living cells. It is found that Wzt forms a rhombus-shaped homo-tetramer which becomes a square upon co-expression with Wzm, and that Wzm forms a square-shaped homo-tetramer both in the presence and absence of Wzt. Based on these results, we propose a structural model for the double-tetramer complex formed by the bi-component ABC transporter in living cells. An understanding of the structure and behavior of this ABC transporter will help develop antibiotics targeting the biosynthesis of the A-band LPS endotoxin.

A deletion in the wapB promoter in many serotypes of Pseudomonas aeruginosa accounts for the lack of a terminal glucose residue in the core oligosaccharide and resistance to killing by R3-pyocin

Pseudomonas aeruginosa is an opportunistic human pathogen producing a variety of virulence factors. One of them is lipopolysaccharide, consisting of endotoxic lipid A and long-chain O-antigen polysaccharide, which are connected together through a short linker region, called core oligosaccharide. Chemical structures of the core oligosaccharide are well conserved, with one exception, in that certain strains of P. aeruginosa add a terminal glucose residue (Glc(IV) ) to core by a transferase reaction, due to the activity of a glucosyltransferase, WapB. Here, we investigated the regulation of wapB expression. Our results showed that while the majority of analysed genomes of P. aeruginosa contain wapB, many of these have a conserved identical 5-nucleotide deletion in the upstream region that inactivated the promoter. This deletion is within the -10 hexamer that is recognized by a principle sigma factor (RpoD, or σ70) as proven by data from an electromobility shift assay. These results provide the molecular basis of why LPS core of many P. aeruginosa strains is lacking Glc(IV) . In addition, we show that absence of Glc(IV) due to an inactive wapB promoter confers resistance to killing by R3-pyocin, a phage tail-like bacteriocin of P. aeruginosa.

A convenient synthesis of GDP-D-rhamnose: the donor substrate for D-rhamnosyltransferase WbpZ from Pseudomonas aeruginosa PAO1

Gram negative bacteria have lipopolysaccharides (LPS) that are critical for their survival. LPS molecules are composed of antigenic exopolysaccharide chains (O antigens). We are interested in discovering the enzymes involved in the biosynthesis of O antigens in Pseudomonas aeruginosa. The common polysaccharide antigen contains α-linked D-rhamnose residues. We have now synthesized GDP-D-rhamnose by a convenient synthesis in aqueous solution, and have shown that it can be used without extensive purification as the donor substrate for D-rhamnosyltransferase (WbpZ) from the P. aeruginosa strain PAO1. The availability of this nucleotide sugar preparation allows for characterization of D-rhamnosyltransferases.

A vaccine and diagnostic target for Clostridium bolteae, an autism-associated bacterium

Constipation and diarrhea are common in autistic patients. Treatment with antibiotics against bacteria appears to partially alleviate autistic-related symptoms. Clostridium bolteae is a bacterium that has been shown to be overabundant in the intestinal tract of autistic children suffering from gastric intestinal ailments, and as such is an organism that could potentially aggravate gastrointestinal symptoms. We set out to investigate the cell-wall polysaccharides of C. bolteae in order to evaluate their structure and immunogenicity. Our explorations revealed that C. bolteae produces a conserved specific capsular polysaccharide comprised of rhamnose and mannose units: [→3)-α-D-Manp-(1→4)-β-d-Rhap-(1→], which is immunogenic in rabbits. These findings are the first description of a C. bolteae immunogen and indicate the prospect of using this polysaccharide as a vaccine to reduce or prevent C. bolteae colonization of the intestinal tract in autistic patients, and as a diagnostic marker for the rapid detection of C. bolteae in a clinical setting.

Strategies developed by the marine bacterium Pseudomonas fluorescens BA3SM1 to resist metals: A proteome analysis

A global proteomic evaluation of the response of the marine bacterium Pseudomonas fluorescens BA3SM1 to Cd, Zn and Cu was performed by two dimensional gel electrophoresis followed by mass spectrometry. When stressed with Cd, the most toxic metal for P. fluorescens BA3SM1, cell growth is rapidly affected and the number of proteins up-regulated (sixteen for 0.4 mM Cd) remains low in comparison with results obtained for Zn and Cu (twenty eight for 1.5mM Zn and forty four for 1.5 mM Cu). The changes in protein expression indicate that the cell adapts to metals by inducing essentially seven defense mechanisms: cell aggregation/biofilm formation (Zn=Cu>Cd); modification of envelope properties to increase the extracellular metal biosorption and/or control the uptake of metal (Cu>Zn); metal export (Cd=Zn and probably Cu); responses to oxidative stress (Cu>Zn>Cd); intracellular metal sequestration (Zn=Cu and probably Cd); hydrolysis of abnormally folded proteins (Cd=Cu), and the over-synthesis of proteins inhibited by metal (Cd>Cu>Zn). To the best of our knowledge, this is the first report showing that a marine P. fluorescens is able to acquire a metal-resistant phenotype, making the strain BA3SM1 a promising agent for bioremediation processes.

PelA deacetylase activity is required for Pel polysaccharide synthesis in Pseudomonas aeruginosa

The Pel polysaccharide serves as an intercellular adhesin for the formation and maintenance of biofilms in the opportunistic pathogen Pseudomonas aeruginosa. Pel biosynthesis requires the products of a seven-gene operon, pelA-pelG, all of which are necessary for Pel-dependent biofilm formation and Pel-related phenotypes. One of the genes, pelA, encodes a protein with a predicted polysaccharide deacetylase domain. In this work, the role of the putative deacetylase domain in Pel production was examined. We first established that purified recombinant PelA hydrolyzed the pseudosubstrate p-nitrophenyl acetate in vitro, and site-specific mutations of predicted deacetylase active-site residues reduced activity greater than 10-fold. Additionally, these mutants were deficient in Pel-dependent biofilm formation and wrinkly colony morphology in vivo. Subcellular fractionation experiments demonstrate that PelA localizes to both the membrane and periplasmic fractions. Finally, antiserum against the Pel polysaccharide was generated, and PelA deacetylase mutants do not produce Pel-reactive material. Taken together, these results suggest that the deacetylase activity of PelA is important for the production of the Pel polysaccharide.

Non-apoptotic toxicity of Pseudomonas aeruginosa toward murine cells

Although P. aeruginosa is especially dangerous in cystic fibrosis (CF), there is no consensus as to how it kills representative cell types that are of key importance in the lung. This study concerns the acute toxicity of the sequenced strain, PAO1, toward a murine macrophage cell line (RAW 264.7). Toxicity requires brief contact with the target cell, but is then delayed for more than 12 h. None of the classical toxic effectors of this organism is required and cell death occurs without phagocytosis or acute perturbation of the actin cytoskeleton. Apoptosis is not required for toxicity toward either RAW 264.7 cells or for alveolar macrophages. Transcriptional profiling shows that encounter between PAO1 and RAW 264.7 cells elicits an early inflammatory response, followed by growth arrest. As an independent strategy to understand the mechanism of toxicity, we selected variant RAW 264.7 cells that resist PAO1. Upon exposure to P. aeruginosa, they are hyper-responsive with regard to classical inflammatory cytokine production and show transient downregulation of transcripts that are required for cell growth. They do not show obvious morphologic changes. Although they do not increase interferon transcripts, when exposed to PAO1 they dramatically upregulate a subset of the responses that are characteristic of exposure to g-interferon, including several guanylate-binding proteins. The present observations provide a novel foundation for learning how to equip cells with resistance to a complex challenge.

The exopolysaccharide gene cluster Bcam1330-Bcam1341 is involved in Burkholderia cenocepacia biofilm formation, and its expression is regulated by c-di-GMP and Bcam1349

In Burkholderia cenocepacia, the second messenger cyclic diguanosine monophosphate (c-di-GMP) has previously been shown to positively regulate biofilm formation and the expression of cellulose and type-I fimbriae genes through binding to the transcriptional regulator Bcam1349. Here, we provide evidence that cellulose and type-I fimbriae are not involved in B. cenocepacia biofilm formation in flow chambers, and we identify a novel Bcam1349/c-di-GMP-regulated exopolysaccharide gene cluster which is essential for B. cenocepacia biofilm formation. Overproduction of Bcam1349 in trans promotes wrinkly colony morphology, pellicle, and biofilm formation in B. cenocepacia. A screen for transposon mutants unable to respond to the overproduction of Bcam1349 led to the identification of a 12-gene cluster, Bcam1330-Bcam1341, the products of which appear to be involved in the production of a putative biofilm matrix exopolysaccharide and to be essential for flow-chamber biofilm formation. We demonstrate that Bcam1349 binds to the promoter region of genes in the Bcam1330-Bcam1341 cluster and that this binding is enhanced by the presence of c-di-GMP. Furthermore, we demonstrate that overproduction of both c-di-GMP and Bcam1349 leads to increased transcription of these genes, indicating that c-di-GMP and Bcam1349 functions together in regulating exopolysaccharide production from the Bcam1330-Bcam1341 gene cluster. Our results suggest that the product encoded by the Bcam1330-Bcam1341 gene cluster is a major exopolysaccharide that provides structural stability to the biofilms formed by B. cenocepacia, and that its production is regulated by c-di-GMP through binding to and promotion of the activity of the transcriptional regulator Bcam1349.

Molecular Characterization of Lipopolysaccharide Binding to Human α-1-Acid Glycoprotein

The ability of AGP to bind circulating lipopolysaccharide (LPS) in plasma is believed to help reduce the proinflammatory effect of bacterial lipid A molecules. Here, for the first time we have characterized human AGP binding characteristics of the LPS from a number of pathogenic Gram-negative bacteria: Escherichia coli, Salmonella typhimurium, Klebsiella pneumonia, Pseudomonas aeruginosa, and Serratia marcescens. The binding affinity and structure activity relationships (SAR) of the AGP-LPS interactions were characterized by surface plasma resonance (SPR). In order to dissect the contribution of the lipid A, core oligosaccharide and O-antigen polysaccharide components of LPS, the AGP binding affinity of LPS from smooth strains, were compared to lipid A, Kdo2-lipid A, R_a, R_d, and R_e rough LPS mutants. The SAR analysis enabled by the binding data suggested that, in addition to the important role played by the lipid A and core components of LPS, it is predominately the unique species- and strain-specific carbohydrate structure of the O-antigen polysaccharide that largely determines the binding affinity for AGP. Together, these data are consistent with the role of AGP in the binding and transport of LPS in plasma during acute-phase inflammatory responses to invading Gram-negative bacteria.

Molecular basis for the increased polymyxin susceptibility of Klebsiella pneumoniae strains with under-acylated lipid A

The impact of under-acylation of lipid A on the interaction between Klebsiella pneumoniae LPS and polymyxins B and E was examined with fluorometric and calorimetric methods, and by (1)H NMR, using a paired wild type (WT) and the ΔlpxM mutant strains B5055 and B5055ΔlpxM, which predominantly express LPS with hexa- and penta-acylated lipid A structures respectively. LPS from B5055ΔlpxM displayed a fourfold increased binding affinity for polymyxins B and E compared with the B5055 WT LPS. EC50 values were consistent with polymyxin minimum inhibitory concentration (MIC) values for each strain. Accordingly, polymyxin exposure considerably enhanced the permeability of the B5055ΔlpxM OM. Analysis of the melting profiles of isolated LPS aggregates suggested that bactericidal polymyxin activity may relate to the acyl chains' phase of the outer membrane (OM). The enhanced polymyxin susceptibility of B5055ΔlpxM may be attributable to the favorable insertion of polymyxins into the more fluid OM compared with B5055. Molecular models of the polymyxin B-lipid A complex illuminate the key role of the lipid A acyl chains for complexation of polymyxin. The data provide important insight into the molecular basis for the increased polymyxin susceptibility of K. pneumoniae strains with under-acylated lipid A. Under-acylation appears to facilitate the integration of the N-terminal fatty-acyl chain of polymyxin into the OM resulting in an increased susceptibility to its antimicrobial activity/activities.

Synthesis of multiple Pseudomonas aeruginosa biofilm matrix exopolysaccharides is post-transcriptionally regulated

Exopolysaccharide is a critical biofilm matrix component, yet little is known about how the synthesis of multiple exopolysaccharides is regulated. Pseudomonas aeruginosa can produce several biofilm matrix exopolysaccharides that include alginate, Psl and Pel. Here we demonstrated that AlgC, a key enzyme that provides sugar precursors for the synthesis of alginate and lipopolysaccharides (LPS) is also required for both Psl and Pel production. We showed that forced-synthesis of Psl in alginate-producing mucoid bacteria reduced alginate production but this was not due to transcription of the alginate biosynthesis-operon. Likewise, when either alginate or Psl were overproduced, levels of B-band LPS decreased. Induction of Pel resulted in a reduction of Psl levels. Because the effects of reduced exopolysaccharide synthesis when another is overproduced didn't appear to be regulated at the transcriptional level, this suggests that the biosynthesis pathways of Psl, Pel, alginate, and LPS compete for common sugar precursors. As AlgC is the only enzyme that provides precursors for each of these exopolysaccharides, we propose that AlgC is a key checkpoint enzyme that coordinates the total amount of exopolysaccharide biosynthesis by controlling sugar precursor pool. Our data also provide a plausible strategy that P.aeruginosa utilizes to modulate its biofilm matrix exopolysaccharides.

Pseudomonas biofilm matrix composition and niche biology

Biofilms are a predominant form of growth for bacteria in the environment and in the clinic. Critical for biofilm development are adherence, proliferation, and dispersion phases. Each of these stages includes reinforcement by, or modulation of, the extracellular matrix. Pseudomonas aeruginosa has been a model organism for the study of biofilm formation. Additionally, other Pseudomonas species utilize biofilm formation during plant colonization and environmental persistence. Pseudomonads produce several biofilm matrix molecules, including polysaccharides, nucleic acids, and proteins. Accessory matrix components shown to aid biofilm formation and adaptability under varying conditions are also produced by pseudomonads. Adaptation facilitated by biofilm formation allows for selection of genetic variants with unique and distinguishable colony morphology. Examples include rugose small-colony variants and wrinkly spreaders (WS), which over produce Psl/Pel or cellulose, respectively, and mucoid bacteria that over produce alginate. The well-documented emergence of these variants suggests that pseudomonads take advantage of matrix-building subpopulations conferring specific benefits for the entire population. This review will focus on various polysaccharides as well as additional Pseudomonas biofilm matrix components. Discussions will center on structure-function relationships, regulation, and the role of individual matrix molecules in niche biology.

Lipopolysaccharide of Coxiella burnetii

A lipopolysaccharide (LPS) is considered to be one of the major determinants of virulence expression and infection of virulent Coxiella burnetii. The LPSs from virulent phase I (LPS I) and from avirulent phase II (LPS II) bacteria were investigated for their chemical composition, structure and biological properties. LPS II is of rough (R) type in contrast to LPS I, which is phenotypically smooth (S) and contains a noticeable amount of two sugars virenose (Vir) and dihydrohydroxystreptose (Strep), which have not been found in other LPSs and can be considered as unique biomarkers of the bacterium. Both sugars were suggested to be located mostly in terminal positions of the O-specific chain of LPS I (O-PS I) and to be involved in the immunobiology of Q fever. There is a need to establish a more detailed chemical structure of LPS I in connection with prospective, deeper studies on mechanisms of pathogenesis and immunity of Q fever, its early and reliable diagnosis, and effective prophylaxis against the disease. This will also help to better understanding of host-pathogen interactions and contribute to improved modulation of pathological reactions which in turn are prerequisite for research and development of vaccines of new type. A fundamental understanding of C. burnetii LPS biosynthesis is still lacking. The intracellular nature of the bacterium, lack of genetic tools and its status as a selected agent have made elucidating basic physiological mechanisms challenging. The GDP-β-D-Vir biosynthetic pathway proposed most recently is an important initial step in this endeavour. The current advanced technologies providing the genetic tools necessary to screen C. burnetii mutants and propagate isogenic mutants might speed the discovery process.

Co-evolution with lytic phage selects for the mucoid phenotype of Pseudomonas fluorescens SBW25

The effects of co-evolution with lytic phage on bacterial virulence-related traits are largely unknown. In this study we investigate the incidence of the mucoid phenotype of the bacterium Pseudomonas fluorescens SBW25 in response to co-evolution with the lytic phage phi2 (φ2). The mucoid phenotype of Pseudomonas spp. is due to overproduction of alginate and is a considerable virulence factor contributing to the intractability of infections most notably in cystic fibrosis (CF) lung, but also in pathogenic infections of plants. Our data show that this phenotype can evolve as an adaptive response to phage predation and is favoured under specific abiotic conditions, in particular a homogenous spatial structure and a high rate of nutrient replacement. The mucoid phenotype remains partially sensitive to phage infection, which facilitates 'apparent competition' with phage-sensitive competitors, partially offsetting the costs of alginate production. Although P. fluorescens SBW25 is not a pathogen, several key characteristics typical of Pseudomonas aeruginosa clinical isolates from CF lung were noted, including loss of motility on mucoid conversion and a high rate of spontaneous reversion to the wild-type phenotype. Although the genetic mechanisms of this phenotype remain unknown, they do not include mutations at many of the commonly reported loci implicated in mucoid conversion, including mucA and algU. These data not only further our understanding of the potential role phage have in the ecology and evolution of bacteria virulence in both natural and clinical settings, but also highlight the need to consider both biotic and abiotic variables if bacteriophages are to be used therapeutically.

Multifunctional membrane vesicles in Pseudomonas aeruginosa

Gram-negative bacteria secrete small particles called membrane vesicles (MVs) into the extracellular milieu. While MVs have important roles in delivering toxins from pathogenic bacteria to eukaryotic cells, these vesicles also play ecological roles necessary for survival in various environmental conditions. Pseudomonas aeruginosa, which lives in soil, ocean, plant, animal and human environments, has become a model organism for studying these small extracellular particles. Such studies have increased our understanding of the function and biogenesis of bacterial MVs. Pseudomonas aeruginosa MVs possess versatile components and chemical substances with unique structures. These characteristics allow MVs to play their multifunctional biological roles, including microbial interaction, maintenance of biofilm structure and host infection. This review summarizes the comprehensive biochemical and physiochemical properties of MVs derived from P. aeruginosa. These studies will help us understand their biological roles of MVs not only in pathogenicity but also in microbial ecology. Also, the mechanisms of MV production, as currently understood, are discussed.