Alginate biosynthetic enzymes in mucoid and nonmucoid Pseudomonas aeruginosa: overproduction of phosphomannose isomerase, phosphomannomutase, and GDP-mannose pyrophosphorylase by overexpression of the phosphomannose isomerase (pmi) gene

Specific and Global RNA Regulators in Pseudomonas aeruginosa

Pseudomonas aeruginosa (Pae) is an opportunistic pathogen showing a high intrinsic resistance to a wide variety of antibiotics. It causes nosocomial infections that are particularly detrimental to immunocompromised individuals and to patients suffering from cystic fibrosis. We provide a snapshot on regulatory RNAs of Pae that impact on metabolism, pathogenicity and antibiotic susceptibility. Different experimental approaches such as in silico predictions, co-purification with the RNA chaperone Hfq as well as high-throughput RNA sequencing identified several hundreds of regulatory RNA candidates in Pae. Notwithstanding, using in vitro and in vivo assays, the function of only a few has been revealed. Here, we focus on well-characterized small base-pairing RNAs, regulating specific target genes as well as on larger protein-binding RNAs that sequester and thereby modulate the activity of translational repressors. As the latter impact large gene networks governing metabolism, acute or chronic infections, these protein-binding RNAs in conjunction with their cognate proteins are regarded as global post-transcriptional regulators.

A mutant of phosphomannomutase1 retains full enzymatic activity, but is not activated by IMP: Possible implications for the disease PMM2-CDG

The most frequent disorder of glycosylation, PMM2-CDG, is caused by a deficiency of phosphomannomutase activity. In humans two paralogous enzymes exist, both of them require mannose 1,6-bis-phosphate or glucose 1,6-bis-phosphate as activators, but only phospho-mannomutase1 hydrolyzes bis-phosphate hexoses. Mutations in the gene encoding phosphomannomutase2 are responsible for PMM2-CDG. Although not directly causative of the disease, the role of the paralogous enzyme in the disease should be clarified. Phosphomannomutase1 could have a beneficial effect, contributing to mannose 6-phosphate isomerization, or a detrimental effect, hydrolyzing the bis-phosphate hexose activator. A pivotal role in regulating mannose-1phosphate production and ultimately protein glycosylation might be played by inosine monophosphate that enhances the phosphatase activity of phosphomannomutase1. In this paper we analyzed human phosphomannomutases by conventional enzymatic assays as well as by novel techniques such as 31P-NMR and thermal shift assay. We characterized a triple mutant of phospomannomutase1 that retains mutase and phosphatase activity, but is unable to bind inosine monophosphate.

Functional interactions among filamentous Epsilonproteobacteria and Bacteroidetes in a deep-sea hydrothermal vent biofilm

Little is known about how lithoautotrophic primary production is connected to microbial organotrophic consumption in hydrothermal systems. Using a multifaceted approach, we analysed the structure and metabolic capabilities within a biofilm growing on the surface of a black smoker chimney in the Loki's Castle vent field. Imaging revealed the presence of rod-shaped Bacteroidetes growing as ectobionts on long, sheathed microbial filaments (> 100 μm) affiliated with the Sulfurovum genus within Epsilonproteobacteria. The filaments were composed of a thick (> 200 nm) stable polysaccharide, representing a substantial fraction of organic carbon produced by primary production. An integrated -omics approach enabled us to assess the metabolic potential and in situ metabolism of individual taxonomic and morphological groups identified by imaging. Specifically, we provide evidence that organotrophic Bacteroidetes attach to and glide along the surface of Sulfurovum filaments utilizing organic polymers produced by the lithoautotrophic Sulfurovum. Furthermore, in situ expression of acetyl-CoA synthetase by Sulfurovum suggested the ability to assimilate acetate, indicating recycling of organic matter in the biofilm. This study expands our understanding of the lifestyles of Epsilonproteobacteria in hydrothermal vents, their metabolic properties and co-operative interactions in deep-sea hydrothermal vent food webs.

Post-transcriptional regulation of the virulence-associated enzyme AlgC by the σ(22) -dependent small RNA ErsA of Pseudomonas aeruginosa

The small RNA ErsA of Pseudomonas aeruginosa, transcribed from the same genomic context of the well-known Escherichia coli Spot 42, has been characterized. We show that, different from Spot 42, ErsA is under the transcriptional control of the envelope stress response, which is known to impact the pathogenesis of P. aeruginosa through the activity of the alternative sigma factor σ(22) . The transcriptional responsiveness of ErsA RNA also spans infection-relevant cues that P. aeruginosa can experience in mammalian hosts, such as limited iron availability, temperature shifts from environmental to body temperature and reduced oxygen conditions. Another difference between Spot 42 and ErsA is that ErsA does not seem to be involved in the regulation of carbon source catabolism. Instead, our results suggest that ErsA is linked to anabolic functions for the synthesis of exoproducts from sugar precursors. We show that ErsA directly operates in the negative post-transcriptional regulation of the algC gene that encodes the virulence-associated enzyme AlgC, which provides sugar precursors for the synthesis of several P. aeruginosa polysaccharides. Like ErsA, the activation of algC expression is also dependent on σ(22) . Altogether, our results suggest that ErsA and σ(22) combine in an incoherent feed-forward loop to fine-tune AlgC enzyme expression.

Molecular basis of tobacco-induced bacterial biofilms: an in vitro study

OBJECTIVE

To evaluate changes in the expression of biofilm-related genes when exposed to tobacco smoke and oxidative stress.

STUDY DESIGN

Experimental, in vitro. Setting Laboratories of Rhinology and Microbiology, University of Pennsylvania.

SUBJECTS AND METHODS

Bacterial biofilm mass was measured using crystal violet staining and measurement of the optical density. Biofilm-related genes of the Pseudomonas aeruginosa PAO1 strain (pilF, flgK, lasI, lasB, rhlA, and algC) were studied following repetitive exposure to exogenous tobacco smoke and hydrogen peroxide. This was done using a reporter plasmid.

RESULTS

After 1 exposure to smoke, there was no change in biofilm formation. However, after 2 and 3 exposures, the biofilm formed had an increased mass (P < .05). With respect to oxidative stress in the form of H(2)O(2), bacterial cultures demonstrated a dose- and time-dependent induction of biofilm formation compared with control conditions. Gene expression following repetitive smoke exposure demonstrated an increase in expression of pilF, flgK, algC, and lasI genes (P < .05); a decrease in rhlA (P < .05); and no significant change in the lasB gene (P = 0.1). Gene expression following H(2)O(2) exposure demonstrated an increase in pilF (P < .05), whereas the other genes failed to demonstrate a statistical change.

CONCLUSIONS

Repetitive tobacco smoke exposure leads to molecular changes in biofilm-related genes, and exposure to oxidative stress in the form of H(2)O(2) induces biofilm growth in PAO1. This could represent adaptative changes due to oxidative stress or chemically mediated through any of the several chemicals encountered in tobacco smoke and may explain increased biofilm formation in microbes isolated from smokers.

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.

Characterization of the GDP-D-mannose biosynthesis pathway in Coxiella burnetii: the initial steps for GDP-β-D-virenose biosynthesis

Coxiella burnetii, the etiologic agent of human Q fever, is a Gram-negative and naturally obligate intracellular bacterium. The O-specific polysaccharide chain (O-PS) of the lipopolysaccharide (LPS) of C. burnetii is considered a heteropolymer of the two unusual sugars β-D-virenose and dihydrohydroxystreptose and mannose. We hypothesize that GDP-D-mannose is a metabolic intermediate to GDP-β-D-virenose. GDP-D-mannose is synthesized from fructose-6-phosphate in 3 successive reactions; Isomerization to mannose-6-phosphate catalyzed by a phosphomannose isomerase (PMI), followed by conversion to mannose-1-phosphate mediated by a phosphomannomutase (PMM) and addition of GDP by a GDP-mannose pyrophosphorylase (GMP). GDP-D-mannose is then likely converted to GDP-6-deoxy-D-lyxo-hex-4-ulopyranose (GDP-Sug), a virenose intermediate, by a GDP-mannose-4,6-dehydratase (GMD). To test the validity of this pathway in C. burnetii, three open reading frames (CBU0671, CBU0294 and CBU0689) annotated as bifunctional type II PMI, as PMM or GMD were functionally characterized by complementation of corresponding E. coli mutant strains and in enzymatic assays. CBU0671, failed to complement an Escherichia coli manA (PMM) mutant strain. However, complementation of an E. coli manC (GMP) mutant strain restored capsular polysaccharide biosynthesis. CBU0294 complemented a Pseudomonas aeruginosa algC (GMP) mutant strain and showed phosphoglucomutase activity (PGM) in a pgm E. coli mutant strain. Despite the inability to complement a manA mutant, recombinant C. burnetii PMI protein showed PMM enzymatic activity in biochemical assays. CBU0689 showed dehydratase activity and determined kinetic parameters were consistent with previously reported data from other organisms. These results show the biological function of three C. burnetii LPS biosynthesis enzymes required for the formation of GDP-D-mannose and GDP-Sug. A fundamental understanding of C. burnetii genes that encode PMI, PMM and GMP is critical to fully understand the biosynthesic pathway of GDP-β-D-virenose and LPS structure in C. burnetii.

The Azospirillum brasilense Sp7 noeJ and noeL genes are involved in extracellular polysaccharide biosynthesis

Azospirillum brasilense is a plant root-colonizing bacterium that exerts beneficial effects on the growth of many agricultural crops. Extracellular polysaccharides of the bacterium play an important role in its interactions with plant roots. The pRhico plasmid of A. brasilense Sp7, also named p90, carries several genes involved in synthesis and export of cell surface polysaccharides. We generated two Sp7 mutants impaired in two pRhico-located genes, noeJ and noeL, encoding mannose-6-phosphate isomerase and GDP-mannose 4,6-dehydratase, respectively. Our results demonstrate that in A. brasilense Sp7, noeJ and noeL are involved in lipopolysaccharide and exopolysaccharide synthesis. noeJ and noeL mutant strains were significantly altered in their outer membrane and cytoplasmic/periplasmic protein profiles relative to the wild-type strain. Moreover, both noeJ and noeL mutations significantly affected the bacterial responses to several stresses and antimicrobial compounds. Disruption of noeL, but not noeJ, affected the ability of the A. brasilense Sp7 to form biofilms. The pleiotropic alterations observed in the mutants could be due, at least partially, to their altered lipopolysaccharides and exopolysaccharides relative to the wild-type.

Biosynthetic pathway of sugar nucleotides essential for welan gum production in Alcaligenes sp. CGMCC2428

Welan gum is a microbial polysaccharide produced by Alcaligenes sp. CGMCC2428 that has D-glucose, D-glucuronic acid, D-glucose, and L-rhamnose as the main structural unit. The biosynthetic pathway of sugar nucleotides essential for producing welan gum in this strain was established in the following ways: (1) the detection of the presence of several intermediates and key enzymes; (2) the analysis of the response upon addition of precursors to the culture medium; (3) the correlation of the activities between several key enzymes with the yields of welan gum. With addition of 200-microM glucose-6-phosphate and fructose-6-phosphate, the production of welan gum was improved by 18%. The activities of phosphoglucomutase, phosphomannose isomerase, UDP-glucose pyrophosphorylase, and dTDP-glucose pyrophosphorylase, correlated well with the yields of welan gum. According to these findings, the biosynthetic pathway was proposed to involve the metabolism of glucose via two discrete systems. The first involves conversion of glucose to glucose-6-phosphate, with further reactions producing glucose-1-phosphate and fructose-6-phosphate, which are metabolized to the nucleotide sugar precursors of welan gum. The second system involves metabolism of glucose to synthesize the basic structural skeleton of the cell via central metabolic pathways, including the Entner-Doudoroff pathway, the pentose phosphate pathway, and the tricarboxylic acid cycle.

Phosphomannose isomerase and phosphomannomutase gene disruptions in Streptomyces nodosus: impact on amphotericin biosynthesis and implications for glycosylation engineering

Streptomycetes synthesise several bioactive natural products that are modified with sugar residues derived from GDP-mannose. These include the antifungal polyenes, the antibacterial antibiotics hygromycin A and mannopeptimycins, and the anticancer agent bleomycin. Three enzymes function in biosynthesis of GDP-mannose from the glycolytic intermediate fructose 6-phosphate: phosphomannose isomerase (PMI), phosphomannomutase (PMM) and GDP-mannose pyrophosphorylase (GMPP). Synthesis of GDP-mannose from exogenous mannose requires hexokinase or phosphotransferase enzymes together with PMM and GMPP. In this study, a region containing genes for PMI, PMM and GMPP was cloned from Streptomyces nodosus, producer of the polyenes amphotericins A and B. Inactivation of the manA gene for PMI resulted in production of amphotericins and their aglycones, 8-deoxyamphoteronolides. A double mutant lacking the PMI and PMM genes produced 8-deoxyamphoteronolides in good yields along with trace levels of glycosylated amphotericins. With further genetic engineering these mutants may activate alternative hexoses as GDP-sugars for transfer to aglycones in vivo.

Overexpression of Mycobacterium tuberculosis manB, a phosphomannomutase that increases phosphatidylinositol mannoside biosynthesis in Mycobacterium smegmatis and mycobacterial association with human macrophages

Mycobacterium tuberculosis (M. tb) pathogenesis involves the interaction between the mycobacterial cell envelope and host macrophage, a process mediated, in part, by binding of the mannose caps of M. tb lipoarabinomannan (ManLAM) to the macrophage mannose receptor (MR). A presumed critical step in the biosynthesis of ManLAM, and other mannose-containing glycoconjugates, is the conversion of mannose-6-phosphate to mannose-1-phosphate, by a phosphomannomutase (PMM), to produce GDP-mannose, the primary mannose-donor in mycobacteria. We have identified four M. tb H37Rv genes with similarity to known PMMs. Using in vivo complementation of PMM and phosphoglucomutase (PGM) deficient strains of Pseudomonas aeruginosa, and an in vitro enzyme assay, we have identified both PMM and PGM activity from one of these genes, Rv3257c (MtmanB). MtmanB overexpression in M. smegmatis produced increased levels of LAM, lipomannan, and phosphatidylinositol mannosides (PIMs) compared with control strains and led to a 13.3 +/- 3.9-fold greater association of mycobacteria with human macrophages, in a mannan-inhibitable fashion. This increased association was mediated by the overproduction of higher order PIMs that possess mannose cap structures. We conclude that MtmanB encodes a functional PMM involved in the biosynthesis of mannosylated lipoglycans that participate in the association of mycobacteria with macrophage phagocytic receptors.

Inhibition of Type I and Type II Phosphomannose Isomerases by the Reaction Intermediate Analogue 5-Phospho-d-Arabinonohydroxamic Acid Supports a Catalytic Role for the Metal Cofactor

The phosphomannose isomerases (PMI) comprise three families of proteins: type I, type II, and type III PMIs. Members of all three families catalyze the reversible isomerization of D-mannose 6-phosphate (M6P) and D-fructose 6-phosphate (F6P) but share little or no sequence identity. Because (1) PMIs are essential for the survival of several microorganisms, including yeasts and bacteria, and (2) the PMI enzymes from several pathogens do not share significant sequence identity to the human protein, PMIs have been considered as potential therapeutic targets. Elucidation of the catalytic and regulatory mechanisms of the different types of PMIs is strongly needed for rational species-specific drug design. To date, inhibition and crystallographic studies of all PMIs are still largely unexplored. As part of our research program on aldose-ketose isomerases, we report in this paper the evaluation of two new inhibitors of type I and type II PMIs from baker's yeast and Pseudomonas aeruginosa, respectively. We found that 5-phospho-D-arabinonohydroxamic acid (5PAH), which is the most potent inhibitor of phosphoglucose isomerase (PGI), is by far the best inhibitor ever reported of both type I and type II PMI-catalyzed isomerization of M6P to F6P. 5PAH, which has an inhibition constant at least 3 orders of magnitude smaller than that of previously reported PMI inhibitors, may be the first high-energy intermediate analogue inhibitor of the enzymes. We also tested the related molecule 5-phospho-D-arabinonate (5PAA), which is a strong competitive inhibitor of PGI, and found that it does not inhibit either PMI. All together, our results are consistent with a catalytic role for the metal cofactor in PMI activity.

Requirement for phosphoglucomutase in exopolysaccharide biosynthesis in glucose- and lactose-utilizing Streptococcus thermophilus

To study the influence of phosphoglucomutase (PGM) activity on exopolysaccharide (EPS) synthesis in glucose- and lactose-growing Streptococcus thermophilus, a knockout PGM mutant and a strain with elevated PGM activity were constructed. The pgmA gene, encoding PGM in S. thermophilus LY03, was identified and cloned. The gene was functional in Escherichia coli and was shown to be expressed from its own promoter. The pgmA-deficient mutant was unable to grow on glucose, while the mutation did not affect growth on lactose. Overexpression of pgmA had no significant effect on EPS production in glucose-growing cells. Neither deletion nor overexpression of pgmA changed the growth or EPS production on lactose. Thus, the EPS precursors in lactose-utilizing S. thermophilus are most probably formed from the galactose moiety of lactose via the Leloir pathway, which circumvents the need for a functional PGM.

Enzymes leading to the nucleotide sugar precursors for exopolysaccharide synthesis in Burkholderia cepacia

Based on the chemical composition of the exopolysaccharide produced by the cystic fibrosis bacterial isolate Burkholderia cepacia IST408, we postulated and confirmed, based on the specificity of enzymes detected in crude cell-free extracts, the pathway leading to the presumptive activated sugar precursors: UDP-D-glucose, UDP-D-galactose, UDP-D-glucuronic acid, GDP-D-mannose, and GDP-D-rhamnose. Results also suggest that regulation of the expression of the mucoid phenotype in B. cepacia does not occur at the level of synthesis of any of these enzymes.

Non-typeable Haemophilus influenzae adhere to and invade human bronchial epithelial cells via an interaction of lipooligosaccharide with the PAF receptor

Adherence and invasion are thought to be key events in the pathogenesis of non-typeable Haemophilus influenzae (NTHi). The role of NTHi lipooligosaccharide (LOS) in adherence was examined using an LOS-coated polystyrene bead adherence assay. Beads coated with NTHi 2019 LOS adhered significantly more to 16HBE14 human bronchial epithelial cells than beads coated with truncated LOS isolated from an NTHi 2019 pgmB:ermr mutant (P = 0.037). Adherence was inhibited by preincubation of cell monolayers with NTHi 2019 LOS (P = 0.0009), but not by preincubation with NTHi 2019 pgmB:ermr LOS. Competitive inhibition studies with a panel of compounds containing structures found within NTHi LOS suggested that a phosphorylcholine (ChoP) moiety was involved in adherence. Further experiments revealed that mutations affecting the oligosaccharide region of LOS or the incorporation of ChoP therein caused significant decreases in the adherence to and invasion of bronchial cells by NTHi 2019 (P < 0.01). Analysis of infected monolayers by confocal microscopy showed that ChoP+ NTHi bacilli co-localized with the PAF receptor. Pretreatment of bronchial cells with a PAF receptor antagonist inhibited invasion by NTHi 2109 and two other NTHi strains expressing ChoP+ LOS glycoforms exhibiting high reactivity with an anti-ChoP antibody on colony immunoblots. These data suggest that a particular subset of ChoP+ LOS glycoforms could mediate NTHi invasion of bronchial cells by means of interaction with the PAF receptor.

Identification of the pgmG gene, encoding a bifunctional protein with phosphoglucomutase and phosphomannomutase activities, in the gellan gum-producing strain Sphingomonas paucimobilis ATCC 31461

The pgmG gene of Sphingomonas paucimobilis ATCC 31461, the industrial gellan gum-producing strain, was cloned and sequenced. It encodes a 50,059-Da polypeptide that has phosphoglucomutase (PGM) and phosphomannomutase (PMM) activities and is 37 to 59% identical to other bifunctional proteins with PGM and PMM activities from gram-negative species, including Pseudomonas aeruginosa AlgC. Purified PgmG protein showed a marked preference for glucose-1-phosphate (G1P); the catalytic efficiency was about 50-fold higher for G1P than it was for mannose-1-phosphate (M1P). The estimated apparent K(m) values for G1P and M1P were high, 0.33 and 1.27 mM, respectively. The pgmG gene allowed the recovery of alginate biosynthetic ability in a P. aeruginosa mutant with a defective algC gene. This result indicates that PgmG protein can convert mannose-6-phosphate into M1P in the initial steps of alginate biosynthesis and, together with other results, suggests that PgmG may convert glucose-6-phosphate into G1P in the gellan pathway.

A phosphoglucomutase-like gene essential for the optimal expression of methicillin resistance in Staphylococcus aureus: molecular cloning and DNA sequencing

We describe here the cloning and sequencing of a new auxiliary gene identified by Tn551 insertional mutagenesis of the highly and homogeneously methicillin-resistant Staphylococcus aureus strain COL. The insertionally inactivated mutant RUSA315 had intact mecA and normal amounts of PBP2A, but drastically reduced antibiotic resistance (drop in methicillin MIC from 1600 to 1.5 micrograms ml-1), a unique heterogeneous phenotype, and a compositional change in the cell wall characterized by the complete disappearance of the unsubstituted disaccharide pentapeptide from the peptidoglycan. Cloning in E. coli followed by sequencing located the Tn551 insert omega 720 in an open reading frame of 451 codons, provisionally called femR315, defining a polypeptide with a deduced amino acid sequence that showed over 26% sequence identity and 57% overall sequence similarity with the phosphoglucomutase (PGM) gene of E. coli. The Tn551 insertion site of a previously described mutant 12F (femD) also lies in the same gene as femR315. The wild-type form of femR315 subcloned in a shuttle vector fully restored expression of high level (parental) methicillin resistance in mutant RUSA315. The exact biochemical function of femR315 is not known. However, enzymes similar to PGM catalyze the isomerization of hexose and hexosamine phosphates leading to the formation of glucosamine-1-P, which is an obligate precursor in the biosynthesis of UDP-N-acetylglucosamine (UDP-NAGA). We propose that the suppression of methicillin resistance in RUSA315 is related to some functional or quantitative abnormality of UDP-NAGA metabolism.

Influence of macrolides on guanosine diphospho-D-mannose dehydrogenase activity in Pseudomonas biofilm

The formation of biofilm is regarded as a major cause of intractable infectious disease. Our studies were done to elucidate the action of a 14-membered-ring macrolide (erythromycin; EM) and a 16-membered-ring macrolide (midecamycin; MDM) on guanosine diphospho-d-mannose dehydrogenase (GDP-mannose dehydrogenase; GMD), one of the constituents of bacterial biofilm that is known to produce alginate. The mucoid type of Pseudomonas aeruginosa PT-1578 and the non-mucoid type of P. aeruginosa PAO1 were grown with nutrient-rich and nutrient-poor media. Comparative measurements were made of their GMD enzyme activities, with glucose-6-phosphate dehydrogenase (G6PDH), a cell membrane enzyme, used as a control. It was found that the GMD enzyme activity of mucoid type of Pseudomonas bacteria increased when they were grown on nutrient-poor media. Measurements were also made to determine the effects of EM and MDM against GMD and G6PDH enzyme activities. In media with either EM or MDM added, the production of G6PDH was not inhibited, irrespective of the concentration of EM or MDM. However, EM was effective against the production of GMD, showing a concentration-dependent effect. Scanning electron microscopy studies were also carried out to determine the effects of both macrolides on bacterial alginate production. It was found that reduction of alginate content occurred after the addition of EM. When environmental conditions for bacteria deteriorate, GMD enzyme is activated, production of alginate is initiated, and then biofilm is formed. Our results suggest that EM may have an inhibitory effect on the GMD production cycle, hence inhibiting the formation of biofilm. This may explain the differences in the clinical usefulness of 14-membered-and 16-membered-ring macrolides against biofilm disease.

Biosynthesis of mannosylglycerate in the thermophilic bacterium Rhodothermus marinus. Biochemical and genetic characterization of a mannosylglycerate synthase

The biosynthetic reaction scheme for the compatible solute mannosylglycerate in Rhodothermus marinus is proposed based on measurements of the relevant enzymatic activities in cell-free extracts and in vivo (13)C labeling experiments. The synthesis of mannosylglycerate proceeded via two alternative pathways; in one of them, GDP mannose was condensed with D-glycerate to produce mannosylglycerate in a single reaction catalyzed by mannosylglycerate synthase, in the other pathway, a mannosyl-3-phosphoglycerate synthase catalyzed the conversion of GDP mannose and D-3-phosphoglycerate into a phosphorylated intermediate, which was subsequently converted to mannosylglycerate by the action of a phosphatase. The enzyme activities committed to the synthesis of mannosylglycerate were not influenced by the NaCl concentration in the growth medium. However, the combined mannosyl-3-phosphoglycerate synthase/phosphatase system required the addition of NaCl or KCl to the assay mixture for optimal activity. The mannosylglycerate synthase enzyme was purified and characterized. Based on partial sequence information, the corresponding mgs gene was identified from a genomic library of R. marinus. In addition, the mgs gene was overexpressed in Escherichia coli with a high yield. The enzyme had a molecular mass of 46,125 Da, and was specific for GDP mannose and D-glycerate. This is the first report of the characterization of a mannosylglycerate synthase.

Genetic evidence for the role of GDP-mannose in plant ascorbic acid (vitamin C) biosynthesis

Vitamin C (L-ascorbic acid; AsA) acts as a potent antioxidant and cellular reductant in plants and animals. AsA has long been known to have many critical physiological roles in plants, yet its biosynthesis is only currently being defined. A pathway for AsA biosynthesis that features GDP-mannose and L-galactose has recently been proposed for plants. We have isolated a collection of AsA-deficient mutants of Arabidopsis thaliana that are valuable tools for testing of an AsA biosynthetic pathway. The best-characterized of these mutants (vtc1) contains approximately 25% of wild-type AsA and is defective in AsA biosynthesis. By using a combination of biochemical, molecular, and genetic techniques, we have demonstrated that the VTC1 locus encodes a GDP-mannose pyrophosphorylase (mannose-1-P guanyltransferase). This enzyme provides GDP-mannose, which is used for cell wall carbohydrate biosynthesis and protein glycosylation as well as for AsA biosynthesis. In addition to genetically defining the first locus involved in AsA biosynthesis, this work highlights the power of using traditional mutagenesis techniques coupled with the Arabidopsis Genome Initiative to rapidly clone physiologically important genes.

Pattern of changes in the activity of enzymes of GDP-D-mannuronic acid synthesis and in the level of transcription of algA, algC and algD genes accompanying the loss and emergence of mucoidy in Pseudomonas aeruginosa

The low activity levels of the four GDP-D-mannuronic acid-forming enzymes, even in highly alginate-producing strains of Pseudomonas aeruginosa, have made it difficult to compare enzyme activities accompanying the loss/acquisition of mucoidy. Using optimized conditions, we compared the specific activity of these enzymes in three different mucoid P. aeruginosa cystic fibrosis isolates, in their nonmucoid spontaneous variants, and in mucoid variants that emerged during extended incubation of these nonmucoid forms in acetamide broth. A correlation was established between the promptness of emergence of the mucoid forms and the differing sensitivity to nutrient-limitation-induced death of the nonmucoid compared with the isogenic mucoid population. Consistent with the undetectable levels of algD mRNA in nonmucoid forms and with the concept that the step catalyzed by the algD-encoded GDP-mannose dehydrogenase (GMD) is a key step in control of the alginate pathway, GMD activity was undetectable or showed negligible values in nonmucoid variants and correlated with alginate production. However, phosphomannose isomerase (PMI), phosphomannomutase (PMM), and GDP-mannose pyrophosphorylase (GMP) activities in the nonmucoid forms were only slightly (40-70%) below the values in the mucoid forms. Nevertheless, no transcripts homologous to algA (encoding a bifunctional enzyme that possesses both PMI and GMP activities) were detected in the nonmucoid form, and the levels of algC (encoding PMM) transcripts, although detectable in the nonmucoid variants, were, in general, much higher in the mucoid forms. These apparently intriguing observations were cleared up by the identification of two algA functional homologues in P. aeruginosa, recently reported by others, and by the identification of one algC homologue, in contig225 of the PAO1 genome sequence, defining a polypeptide with a deduced amino acid sequence that showed significant homology with that of enzymes of the phosphohexomutase family found in databases. Results are also consistent with the requirement of PMI, GMP and PMM activities for the supply of GDP-D-mannose to (at least) A-band lipopolysaccharide synthesis, while GMD channels this precursor into the alginate pathway.

Cloning of the aceF gene encoding the phosphomannose isomerase and GDP-mannose pyrophosphorylase activities involved in acetan biosynthesis in Acetobacter xylinum

The aceF gene from Acetobacter xylinum was identified and cloned from a genomic DNA library. The complete DNA sequence was determined and computer analysis of the translated gene sequence revealed homology with the deduced amino acid sequence of xanB from Xanthomonas campestris. Therefore aceF is likely to encode a bifunctional enzyme with mannose-6-phosphate isomerase (PMI) and GDP-mannose pyrophosphorylase (GMP) activities. PMI and GMP activities were detected in strains of Escherichia coli expressing the cloned aceF gene.

Abnormal metabolism of mannose in families with carbohydrate-deficient glycoprotein syndrome type 1

Patients with carbohydrate-deficient glycoprotein syndrome (CDGS) Type 1 underglycosylate many glycoproteins by failing to add entire N-linked carbohydrate chains to them. The primary defect in these patients has been reported as a > 90% deficiency in phosphomannomutase activity (PMM), the enzyme that converts mannose-6-phosphate to mannose-1-phosphate. This lesion reduces both the amount and the size of the lipid-linked oligosaccharide precursor. We have now analyzed the activity of PMM and the level of glycosylation in cultured fibroblasts as well as the level of blood mannose in seven CDGS Type 1 patients and their parents. All of these patients were approximately 95% deficient in PMM activity and their parents had an average of 51% of control PMM activity. Furthermore, parental fibroblasts showed reduced glycosylation and a higher proportion of truncated N-linked chains compared to those made by control fibroblasts. Addition of 0.25 mM mannose to the culture medium corrected both the underglycosylation and size of the oligosaccharide chains in CDGS Type 1 patients and their parents. Finally, serum from CDGS patients had considerably reduced mannose levels (5-40 microM) compared to normal controls (40-80 microM) and some parents were below normal (16-103 microM). These results suggest that the reduced blood mannose level is a consequence of the PMM deficiency. This is the first inherited disorder in human metabolism that shows a decrease in available mannose. Increasing blood mannose levels might correct some protein underglycosylation in these patients.

Influence of macrolides on mucoid alginate biosynthetic enzyme from Pseudomonas aeruginosa

OBJECTIVE: The long-term administration of erythromycin (EM), clarithromycin (CAM) or azithromycin (AZM) has generally resulted in a favorable outcome for patients with diffuse panbronchiolitis (DPB) infected with mucoid Pseudomonas aeruginosa. To elucidate the mechanism involved, the influence of macrolides on mucoid alginate production by P. aeruginosa was investigated in vitro. METHODS: The macrolides used in this study were EM with a 14-membered ring, AZM with a 15-membered ring, midecamycin (MDM) with a 16-membered ring, and CP-4305, which has had mycarose removed from MDM, The effects of macrolides on mucoid P. aeruginosa were investigated by quantitative assay of alginate production and inhibition of guanosine diphospho-D-mannose dehydrogenase activity. RESULTS: After incubation with EM, AZM and CP-4305, the structural material of P. aeruginosa biofilm was distorted, and the enzymatic activity of GDP-D-mannose dehydrogenase, the most important enzyme in mucoid alginate biosynthesis, was inhibited. However, these effects were not observed with the 16-membered macrolide MDM. CONCLUSIONS: The basic mechanism of clinical efficacy seen characteristically in 14- or 15-membered macrolides for patients with airway biofilm disease depends on the ability of such macrolides to inhibit alginate production by P. aeruginosa. Furthermore, this suggests that the inhibitory effect observed with 14-, 15- and 16-membered macrolides may depend on the sugar chain connected with the macrolide ring.

Effects of growth-inhibitory concentrations of copper on alginate biosynthesis in highly mucoid Pseudomonas aeruginosa

Alginate production and degree of polymerization were affected when the highly mucoid Pseudomonas aeruginosa 8821M was grown with growth-inhibitory concentrations of Cu2+ (supplied as CuCl2; 1-5 mM). The inhibition of alginate biosynthesis was consistent with the decreased activity in Cu2+-stressed cells of phosphomannose isomerase/GDP-mannose pyrophosphorylase (encoded by algA), phosphomannomutase (encoded by algC) and GDP-mannose dehydrogenase (encoded by algD). However, in cells grown with concentrations of CuCl2 below 2 mM, the steady-state mRNA levels from algA, algC, algD and from the regulatory gene algR1 increased moderately. This observation is consistent with the suggested linkage between the control of alginate gene expression and the global regulation involved in the oxidative stress response. At highly inhibitory concentrations the levels of the four alginate gene transcripts decreased from maximal values. The bell-shaped curves, representing the effect of Cu2+ concentration on mRNA levels from the four alginate genes, exhibited similar patterns but did not concur. The decrease of the specific activity of enzymes necessary for GDP-mannuronic acid synthesis in Cu2+-grown cells was correlated with changes in gene expression, with the inhibitory effect of Cu2+ on enzyme activities and with Cu2+-induced oxidative inactivation of enzymes, especially the particularly sensitive phosphomannose isomerase activity.

Oxygen-dependent upregulation of transcription of alginate genes algA, algC and algD in Pseudomonas aeruginosa

The mRNA levels of algA, algC and algD genes increased, coordinately, in cells of the highly mucoid Pseudomonas aeruginosa 8821M grown under increasing dissolved oxygen tensions (DOT) of up to 70% of air saturation. These genes encode the bifunctional protein with phosphomannose isomerase (PMI) and GDP-mannose pyrophosphorylase (GMP) activities (algA), the phosphomannomutase (PMM) (algC) and the GDP-mannose dehydrogenase (GMD) (algD). These four enzyme activities are necessary for the synthesis of GDP-mannuronic acid, which is the activated sugar precursor for alginate polymerization. For growth-limiting DOT--lower than 10% of air saturation--the increase in mRNA levels of algA, algC and algD with oxygen concentration was accompanied by a strong increase in the activity of the encoded enzymes and the consequent increase in alginate synthesis. However, and despite the upregulation of alginate gene transcription by DOT above 10% of air saturation, the activities of the encoded enzymes either maintained (GMP and GMD) or decreased (PMI and PMM) their levels at high oxygen tensions, leading to a slight decrease in alginate synthesis. This has previously been attributed to the oxidative inactivation of alginate enzymes, particularly of PMM and PMI activities.

Glycobiotechnology: enzymes for the synthesis of nucleotide sugars

Complex carbohydrates, as constituting part of glycoconjugates such as glycoproteins, glycolipids, hormones, antibiotics and other secondary metabolites, play an active role in inter- and intracellular communication. The aim of "glycobiotechnology" as an upcoming interdisciplinary research field is to develop highly efficient synthesis strategies, including in vivo and in vitro approaches, in order to bring such complex molecules into analytical and therapeutic studies. The enzymatic synthesis of glycosidic bonds by Leloir-glycosyltransferases is an efficient strategy for obtaining saccharides with absolute stereo- and regioselectivity in high yields and under mild conditions. There are, however, two obstacles hindering the realization of this process on a biotechnological scale, namely the production of recombinant Leloir-glycosyltransferases and the availability of enzymes for the synthesis of nucleotide sugars (the glycosyltransferase donor substrates). The present review surveys some synthetic targets which have attracted the interest of glycobiologists as well as recombinant expression systems which give Leloir-glycosyltransferase activities in the mU and U range. The main part summarizes publications concerned with the complex pathways of primary and secondary nucleotide sugars and the availability and use of these enzymes for synthesis applications. In this context, a survey of our work will demonstrate how enzymes from different sources and pathways can be combined for the synthesis of nucleotide deoxysugars and oligosaccharides.

Cloning and functional analysis of the pmmA gene encoding phosphomannomutase from the photosynthetic prokaryote Prochlorothrix hollandica

The pmmA gene encoding a bifunctional phosphomannomutase/phosphoglucomutase (PMM/PGM) from the photosynthetic prokaryote, Prochlorothrix hollandica has been cloned and sequenced. The gene encodes a 51827 Da polypeptide 48% identical to the PMM of Azospirillum brasilense, 37% identical to the PGMs of pathogenic Neisseria sp. and 37% identical to the bifunctional AlgC PGM/PMM of Pseudomonas aeruginosa. The pmmA gene encodes an enzyme having both PGM and PMM activities as judged by both enzyme assays and complementation analysis in which the cloned gene partially corrected the pgm-1 mutation of Escherichia coli.

Physiological and biochemical changes accompanying the loss of mucoidy by Pseudomonas aeruginosa

Pseudomonas aeruginosa M60, a mucoid strain, was grown in continuous culture (D 0.05 h-1) under ammonia limitation with glucose as the carbon source. Steady-state alginate production occurred for only 1-2 d under these conditions [qalginate 0.097 g alginate h-1 (g dry wt cells)-1], after which time the percentage of mucoid cells and the alginate concentration in the culture decreased in parallel and approached zero after approximately 10 d. These changes were accompanied by similar decreases in the activities of the alginate biosynthetic enzymes (represented by phosphomannomutase and GDP-mannose dehydrogenase) and by a large increase in the activity of the first enzyme of the 'external' non-phosphorylative pathway of glucose metabolism, glucose dehydrogenase. In contrast, the activities of other enzymes associated with this pathway (gluconate dehydrogenase, 2-ketogluconate kinase plus 2-ketogluconate-6-phosphate reductase) or with the 'internal' phosphorylative pathway of glucose metabolism (glucokinase and glucose-6-phosphate dehydrogenase) remained essentially unchanged. The loss of mucoidy and alginate production was accompanied by the appearance of low concentrations of intracellular polyhydroxyalkanoate (PHA) and of extracellular gluconate and 2-ketogluconate (partly at the expense of alginate production and partly as a result of increased glucose consumption). It is suggested that ammonia-limited, glucose-excess cultures of P. aeruginosa growing at low dilution rate are unable fully to regulate the rate at which glucose and/or its 'external' pathway metabolites are taken up by the cell, and therefore form copious amounts of alginate in order both to overcome the potentially deleterious osmotic effects of accumulating surplus intracellular metabolites and to consume the surplus ATP generated by the further oxidation of these metabolites. The loss of mucoidy invokes the use of an alternative, but analogous, strategy via which non-mucoid cells produce an osmotically inactive intracellular product (PHA) plus increased amounts of the extracellular metabolites gluconate and 2-ketogluconate via the low-energy-yielding and, under these conditions, largely dead-end 'external' metabolic pathway.

A putative pathway for perosamine biosynthesis is the first function encoded within the rfb region of Vibrio cholerae O1

The first four genes (rfbA,B,D,E) of the rfb region of Vibrio cholerae O1 are predicted to encode the enzymes required for the biosynthesis of perosamine, which constitutes the backbone structure of the O-antigen of the lipopolysaccharide. Based on homology to known proteins/protein families, the following functions are predicted: RfbA, phosphomannose isomerase-guanosine diphosphomannose pyrophosphorylase; RfbB, phosphomanno-mutase; RfbD, oxido reductase and RfbE, perosamine synthetase (amino-transferase). Thus, perosamine is synthesized from fructose 6-phosphate via the intermediates mannose 6-phosphate by RfbA, to mannose 1-phosphate by RfbB, to GDP-mannose by RfbA, to GDP-4-keto-6-dideoxymannose by RfbD and to GDP-perosamine by RfbE. This final product would then serve as the substrate for the addition of the tetronate, which could then be polymerized into the O-antigen for transfer to the lipid A plus core oligosaccharide and export to the cell surface. The organization of these genes are such that one would expect them to be translationally coupled as part of the rfb operon. However, the absence of readily detectable promoter sequences suggests low levels of transcription, in line with other studies. The nucleotide sequence of these genes is absolutely conserved in the two isolates 569B (classical, Inaba) and O17 (El Tor, Ogawa) which were expected to show maximal sequence variation. This suggests very tight constraints on the micro-evolution within these sequences.

Growth-phase-dependent alginate synthesis, activity of biosynthetic enzymes and transcription of alginate genes in Pseudomonas aeruginosa

Alginate synthesis by the highly mucoid Pseudomonas aeruginosa 8821 M is growth-phase-dependent, and the alginate produced per unit of biomass reaches maximum values in the deceleration phase of growth. However, the degree of polymerization increases as batch growth proceeds, reaching maximum values at the stationary phase of growth. The activity of the four enzymes leading to GDP-mannuronic acid formation, phosphomannose isomerase, phosphomannomutase, GDP-mannose pyrophosphorylase and GDP-mannose dehydrogenase peaked earlier at the late exponential phase. Growth-phase-dependent activity of alginate biosynthetic enzymes correlates with the level of transcription of the encoding alginate genes algA, algC and algD during growth, as indicated by Northern blot hybridization experiments. The pattern of coordinate transcriptional growth-phase regulation of these alginate structural genes concurs with the growth-dependent transcription of the regulatory gene algR1.

Purification and characterization of phosphomannomutase/phosphoglucomutase from Pseudomonas aeruginosa involved in biosynthesis of both alginate and lipopolysaccharide

The algC gene from Pseudomonas aeruginosa has been shown to encode phosphomannomutase (PMM), an essential enzyme for biosynthesis of alginate and lipopolysaccharide (LPS). This gene was overexpressed under control of the tac promoter, and the enzyme was purified and its substrate specificity and metal ion effects were characterized. The enzyme was determined to be a monomer with a molecular mass of 50 kDa. The enzyme catalyzed the interconversion of mannose 1-phosphate (M1P) and mannose 6-phosphate, as well as that of glucose 1-phosphate (G1P) and glucose 6-phosphate. The apparent Km values for M1P and G1P were 17 and 22 microM, respectively. On the basis of Kcat/Km ratio, the catalytic efficiency for G1P was about twofold higher than that for M1P. PMM also catalyzed the conversion of ribose 1-phosphate and 2-deoxyglucose 6-phosphate to their corresponding isomers, although activities were much lower. Purified PMM/phosphoglucomutase (PGM) required Mg2+ for maximum activity; Mn2+ was the only other divalent metal that showed some activation. The presence of other divalent metals in addition to Mg2+ in the reaction inhibited the enzymatic activity. PMM and PGM activities could not be detected in nonmucoid algC mutant strain 8858 and in LPS-rough algC mutant strain AK1012, while they were present in the wild-type strains as well as in algC-complemented mutant strains. This evidence suggests that AlgC functions as PMM and PGM in vivo, converting phosphomannose and phosphoglucose in the biosynthesis of both alginate and LPS.

The Pseudomonas aeruginosa algC gene encodes phosphoglucomutase, required for the synthesis of a complete lipopolysaccharide core

We have constructed strains of Pseudomonas aeruginosa with mutations in the algC gene, previously shown to encode the enzyme phosphomannomutase. The algC mutants of a serotype O5 strain (PAO1) and a serotype O3 strain (PAC1R) did not express lipopolysaccharide (LPS) O side chains or the A-band (common antigen) polysaccharide. The migration of LPS from the algC mutant strains in Tricine-sodium dodecyl sulfate-polyacrylamide gels was similar to that of LPS from a PAO1 LPS-rough mutant, strain AK1012, and from a PAC1R LPS-rough mutant, PAC605, each previously shown to be deficient in the incorporation of glucose onto the LPS core (K. F. Jarrell and A. M. Kropinski, J. Virol. 40:411-420, 1981, and P. S. N. Rowe and P. M. Meadow, Eur. J. Biochem. 132:329-337, 1983). We show that, as expected, the algC mutant strains had no detectable phosphomannomutase activity and that neither algC strain had detectable phosphoglucomutase (PGM) activity. To confirm that the PGM activity was encoded by the algC gene, we transferred the cloned, intact P. aeruginosa algC gene to a pgm mutant of Escherichia coli and observed complementation of the pgm phenotype. Our finding that the algC gene product has PGM activity and that strains with mutations in this gene produce a truncated LPS core suggests that the synthesis of glucose 1-phosphate is necessary in the biosynthesis of the P. aeruginosa LPS core. The data presented here thus demonstrate that the algC gene is required for the synthesis of a complete LPS core in two strains with different LPS core and O side chain structures.

Pseudomonas aeruginosa: genes and enzymes of alginate synthesis

Alginate is an important virulence factor of Pseudomonas aeruginosa, a bacterium that colonizes the pulmonary tracts of cystic fibrosis patients. Alginate is also widely used in the food, pharmaceutical and chemical industries, and consequently there is considerable interest in the molecular biology and biochemistry of alginate synthesis. As well as its therapeutic potential, research on mucoid P. aeruginosa may provide a lead to an alternative source of alginate for industrial use.

Pseudomonas aeruginosa AlgG is a polymer level alginate C5-mannuronan epimerase

Alginate is a viscous extracellular polymer produced by mucoid strains of Pseudomonas aeruginosa that cause chronic pulmonary infections in patients with cystic fibrosis. Alginate is polymerized from GDP-mannuronate to a linear polymer of beta-1-4-linked residues of D-mannuronate and its C5-epimer, L-guluronate. We previously identified a gene called algG in the alginate biosynthetic operon that is required for incorporation of L-guluronate residues into alginate. In this study, we tested the hypothesis that the product of algG is a C5-epimerase that directly converts D-mannuronate to L-guluronate. The DNA sequence of algG was determined, and an open reading frame encoding a protein (AlgG) of approximately 60 kDa was identified. The inferred amino terminus of AlgG protein contained a putative signal sequence of 35 amino acids. Expression of algG in Escherichia coli demonstrated both 60-kDa pre-AlgG and 55-kDa mature AlgG proteins, the latter of which was localized to the periplasm. An N-terminal analysis of AlgG showed that the signal sequence was removed in the mature form. Pulse-chase experiments in both E. coli and P. aeruginosa provided evidence for conversion of the 60- to the 55-kDa size in vivo. Expression of algG from a plasmid inan algG (i.e., polymannuronate-producing) mutant of P. aeruginosa restored production of an alginate containing L-guluronate residues. The observation that AlgG is apparently processed and exported from the cytoplasm suggested that it may act as a polymer-level mannuronan C5-epimerase. An in vitro assay for mannuronan C5 epimerization was developed wherein extracts of E. coli expressing high levels of AlgG were incubated with polymannuronate. Epimerization of D-mannuronate to L-guluronate residues in the polymer was detected enzymatically, using a L-guluronate-specific alginate lyase of Klebsiella aerogenes. Epimerization was also detected in the in vitro reaction between recombinant AlgG and poly-D-mannuronate, using high-performance anion-exchange chromatography. The epimerization reaction was detected only when acetyl groups were removed from the poly-D-mannuronate substrate, suggesting that AlgG epimerization activity in vivo may be sensitive to acetylation of the D-mannuronan residues. These results demonstrate that AlgG has polymer-level mannuronan C5-epimerase activity.

Cloning, sequencing, and overexpression in Escherichia coli of the alpha-D-glucose-1-phosphate cytidylyltransferase gene isolated from Yersinia pseudotuberculosis

A clone of Yersinia pseudotuberculosis DNA carrying the ascA gene was constructed, and the corresponding protein was successfully overexpressed in Escherichia coli. A protocol consisting of DEAE-cellulose and Sephadex G-100 column chromatography was developed and led to a nearly homogeneous purification of the ascA product. Initial characterization showed that the ascA-encoded protein is actually the alpha-D-glucose-1-phosphate cytidylyltransferase which catalyzes the first step of the biosynthesis of CDP-ascarylose (CDP-3,6-dideoxy-L-arabino-hexose), converting alpha-D-glucose-1-phosphate to CDP-D-glucose. In contrast to early studies suggesting that this enzyme was a monomeric protein of 111 kDa, the purified cytidylyltransferase from Y. pseudotuberculosis was found to consist of four identical subunits, each with a molecular mass of 29 kDa. This assignment is supported by the fact that the ascA gene, as a part of the ascarylose biosynthetic cluster, exhibits high sequence homology with other nucleotidylyltransferases, and its product shows high cytidylyltransferase activity. Subsequent amino acid comparison with other known nucleotidylyltransferases has allowed a definition of the important active-site residues within this essential catalyst. These comparisons have also afforded the inclusion of the cytidylyltransferase into the mechanistic convergence displayed by this fundamental class of enzyme.

Exopolysaccharide production in biofilms: substratum activation of alginate gene expression by Pseudomonas aeruginosa

Reporter gene technology was employed to detect the activity of an alginate promoter of Pseudomonas aeruginosa when the organism was grown as a biofilm on a Teflon mesh substratum and as planktonic cells in liquid medium. Alginate biosynthetic activity was determined with a mucoid cell line derived from a cystic fibrosis isolate and containing an alginate algC promoter fused to a lacZ reporter gene. Reporter activity was demonstrated with chromogenic and fluorogenic substrates for beta-galactosidase. Expression of algC was shown to be upregulated in biofilm cells compared with planktonic cells in liquid medium. Gene up-expression correlated with alginate biosynthesis as measured by Fourier transform infrared spectroscopy, uronic acid accumulation, and alginate-specific enzyme-linked immunosorbent assay. The algC promoter was shown to have maximum activity in planktonic cultures during the late lag and early log phases of the cell growth cycle. During a time course experiment, biofilm algC activity exceeded planktonic activity except during the period immediately following inoculation into fresh medium. In continuous-culture experiments, conversion of lacZ substrate was demonstrated microscopically in individual cells by epifluorescence microscopy.

Manipulation of Pseudomonas aeruginosa alginate pathway by varying the level of biosynthetic enzymes and growth temperature

The manipulation of the alginate pathway in two Pseudomonas aeruginosa mucoid variants was attempted at growth temperatures within the range 20 degrees C-40 degrees C. This was carried out by increasing the level of either phosphomannose isomerase (PMI) and GDP-mannose pyrophosphorylase (GMP) or GDP-mannose dehydrogenase (GMD) encoded by algA or algD respectively, present in recombinant plasmids derived from the controlled expression vector pMMB24. The specific growth rate of cells expressing either algA or algD genes from recombinant plasmids was lower than that of cells harbouring the cloning vector only. Stimulation of alginate synthesis was observed when the expression of the alginate genes was low, in the absence of isopropyl-beta-D-thiogalactopyranoside (IPTG) induction. The further increase of the level of alginate enzymes in induced cells, without the simultaneous increase of other limiting steps, had no positive effect on the strictly regulated alginate pathway. Temperature profiles for alginate synthesis were modified reflecting changes in rate limiting steps. Limitations on the polymerization ability and the competition between cell growth and alginate synthesis were possibly involved in the modification of the temperature profiles for alginate production, or in the decrease of the molecular weight of polymers produced by recombinants under conditions that led to highly active alginate synthesis. The acetyl content of alginates produced by the recombinants was higher than that of the biopolymer controls, possibly due to the higher acetyl-CoA availability in slower growing cells.

Identification, expression, and DNA sequence of the GDP-mannose biosynthesis genes encoded by the O7 rfb gene cluster of strain VW187 (Escherichia coli O7:K1)

The O7-specific lipopolysaccharide (LPS) in strains of Escherichia coli consists of a repeating unit made of galactose, mannose, rhamnose, 4-acetamido-2,6-dideoxyglucose, and N-acetylglucosamine. We have recently cloned and characterized genetically the O7-specific LPS biosynthesis region (rfbEcO7) of the E. coli O7:K1 strain VW187 (C. L. Marolda, J. Welsh, L. Dafoe, and M. A. Valvano, J. Bacteriol. 172:3590-3599, 1990). In this study, we localized the gnd gene encoding gluconate-6-phosphate dehydrogenase at one end of the rfbEcO7 gene cluster and sequenced that end of the cluster. Three open reading frames (ORF) encoding polypeptides of 275, 464, and 453 amino acids were identified upstream of gndEcO7, all transcribed toward the gnd gene. ORF275 had 45% similarity at the protein level with ORF16.5, which occupies a similar position in the Salmonella enterica LT2 rfb region, and presumably encodes a nucleotide sugar transferase. The polypeptides encoded by ORFs 464 and 453 were expressed under the control of the ptac promoter and visualized in Coomassie blue-stained sodium dodecyl sulfate-polyacrylamide gels and by maxicell analysis. ORF464 expressed GDP-mannose pyrophosphorylase and ORF453 encoded a phosphomannomutase, the enzymes for the biosynthesis pathway of GDP-mannose, one of the nucleotide sugar precursors for the formation of the O7 repeating unit. They were designated rfbMEcO7 and rfbKEcO7, respectively. The RfbMEcO7 polypeptide was homologous to the corresponding protein in S. enterica LT2, XanB of Xanthomonas campestris, and AlgA of Pseudomonas aeruginosa, all GDP-mannose pyrophosphorylases. RfbKEcO7 was very similar to CpsG of S. enterica LT2, an enzyme presumably involved in the biosynthesis of the capsular polysaccharide colanic acid, but quite different from the corresponding RfbK protein of S. enterica LT2.

Alginate synthesis in Pseudomonas aeruginosa: environmental regulation of the algC promoter

The exopolysaccharide alginate is a major virulence factor of Pseudomonas aeruginosa strains that infect the lungs of cystic fibrosis patients. The synthesis of alginate is almost uniquely associated with the pathogenicity of P. aeruginosa within the environment of the cystic fibrosis lung. The gene algC is one of the essential alginate biosynthetic genes and codes for the enzyme phosphomannomutase. In this report, we present data on the transcriptional regulation of algC expression. The activity of the algC promoter is modulated by the response regulator, AlgR1, a member of the two-component signal transduction protein family, which also regulates other alginate-specific promoters. In both mucoid (alginate-positive) and nonmucoid (alginate-negative) P. aeruginosa strains, transcriptional activation of algC increased with the osmolarity of the culture medium. This osmolarity-induced activation was found to be dependent on AlgR1. AlgR1 was found to interact directly with the algC promoter. Deletion mapping, in conjunction with mobility shift assays, showed that AlgR1 specifically bound with two regions of algC upstream DNA. A fragment spanning nucleotide positions -378 to -73 showed strong specific binding, while a fragment located between positions -73 and +187 interacted relatively weakly with AlgR1. Phosphorylation of the AlgR1 protein resulted in the stimulation of its in vitro ability to bind to the algC promoter region (a fragment spanning nucleotides -378 to -73). Transcription from the algC promoter, which has significant homology with the RNA polymerase sigma-54 (RpoN) recognition sequence, decreased in an rpoN mutant of P. aeruginosa.

IgG subclass antibody responses to alginate from Pseudomonas aeruginosa in patients with cystic fibrosis and chronic P. aeruginosa infection

Chronic bronchopulmonary infection with alginate-producing, mucoid Pseudomonas aeruginosa is characteristically associated with cystic fibrosis (CF). A significant correlation between the antibody response to alginate and poor lung function has been reported. Enzyme-linked immunosorbent assays were developed for the quantitation of human IgG1, IgG2, IgG3, and IgG4 antibodies to P. aeruginosa alginate. We investigated the pattern of IgG subclass antibodies against P. aeruginosa alginate in serum of patients with CF, others with chronic P. aeruginosa infection, and healthy controls. Healthy controls and patients with CF, before they acquired P. aeruginosa infection, had no or very low titers of antibodies against P. aeruginosa alginate. The latter with chronic infection had significantly higher antibody levels than all others groups, including patients with chronic P. aeruginosa infection but no CF. CF with chronic P. aeruginosa infection led to an inverse correlation between lung function parameters and levels of IgG3 and IgG4. Fifty-seven patients with CF have been followed for an average of 12 years with multiple antibody assays covering the preinfection, early, and late stage of chronic infection. All of them developed IgG1 and IgG3 antibodies to alginate at the start of infection. IgG2 antibodies developed later and showed only a slow increase during the chronic infection. Patients who died had significantly higher IgG2 anti-alginate antibody levels than other investigated groups. Elevated levels of IgG2 and IgG3 antibodies to P. aeruginosa alginate are a sign of poor prognosis in CF.

Genetics of xanthan production in Xanthomonas campestris: the xanA and xanB genes are involved in UDP-glucose and GDP-mannose biosynthesis

The nucleotide sequence of a 3.4-kb EcoRI-PstI DNA fragment of Xanthomonas campestris pv. campestris revealed two open reading frames, which were designated xanA and xanB. The genes xanA and xanB encode proteins of 448 amino acids (molecular weight of 48,919) and 466 amino acids (molecular weight of 50,873), respectively. These genes were identified by analyzing insertion mutants which were known to be involved in xanthan production. Specific tests for the activities of enzymes involved in the biosynthesis of UDP-glucose and GDP-mannose indicated that the xanA gene product was involved in the biosynthesis of both glucose 1-phosphate and mannose 1-phosphate. The deduced amino acid sequence of xanB showed a significant degree of homology (59%) to the phosphomannose isomerase of Pseudomonas aeruginosa, a key enzyme in the biosynthesis of alginate. Moreover, biochemical analysis and complementation experiments with the Escherichia coli manA fragment revealed that xanB encoded a bifunctional enzyme, phosphomannose isomerase-GDP-mannose pyrophosphorylase.

Role of alginate in infection with mucoid Pseudomonas aeruginosa in cystic fibrosis

BACKGROUND

Chronic bronchopulmonary infection with mucoid, alginate producing Pseudomonas aeruginosa occurs characteristically in patients with cystic fibrosis. Alginate may be a virulence factor for P aeruginosa infection in such patients.

METHODS

Forced vital capacity (FVC), nutritional state and the antibody response to P aeruginosa were determined at regular intervals from three years before chronic P aeruginosa infection to 10 years afterwards in 73 patients with cystic fibrosis. All patients were treated intensively with antipseudomonal chemotherapy during the study period.

RESULTS

FVC was reduced in all patients who subsequently developed P aeruginosa infection before they acquired the infection, indicating significant pre-existing lung damage when compared with patients who remained free of P aeruginosa. Lung function and nutritional state remained unchanged after 10 years of infection, except in the patients who died of P aeruginosa lung infection. The FVC and height and weight of patients infected with nonmucoid strains of P aeruginosa were similar to those of uninfected patients. Patients infected with mucoid strains had poorer lung function and nutritional state for the first five years after infection compared with patients with nonmucoid strains. Such infection was also associated with greater IgG and IgA antibody responses to P aeruginosa standard antigen compared with nonmucoid infection. Concentrations of antibody to alginate were similar in patients with non-mucoid and mucoid infection. Noticeably increased concentrations of IgA antibodies to P aeruginosa standard antigen were observed early after the onset of infection in patients who subsequently died.

CONCLUSION

Alginate producing P aeruginosa infection is associated with a hyperimmune response and poor clinical condition, suggesting that alginate production is a virulence factor in such infections in patients with cystic fibrosis.

Alginate biosynthesis in mucoid recombinants of Pseudomonas aeruginosa overproducing GDP-mannose dehydrogenase

The Pseudomonas aeruginosa algD gene, encoding GDP-mannose dehydrogenase (GMD) and cloned at Chakrabarty's Laboratory in the expression vector pMMB24 (plasmid pVD211), was mobilized into P.aeruginosa strains 8821 and 8821M. Strain 8821M was a high-alginate-producing variant, spontaneously obtained from mucoid strain 8821, with derepressed levels of GMD, a key enzyme in the regulation of alginate biosynthesis, leading to the irreversible oxidation of GDP-mannose to GDP-mannuronic acid. A slight increase in the level of GMD, in both strains harboring the plasmid pVD211 and batch-grown at 37 degrees C without IPTG induction, led to the increase of production rate and the final concentration of alginate produced by control strains harboring the cloning vector. However, the viscosity of the aqueous solutions prepared with the alginate (3 g l-1) produced by mucoid strains harboring pVD211 was lower than those with the alginate produced by the controls (shear rates in the range 0.6-12 s-1). The specific activity of GMD assayed in crude extracts from cells harboring pVD211 and subjected to IPTG induction (0.5 and 3 mM) presented the highest values. However, either the rate of biosynthesis and final concentration of alginate or the viscosity of solutions prepared with the alginate produced by recombinants grown with IPTG were lower than that possible without overproduction. Therefore, the stimulation of the alginate pathway only by manipulating the rate of the step catalysed by GMD, although possible within certain levels, was at the expense of the final exopolysaccharide quality.

Conjugal transfer of recombinant plasmids into gellan gum-producing and non-producing variants of Pseudomonas elodea ATCC 31461

The conjugal transfer of recombinant plasmids into a gellan gum-producing, rifampicin-resistant strain of Pseudomonas elodea and into one of its non-producing variants, was studied in order to facilitate the cloning of gellan genes. The mobilization frequency of recombinant plasmids derived from pKT240, and of cosmid pJRD215 from Escherichia coli HB101 (hsdM), into the mucoid strain was below the values for the non-mucoid variant and decreased exponentially with plasmid size. Reducing the mating time on solid surfaces led to higher mobilization frequencies. Under optimal conditions, a gene bank (40-50 kb) constructed in the cosmid pJRD215 was efficiently mobilized into Gel- mutants during complementation experiments.