Cloning of Escherichia coli and Pseudomonas aeruginosa phosphomannose isomerase genes and their expression in alginate-negative mutants of Pseudomonas aeruginosa

Alginate: Enhancement Strategies for Advanced Applications

Alginate is an excellent biodegradable and renewable material that is already used for a broad range of industrial applications, including advanced fields, such as biomedicine and bioengineering, due to its excellent biodegradable and biocompatible properties. This biopolymer can be produced from brown algae or a microorganism culture. This review presents the principles, chemical structures, gelation properties, chemical interactions, production, sterilization, purification, types, and alginate-based hydrogels developed so far. We present all of the advanced strategies used to remarkably enhance this biopolymer’s physicochemical and biological characteristics in various forms, such as injectable gels, fibers, films, hydrogels, and scaffolds. Thus, we present here all of the material engineering enhancement approaches achieved so far in this biopolymer in terms of mechanical reinforcement, thermal and electrical performance, wettability, water sorption and diffusion, antimicrobial activity, in vivo and in vitro biological behavior, including toxicity, cell adhesion, proliferation, and differentiation, immunological response, biodegradation, porosity, and its use as scaffolds for tissue engineering applications. These improvements to overcome the drawbacks of the alginate biopolymer could exponentially increase the significant number of alginate applications that go from the paper industry to the bioprinting of organs.

Influence of the Photorhabdus luminescens phosphomannose isomerase gene, manA, on mannose utilization, exopolysaccharide structure, and biofilm formation

Extracellular polysaccharide (EPS) is produced by diverse bacterial pathogens and fulfills assorted roles, including providing a structural matrix for biofilm formation and more specific functions in virulence, such as protection against immune defenses. We report here the first investigation of some of the genes important for biofilm formation in Photorhabdus luminescens and demonstrate the key role of the phosphomannose isomerase gene, manA, in the structure of functional EPS. Phenotypic analyses of a manA-deficient mutant showed the importance of EPS in motility, insect virulence, and biofilm formation on abiotic surfaces as well as the requirement of this gene for the use of mannose as the sole carbon source. Conversely, this defect had no apparent impact on symbiosis with the heterorhabditid nematode vector. A more detailed analysis of biofilm formation revealed that the manA mutant was able to attach to surfaces with the same efficiency as that of the wild-type strain but could not develop the more extended biofilm matrix structures. A compositional analysis of P. luminescens EPS reveals how the manA mutation has a major effect on the formation of a complete, branched EPS.

Identification of mannose uptake and catabolism genes in Corynebacterium glutamicum and genetic engineering for simultaneous utilization of mannose and glucose

Here, focus is on Corynebacterium glutamicum mannose metabolic genes with the aim to improve this industrially important microorganism's ability to ferment mannose present in mixed sugar substrates. cgR_0857 encodes C. glutamicum's protein with 36% amino acid sequence identity to mannose 6-phosphate isomerase encoded by manA of Escherichia coli. Its deletion mutant did not grow on mannose and exhibited noticeably reduced growth on glucose as sole carbon sources. In effect, C. glutamicum manA is not only essential for growth on mannose but also important in glucose metabolism. A double deletion mutant of genes encoding glucose and fructose permeases (ptsG and ptsF, respectively) of the phosphoenolpyruvate-dependent phosphotransferase system (PTS) was not able to grow on mannose unlike the respective single deletion mutants with mannose utilization ability. A mutant deficient in ptsH, a general PTS gene, did not utilize mannose. These indicate that the glucose-PTS and fructose-PTS are responsible for mannose uptake in C. glutamicum. When cultured with a glucose and mannose mixture, mannose utilization of manA-overexpressing strain CRM1 was significantly higher than that of its wild-type counterpart, but with a strong preference for glucose. ptsF-overexpressing strain CRM2 co-utilized mannose and glucose, but at a total sugar consumption rate much lower than that of the wild-type strain and CRM1. Strain CRM3 overexpressing both manA and ptsF efficiently co-utilized mannose and glucose. Under oxygen-deprived conditions, high volumetric productivity of organic acids concomitant with the simultaneous consumption of the mixed sugars was achieved by the densely packed growth-arrested CRM3 cells.

Characterization of the Aspergillus fumigatus phosphomannose isomerase Pmi1 and its impact on cell wall synthesis and morphogenesis

Phosphomannose isomerase (PMI) is an enzyme catalysing the interconversion of mannose 6-phosphate (Man-6-P) and fructose 6-phosphate (Fru-6-P). The reaction catalysed by PMI is the first committed step in the synthesis of mannose-containing sugar chains and provides a link between glucose metabolism and mannosylation. In this study, the pmi1 gene was identified to encode PMI in the human fungal pathogen Aspergillus fumigatus. Characterization of A. fumigatus Pmi1 expressed in Escherichia coli revealed that this PMI mainly catalysed the conversion of Fru-6-P to Man-6-P and that its binding affinity for Man-6-P was similar to that of yeast PMIs, but different to those of PMIs from bacteria or animals. Loss of pmi1 was lethal unless Man was provided in the growth medium. However, a Δpmi1 mutant cell showed a significantly reduced growth rate at a high concentration of Man. Biochemical analysis revealed that both inadequate and replete Man led to an accumulation of intracellular Man-6-P and a reduction in the amount of α-glucan in the cell wall. Uncoupling of the link between energy production and glycosylation by deletion of the pmi1 gene led to phenotypes such as defects in cell wall integrity, abnormal morphology and reduced conidiation. Our results reveal that PMI activity is essential for viability and plays a central regulatory role in both cell wall synthesis and energy production in A. fumigatus.

Bacterial proteins and CpG-rich extrachromosomal DNA in potential cancer therapy

Bacterial proteins such as azurin and Laz have recently been shown to enter preferentially to cancer cells and kill them by multiple mechanisms. Historically, bacterial DNA, particularly the unmethylated CpG dinucleotides, have been shown to trigger activation of specific Toll-like receptors (TLRs) in immune cells, leading to various cytokine and chemokine production that allows cancer cell death and their regression. However, the enhanced release of specific protein or extrachromosomal DNA by bacteria in response to exposure to cancer cells has not been previously demonstrated. In this review, we discuss how an opportunistic, extracellular pathogenic bacterium, Pseudomonas aeruginosa, senses the presence of cancer cells and releases a specific protein or extrachromosomal DNA with antitumor activity for inhibition of cancer cell growth.

Identification and characterization of the Cryptococcus neoformans phosphomannose isomerase-encoding gene, MAN1, and its impact on pathogenicity

The polysaccharide capsule surrounding Cryptococcus neoformans comprises manose, xylose and glucuronic acid, of which mannose is the major constituent. The GDP-mannose biosynthesis pathway is highly conserved in fungi and consists of three key enzymes: phosphomannose isomerase (PMI), phosphomannomutase (PMM) and GDP-mannose pyrophosphorylase (GMP). The MAN1 gene, encoding for the PMI enzyme, was isolated and sequenced from C. neoformans, and a disruption of the MAN1 gene was generated. One MAN1 disruption mutant, man1, which showed poor capsule formation, reduced polysaccharide secretion and morphological abnormalities, was chosen for virulence studies. In both the rabbit and the mouse models of invasive cryptococcosis, man1 was shown to be severely impaired in its virulence, with complete elimination of the yeast from the host. A reconstituted strain of man1 was constructed using gene replacement at the native locus. The wild-type and reconstituted strains were significantly more virulent than the knock-out mutant in both animal models. Our findings reveal that PMI activity is essential for the survival of C. neoformans in the host. The fact that the man1 mutant was not pathogenic suggests that blocking mannose synthesis could be fungicidal in the mammalian host and thus an excellent target for antifungal drug development.

Real-time PCR used to measure stress-induced changes in the expression of the genes of the alginate pathway of Pseudomonas aeruginosa

AIMS

To measure the concentration of mRNAs transcribed from four genes involved in alginate production using real-time PCR.

METHODS AND RESULTS

The mRNA concentrations in cells grown in normal and stress conditions were compared. A difference in the expression of algD, the key gene leading to overproduction of alginate, was detected between alginate-producing and non-alginate-producing strains grown under normal conditions. After growth on 3% ethanol (known to stimulate alginate production), but not after heat-shock, an increase in algD mRNA levels and a corresponding decrease in mucB (a regulatory gene) mRNA levels were detected in all strains.

CONCLUSION

The quantitative results suggest that the mucB gene may have a role in recognition of stress conditions, and that having a disrupted mucA gene does not always result in a mucoid phenotype.

SIGNIFICANCE AND IMPACT OF THE STUDY

Real-time PCR can be used to quantify mRNA and is a convenient method of analysing bacterial gene expression.

Bacterial alginate biosynthesis--recent progress and future prospects

The extracellular polysaccharide alginate has been widely associated with chronic Pseudomonas aeruginosa infections in the cystic fibrosis lung. However, it is clear that alginate biosynthesis is a more widespread phenomenon. Alginate plays a key role as a virulence factor of plant-pathogenic pseudomonads, in the formation of biofilms and with the encystment process of Azotobacter spp.

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.

Microbial pathogenesis in cystic fibrosis: mucoid Pseudomonas aeruginosa and Burkholderia cepacia

Respiratory infections with Pseudomonas aeruginosa and Burkholderia cepacia play a major role in the pathogenesis of cystic fibrosis (CF). This review summarizes the latest advances in understanding host-pathogen interactions in CF with an emphasis on the role and control of conversion to mucoidy in P. aeruginosa, a phenomenon epitomizing the adaptation of this opportunistic pathogen to the chronic chourse of infection in CF, and on the innate resistance to antibiotics of B. cepacia, person-to-person spread, and sometimes rapidly fatal disease caused by this organism. While understanding the mechanism of conversion to mucoidy in P. aeruginosa has progressed to the point where this phenomenon has evolved into a model system for studying bacterial stress response in microbial pathogenesis, the more recent challenge with B. cepacia, which has emerged as a potent bona fide CF pathogen, is discussed in the context of clinical issues, taxonomy, transmission, and potential modes of pathogenicity.

Hyphal tip extension in Aspergillus nidulans requires the manA gene, which encodes phosphomannose isomerase

A strain of Aspergillus nidulans carrying a temperature-sensitive mutation in the manA gene produces cell walls depleted of D-mannose and forms hyphal tip balloons at the restrictive temperature (B.P. Valentine and B.W. Bainbridge, J. Gen. Microbiol. 109:155-168, 1978). We have isolated and characterized the manA gene and physically located it between 3.5 and 5.5 kb centromere distal of the riboB locus on chromosome VIII. The manA gene contains four introns and encodes a 50.6-kDa protein which has significant sequence identity to type I phosphomannose isomerase proteins from other eukaryotes. We have constructed by integrative transformation a null mutation in the manA gene which can only be maintained in a heterokaryotic strain with wild-type manA+ nuclei. Thus, a manA null mutation is lethal in A. nidulans. The phenotype of the mutation was analyzed in germinating conidia. Such conidia are able to commence germination but swell abnormally, sometimes producing a misshapen germ tube, before growth ceases. The reason for the lethality is probably the lack of synthesis of mannose-containing cell wall polymers that must be required for normal cell wall development in growing hyphae.

Hyphal tip extension in Aspergillus nidulans requires the manA gene, which encodes phosphomannose isomerase

A strain of Aspergillus nidulans carrying a temperature-sensitive mutation in the manA gene produces cell walls depleted of D-mannose and forms hyphal tip balloons at the restrictive temperature (B.P. Valentine and B.W. Bainbridge, J. Gen. Microbiol. 109:155-168, 1978). We have isolated and characterized the manA gene and physically located it between 3.5 and 5.5 kb centromere distal of the riboB locus on chromosome VIII. The manA gene contains four introns and encodes a 50.6-kDa protein which has significant sequence identity to type I phosphomannose isomerase proteins from other eukaryotes. We have constructed by integrative transformation a null mutation in the manA gene which can only be maintained in a heterokaryotic strain with wild-type manA+ nuclei. Thus, a manA null mutation is lethal in A. nidulans. The phenotype of the mutation was analyzed in germinating conidia. Such conidia are able to commence germination but swell abnormally, sometimes producing a misshapen germ tube, before growth ceases. The reason for the lethality is probably the lack of synthesis of mannose-containing cell wall polymers that must be required for normal cell wall development in growing hyphae.

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.

Genetic analysis of the alginate biosynthetic gene cluster of Pseudomonas aeruginosa shows evidence of an operonic structure

Strains of Pseudomonas aeruginosa causing pulmonary infections in cystic fibrosis patients have an unusual mucoid phenotype because of production of the capsule-like exopolysaccharide, alginate. Transcriptional activation of algD, the first gene of a large alginate biosynthetic gene cluster, is associated with conversion to the alginate-producing (Alg+) phenotype. In this study, we examined the regulation of alginate genes immediately downstream of algD. Mutants of the Alg+ strain FRD1 were constructed by gene replacement with defined Tn501 (8.2kb) insertions in the alginate biosynthetic gene cluster, resulting in an Alg- phenotype. The Alg+ phenotype of these mutants was restored by integration of narrow-host-range plasmids containing DNA fragments from P. aeruginosa that reconstructed a continuous alginate gene cluster. A broad-host-range plasmid containing the entire alginate gene cluster except for the terminal gene, algA, was unable to complement an alG::Tn501 mutant unless algA was transcribed from a second plasmid. This indicated that any Tn501 insertion in the cluster was polar on downstream alginate genes. Northern blot hybridization experiments also showed that a transposon insertion downstream of algD adversely affected algG and algA transcription. These results provided evidence that the alginate biosynthetic gene cluster has an operonic structure and is cotranscribed from the algD promoter.

The Rhizobium meliloti pmi gene encodes a new type of phosphomannose isomerase

Interspecific complementation of a Xanthomonas campestris pv. campestris phosphomannose isomerase (PMI) mutant was used to isolate a cosmid from a genomic library of Rhizobium meliloti 2011 carrying the pmi gene of this strain. Subcloning experiments localized the coding region to a 2.0-kb SalI-ClaI fragment. Nucleotide sequence analysis of this fragment indicated the presence of two open reading frames (ORFs), coding for 18- and 43-kDa polypeptides. The analysis of the gene function by gene disruption experiments showed that ORF2 codes for pmi. A comparison of the deduced amino acid sequence with the corresponding sequences of the Pseudomonas aeruginosa and Escherichia coli PMIs revealed no significant homology, indicating that the isolated gene encodes a new type of PMI. The construction of a pmi-deficient mutant of R. meliloti using the sacB-sacR cassette technique showed that the loss of PMI activity does not affect the symbiotic properties of this strain.

PMI40, an intron-containing gene required for early steps in yeast mannosylation

We have previously described a temperature-sensitive pmi40-1 mutant of Saccharomyces cerevisiae which is defective in glycosylation and secretion because of a thermolabile phosphomannose isomerase (PMI) activity. Inactivation of PMI at the restrictive temperature of 37 degrees C prevents synthesis of the GDP-mannose and dolichol-phosphate-mannose required for a number of critical mannosyl transfer reactions and results in cell death. Here, we report the isolation of the PMI40 gene by complementation of the corresponding mutation. The PMI40 gene contains an efficiently spliced intron which differs from the majority of those so far identified in S. cerevisiae in that it is short and the branch-forming structure has an AACTAAC motif replacing the highly conserved consensus TACTAAC. The 48.2-kDa protein predicted to be encoded by PMI40 contains amino acid sequences corresponding to those of internal peptides derived from purified S. cerevisiae PMI. Deletion of the PMI40 coding sequence results in a strain requiring D-mannose for growth. The PMI40 gene is located on chromosome V, and its transcription is increased 12-fold when cells are grown on D-mannose as sole carbon source instead of D-glucose. PMI enzyme activity, however, is not increased in D-mannose-grown cells, and PMI protein levels remain constant, suggesting that the PMI40 gene is subject to additional levels of regulation.

PMI40, an intron-containing gene required for early steps in yeast mannosylation

We have previously described a temperature-sensitive pmi40-1 mutant of Saccharomyces cerevisiae which is defective in glycosylation and secretion because of a thermolabile phosphomannose isomerase (PMI) activity. Inactivation of PMI at the restrictive temperature of 37 degrees C prevents synthesis of the GDP-mannose and dolichol-phosphate-mannose required for a number of critical mannosyl transfer reactions and results in cell death. Here, we report the isolation of the PMI40 gene by complementation of the corresponding mutation. The PMI40 gene contains an efficiently spliced intron which differs from the majority of those so far identified in S. cerevisiae in that it is short and the branch-forming structure has an AACTAAC motif replacing the highly conserved consensus TACTAAC. The 48.2-kDa protein predicted to be encoded by PMI40 contains amino acid sequences corresponding to those of internal peptides derived from purified S. cerevisiae PMI. Deletion of the PMI40 coding sequence results in a strain requiring D-mannose for growth. The PMI40 gene is located on chromosome V, and its transcription is increased 12-fold when cells are grown on D-mannose as sole carbon source instead of D-glucose. PMI enzyme activity, however, is not increased in D-mannose-grown cells, and PMI protein levels remain constant, suggesting that the PMI40 gene is subject to additional levels of regulation.

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.

Sequence of the phosphomannose isomerase-encoding gene of Salmonella typhimurium

The pmi gene, encoding phosphomannose isomerase, of Salmonella typhimurium, was cloned in Escherichia coli K-12, and the protein product visualised in minicells. The cloned gene was sequenced; there was 77.4% nucleotide homology between the cloned pmi gene and the analogous manA gene of E. coli K-12, and 86.2% amino acid sequence homology between their presumptive gene products.

Alginate synthesis by Pseudomonas aeruginosa: a key pathogenic factor in chronic pulmonary infections of cystic fibrosis patients

Pulmonary infection by mucoid, alginate-producing Pseudomonas aeruginosa is the leading cause of mortality among patients suffering from cystic fibrosis. Alginate-producing P. aeruginosa is uniquely associated with the environment of the cystic fibrosis-affected lung, where alginate is believed to increase resistance to both the host immune system and antibiotic therapy. Recent evidence indicates that P. aeruginosa is most resistant to antibiotics when the infecting cells are present as a biofilm, as they appear to be in the lungs of cystic fibrosis patients. Inhibition of the protective alginate barrier with nontoxic compounds targeted against alginate biosynthetic and regulatory proteins may prove useful in eradicating P. aeruginosa from this environment. Our research has dealt with elucidating the biosynthetic pathway and regulatory mechanism(s) responsible for alginate synthesis by P. aeruginosa. This review summarizes reports on the role of alginate in cystic fibrosis-associated pulmonary infections caused by P. aeruginosa and provides details about the biosynthesis and regulation of this exopolysaccharide.

Microbiology of airway disease in patients with cystic fibrosis

Individuals with cystic fibrosis have abbreviated life spans primarily due to chronic airway infection. A limited number of types of organisms are responsible for these infections, with Staphylococcus aureus and Pseudomonas aeruginosa being of primary importance. In the pre-antibiotic era, greater than 90% of deaths due to infection were caused by S. aureus and death usually occurred in the first 2 years of life. With the advent of effective antistaphylococcal therapy, life spans increased and P. aeruginosa became the pathogen of primary importance. P. aeruginosa isolates recovered from patients with cystic fibrosis have a unique phenotypic characteristic referred to as "mucoid." The mucoid phenotype is due to the production of a mucoid exopolysaccharide. A mucoid exopolysaccharide is believed to play a central role in the establishment of chronic pseudomonal lung infection in these patients. A third organism, Pseudomonas cepacia, has recently been detected in the airways of older patients with cystic fibrosis and is associated with increased mortality. The virulence of P. cepacia is not understood, but the organism is extremely refractory to antimicrobial therapy. Other bacteria, including Haemophilus influenzae and members of the family Enterobacteriaceae, appear to play a secondary role in airway infection. Aspergillus fumigatus is the most important fungal agent causing allergic bronchopulmonary disease. The role of viruses has only recently been examined. At least in some patients with cystic fibrosis, respiratory syncytial virus may be important in predisposing to subsequent bacterial infections.

DNA sequence and expression analysis of algP and algQ, components of the multigene system transcriptionally regulating mucoidy in Pseudomonas aeruginosa: algP contains multiple direct repeats

The complete nucleotide sequence of a 3.2-kilobase-pair chromosomal region containing the algP and algQ genes was determined. The algQ gene encodes an acidic 18-kilodalton polypeptide required for transcriptional activation of the algD gene. The algD gene product catalyzes a critical step in alginate biosynthesis, and its overproduction is necessary for the emergence of mucoid Pseudomonas aeruginosa during chronic infections in cystic fibrosis. A novel genetic element, algP, was identified immediately downstream of algQ. This gene appears to act synergistically with algQ. Unlike a biosynthetic gene, algD, and another regulatory gene, algR, which undergo transcriptional activation in mucoid cells, both algP and algQ are equally transcribed in mucoid and nonmucoid isogenic strains of P. aeruginosa. The promoter regions of algP and algQ were mapped by using S1 nuclease protection analysis. The algQ promoter was also analyzed and showed activity in an in vitro transcriptional runoff assay with major RNA polymerase species from P. aeruginosa and Escherichia coli. The putative algQ and algP promoter sequences, unlike algD and algR, resemble sigma 70-utilized promoters from E. coli and appeared constitutively transcribed at a low level in P. aeruginosa. The algP gene has an unusual DNA sequence, with multiple direct repeats organized in six highly conserved, tandemly arranged, 75-base-pair (bp) units. At a lower level, this sequence had 45 degenerate repeats of 12 bp overlapping with the 75-bp repeats and extending beyond the region of 75-bp repeats. The algP repeats appeared important for the function of the algQ-algP regulatory region in maintaining mucoidy.

Decreased outer membrane permeability in imipenem-resistant mutants of Pseudomonas aeruginosa

The outer membrane of imipenem-resistant mutants of Pseudomonas aeruginosa was shown to have decreased permeability to imipenem but not to cephaloridine. These experiments were performed with intact cells and liposomes containing imipenem-hydrolyzing beta-lactamase derived from Pseudomonas maltophilia, in both cases utilizing an imipenem concentration of 50 microM. In contrast, liposome swelling assays using imipenem at 8 mM detected no significant difference between the imipenem-resistant mutants and their parents. It was found that the outer membrane of P. aeruginosa has a saturable specific channel through which imipenem travels mainly at low concentrations, whereas at high concentrations this pathway is obscured by diffusion through nonspecific porin channels.

Isolation of Zoogloea ramigera I-16-M exopolysaccharide biosynthetic genes and evidence for instability within this region

The genetics of the biosynthesis of an exocellular polysaccharide (EPS) from Zoogloea ramigera I-16-M is being investigated. Tn5 insertion mutants deficient in EPS production were isolated by screening for the absence of fluorescence on plates containing the dye Cellufluor (Polysciences Chemicals). Complementation of these mutations was achieved with a Z. ramigera I-16-M gene library constructed in a broad-host-range cosmid vector and introduced into the I-16-M mutants by conjugation. Four recombinant plasmids able to restore EPS production to all of these mutants were found to contain at least 14 kilobases of common insert DNA. Subcloning of the common region and restriction mapping the locations of Tn5 insertions have identified two complementation groups contained within a chromosomal segment of DNA that is between 4.6 and 6.5 kilobases in size. We have clearly demonstrated genetic instability in this region which leads to spontaneous deletions and possibly rearrangements resulting in the loss of EPS production.

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

The specific activities of phosphomannose isomerase (PMI), phosphomannomutase (PMM), GDP-mannose pyrophosphorylase (GMP), and GDP-mannose dehydrogenase (GMD) were compared in a mucoid cystic fibrosis isolate of Pseudomonas aeruginosa and in two spontaneous nonmucoid revertants. In both revertants some or all of the alginate biosynthetic enzymes we examined appeared to be repressed, indicating that the loss of the mucoid phenotype may be a result of decreased formation of sugar-nucleotide precursors. The introduction and overexpression of the cloned P. aeruginosa phosphomannose isomerase (pmi) gene in both mucoid and nonmucoid strains led not only to the appearance of PMI levels in cell extracts several times higher than those present in the wild-type mucoid strain, but also in higher PMM and GMP specific activities. In extracts of both strains, however, the specific activity of GMD did not change as a result of pmi overexpression. In contrast, the introduction of the cloned Escherichia coli manA (pmi) gene in P. aeruginosa caused an increase in only PMI and PMM activities, having no effect on the level of GMP. This suggests that an increase in PMI activity alone does not induce high GMP activity in P. aeruginosa. The heterologous overexpression of the P. aeruginosa pmi gene in the E. coli manA mutant CD1 led to the appearance in cell extracts of not only PMI activity but also GMP activity, both of which are normally undetectable in extracts of CD1. We discuss the implications of these results and propose a mechanism by which overexpression of the P. aeruginosa pmi gene can cause an elevation in both PMM and GMP activities.

Pseudomonas aeruginosa infection in cystic fibrosis: nucleotide sequence and transcriptional regulation of the algD gene

Pulmonary infection by mucoid, alginate producing, Pseudomonas aeruginosa is a major complication in patients suffering from cystic fibrosis (CF). To analyze the mechanisms leading to the emergence of mucoid P. aeruginosa in CF lungs, control of the algD gene coding for GDPmannose dehydrogenase was studied. Transcriptional activation of algD was shown to be necessary for alginate production. Sequencing of algD and its promoter revealed multiple direct repeats upstream of the transcription start and throughout the promoter region. Using the algD-xy1E transcriptional fusion the algD promoter was demonstrated to be under positive control by the algR gene. This gene has previously been shown to undergo antibiotic promoted chromosomal amplification resulting in the emergence of the mucoid phenotype. These findings provide a basis for better understanding the control of mucoidy in P. aeruginosa.

Construction and characterization of Pseudomonas aeruginosa algB mutants: role of algB in high-level production of alginate

The algB gene, which is involved in the production of alginate in Pseudomonas aeruginosa, was localized to approximately 2.2 kilobases of DNA from strain FRD by using transposon Tn501 insertion mutagenesis, subcloning, and complementation techniques. The previously reported alg-50(Ts) mutation, which confers the phenotype of temperature-sensitive alginate production, was here designated as an algB allele. A transduction-mediated gene replacement technique was used for site-directed mutagenesis to isolate and characterize algB::Tn501 mutants of P. aeruginosa FRD. Although algB::Tn501 mutants had a nonmucoid phenotype (indicating an alginate deficiency), they still produced about 1 to 5% of wild-type levels of alginate in most growth media and up to 16% in very rich media. The algB::Tn501 mutations had no apparent effect on growth rate or growth requirements. Using another gene replacement technique called excision marker rescue, we constructed a chromosomal algB deletion (delta algB) mutant of P. aeruginosa FRD. The delta algB mutant also produced low levels of alginate as did the algB::Tn501 mutants. The alginate produced by algB::Tn501 mutants resembled wild-type alginate by all criteria studied: molecular weight, acetylation, and proportion of mannuronic and guluronic acids. Thus, the algB gene product is apparently involved in the high-level production of alginate by P. aeruginosa and is not directly involved in the pathway leading to its biosynthesis. Chromosomal mapping of an algB::Tn501 insertion showed linkage to the trp-2 marker on the FRD chromosome as does the algB50(Ts) mutation. The excision marker rescue technique was also used to place the algB::Tn501 marker on the chromosome of characterized strains of P. aeruginosa PAO. The algB::Tn501 mutation mapped near 21 min on the PAO chromosome.

Gene algD coding for GDPmannose dehydrogenase is transcriptionally activated in mucoid Pseudomonas aeruginosa

Transcriptional regulation of alginate biosynthesis by Pseudomonas aeruginosa was studied. A DNA region complementing the alg-5 mutation within the alginate gene cluster was found by RNA-DNA dot blot and Northern hybridization to be transcriptionally activated in mucoid P. aeruginosa. This region was subcloned as a 3.2-kilobase BglII-ClaI DNA fragment on the broad-host-range controlled transcription vector pMMB24, and gene products were analyzed by expression from the tac promoter. A 48-kilodalton polypeptide was detected in extracts of P. aeruginosa and 35S-labeled Escherichia coli maxicells. By using the same expression system, GDPmannose dehydrogenase activity was detected in both P. aeruginosa and E. coli. Thus, gene algD coding for this enzyme was found to be present in the transcriptionally active DNA area. Insertion of the xylE gene within the BglII-ClaI fragment disrupted the induction of the 48-kilodalton polypeptide, GDPmannose dehydrogenase activity, and alg-5 complementing ability. With the algD-xylE transcription fusion, activation of algD gene expression was shown to occur in mucoid P. aeruginosa of different origins. In addition, regulation of the algD promoter activity was demonstrated to be mediated by a diffusible factor.

Overproduction and assay of Pseudomonas aeruginosa phosphomannose isomerase

Phosphomannose isomerase activity was undetectable in extracts of mucoid (alginate-producing) Pseudomonas aeruginosa. When a P. aeruginosa gene previously shown to complement an alginate-negative mutant was overexpressed under the control of the tac promoter in the broad-host-range controlled-expression vector pMMB22, phosphomannose isomerase activity could be measured in extracts of P. aeruginosa and in a manA (phosphomannose isomerase-negative) mutant of Escherichia coli. P. aeruginosa extracts containing induced levels of enzyme were shown to interconvert fructose 6-phosphate and mannose 6-phosphate. A 56,000-dalton polypeptide was visualized on sodium dodecyl sulfate-polyacrylamide gels after induction in both hosts. When RNA-DNA dot- blot hybridization analysis was used, transcription of algA, the gene coding for P. aeruginosa phosphomannose isomerase, was not measurable from the chromosomes of either mucoid or nonmucoid P. aeruginosa. However, a high level of algA transcription was detected after expression of algA under tac promoter control in pMMB22.

Expression of biosynthetic genes from Pseudomonas aeruginosa and Escherichia coli in the heterologous host

We examine the expression of constitutive or repressible, monocistronic genes from Pseudomonas aeruginosa and Escherichia coli after their transfer to the heterologous host. To this end, chromosomal DNA from P. aeruginosa was cloned into the mobilizable broad-host-range vector pKT240; recombinant plasmids carrying the argA, argF, or proC genes were identified by complementation of the corresponding auxotrophic mutations. The isofunctional E. coli genes and the E. coli proB gene were subcloned into pKT240 from existing recombinant plasmids. The enzyme expression specified by the Pseudomonas genes in E. coli, calculated per gene copy, ranged from 0.3%-5% of the levels observed in Pseudomonas. Fusion of the P. aeruginosa proC gene to the E. coli consensus tac promoter resulted in very high proC enzyme production in E. coli, indicating that, at least in this case, the expression barrier is essentially at the level of transcriptional initiation. The E. coli argA and argF enzymes, which are controlled by repression in their native host, were synthesized constitutively in P. aeruginosa at 5% of the levels measured in E. coli under derepressed conditions. The constitutive E. coli proB and proC genes were expressed at high levels (ca. 50%) in the heterologous host. These results support the idea that P. aeruginosa may be a more permissive host than E. coli for the heterologous expression of genes from gram-negative bacteria.

Gene amplification induces mucoid phenotype in rec-2 Pseudomonas aeruginosa exposed to kanamycin

Gene amplification in the chromosome of rec-2 Pseudomonas aeruginosa PAO2003 upon growth on kanamycin-supplemented media led to a stable mucoid phenotype. The chromosomal region controlling alginate biosynthesis was shown to be amplified four to six times as a direct tandem repeat of at least 16.8 kilobase pairs. This amplification was deduced from Southern DNA-DNA hybridization patterns of the chromosomal DNA digested with restriction endonucleases BglII and EcoRI and probed with a cloned DNA segment complementing the alg-22 mutation. The part of the amplified unit carrying the novel DNA joint was cloned. The EcoRI junction fragment was further subcloned and used to probe chromosomes of parental strain PAO2003 and mucoid variant VD2003M. As predicted, the EcoRI junction fragment hybridized to the two chromosomal fragments required to produce the novel junction. Though the mucoid phenotype caused by gene amplification was stable, nonmucoid revertants were obtained at a low frequency on tetracycline-containing media. Southern hybridization of chromosomal DNA from a nonmucoid revertant revealed a reduction in the copy number of amplified DNA. These results suggest a direct relationship between amplification of this chromosomal segment and the induction of mucoidy.

Nucleotide sequence analysis of the phosphomannose isomerase gene (pmi) of Pseudomonas aeruginosa and comparison with the corresponding Escherichia coli gene manA

Phosphomannose isomerase (PMI) has been proposed to catalyze the first step of the alginic acid biosynthetic pathway in Pseudomonas aeruginosa. The nucleotide sequence of the P. aeruginosa pmi gene contained on a 2.0-kb BamHI-SstI DNA fragment has been determined. The gene was defined by the start and stop codons and by in vitro disruption of an open reading frame of 1440 bp corresponding to a polypeptide product with a predicted Mr of 52 860. This polypeptide displayed an apparent Mr of approx. 56 000 upon electrophoresis of a maxicell extract on sodium dodecyl sulfate-polyacrylamide gels. The codon utilization of the pmi gene was distinct in the wobble base preference and influenced by the high G + C content (66 mol%) of the P. aeruginosa DNA. Computer assisted matching analysis failed to demonstrate any significant homology at the nucleotide level between the P. aeruginosa pmi and Escherichia coli manA (pmi) genes. However, sequences homologous to the P. aeruginosa pmi gene were found in other Pseudomonas species, such as P. putida and P. mendocina, and in Azotobacter vinelandii, all capable of producing alginic acid.

Clustering of mutations affecting alginic acid biosynthesis in mucoid Pseudomonas aeruginosa

A 10-kilobase DNA fragment previously shown to contain the phosphomannose isomerase gene (pmi) of Pseudomonas aeruginosa was used to construct a pBR325-based hybrid that can be propagated in P. aeruginosa only by the formation of a chromosomal-plasmid cointegrate. This plasmid, designated pAD4008, was inserted into the P. aeruginosa chromosome by recombination at a site of homology between the cloned P. aeruginosa DNA and the chromosome. Mobilization of pAD4008 into P. aeruginosa PAO and 8830 and selection for the stable acquisition of tetracycline resistance resulted in specific and predictable changes in the pattern of endonuclease restriction sites in the phosphomannose isomerase gene region of the chromosomes. Chromosomal DNA from the tetracycline-resistant transformants was used to clone the drug resistance determinant with Bg/II or XbaI, thereby allowing the "walking" of the P. aeruginosa chromosome in the vicinity of the pmi gene. Analysis of overlapping tetracycline-resistant clones indicated the presence of sequences homologous to the DNA insert of plasmid pAD2, a recombinant clone of P. aeruginosa origin previously shown to complement several alginate-negative mutants. Restriction mapping, subcloning, and complementation analysis of a 30-kilobase DNA region demonstrated the tight clustering of several genetic loci involved in alginate biosynthesis. Furthermore, the tetracycline resistance determinant in PAO strain transformed by pAD4008 was mapped on the chromosome by plasmid FP2-mediated conjugation and was found to be located near 45 min.

Fructose 1,6-bisphosphate aldolase activity is essential for synthesis of alginate from glucose by Pseudomonas aeruginosa

We have isolated a mutant of Pseudomonas aeruginosa deficient in fructose 1,6-bisphosphate aldolase activity. This mutant, similar to the mutants deficient in any of the Entner-Doudoroff pathway enzymes, does not allow appreciable alginate formation from glucose and gluconate, but allows alginate synthesis from mannitol and fructose. This suggests that glucose and gluconate must be converted to fructose 1,6-bisphosphate via the Entner-Doudoroff pathway enzymes and fructose 1,6-bisphosphate aldolase.