Two genes for carbohydrate catabolism are divergently transcribed from a region of DNA containing the hexC locus in Pseudomonas aeruginosa PAO1

NADH-Mediated Gene Expression in Streptococcus pneumoniae and Role of Rex as a Transcriptional Repressor of the Rex-Regulon

Nicotinamide adenine dinucleotides (NAD(H)) play a vital role in various biological processes, including keeping the cellular redox balance. In this study, we investigate the regulatory responses of Streptococcus pneumoniae D39 to NADH and characterize the role of the Rex protein as a transcriptional repressor of the gapN, fba, pncB, adhB2, gap, and adhE genes. Transcriptomic analysis was used to observe the response of S. pneumoniae D39 to NADH. Our microarray studies revealed elevated expression of various genes/operons involved in transport and biosynthesis of niacin (gapN, fba, pncB, adhB2, gap, and adhE). Promoter lacZ-fusion assays and microarray studies with the rex mutant revealed the role of Rex as a transcriptional repressor of gapN, fba, pncB, adhB2, gap, and adhE involved in niacin uptake and biosynthesis, in the presence of NADH. We predict the operator site (5′-TTGTKAWAAWWTTCACAA-3′) of Rex in the regulatory regions of Rex-regulated genes that was subsequently validated by promoter mutational experiments.

Characterization of NAD salvage pathways and their role in virulence in Streptococcus pneumoniae

NAD is a necessary cofactor present in all living cells. Some bacteria cannot de novo synthesize NAD and must use the salvage pathway to import niacin or nicotinamide riboside via substrate importers NiaX and PnuC, respectively. Although homologues of these two importers and their substrates have been identified in other organisms, limited data exist in Streptococcus pneumoniae, specifically, on its effect on overall virulence. Here, we sought to characterize the substrate specificity of NiaX and PnuC in Str. pneumoniae TIGR4 and the contribution of these proteins to virulence of the pathogen. Although binding affinity of each importer for nicotinamide mononucleotide may overlap, we found NiaX to specifically import nicotinamide and nicotinic acid, and PnuC to be primarily responsible for nicotinamide riboside import. Furthermore, a pnuC mutant is completely attenuated during both intranasal and intratracheal infections in mice. Taken together, these findings underscore the importance of substrate salvage in pneumococcal pathogenesis and indicate that PnuC could potentially be a viable small-molecule therapeutic target to alleviate disease progression in the host.

Oxidative stress response in Pseudomonas putida

Pseudomonas putida is widely distributed in nature and is capable of degrading various organic compounds due to its high metabolic versatility. The survival capacity of P. putida stems from its frequent exposure to various endogenous and exogenous oxidative stresses. Oxidative stress is an unavoidable consequence of interactions with various reactive oxygen species (ROS)-inducing agents existing in various niches. ROS could facilitate the evolution of bacteria by mutating genomes. Aerobic bacteria maintain defense mechanisms against oxidative stress throughout their evolution. To overcome the detrimental effects of oxidative stress, P. putida has developed defensive cellular systems involving induction of stress-sensing proteins and detoxification enzymes as well as regulation of oxidative stress response networks. Genetic responses to oxidative stress in P. putida differ markedly from those observed in Escherichia coli and Salmonella spp. Two major redox-sensing transcriptional regulators, SoxR and OxyR, are present and functional in the genome of P. putida. However, the novel regulators FinR and HexR control many genes belonging to the E. coli SoxR regulon. Oxidative stress can be generated by exposure to antibiotics, and iron homeostasis in P. putida is crucial for bacterial cell survival during treatment with antibiotics. This review highlights and summarizes current knowledge of oxidative stress in P. putida, as a model soil bacterium, together with recent studies from molecular genetics perspectives.

Regulation of glucose metabolism in Pseudomonas: the phosphorylative branch and entner-doudoroff enzymes are regulated by a repressor containing a sugar isomerase domain

In Pseudomonas putida, genes for the glucose phosphorylative pathway and the Entner-Doudoroff pathway are organized in two operons; one made up of the zwf, pgl, and eda genes and another consisting of the edd, glk, gltR2, and gltS genes. Divergently with respect to the edd gene is the gap-1 gene. Expression from P(zwf), P(edd), and P(gap) is modulated by HexR in response to the availability of glucose in the medium. To study the regulatory process in greater detail we purified HexR and showed that it is a monomer in solution. Electrophoretic mobility shift assays and isothermal titration calorimetry assays were done showing that HexR recognizes the P(edd), P(zwf), and P(gap-1) promoters with affinity in the nanomolar range. DNA footprinting assays identified the binding site between +30 and +1 at P(zwf), between +16 and +41 at P(edd), and between -6 and +18 at P(gap-1). Based on DNA sequence alignment of the target sites and isothermal titration calorimetry data, two monomers of HexR bind to a pseudopalindrome with a consensus sequence of 5'-TTGTN(7-8)ACAA-3'. Binding of the Entner-Doudoroff pathway intermediate 2-keto-3-deoxy-6-phosphogluconate to HexR released the repressor from its target operators, whereas other chemicals such as glucose, glucose 6-phosphate, and 6-phosphogluconate did not induce complex dissociation. The phosphorylated effector is likely to be recognized by a sugar isomerase domain located at the C-terminal end of HexR, whereas the helix-turn-helix DNA binding domain of HexR exhibits high similarity to proteins of the RpiR family of regulators.

Intracellular 2-keto-3-deoxy-6-phosphogluconate is the signal for carbon catabolite repression of phenylacetic acid metabolism in Pseudomonas putida KT2440

The growth pattern of Pseudomonas putida KT2440 in the presence of glucose and phenylacetic acid (PAA), where the sugar is used in preference to the aromatic compound, suggests that there is carbon catabolite repression (CCR) of PAA metabolism by glucose or gluconate. Furthermore, CCR is regulated at the transcriptional level. However, this CCR phenomenon does not occur in PAA-amended minimal medium containing fructose, pyruvate or succinate. We previously identified 2-keto-3-deoxy-6-phosphogluconate (KDPG) as an inducer of glucose metabolism, and this has led to this investigation into the role of KDPG as a signal compound for CCR. Two mutant strains, the edd mutant (non-KDPG producer) and the eda mutant (KDPG overproducer), grew in the presence of PAA but not in the presence of glucose. The edd mutant utilized PAA even in the presence of glucose, indicating that CCR had been abolished. This observation has additional support from the finding that there is high phenylacetyl-CoA ligase activity in the edd mutant, even in the presence of glucose+PAA, but not in wild-type cells under the same conditions. Unlike the edd mutant, the eda mutant did not grow in the presence of glucose+PAA. Interestingly, there was no uptake and/or metabolism of PAA in the eda mutant cells under the same conditions. Targeted disruption of PaaX, a repressor of the PAA operon, had no effect on CCR of PAA metabolism in the presence of glucose, suggesting that there is another transcriptional repression system associated with the KDPG signal. This is the first study to demonstrate that KDPG is the true CCR signal of PAA metabolism in P. putida KT2440.

Dual regulation of zwf-1 by both 2-keto-3-deoxy-6-phosphogluconate and oxidative stress in Pseudomonas putida

Northern blot analysis and a GFP-based reporter assay showed that zwf-1, which encodes glucose-6-phosphate dehydrogenase, was highly induced when Pseudomonas putida KT2440 was cultured in minimal medium containing glucose or gluconate. However, zwf-1 expression was not detected in the presence of pyruvate or succinate. The use of a knockout mutant of HexR, a putative transcription regulator, resulted in constitutively high expression of zwf-1, regardless of the carbon source. An electrophoretic mobility shift assay showed that HexR protein binds to the zwf-1 promoter region and that HexR binding is inhibited by 2-keto-3-deoxy-6-phosphogluconate (KDPG). Despite the presence of gluconate, the edd mutant (non-KDPG producer) was not able to induce the zwf-1 gene. The eda mutant (KDPG overproducer) featured a constitutively high level of zwf-1 expression. Interestingly, zwf-1 was also highly expressed in the presence of oxidative stress-inducing reagents. The level of zwf-1 induction in wild-type cells undergoing oxidative stress did not differ significantly from that observed with the hexR mutant under normal conditions. Interestingly, the hexR mutant was more tolerant of oxidative stress than the wild-type. Expression of zwf-1 was induced by oxidative stress in the edd mutant. Thus, KDPG, a real inducer of zwf-1 gene expression, was not necessary for oxidative-stress induction. In vitro binding of HexR to its cognate promoter region was diminished by menadione and cumene hydroperoxide. The data suggested that HexR might be a dual-sensing regulator of zwf-1 induction that is able to respond to both KDPG and oxidative stress.

A set of activators and repressors control peripheral glucose pathways in Pseudomonas putida to yield a common central intermediate

Pseudomonas putida KT2440 channels glucose to the central Entner-Doudoroff intermediate 6-phosphogluconate through three convergent pathways. The genes for these convergent pathways are clustered in three independent regions on the host chromosome. A number of monocistronic units and operons coexist within each of these clusters, favoring coexpression of catabolic enzymes and transport systems. Expression of the three pathways is mediated by three transcriptional repressors, HexR, GnuR, and PtxS, and by a positive transcriptional regulator, GltR-2. In this study, we generated mutants in each of the regulators and carried out transcriptional assays using microarrays and transcriptional fusions. These studies revealed that HexR controls the genes that encode glucokinase/glucose 6-phosphate dehydrogenase that yield 6-phosphogluconate; the genes for the Entner-Doudoroff enzymes that yield glyceraldehyde-3-phosphate and pyruvate; and gap-1, which encodes glyceraldehyde-3-phosphate dehydrogenase. GltR-2 is the transcriptional regulator that controls specific porins for the entry of glucose into the periplasmic space, as well as the gtsABCD operon for glucose transport through the inner membrane. GnuR is the repressor of gluconate transport and gluconokinase responsible for the conversion of gluconate into 6-phosphogluconate. PtxS, however, controls the enzymes for oxidation of gluconate to 2-ketogluconate, its transport and metabolism, and a set of genes unrelated to glucose metabolism.

Simultaneous catabolite repression between glucose and toluene metabolism in Pseudomonas putida is channeled through different signaling pathways

Pseudomonas putida KT2440(pWW0) can use toluene via the TOL plasmid-encoded catabolic pathways and can use glucose via a series of three peripheral chromosome-encoded routes that convert glucose into 6-phosphogluconate (6PG), namely, the glucokinase pathway, in which glucose is transformed to 6PG through the action of glucokinase and glucose-6-phosphate dehydrogenase. Alternatively, glucose can be oxidized to gluconate, which can be phosphorylated by gluconokinase to 6PG or oxidized to 2-ketogluconate, which, in turn, is converted into 6PG. Our results show that KT2440 metabolizes glucose and toluene simultaneously, as revealed by net flux analysis of [(13)C]glucose. Determination of glucokinase and gluconokinase activities in glucose metabolism, gene expression assays using a fusion of the promoter of the Pu TOL upper pathway to 'lacZ, and global transcriptomic assays revealed simultaneous catabolite repression in the use of these two carbon sources. The effect of toluene on glucose metabolism was directed to the glucokinase branch and did not affect gluconate metabolism. Catabolite repression of the glucokinase pathway and the TOL pathway was triggered by two different catabolite repression systems. Expression from Pu was repressed mainly via PtsN in response to high levels of 2-dehydro-3-deoxygluconate-6-phosphate, whereas repression of the glucokinase pathway was channeled through Crc.

Convergent peripheral pathways catalyze initial glucose catabolism in Pseudomonas putida: genomic and flux analysis

In this study, we show that glucose catabolism in Pseudomonas putida occurs through the simultaneous operation of three pathways that converge at the level of 6-phosphogluconate, which is metabolized by the Edd and Eda Entner/Doudoroff enzymes to central metabolites. When glucose enters the periplasmic space through specific OprB porins, it can either be internalized into the cytoplasm or be oxidized to gluconate. Glucose is transported to the cytoplasm in a process mediated by an ABC uptake system encoded by open reading frames PP1015 to PP1018 and is then phosphorylated by glucokinase (encoded by the glk gene) and converted by glucose-6-phosphate dehydrogenase (encoded by the zwf genes) to 6-phosphogluconate. Gluconate in the periplasm can be transported into the cytoplasm and subsequently phosphorylated by gluconokinase to 6-phosphogluconate or oxidized to 2-ketogluconate, which is transported to the cytoplasm, and subsequently phosphorylated and reduced to 6-phosphogluconate. In the wild-type strain, glucose was consumed at a rate of around 6 mmol g(-1) h(-1), which allowed a growth rate of 0.58 h(-1) and a biomass yield of 0.44 g/g carbon used. Flux analysis of (13)C-labeled glucose revealed that, in the Krebs cycle, most of the oxalacetate fraction was produced by the pyruvate shunt rather than by the direct oxidation of malate by malate dehydrogenase. Enzymatic and microarray assays revealed that the enzymes, regulators, and transport systems of the three peripheral glucose pathways were induced in response to glucose in the outer medium. We generated a series of isogenic mutants in one or more of the steps of all three pathways and found that, although all three functioned simultaneously, the glucokinase pathway and the 2-ketogluconate loop were quantitatively more important than the direct phosphorylation of gluconate. In physical terms, glucose catabolism genes were organized in a series of clusters scattered along the chromosome. Within each of the clusters, genes encoding porins, transporters, enzymes, and regulators formed operons, suggesting that genes in each cluster coevolved. The glk gene encoding glucokinase was located in an operon with the edd gene, whereas the zwf-1 gene, encoding glucose-6-phosphate dehydrogenase, formed an operon with the eda gene. Therefore, the enzymes of the glucokinase pathway and those of the Entner-Doudoroff pathway are physically linked and induced simultaneously. It can therefore be concluded that the glucokinase pathway is a sine qua non condition for P. putida to grow with glucose.

Genetic mechanisms involved in the repression of flagellar assembly by Pseudomonas aeruginosa in human mucus

Pseudomonas aeruginosa downregulates flagellin transcription when it is grown in purulent mucus from patients with cystic fibrosis (CF) and non-CF bronchiectasis. This response possibly abrogates the potent inflammatory response mediated by the interaction of flagellin with Toll-like receptor 5. The molecular mechanisms involved are thus far unknown. Known flagellar transcriptional regulators were not involved, thus Tn5 mutagenesis was used to ascertain whether novel regulators existed. Five clones with independent Tn5 insertions in flgM showed derepression of flagellin synthesis, suggesting that FlgM was involved in this phenomenon. Furthermore, examination of mucus-grown bacteria showed FlgM accumulation and overexpression of fliA in mucus-grown bacteria reversed the repression of flagellin synthesis. A related study from our laboratory had identified neutrophil elastase in mucus as the molecule responsible for fliC repression, therefore we examined whether loss of the flagellar hook (FlgE), by proteolysis was involved, because the flagellar hook is required for FlgM export. Western immunoblot of membranes from mucus-grown bacteria showed the absence of FlgE, despite the fact that the protein is made and the operon encoding FlgE is upregulated in mucus. A model is proposed wherein neutrophil elastase in mucus proteolytically cleaves the flagellar hook, thus completion of the hook basal body is never sensed, resulting in FlgM accumulation within the cell, causing repression of flagellin synthesis. We speculate that the cyclical bouts of inflammation observed in CF patients may result from flagellin synthesis and its repression, caused by presence of neutrophils at the site of infection.

FlhA, a component of the flagellum assembly apparatus of Pseudomonas aeruginosa, plays a role in internalization by corneal epithelial cells

Pseudomonas aeruginosa invades various epithelial cell types in vitro and in vivo. The P. aeruginosa genome possesses a gene (flhA) which encodes a protein that is believed to be part of the export apparatus for flagellum assembly and which is homologous to invA of Salmonella spp. Because invA is required for invasion of Salmonella spp., a role for flhA in P. aeruginosa invasion was explored using cultured rabbit corneal epithelial cells. An flhA mutant of P. aeruginosa strain PAO1 was constructed and was shown to be nonmotile. Complementation with flhA in trans restored motility. Corneal cells were infected for 3 h with the wild type (PAO1), the flhA mutant, the flhA mutant complemented with flhA in trans, an flhA mutant containing the plasmid vector control, or an fliC mutant (nonmotile mutant control). Invasion was quantified by amikacin exclusion assays. Both the flhA and the fliC mutants invaded at a lower level than the wild-type strain did, suggesting that both fliC and flhA played roles in invasion. However, loss of motility was not sufficient to explain the reduced invasion by flhA mutants, since centrifugation of bacteria onto cells did not restore invasion to wild-type levels. Unexpectedly, the flhA mutant adhered significantly better to corneal epithelial cells than wild-type bacteria or the fliC mutant did. The percentage of adherent bacteria that invaded was reduced by approximately 80% for the flhA mutant and approximately 50% for the fliC mutant, showing that only part of the role of flhA in invasion involves fliC. Invasion was restored by complementing the flhA mutant with flhA in trans but not by the plasmid vector control. Intracellular survival assays, in which intracellular bacteria were enumerated after continued incubation in the presence of antibiotics, showed that although flhA and fliC mutants had a reduced capacity for epithelial cell entry, they were not defective in their ability to survive within those cells after entry. These results suggest that the flagellum assembly type III secretion system plays a role in P. aeruginosa invasion of epithelial cells. Since the flhA mutants were not defective in their ability to adhere to corneal epithelial cells, to retain viability at the cell surface, or to survive inside epithelial cells after entry, the role of flhA in invasion of epithelial cells is likely to occur during the process of bacterial internalization.

The Pseudomonas aeruginosa devB/SOL homolog, pgl, is a member of the hex regulon and encodes 6-phosphogluconolactonase

A cyclic version of the Entner-Doudoroff pathway is used by Pseudomonas aeruginosa to metabolize carbohydrates. Genes encoding the enzymes that catabolize intracellular glucose to pyruvate and glyceraldehyde 3-phosphate are coordinately regulated, clustered at 39 min on the chromosome, and collectively form the hex regulon. Within the hex cluster is an open reading frame (ORF) with homology to the devB/SOL family of unidentified proteins. This ORF encodes a protein of either 243 or 238 amino acids; it overlaps the 5' end of zwf (encodes glucose-6-phosphate dehydrogenase) and is followed immediately by eda (encodes the Entner-Doudoroff aldolase). The devB/SOL homolog was inactivated in P. aeruginosa PAO1 by recombination with a suicide plasmid containing an interrupted copy of the gene, creating mutant strain PAO8029. PAO8029 grows at 9% of the wild-type rate using mannitol as the carbon source and at 50% of the wild-type rate using gluconate as the carbon source. Cell extracts of PAO8029 were specifically deficient in 6-phosphogluconolactonase (Pgl) activity. The cloned devB/SOL homolog complemented PAO8029 to restore normal growth on mannitol and gluconate and restored Pgl activity. Hence, we have identified this gene as pgl and propose that the devB/SOL family members encode 6-phosphogluconolactonases. Interestingly, three eukaryotic glucose-6-phosphate dehydrogenase (G6PDH) isozymes, from human, rabbit, and Plasmodium falciparum, contain Pgl domains, suggesting that the sequential reactions of G6PDH and Pgl are incorporated in a single protein. 6-Phosphogluconolactonase activity is induced in P. aeruginosa PAO1 by growth on mannitol and repressed by growth on succinate, and it is expressed constitutively in P. aeruginosa PAO8026 (hexR). Taken together, these results establish that Pgl is an essential enzyme of the cyclic Entner-Doudoroff pathway encoded by pgl, a structural gene of the hex regulon.

fleN, a gene that regulates flagellar number in Pseudomonas aeruginosa

The single polar flagellum of Pseudomonas aeruginosa plays an important role in the pathogenesis of infection by this organism. However, regulation of the assembly of this organelle has not been delineated. In analyzing the sequence available at the Pseudomonas genome database, an open reading frame (ORF), flanked by flagellar genes flhF and fliA, that coded for a protein (280 amino acids) with an ATP-binding motif at its N terminus was found. The ORF was inactivated by inserting a gentamicin cassette in P. aeruginosa PAK and PAO1. The resulting mutants were nonmotile on motility agar plates, but under a light microscope they exhibited random movement and tumbling behavior. Electron microscopic studies of the wild-type and mutant strains revealed that the mutants were multiflagellate, with three to six polar flagella per bacterium as rather than one as in the wild type, indicating that this ORF was involved in regulating the number of flagella and chemotactic motility in P. aeruginosa. The ORF was named fleN. An intact copy of fleN on a plasmid complemented the mutant by restoring motility and monoflagellate status. The beta-galactosidase activities of eight flagellar operon or gene promoters in the wild-type and fleN mutant strains revealed a direct correlation between six promoters that were upregulated in the fleN mutant (fliLMNOPQ, flgBCDE, fliEFG, fliDS orf126, fleSR, and fliC) and positive regulation by FleQ, an NtrC-like transcriptional regulator for flagellar genes. Based on these results, we propose a model where FleN influences FleQ activity (directly or indirectly) in regulating flagellar number in P. aeruginosa.

Cloning and characterization of the Pseudomonas aeruginosa zwf gene encoding glucose-6-phosphate dehydrogenase, an enzyme important in resistance to methyl viologen (paraquat)

In this study, we cloned the Pseudomonas aeruginosa zwf gene, encoding glucose-6-phosphate dehydrogenase (G6PDH), an enzyme that catalyzes the NAD+- or NADP+-dependent conversion of glucose-6-phosphate to 6-phosphogluconate. The predicted zwf gene product is 490 residues, which could form a tetramer with a molecular mass of approximately 220 kDa. G6PDH activity and zwf transcription were maximal in early logarithmic phase when inducing substrates such as glycerol, glucose, or gluconate were abundant. In contrast, both G6PDH activity and zwf transcription plummeted dramatically when bacteria approached stationary phase, when inducing substrate was limiting, or when the organisms were grown in a citrate-, succinate-, or acetate-containing basal salts medium. G6PDH was purified to homogeneity, and its molecular mass was estimated to be approximately 220 kDa by size exclusion chromatography. Estimated Km values of purified G6PDH acting on glucose-6-phosphate, NADP+, and NAD+ were 530, 57, and 333 microM, respectively. The specific activities with NAD+ and NADP+ were calculated to be 176 and 69 micromol/min/mg. An isogenic zwf mutant was unable to grow on minimal medium supplemented with mannitol. The mutant also demonstrated increased sensitivity to the redox-active superoxide-generating agent methyl viologen (paraquat). Since one by-product of G6PDH activity is NADPH, the latter data suggest that this cofactor is essential for the activity of enzymes critical in defense against paraquat toxicity.

The Pseudomonas aeruginosa flagellar cap protein, FliD, is responsible for mucin adhesion

Mucin-specific adhesion of Pseudomonas aeruginosa plays an important role in the initial colonization of this organism in the airways of cystic fibrosis patients. We report here that the flagellar cap protein, FliD, participates in this adhesion process. A polar chromosomal insertional mutation in the P. aeruginosa fliD gene made this organism nonadhesive to mucin in an in vitro mucin adhesion assay. The adhesive phenotype was restored by providing the fliD gene alone on a multicopy plasmid, suggesting involvement of this gene in mucin adhesion of P. aeruginosa. Further supporting this observation, the in vitro competition experiments demonstrated that purified FliD protein inhibited the mucin adhesion of nonpiliated P. aeruginosa PAK-NP, while the same concentrations of PilA and FlaG proteins of P. aeruginosa were ineffective in this function. The regulation of the fliD gene was studied and was found to be unique in that the transcription of the fliD gene was independent of the flagellar sigma factor sigma28. Consistent with this finding, no sigma28 binding sequence could be identified in the fliD promoter region. The results of the beta-galactosidase assays suggest that the fliD gene in P. aeruginosa is regulated by the newly described transcriptional regulator FleQ and the alternate sigma factor sigma54 (RpoN).

A transcriptional activator, FleQ, regulates mucin adhesion and flagellar gene expression in Pseudomonas aeruginosa in a cascade manner

Previous work has demonstrated that fleR, the gene for a transcriptional activator belonging to the NtrC subfamily of response regulators, is involved in the regulation of mucin adhesion and flagellar expression by Pseudomonas aeruginosa. This report describes the identification and characterization of fleQ, the gene for another transcriptional regulator which also regulates mucin adhesion and motility in this organism. The complete nucleotide sequence of the fleQ gene was determined on both DNA strands, and an open reading frame (ORF) consisting of 1,493 nucleotides was identified. This ORF coded for a gene product of predicted molecular weight, as confirmed by the overexpression of the fleQ gene as a fusion protein under an inducible promoter. The fleQ gene is flanked by a flagellar operon, fliDSorf126, at the 5' end and the fleSR operon on the 3' end. FleQ also had striking homology to a number of proteins belonging to the NtrC subfamily of response regulators, which work in concert with the alternate sigma factor RpoN (sigma54) to activate transcription. However, FleQ lacks the residues corresponding to Asp-54 and Lys-104 of the NtrC protein which are conserved in most of the members belonging to this subfamily of regulators. In addition, unlike some of the other transcriptional activators of this group, FleQ does not appear to have a cognate sensor kinase. A chromosomal insertional mutation in the fleQ gene abolished mucin adhesion and motility of P. aeruginosa PAK and PAK-NP. Both of these functions were regained by providing the complete fleQ gene on a multicopy plasmid. The location of fleQ immediately upstream of the fleSR operon, which is also necessary for the same process, suggested that these regulators may interact in some way. We therefore examined the regulation of the fleSR operon by fleQ and vice versa. Promoter fusion experiments showed that the fleSR operon was regulated by RpoN and FleQ. On the other hand, the fleQ promoter was independent of RpoN and FleR. FleQ, thus, adds another level of regulation to motility and adhesion in P. aeruginosa, above that of fleSR. We therefore propose the existence of a regulatory cascade which consists of at least two transcriptional regulators, FleQ and FleR, in the control of motility and adhesion in P. aeruginosa.

Cloning and characterization of Pseudomonas aeruginosa fliF, necessary for flagellar assembly and bacterial adherence to mucin

Pseudomonas aeruginosa adheres to the mucosal surfaces of the lungs. This process appears to be mediated by nonpilus adhesins which bind to mucin. To find this nonpilus adhesin(s), mutagenesis of a nonpiliated mutant of P. aeruginosa with transposon Tn5G, followed by a screen for mucin adhesion, was used to isolate a series of mutants unable to adhere to mucin. All of these mutants were also found to be defective in motility. One such mutant, PAK-RR20, is characterized here. The site of the transposon insertion in PAK-RR20 was localized to a gene which is homologous to the fliF gene of other organisms and was flanked by other motility-related genes, fliE and fliG. Both adhesion and motility defects in PAK-RR20 were complemented by providing the fliF gene in trans. Since complementation could have been due to the presence of an internal promoter in the fliF gene or in the Tn5G transposon, which allowed the transcription of the downstream genes, another chromosomal mutant of the fliF gene was constructed by insertional inactivation with an antibiotic resistance cassette. This mutant was also nonmotile and nonadhesive. However, the two defects in this new mutant could not be complemented by the fliF gene in trans, consistent with the interpretation that there is no internal fliF promoter but possibly a functional promoter in the Tn5G transposon. The complete nucleotide sequences of the fliE and fliF genes and a partial nucleotide sequence of the fliG gene of P. aeruginosa were determined. Control of the promoter upstream of the fliE gene was analyzed by construction of a fliE-lacZ fusion and the introduction of this construct into strains of P. aeruginosa with mutations in several regulatory genes. Beta-Galactosidase expression measurements indicated that the fliE promoter does not utilize RpoF (sigma(28)) or RpoN (sigma(54)) sigma factors. The characterization of this gene as being responsible for the loss of adhesion indicates that basal body structures are probably important for localization of the adhesin.

Isolation and sequence analysis of the Pseudomonas syringae pv. tomato gene encoding a 2,3-diphosphoglycerate-independent phosphoglyceromutase

Pseudomonas syringae pv. tomato DC3481, a Tn5-induced mutant of the tomato pathogen DC3000, cannot grow and elicit disease symptoms on tomato seedlings. It also cannot grow on minimal medium containing malate, citrate, or succinate, three of the major organic acids found in tomatoes. We report here that this mutant also cannot use, as a sole carbon and/or energy source, a wide variety of hexoses and intermediates of hexose catabolism. Uptake studies have shown that DC3481 is not deficient in transport. A 3.8-kb EcoRI fragment of DC3000 DNA, which complements the Tn5 mutation, has been cloned and sequenced. The deduced amino acid sequences of two of the three open reading frames (ORFs) present on this fragment, ORF2 and ORF3, had no significant homology with sequences in the GenBank databases. However, the 510-amino-acid sequence of ORF1, the site of the Tn5 insertion, strongly resembled the deduced amino acid sequences of the Bacillus subtilis and Zea mays genes encoding 2,3-diphosphoglycerate (DPG)-independent phosphoglyceromutase (PGM) (52% identity and 72% similarity and 37% identity and 57% similarity, respectively). PGMs not requiring the cofactor DPG are usually found in plants and algae. Enzyme assays confirmed that P. syringae PGM activity required an intact ORF1. Not only is DC3481 the first PGM-deficient pseudomonad mutant to be described, but the P. syringae pgm gene is the first gram-negative bacterial gene identified that appears to code for a DPG-independent PGM. PGM activity appears essential for the growth and pathogenicity of P. syringae pv. tomato on its host plant.