Chromosomal location of genes participating in the degradation of purines in Pseudomonas aeruginosa

A complete nicotinate degradation pathway in the microbial eukaryote Aspergillus nidulans

Several strikingly different aerobic and anaerobic pathways of nicotinate breakdown are extant in bacteria. Here, through reverse genetics and analytical techniques we elucidated in Aspergillus nidulans, a complete eukaryotic nicotinate utilization pathway. The pathway extant in this fungus and other ascomycetes, is quite different from bacterial ones. All intermediate metabolites were identified. The cognate proteins, encoded by eleven genes (hxn) mapping in three clusters are co-regulated by a specific transcription factor. Several enzymatic steps have no prokaryotic equivalent and two metabolites, 3-hydroxypiperidine-2,6-dione and 5,6-dihydroxypiperidine-2-one, have not been identified previously in any organism, the latter being a novel chemical compound. Hydrolytic ring opening results in α-hydroxyglutaramate, a compound not detected in analogous prokaryotic pathways. Our earlier phylogenetic analysis of Hxn proteins together with this complete biochemical pathway illustrates convergent evolution of catabolic pathways between fungi and bacteria.

A novel nicotinate degradation pathway is described in Aspergillus nidulans, with metabolic products identified that were not previously found in prokaryotic species. This is the first such pathway to be described in a eukaryote.

Anti-Inflammatory Metabolites in the Pathogenesis of Bacterial Infection

Host and pathogen metabolism have a major impact on the outcome of infection. The microenvironment consisting of immune and stromal cells drives bacterial proliferation and adaptation, while also shaping the activity of the immune system. The abundant metabolites itaconate and adenosine are classified as anti-inflammatory, as they help to contain the local damage associated with inflammation, oxidants and proteases. A growing literature details the many roles of these immunometabolites in the pathogenesis of infection and their diverse functions in specific tissues. Some bacteria, notably P. aeruginosa, actively metabolize these compounds, others, such as S. aureus respond by altering their own metabolic programs selecting for optimal fitness. For most of the model systems studied to date, these immunometabolites promote a milieu of tolerance, limiting local immune clearance mechanisms, along with promoting bacterial adaptation. The generation of metabolites such as adenosine and itaconate can be host protective. In the setting of acute inflammation, these compounds also represent potential therapeutic targets to prevent infection.

Regulation of uric acid and glyoxylate metabolism by UgmR protein in Pseudomonas aeruginosa

The opportunistic pathogen Pseudomonas aeruginosa has evolved several systems to adapt to complex environments. The GntR family proteins play important roles in the regulation of metabolic processes and bacterial pathogenesis. In this study, we uncovered that the gene clusters of PA1513-PA1518 and PA1498-PA1502 in P. aeruginosa are required for uric acid and glyoxylate metabolism, respectively. We also identified a GntR family regulator UgmR that is involved in regulation of uric acid and glyoxylate metabolism. Promoter activity measurement and biochemical assays revealed that the UgmR directly represses the transcriptional activity of PA1513-PA1518 and PA1498-PA1502, and this inhibition was relieved by the addition of uric acid. Importantly, further experiments showed that UgmR also participates in the glyoxylate shunt. Collectively, these findings contribute to a better understanding of the UgmR factor involved in uric acid and glyoxylate metabolism, which provide insights into the complex metabolic pathways in P. aeruginosa. This article is protected by copyright. All rights reserved.

Application of Phenotype Microarray for Profiling Carbon Sources Utilization between Biofilm and Non-Biofilm of Pseudomonas aeruginosa from Clinical Isolates

BACKGROUND

This is the fastest work in obtaining the metabolic profiles of Pseudomonas aeruginosa in order to combat the infection diseases which leads to high morbidity and mortality rates. Pseudomonas aeruginosa is a high versatility of gram-negative bacteria that can undergo aerobic and anaerobic respiration. Capabilities in deploying different carbon sources, energy metabolism and regulatory system, ensure the survival of this microorganism in the diverse environment condition. Determination of differences in carbon sources utilization among biofilm and non-biofilm of Pseudomonas aeruginosa provides a platform in understanding the metabolic activity of the microorganism.

METHODS

The study was carried out from September 2017 to February 2019. Four archive isolates forming strong and intermediate biofilm and non-biofilms producer were subcultured from archive isolates. ATCC 27853 P. aeruginosa was used as a negative control or non-biofilm producing microorganism. Biofilm formation was confirmed by Crystal Violet Assay (CVA) and Congo Red Agar (CRA). Metabolic profiles of the biofilm and non-biofilms isolates were determined by phenotype microarrays (Biolog Omnilog).

RESULTS AND DISCUSSION

In this study, Pseudomonas aeruginosa biofilm isolates utilized uridine, L-threonine and L-serine while non-biofilm utilized adenosine, inosine, monomethyl, sorbic acid and succinamic acid.

CONCLUSION

The outcome of this result will be used for future studies to improve detection or inhibit the growth of P. aeruginosa biofilm and non-biofilm respectively.

Dynamics of cheater invasion in a cooperating population of Pseudomonas aeruginosa

Pseudomonas aeruginosa quorum sensing (QS) regulates expression of dozens of genes in a cell density-dependent manner. Many QS-regulated genes code for production of extracellular factors, “public goods” that can benefit the entire population. This cooperation encourages individuals to cheat by using but not producing public goods. QS also controls expression of a limited number of genes encoding “private” cellular enzymes like Nuh, an enzyme involved in adenosine catabolism. Growth of P. aeruginosa on casein requires QS-regulated production of an extracellular protease and is an example of cooperative behavior. When P. aeruginosa is transferred daily on casein, QS mutants emerge. These cheaters have mutations in lasR, which encodes the primary QS transcription factor. When growth is on casein and adenosine, cheater emergence is constrained. Here, we report the dynamics of LasR mutant invasion during growth on casein or casein plus adenosine. We show that LasR mutants have the greatest advantage during early to mid-logarithmic growth on casein. Addition of adenosine to casein medium constrains cheaters throughout growth. Our data support the view that co-regulation of the public protease and the private nucleosidase by QS stabilizes cooperation, and the data are not consistent with other proposed alternate hypotheses.

Gene Duplication in Pseudomonas aeruginosa Improves Growth on Adenosine

The laboratory strain of Pseudomonas aeruginosa, PAO1, activates genes for catabolism of adenosine using quorum sensing (QS). However, this strain is not well-adapted for growth on adenosine, with doubling times greater than 40 h. We previously showed that when PAO1 is grown on adenosine and casein, variants emerge that grow rapidly on adenosine. To understand the mechanism by which this adaptation occurs, we performed whole-genome sequencing of five isolates evolved for rapid growth on adenosine. All five genomes had a gene duplication-amplification (GDA) event covering several genes, including the quorum-regulated nucleoside hydrolase gene, nuh, and PA0148, encoding an adenine deaminase. In addition, two of the growth variants also exhibited a nuh promoter mutation. We recapitulated the rapid growth phenotype with a plasmid containing six genes common to all the GDA events. We also showed that nuh and PA0148, the two genes at either end of the common GDA, were sufficient to confer rapid growth on adenosine. Additionally, we demonstrated that the variant nuh promoter increased basal expression of nuh but maintained its QS regulation. Therefore, GDA in P. aeruginosa confers the ability to grow efficiently on adenosine while maintaining QS regulation of nucleoside catabolism.IMPORTANCEPseudomonas aeruginosa thrives in many habitats and is an opportunistic pathogen of humans. In these diverse environments, P. aeruginosa must adapt to use myriad potential carbon sources. P. aeruginosa PAO1 cannot grow efficiently on nucleosides, including adenosine; however, it can acquire this ability through genetic adaptation. We show that the mechanism of adaptation is by amplification of a specific region of the genome and that the amplification preserves the regulation of the adenosine catabolic pathway by quorum sensing. These results demonstrate an underexplored mechanism of adaptation by P. aeruginosa, with implications for phenotypes such as development of antibiotic resistance.

Why Quorum Sensing Controls Private Goods

Cell-cell communication, also termed quorum sensing (QS), is a widespread process that coordinates gene expression in bacterial populations. The generally accepted view is that QS optimizes the cell density-dependent benefit attained from cooperative behaviors, often in the form of secreted products referred to as "public goods." This view is challenged by an increasing number of cell-associated products or "private goods" reported to be under QS-control for which a collective benefit is not apparent. A prominent example is nucleoside hydrolase from Pseudomonas aeruginosa, a periplasmic enzyme that catabolizes adenosine. Several recent studies have shown that private goods can function to stabilize cooperation by co-regulated public goods, seemingly explaining their control by QS. Here we argue that this property is a by-product of selection for other benefits rather than an adaptation. Emphasizing ecophysiological context, we propose alternative explanations for the QS control of private goods. We suggest that the benefit attained from private goods is associated with high cell density, either because a relevant ecological condition correlates with density, or because the private good is, directly or indirectly, involved in cooperative behavior. Our analysis helps guide a systems approach to QS, with implications for antivirulence drug design and synthetic biology.

Uric acid in plants and microorganisms: Biological applications and genetics - A review

Uric acid increased accumulation and/or reduced excretion in human bodies is closely related to pathogenesis of gout and hyperuricemia. It is highly affected by the high intake of food rich in purine. Uric acid is present in both higher plants and microorganisms with species dependent concentration. Urate-degrading enzymes are found both in plants and microorganisms but the mechanisms by which plant degrade uric acid was found to be different among them. Higher plants produce various metabolites which could inhibit xanthine oxidase and xanthine oxidoreductase, so prohibit the oxidation of hypoxanthine to xanthine then to uric acid in the purine metabolism. However, microorganisms produce group of degrading enzymes uricase, allantoinase, allantoicase and urease, which catalyze the degradation of uric acid to the ammonia. In humans, researchers found that several mutations caused a pseudogenization (silencing) of the uricase gene in ancestral apes which exist as an insoluble crystalloid in peroxisomes. This is in contrast to microorganisms in which uricases are soluble and exist either in cytoplasm or peroxisomes. Moreover, many recombinant uricases with higher activity than the wild type uricases could be induced successfully in many microorganisms. The present review deals with the occurrence of uric acid in plants and other organisms specially microorganisms in addition to the mechanisms by which plant extracts, metabolites and enzymes could reduce uric acid in blood. The genetic and genes encoding for uric acid in plants and microorganisms are also presented.

The identification of an integral membrane, cytochrome c urate oxidase completes the catalytic repertoire of a therapeutic enzyme

In living organisms, the conversion of urate into allantoin requires three consecutive enzymes. The pathway was lost in hominid, predisposing humans to hyperuricemia and gout. Among other species, the genomic distribution of the two last enzymes of the pathway is wider than that of urate oxidase (Uox), suggesting the presence of unknown genes encoding Uox. Here we combine gene network analysis with association rule learning to identify the missing urate oxidase. In contrast with the known soluble Uox, the identified gene (puuD) encodes a membrane protein with a C-terminal cytochrome c. The 8-helix transmembrane domain corresponds to DUF989, a family without similarity to known proteins. Gene deletion in a PuuD-encoding organism (Agrobacterium fabrum) abolished urate degradation capacity; the phenotype was fully restored by complementation with a cytosolic Uox from zebrafish. Consistent with H₂O₂ production by zfUox, urate oxidation in the complemented strain caused a four-fold increase of catalase. No increase was observed in the wild-type, suggesting that urate oxidation by PuuD proceeds through cytochrome c-mediated electron transfer. These findings identify a missing link in purine catabolism, assign a biochemical activity to a domain of unknown function (DUF989), and complete the catalytic repertoire of an enzyme useful for human therapy.

Microbial urate catabolism: characterization of HpyO, a non-homologous isofunctional isoform of the flavoprotein urate hydroxylase HpxO

In aerobic cells, urate is oxidized to 5-hydroxyisourate by two distinct enzymes: a coenzyme-independent urate oxidase (EC 1.7.3.3) found in eukaryotes and bacteria like Bacillus subtilis and a prokaryotic flavoprotein urate hydroxylase (HpxO) originally found in some Klebsiella species. More cases of analogous or non-homologous isofunctional enzymes (NISE) for urate catabolism have been hypothesized by inspecting bacterial genomes. Here, we used a functional complementation approach in which a candidate gene for urate oxidation is integrated by homologous recombination in the Acinetobacter baylyi ADP1 genome at the locus of its original hpxO gene. Catabolism of urate was restored in A. baylyi ADP1 expressing a FAD-dependent protein from Xanthomonas campestris, representing a new urate hydroxylase family that we called HpyO. This enzyme was kinetically characterized and compared with other HpxO enzymes. In contrast to the latter, HpyO is a typical Michaelian enzyme. This work provides the first experimental evidences for the function of HpyO in bacterial urate catabolism and establishes it as a NISE of HpxO.

MicroScope: a platform for microbial genome annotation and comparative genomics

The initial outcome of genome sequencing is the creation of long text strings written in a four letter alphabet. The role of in silico sequence analysis is to assist biologists in the act of associating biological knowledge with these sequences, allowing investigators to make inferences and predictions that can be tested experimentally. A wide variety of software is available to the scientific community, and can be used to identify genomic objects, before predicting their biological functions. However, only a limited number of biologically interesting features can be revealed from an isolated sequence. Comparative genomics tools, on the other hand, by bringing together the information contained in numerous genomes simultaneously, allow annotators to make inferences based on the idea that evolution and natural selection are central to the definition of all biological processes. We have developed the MicroScope platform in order to offer a web-based framework for the systematic and efficient revision of microbial genome annotation and comparative analysis (http://www.genoscope.cns.fr/agc/microscope). Starting with the description of the flow chart of the annotation processes implemented in the MicroScope pipeline, and the development of traditional and novel microbial annotation and comparative analysis tools, this article emphasizes the essential role of expert annotation as a complement of automatic annotation. Several examples illustrate the use of implemented tools for the review and curation of annotations of both new and publicly available microbial genomes within MicroScope's rich integrated genome framework. The platform is used as a viewer in order to browse updated annotation information of available microbial genomes (more than 440 organisms to date), and in the context of new annotation projects (117 bacterial genomes). The human expertise gathered in the MicroScope database (about 280,000 independent annotations) contributes to improve the quality of microbial genome annotation, especially for genomes initially analyzed by automatic procedures alone.Database URLs: http://www.genoscope.cns.fr/agc/mage and http://www.genoscope.cns.fr/agc/microcyc.

Logical identification of an allantoinase analog (puuE) recruited from polysaccharide deacetylases

The hydrolytic cleavage of the hydantoin ring of allantoin, catalyzed by allantoinase, is required for the utilization of the nitrogen present in purine-derived compounds. The allantoinase gene (DAL1), however, is missing in many completely sequenced organisms able to use allantoin as a nitrogen source. Here we show that an alternative allantoinase gene (puuE) can be precisely identified by analyzing its logic relationship with three other genes of the pathway. The novel allantoinase is annotated in structure and sequence data bases as polysaccharide deacetylase for its homology with enzymes that catalyze hydrolytic reactions on chitin or peptidoglycan substrates. The recombinant PuuE protein from Pseudomonas fluorescens exhibits metal-independent allantoinase activity and stereospecificity for the S enantiomer of allantoin. The crystal structures of the protein and of protein-inhibitor complexes reveal an overall similarity with the polysaccharide deacetylase beta/alpha barrel and remarkable differences in oligomeric assembly and active site geometry. The conserved Asp-His-His metal-binding triad is replaced by Glu-His-Trp, a configuration that is distinctive of PuuE proteins within the protein family. An extra domain at the top of the barrel offers a scaffold for protein tetramerization and forms a small substrate-binding cleft by hiding the large binding groove of polysaccharide deacetylases. Substrate positioning at the active site suggests an acid/base mechanism of catalysis in which only one member of the catalytic pair of polysaccharide deacetylases has been conserved. These data provide a structural rationale for the shifting of substrate specificity that occurred during evolution.

Genome-scale metabolic network analysis of the opportunistic pathogen Pseudomonas aeruginosa PAO1

Pseudomonas aeruginosa is a major life-threatening opportunistic pathogen that commonly infects immunocompromised patients. This bacterium owes its success as a pathogen largely to its metabolic versatility and flexibility. A thorough understanding of P. aeruginosa's metabolism is thus pivotal for the design of effective intervention strategies. Here we aim to provide, through systems analysis, a basis for the characterization of the genome-scale properties of this pathogen's versatile metabolic network. To this end, we reconstructed a genome-scale metabolic network of Pseudomonas aeruginosa PAO1. This reconstruction accounts for 1,056 genes (19% of the genome), 1,030 proteins, and 883 reactions. Flux balance analysis was used to identify key features of P. aeruginosa metabolism, such as growth yield, under defined conditions and with defined knowledge gaps within the network. BIOLOG substrate oxidation data were used in model expansion, and a genome-scale transposon knockout set was compared against in silico knockout predictions to validate the model. Ultimately, this genome-scale model provides a basic modeling framework with which to explore the metabolism of P. aeruginosa in the context of its environmental and genetic constraints, thereby contributing to a more thorough understanding of the genotype-phenotype relationships in this resourceful and dangerous pathogen.

Impact of quorum sensing on fitness of Pseudomonas aeruginosa

In Pseudomonas aeruginosa, cell-cell communication based on N-acyl-homoserine lactone (AHL) signal molecules (termed quorum sensing) is known to control the production of extracellular virulence factors. Hence, in pathogenic interactions with host organisms, the quorum-sensing (QS) machinery can confer a selective advantage on P. aeruginosa. However, as shown by transcriptomic and proteomic studies, many intracellular metabolic functions are also regulated by quorum sensing. Some of these serve to regenerate the AHL precursors methionine and S-adenosyl-methionine and to degrade adenosine via inosine and hypoxanthine. The fact that a significant percentage of clinical and environmental isolates of P. aeruginosa is defective for QS because of mutation in the major QS regulatory gene lasR, raises the question of whether the QS machinery can have a negative impact on the organism's fitness. In vitro, lasR mutants have a higher probability to escape lytic death in stationary phase under alkaline conditions than has the QS-proficient wild type. Similar selective forces might also operate in natural environments.

Quorum-sensing-negative (lasR) mutants of Pseudomonas aeruginosa avoid cell lysis and death

In Pseudomonas aeruginosa, N-acylhomoserine lactone signals regulate the expression of several hundreds of genes, via the transcriptional regulator LasR and, in part, also via the subordinate regulator RhlR. This regulatory network termed quorum sensing contributes to the virulence of P. aeruginosa as a pathogen. The fact that two supposed PAO1 wild-type strains from strain collections were found to be defective for LasR function because of independent point mutations in the lasR gene led to the hypothesis that loss of quorum sensing might confer a selective advantage on P. aeruginosa under certain environmental conditions. A convenient plate assay for LasR function was devised, based on the observation that lasR mutants did not grow on adenosine as the sole carbon source because a key degradative enzyme, nucleoside hydrolase (Nuh), is positively controlled by LasR. The wild-type PAO1 and lasR mutants showed similar growth rates when incubated in nutrient yeast broth at pH 6.8 and 37 degrees C with good aeration. However, after termination of growth during 30 to 54 h of incubation, when the pH rose to > or = 9, the lasR mutants were significantly more resistant to cell lysis and death than was the wild type. As a consequence, the lasR mutant-to-wild-type ratio increased about 10-fold in mixed cultures incubated for 54 h. In a PAO1 culture, five consecutive cycles of 48 h of incubation sufficed to enrich for about 10% of spontaneous mutants with a Nuh(-) phenotype, and five of these mutants, which were functionally complemented by lasR(+), had mutations in lasR. The observation that, in buffered nutrient yeast broth, the wild type and lasR mutants exhibited similar low tendencies to undergo cell lysis and death suggests that alkaline stress may be a critical factor providing a selective survival advantage to lasR mutants.

Functional analysis of 14 genes that constitute the purine catabolic pathway in Bacillus subtilis and evidence for a novel regulon controlled by the PucR transcription activator

The soil bacterium Bacillus subtilis has developed a highly controlled system for the utilization of a diverse array of low-molecular-weight compounds as a nitrogen source when the preferred nitrogen sources, e.g., glutamate plus ammonia, are exhausted. We have identified such a system for the utilization of purines as nitrogen source in B. subtilis. Based on growth studies of strains with knockout mutations in genes, complemented with enzyme analysis, we could ascribe functions to 14 genes encoding enzymes or proteins of the purine degradation pathway. A functional xanthine dehydrogenase requires expression of five genes (pucA, pucB, pucC, pucD, and pucE). Uricase activity is encoded by the pucL and pucM genes, and a uric acid transport system is encoded by pucJ and pucK. Allantoinase is encoded by the pucH gene, and allantoin permease is encoded by the pucI gene. Allantoate amidohydrolase is encoded by pucF. In a pucR mutant, the level of expression was low for all genes tested, indicating that PucR is a positive regulator of puc gene expression. All 14 genes except pucI are located in a gene cluster at 284 to 285 degrees on the chromosome and are contained in six transcription units, which are expressed when cells are grown with glutamate as the nitrogen source (limiting conditions), but not when grown on glutamate plus ammonia (excess conditions). Our data suggest that the 14 genes and the gde gene, encoding guanine deaminase, constitute a regulon controlled by the pucR gene product. Allantoic acid, allantoin, and uric acid were all found to function as effector molecules for PucR-dependent regulation of puc gene expression. When cells were grown in the presence of glutamate plus allantoin, a 3- to 10-fold increase in expression was seen for most of the genes. However, expression of the pucABCDE unit was decreased 16-fold, while expression of pucR was decreased 4-fold in the presence of allantoin. We have identified genes of the purine degradation pathway in B. subtilis and showed that their expression is subject to both general nitrogen catabolite control and pathway-specific control.

Transcriptional control of the hydrogen cyanide biosynthetic genes hcnABC by the anaerobic regulator ANR and the quorum-sensing regulators LasR and RhlR in Pseudomonas aeruginosa

Virulence factors of Pseudomonas aeruginosa include hydrogen cyanide (HCN). This secondary metabolite is maximally produced at low oxygen tension and high cell densities during the transition from exponential to stationary growth phase. The hcnABC genes encoding HCN synthase were identified on a genomic fragment complementing an HCN-deficient mutant of P. aeruginosa PAO1. The hcnA promoter was found to be controlled by the FNR-like anaerobic regulator ANR and by the quorum-sensing regulators LasR and RhlR. Primer extension analysis revealed two transcription starts, T1 and T2, separated by 29 bp. Their function was confirmed by transcriptional lacZ fusions. The promoter sequence displayed an FNR/ANR box at -42.5 bp upstream of T2 and a lux box centered around -42.5 bp upstream of T1. Expression of the hcn genes was completely abolished when this lux box was deleted or inactivated by two point mutations in conserved nucleotides. The lux box was recognized by both LasR [activated by N-(oxododecanoyl)-homoserine lactone] and RhlR (activated by N-butanoyl-homoserine lactone), as shown by expression experiments performed in quorum-sensing-defective P. aeruginosa mutants and in the N-acyl-homoserine lactone-negative heterologous host P. fluorescens CHA0. A second, less conserved lux box lying 160 bp upstream of T1 seems to account for enhanced quorum-sensing-dependent expression. Without LasR and RhlR, ANR could not activate the hcn promoter. Together, these data indicate that expression of the hcn promoter from T1 can occur under quorum-sensing control alone. Enhanced expression from T2 appears to rely on a synergistic action between LasR, RhlR, and ANR.

Inactivation of the ampD gene in Pseudomonas aeruginosa leads to moderate-basal-level and hyperinducible AmpC beta-lactamase expression

It has been shown in enterobacteria that mutations in ampD provoke hyperproduction of chromosomal beta-lactamase, which confers to these organisms high levels of resistance to beta-lactam antibiotics. In this study, we investigated whether this genetic locus was implicated in the altered AmpC beta-lactamase expression of selected clinical isolates and laboratory mutants of Pseudomonas aeruginosa. The sequences of the ampD genes and promoter regions from these strains were determined and compared to that of wild-type ampD from P. aeruginosa PAO1. Although we identified numerous nucleotide substitutions, they resulted in few amino acid changes. The phenotypes produced by these mutations were ascertained by complementation analysis. The data revealed that the ampD genes of the P. aeruginosa mutants transcomplemented Escherichia coli ampD mutants to the same levels of beta-lactam resistance and beta-lactamase expression as wild-type ampD. Furthermore, complementation of the P. aeruginosa mutants with wild-type ampD did not restore the inducibility of beta-lactamase to wild-type levels. This shows that the amino acid substitutions identified in AmpD do not cause the altered phenotype of AmpC beta-lactamase expression in the P. aeruginosa mutants. The effects of AmpD inactivation in P. aeruginosa PAO1 were further investigated by gene replacement. This resulted in moderate-basal-level and hyperinducible expression of beta-lactamase accompanied by high levels of beta-lactam resistance. This differs from the stably derepressed phenotype reported in AmpD-defective enterobacteria and suggests that further change at another unknown genetic locus may be causing total derepressed AmpC production. This genetic locus could also be altered in the P. aeruginosa mutants studied in this work.

Quantitative correlation between susceptibility and OprJ production in NfxB mutants of Pseudomonas aeruginosa

Various Pseudomonas aeruginosa PAO1 NfxB mutants were isolated on agar plates containing cefpirome and ofloxacin. They were classified into type A and type B, based on the degrees of changes in their susceptibilities. Type A mutants were four to eight times more resistant to ofloxacin, erythromycin, and new zwitterionic cephems, i.e., cefpirome, cefclidin, cefozopran, and cefoselis, than was the parent strain, PAO1. In contrast, type B mutants were more resistant to tetracycline and chloramphenicol, as well as ofloxacin, erythromycin, and the new zwitterionic cephems, than was PAO1, and they were four to eight times more susceptible to carbenicillin, sulbenicillin, imipenem, panipenem, biapenem, moxalactam, aztreonam, gentamicin, and kanamycin that was PAO1. The changes in susceptibilities of type B mutants were greater than those of type A mutants. The susceptibilities of both type A and type B mutants were restored to the level of PAO1 by transformation with plasmid pNF111, which contained the wild-type nfxB gene, demonstrating that they are NfxB mutants. Immunoblot analysis with a monoclonal antibody to OprJ revealed that type B mutants produced larger amounts of outer membrane protein OprJ than did type A mutants and that PAO1 produced an undetectable amount of it. Moreover, transconjugants obtained with the different types of NfxB mutants as the donor strains showed almost the same phenotypes as the corresponding donor strains. These results suggest that there are at least two nfxB mutations that show different phenotypes and that production of OprJ is associated with changes in susceptibilities of NfxB mutants.

Purification and characterization of the Pseudomonas aeruginosa NfxB protein, the negative regulator of the nfxB gene

The protein NfxB, involved in conferring resistance to quinolones in Pseudomonas aeruginosa, has a helix-turn-helix motif which is similar to that of other DNA-binding proteins. It appears to affect the membrane-associated energy-driven efflux of some antibiotics (H. Nikaido, Science 264:382-388, 1994). We constructed a plasmid that overproduced NfxB in Escherichia coli and purified the protein. Two species of NfxB (23 and 21 kDa), which are probably translated from different initiation codons, were isolated. Both proteins are also expressed in vivo in P. aeruginosa, with the 23-kDa NfxB being the major species. NfxB specifically binds upstream of the nfxB coding region as demonstrated by gel retardation and DNase I footprinting. Expression of the phi (nfxB'-lacZ+) (Hyb) gene was repressed in the presence of the nfxB gene product provided by a second compatible plasmid in E. coli. In the P. aeruginosa wild-type strain (PAO2142), NfxB was undetectable by immunoblotting; however, it was detected in the nfxB missense mutant (PK1013E). These results suggested that NfxB negatively autoregulates the expression of nfxB itself. Since the 54-kDa outer membrane protein (OprJ) (N. Masuda, E. Sakagawa, and S. Ohya, Antimicrob. Agents Chemother. 39:645-649, 1995) was overproduced in nfxB mutants, NfxB may also regulate the expression of membrane proteins that are involved in the drug efflux machinery of P. aeruginosa.

Mechanism of enhanced antipseudomonal activity of BO-2727, a new injectable 1-beta-methyl carbapenem

The mechanism of the enhanced activity of BO-2727 against imipenem-resistant Pseudomonas aeruginosa was studied by using a set of four isogenic strains derived from beta-lactamase-deficient P. aeruginosa PAO4089 (blaJ blaP). Complementation of the blaJ and blaP mutations conferred greater resistance to biapenem, panipenem, and imipenem than to BO-2727 and meropenem, most notably in the outer membrane protein D2-deficient strain. The higher levels of resistance to biapenem, panipenem, and imipenem can be explained by the slow but significant hydrolysis by beta-lactamase, whereas the reduced levels of resistance to BO-2727 and meropenem would be attributable to their stability in the presence of high levels of beta-lactamase and the fact that they cause only low induction of beta-lactamase. It is also noted that the activity of BO-2727 against the beta-lactamase-deficient strain was less affected by the loss of the D2 porin than was that of meropenem, indicating that BO-2727 in comparison with meropenem can overcome an intrinsic resistance caused by the loss of D2. Moreover, comparative in vitro resistance studies have shown that BO-2727 and meropenem selected fewer resistant cells than other carbapenems. In conclusion, BO-2727 exhibited improved activity against imipenem-resistant P. aeruginosa, probably because of its ability to overcome loss of the D2 porin and beta-lactamase hydrolysis.

nfxC-type quinolone resistance in a clinical isolate of Pseudomonas aeruginosa

Quinolone resistance gene nqr-T91 in a clinical isolate of Pseudomonas aeruginosa P1481 was cotransducible with catA1 in P. aeruginosa PAO. The nqr-T91 transductant, PKH-T91, was resistant to norfloxacin, imipenem, and chloramphenicol and showed less norfloxacin accumulation than the parent strain did. Loss of the 46-kDa outer membrane protein (D2) and an increase in the 50-kDa outer membrane protein in PKH-T91 were observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Lipopolysaccharides in the transductant were also changed. These alterations were considered to be related to lower levels of norfloxacin accumulation in PKH-T91. These genetic and biochemical properties suggested that an nfxC type of quinolone-resistant mutation occurred in a clinical isolate of P. aeruginosa P1481.

Positive FNR-like control of anaerobic arginine degradation and nitrate respiration in Pseudomonas aeruginosa

A mutant of Pseudomonas aeruginosa was characterized which could not grow anaerobically with nitrate as the terminal electron acceptor or with arginine as the sole energy source. In this anr mutant, nitrate reductase and arginine deiminase were not induced by oxygen limitation. The anr mutation was mapped in the 60-min region of the P. aeruginosa chromosome. A 1.3-kb chromosomal fragment from P. aeruginosa complemented the anr mutation and also restored anaerobic growth of an Escherichia coli fnr deletion mutant on nitrate medium, indicating that the 1.3-kb fragment specifies an FNR-like regulatory protein. The arcDABC operon, which encodes the arginine deiminase pathway enzymes of P. aeruginosa, was rendered virtually noninducible by a deletion or an insertion in the -40 region of the arc promoter. This -40 sequence (TTGAC....ATCAG) strongly resembled the consensus FNR-binding site (TTGAT....ATCAA) of E. coli. The cloned arc operon was expressed at low levels in E. coli; nevertheless, some FNR-dependent anaerobic induction could be observed. An FNR-dependent E. coli promoter containing the consensus FNR-binding site was expressed well in P. aeruginosa and was regulated by oxygen limitation. These findings suggest that P. aeruginosa and E. coli have similar mechanisms of anaerobic control.

Analysis of cloned structural and regulatory genes for carbohydrate utilization in Pseudomonas aeruginosa PAO

Five of the genes required for phosphorylative catabolism of glucose in Pseudomonas aeruginosa were ordered on two different chromosomal fragments. Analysis of a previously isolated 6.0-kb EcoRI fragment containing three structural genes showed that the genes were present on a 4.6-kb fragment in the order glucose-binding protein (gltB)-glucokinase (glk)-6-phosphogluconate dehydratase (edd). Two genes, glucose-6-phosphate dehydrogenase (zwf) and 2-keto-3-deoxy-6-phosphogluconate aldolase (eda), shown by transductional analysis to be linked to gltB and edd, were cloned on a separate 11-kb BamHI chromosomal DNA fragment and then subcloned and ordered on a 7-kb fragment. The 6.0-kb EcoRI fragment had been shown to complement a regulatory mutation, hexR, which caused noninducibility of four glucose catabolic enzymes. In this study, hexR was mapped coincident with edd. A second regulatory function, hexC, was cloned within a 0.6-kb fragment contiguous to the edd gene but containing none of the structural genes. The phenotypic effect of the hexC locus, when present on a multicopy plasmid, was elevated expression of glucokinase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydratase, and 2-keto-3-deoxy-6-phosphogluconate aldolase activities in the absence of inducer.

New norfloxacin resistance gene in Pseudomonas aeruginosa PAO

A new type of norfloxacin-resistant mutant of Pseudomonas aeruginosa PAO was isolated. This mutant showed cross resistance to imipenem and chloramphenicol and hypersusceptibility to beta-lactam and aminoglycoside antibiotics. The new norfloxacin resistance gene nfxC was mapped near catA (46 min) on the PAO chromosome. Norfloxacin accumulation was decreased in the nfxC mutant; furthermore, the rate of imipenem diffusion through the outer membrane of the nfxC mutant was lower than that of the parent strain. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of outer membrane proteins showed a decrease of a 46-kilodalton protein and an increase of a 50-kilodalton protein in the nfxC mutant. We conclude the nfxC is a new norfloxacin resistance gene that affects outer membrane permeability to quinolones and other antimicrobial agents.

Catabolism of aromatic biogenic amines by Pseudomonas aeruginosa PAO1 via meta cleavage of homoprotocatechuic acid

Pseudomonas aeruginosa PAO1 catabolized the aromatic amines tyramine and octopamine through 4-hydroxyphenylacetic acid and 3,4-dihydroxyphenylacetic acid (HPA). meta ring cleavage was mediated by 3,4-dihydroxyphenylacetate 2,3-dioxygenase (HPADO), producing 2-hydroxy-5-carboxymethylmuconic semialdehyde (MSA). An NAD-dependent dehydrogenase caused the disappearance of the yellow MSA product, probably forming 2-hydroxy-5-carboxymethylmuconic acid. Induction studies with extracts from mutant cells indicated that the inducer of HPADO was HPA and/or MSA. Strains PAO1.221 (tynC1) and PAO1.303 (tynD1) have chromosomal mutations causing a deficiency in the activity necessary for conversion of 4-hydroxyphenylacetic acid to HPA. Genetic analyses showed that the mutations were in different loci. Strains PAO1.197 (tynE1) and PAO1.185 (tynF1) are deficient in HPADO and the NAD-dependent dehydrogenase, respectively. Plasmid pRO1853 was constructed by cloning approximately 7.3 kilobases of PAO1 chromosomal DNA into the BamHI site of the vector plasmid pRO1614. This recombinant plasmid complemented the tynD1, tynE1, and tynF1 mutations. A putative repressor-binding site involved in the regulation of HPADO synthesis was observed for a subcloned fragment of pRO1853. This recombinant plasmid, pRO1863, failed to complement tynE1 or tynF1 but still complemented tynD1. Another construct, pRO1887, contained 9.2 kilobases of PAO1 chromosomal DNA inserted in the PstI site of the vector pRO1727. Plasmid pRO1887 complemented only the tynC1 mutation. Mapping experiments performed with the chromosome-mobilizing plasmid R68.45 located the mutations described above in a cluster at about 35 to 40 min of the PAO1 chromosome map. The mutations were linked to the proA, thr-48, lys-9015, argF10, and argG markers.

Some properties of subunits of DNA gyrase from Pseudomonas aeruginosa PAO1 and its nalidixic acid-resistant mutant

Subunits A and B of DNA gyrase were purified from Pseudomonas aeruginosa PAO1 and its mutant, which was resistant to nalidixic acid. Inhibition tests of DNA gyrases reconstituted with a combination of subunits from the two strains showed that an alteration of subunit A but not subunit B caused bacteria to resist fluoroquinolones.

Mutations producing resistance to norfloxacin in Pseudomonas aeruginosa

Two genetically distinct classes of norfloxacin-resistant Pseudomonas aeruginosa PAO4009 mutants were isolated spontaneously. Two norfloxacin resistance genes, nfxA and nfxB, were mapped hex-9001 and leu-9005 and between pro-9031 and ilv-9023, respectively, on the P. aeruginosa PAO chromosome. The nfxA gene was shown to be an allele of nalA by transductional analysis with bacteriophage F116L. The nfxB mutant showed a 16-fold increase in resistance to norfloxacin and a slight increase in resistance to nalidixic acid. The nfxB mutant was unique in that it showed hypersusceptibility to beta-lactam and aminoglycoside antibiotics. This mutant had about a threefold-lower rate of norfloxacin uptake than that of the wild-type strain or nfxA mutant. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of outer membrane proteins demonstrated the appearance of a 54,000-dalton protein in the nfxB mutant. These findings suggested that the norfloxacin resistance mechanism in the nfxB mutant might be an alteration in outer membrane permeability to norfloxacin.

IS21 insertion in the trfA replication control gene of chromosomally integrated plasmid RP1: a property of stable Pseudomonas aeruginosa Hfr strains

Broad host range IncP-1 plasmids are able to integrate into the chromosome of gram-negative bacteria. Strains carrying an integrated plasmid can be obtained when the markers of a temperature-sensitive (ts) plasmid derivative are selected at non-permissive temperature; in this way Hfr (high frequency) donor strains can be formed. The integrated plasmids, however, tend to be unstable in the absence of continuous selective pressure. In order to obtain stable Hfr donor strains of Pseudomonas aeruginosa PAO, we constructed a derivative of an RP1 (ts) plasmid, pME134, which was defective in the resolvase gene (tnpR) of transposon Tn801. Chromosomal integration of pME134 was selected in a recombination-deficient (rec-102) PAO strain at 43 degrees C. Plasmid integration occurred at different sites resulting in a useful set of Hfr strains that transferred chromosomal markers unidirectionally. The tnpR and rec-102 mutations prevented plasmid excision from the chromosome. In several (but not all) Hfr strains that grew well and retained the integrated plasmid at temperatures below 43 degrees C, the insertion element IS21 of RP1 was found to be inserted into the trfA locus (specifying an essential trans-acting replication function) of the integrated plasmid. One such Hfr strain was rendered rec+; from its chromosome the pME134::IS21 plasmid (= pME14) was excised and transferred by conjugation to Escherichia coli where pME14 could replicate autonomously only when a helper plasmid provided the trfA+ function in trans. Thus, it appears that trfA inactivation favours the stability of chromosomally integrated RP1 in P. aeruginosa.

Chromosomal mapping of mutations affecting glycerol and glucose catabolism in Pseudomonas aeruginosa PAO

Mutations causing deficiencies in the inducible, membrane-associated sn-glycerol-3-phosphate dehydrogenase (glpD) and in inducible glucose transport (glcT) were mapped on the Pseudomonas aeruginosa PAO1 chromosome by using the generalized transducing phages F116L and G101. These mutations, in separate catabolic regulatory units, were cotransducible with a previously described cluster of carbohydrate catabolic gene loci (zwf-1 eda-9001 edd-1) that maps at ca. 50 to 53 min on the chromosome. Mutant strain PFB362 (glcT1) did not transport glucose and did not produce a functional, periplasmic, glucose-binding protein that is required for glucose transport. This mutation was cotransducible with zwf-1 (70%), nalA (29%), and phe-2 (19%) but not with glpD1 or leu-10. The glpD1 mutation in strain PRP408 was cotransducible with zwf-1 (5%), eda-9001 (4%), and edd-1 (1%) and also with ami-151 (17%) and phe-2 (33%). These results expand the number of known carbohydrate catabolism genes that are clustered in the 50- to 55-min region of the PAO1 chromosome and allow us to propose the following relative gene order: ami-151 glpD1 phe-2 nalA zwf-1 eda-9001 edd-1 glcT1 leu-10. Three independently obtained nal determinants for high-level resistance to nalidixic acid, which were employed in these studies, exhibited similar cotransduction frequencies with several flanking marker mutations.

Mutants of Pseudomonas aeruginosa unable to inactivate allantoinase and NADP-dependent glutamate dehydrogenase

Both allantoinase and NADP-GDH in Pseudomonas aeruginosa were inactivated when cells reached the stationary phase of growth. Mutants unable to inactivate these enzymes were isolated. Results with recombinants showed that the mutation is not located in the structural genes of these enzymes but in an independent gene involved in the inactivation.

Revised locations of the hisI and pru (proline utilization) genes on the Pseudomonas aeruginosa chromosome map

The location of genes in the vicinity of the major FP2 origin on the chromosome of Pseudomonas aeruginosa PAO has been revised. The markers hisI (a transduction group of histidine biosynthetic genes) and pru (a gene cluster encoding proline utilization functions) were located in the 90 to 95/0 min chromosome region by a series of plate matings mediated by R68.45. Three-factor-crosses using this plasmid established the following marker order: pur-67 pru hisI/cys-59 proB ilvB/C. Genetic evidence is presented to confirm the previous observations that FP2 can mobilize the chromosome from at least two origins near proB and in both directions. Thus, when markers in this chromosome region are analyzed by FP2 crosses only, the mapping data may be difficult to interpret. This complication can be overcome by the use of R68.45 and Tfr (transposon-facilitated recombination) or Hfr donors.

Clustering of mutations affecting central pathway enzymes of carbohydrate catabolism in Pseudomonas aeruginosa

Mutations in carbohydrate-negative mutants of Pseudomonas aeruginosa PAO1 individually deficient in glucose 6-phosphate dehydrogenase (zwf), 6-phosphogluconate dehydratase (edd), or pyruvate carboxylase (pyc) were mapped on the chromosome by plasmid R68.45-mediated conjugation and by bacteriophage F116L-mediated transduction. Loci for all three genes were located in the 45- to 55-min region of the chromosome; both zwf-1 and edd-1 were linked by transduction to nalA, whereas pyc-2 was linked by conjugation to argF10. The zwf-1 mutation exhibited cotransduction frequencies of greater than 95% with both edd-1 and the hex-9001 marker, a mutation reported to prevent growth on hexoses. The latter mutation was shown to cause a specific deficiency in 2-keto-3-deoxy-6-phosphogluconate aldolase activity and was redesignated eda-9001. These results demonstrate tight clustering of the gene loci for glucose 6-phosphate dehydrogenase and for both enzymes unique to the Entner-Doudoroff pathway in P. aeruginosa. Our evidence suggests supraoperonic clustering of these and other inducible carbohydrate catabolic genes in the 45- to 55-min region of the chromosome.

Mapping of the gene specifying aminoglycoside 3'-phosphotransferase II on the Pseudomonas aeruginosa chromosome

We examined the aminoglycoside inactivation enzymes in Pseudomonas aeruginosa strains, seven clinical isolates and seven laboratory strains without plasmids. All strains were found to possess the enzyme aminoglycoside 3'-phosphotransferase II [APH(3')-II]. We isolated an APH(3')-II-deficient mutant from a PAO strain by mutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine. By plasmid (FP5 or R68.45)-mediated conjugation, we determined the locus of the gene specifying the APH(3')-II between trp-6 and pro-82 on the PAO chromosome and designated this gene aphA. It was concluded that the intrinsic resistance of P. aeruginosa to kanamycins, neomycins, paromomycins, ribostamycin, and butirosins was due to this newly determined gene.

Genetic mapping of bra genes affecting branched-chain amino acid transport in Pseudomonas aeruginosa

Pseudomonas aeruginosa PAO mutants defective in the transport systems for branched-chain amino acids were isolated and characterized. Two mutations in strains selected for trifluoroleucine resistance, braA300 and braB307, were mapped in the met-9020-dcu-9108 and the nar-9011-puuC10 region, respectively. The mutation loci in strains selected for azaleucine resistance, braC310 and bra-311 through bra-314, were all located near the fla genes, with an order of region I fla-bra-region II fla. Strains with braA300 showed a marked reduction in the high-affinity branched-chain amino acid transport system (LIV-I) and a considerable decrease in the lower-affinity system (LIV-II). Strains with braB307 were found to be defective in the LIV-II system. Strains selected for azaleucine resistance were all defective only in the LIV-I system and fell into three phenotypically distinct classes. Strains with braC310 produced a binding protein for leucine, isoleucine, valine, alanine, and threonine (LIVAT-BP) altered in binding ability, indicating that the braC gene is the structural one for the LIVAT-BP. Strains with bra-311 or bra-312 showed a complete loss of production of the LIVAT-BP. Strains with bra-313 or bra-314 produced normal levels of functional LIVAT-BP, suggesting that these mutations are located in a gene(s) other than braC.

Characterization of glutamine-requiring mutants of Pseudomonas aeruginosa

Revertants were isolated from a glutamine-requiring mutant of Pseudomonas aeruginosa PAO. One strain showed thermosensitive glutamine requirement and formed thermolabile glutamine synthase, suggesting the presence of a mutation in the structural gene for glutamine synthetase. The mutation conferring glutamine auxotrophy was subsequently mapped and found to be located at about 15 min on the chromosomal map, close to and before hisII4. Furthermore, in transduction experiments, it appeared to be very closely linked to gln-2022, a suppressor mutation affecting nitrogen control. With immunological techniques, it could be demonstrated that the glutamine auxotrophs form an inactive glutamine synthetase protein which is regulated by glutamine or a product derived from it in a way similar to other nitrogen-controlled proteins.

Nitrogen control in Pseudomonas aeruginosa: mutants affected in the synthesis of glutamine synthetase, urease, and NADP-dependent glutamate dehydrogenase

Mutants were isolated from Pseudomonas aeruginosa that were impaired in the utilization of a number of nitrogen sources. In contrast to the wild-type strain, these mutants appeared to be unable to derepress the formation of glutamine synthetase and urease under nitrogen-limited growth conditions, whereas NADP-dependent glutamate dehydrogenase became derepressed. This GlnR- phenotype appeared to be caused by a mutation located in the early region of the P. aeruginosa PAO chromosomal map, close to hisIV59. Partial suppression of the GlnR- phenotype due to a mutation located close to hisII4 was observed. These revertants were different from both the wild-type strain and the GlnR- mutant with respect to the regulation of the synthesis of glutamine synthetase, urease, and NADP-dependent glutamate dehydrogenase (GlnRc phenotype). Also the regulation of glutamine synthetase activity by adenylylation/deadenylylation was altered in the revertants. The results suggest the presence of a regulatory gene that plays a role in the regulation of enzyme formation in response to the availability of ammonia.

Regulation of amidase formation in mutants from Pseudomonas aeruginosa PAO lacking glutamine synthetase activity

The formation of amidase was studied in mutants from Pseudomonas aeruginosa PAO lacking glutamine synthetase activity. It appeared that catabolite repression of amidase synthesis by succinate was partially relieved when cellular growth was limited by glutamine. Under these conditions, a correlation between amidase and urease formation was observed. The results suggest that amidase formation in strain PAO is subject to nitrogen control and that glutamine or some compound derived from it mediates the nitrogen repression of amidase.

Development of broad-host-range vectors and gene banks: self-cloning of the Pseudomonas aeruginosa PAO chromosome

A host-vector system for Pseudomonas aeruginosa PAO was developed. Scattered regions of the strain PAO chromosome were cloned by direct selection for complementation of auxotrophs or from a DNA gene bank which contains over 1,000 independently isolated chromosome-vector recombinant plasmids. The use of partially digested chromosomal DNA facilitated the selection of a variety of strain PAO chromosomal markers. The progenitor of the vector was a small, multicopy plasmid, pRO1600, found in a PAO strain which had acquired RP1 in a mating experiment. The bacterial host range that could be determined by transformation of vectors produced from pRO1600 resembles that for plasmid RP1. Two derivative plasmids were formed: pRO1613, for cloning DNA cleaved with restriction endonuclease PstI, and pRO1614, which was formed by deleting part of pRO1613 and fusion with plasmid pBR322. Plasmid pRO1614 utilizes known cloning sites within the tetracycline resistance region of pBR322.

Chromosomal locations of catA, pobA, dcu and chu genes in Pseudomonas aeruginosa

Eleven catabolic markers have been located on the chromosome ofPseudomonas aeruginosaPAO using FPS-mediated conjugation and G101 transduction. Most of these markers are located in the region 20–35 min, and the remainder in the region later than 60 min. Fourchugenes concerned in the sequential degradation of choline to glycine are closely linked.

Analysis of flagellar genes in Pseudomonas aeruginosa by use of Rfla plasmids and conjugations

Over 300 flagellar mutants were isolated in Pseudomonas aeruginosa PAO. R-prime plasmids carrying segments of bacterial chromosome which can complement the mutant phenotypes were isolated by means of plasmid R68.45. Among the R-prime plasmids, pMT6 complemented 167 out of 307 mutants examined, and pMT19 complemented the remaining 140 mutants. We found no mutant which was complemented by both of these plasmids. Hence, the flagellar genes were divided into two clusters by these two plasmids, namely, region I on pMT19 and region II on pMT6. By FP5- and R68.45-mediated conjugation, these two regions were located on the P. aeruginosa PAO chromosome with an order of puuF--region I--region II--oru-325.

Nitrogen control in Pseudomonas aeruginosa: a role for glutamine in the regulations of the synthesis of nadp-dependent glutamate dehydrogenase, urease and histidase

In Pseudomonas aeruginosa the formation of urease, histidase and some other enzymes involved in nitrogen assimilation is repressed by ammonia in the growth medium. The key metabolite in this process appears to be glutamine or a product derived from it, since ammonia and glutamate did not repress urease and histidase synthesis in a mutant lacking glutamine synthetase activity when growth was limited for glutamine. The synthesis of these enzymes was repressed in cells growing in the presence of excess glutamine. High levels of glutamine were also required for the derepression of NADP-dependent glutamate dehydrogenase formation in the glutamine synthetase-negative mutant.

Genetic circularity of the Pseudomonas aeruginosa PAO chromosome

Genetic circularity of the Pseudomonas aeruginosa PAO chromosome was demonstrated by a series of two- and three-factor crosses and double-selection experiments with Cma plasmids FP2, FP5, FP110, and R68.45. A range of additional markers, including catabolic markers, were located on the chromosome map. Plasmid FP2, known to have a major origin of chromosome transfer (0 min) was shown to have at least one other minor origin from which it can transfer the chromosome in the direction opposite to that found for the major origin.