Anaerobic regulation of transcription initiation in the arcDABC operon of Pseudomonas aeruginosa

The arcDABC operon of Pseudomonas aeruginosa encodes the enzymes of the arginine deiminase pathway, which is inducible under conditions of oxygen limitation and serves to generate ATP from arginine. The 5' end of arc mRNA extracted from anaerobically grown cells was determined by S1 and primer extension mapping. The transcription initiation site was located upstream of the arcD gene and 41.5 bp downstream of the center of the sequence TTGAC....ATCAG. This sequence, termed the ANR box, is similar to the consensus FNR recognition site of Escherichia coli. Transcription of the arc operon in P. aeruginosa was strongly decreased by a deletion of the TTGAC half site or by a mutation in the anr gene, which is known to code for the FNR-like regulatory protein ANR. During a transition from aerobic to anaerobic growth conditions, the concentrations of arc mRNAs and the levels of the ArcD and ArcA proteins rose in a parallel fashion. Mutational analysis of the arc promoter region led to the conclusion that the distance between the ANR box and the -10 promoter region is important for promoter strength, whereas the -35 region does not appear to be critical for arc promoter function. These findings and previous results indicate that anaerobic induction of the arc operon occurs at the level of transcription and requires the ANR box in cis and the ANR protein in trans.

Anaerobic growth and cyanide synthesis of Pseudomonas aeruginosa depend on anr, a regulatory gene homologous with fnr of Escherichia coli

Anaerobic growth of Pseudomonas aeruginosa on nitrate or arginine requires the anr gene, which codes for a positive control element (ANR) capable of functionally complementing an fnr mutation in Escherichia coli. The anr gene was sequenced; it showed 51% identity with the fnr gene at the amino acid sequence level. Four cysteine residues known to be essential in the FNR protein are conserved in ANR. The anr gene product (deduced Mr 27,129) was visualized by the maxicell method and migrated like a 32 kDa protein in gel electrophoresis under denaturing conditions. An anr mutant of P. aeruginosa constructed by gene replacement was defective in nitrate respiration, arginine deiminase activity, and hydrogen cyanide biosynthesis, underscoring the diverse metabolic functions of ANR during oxygen limitation. Pseudomonas fluorescens, Pseudomonas putida, Pseudomonas syringae, and Pseudomonas mendocina all had a functional analogue of ANR, indicating that similar anaerobic control mechanisms exist in these bacteria.

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.

The istA gene of insertion sequence IS21 is essential for cleavage at the inner 3′ ends of tandemly repeated IS21 elements in vitro

The bacterial 2.1 kb insertion sequence IS21 occurs as a tandem repeat [=(IS21)2] on the broad host range plasmid R68.45. In (IS21)2, the two IS21 elements are separated by 3 bp termed junction sequence. Plasmids carrying (IS21)2 form cointegrates with other replicons at high frequencies. The two IS21 genes, istA and istB, were found to be necessary for cointegrate formation in vivo. Since the outer ends of (IS21)2 are dispensable for cointegrate formation, we favor a transposition model according to which a plasmid carrying (IS21)2 is cleaved at the junction sequence; the opened plasmid is then inserted into a target replicon. Here we show that Escherichia coli cell extracts, which contained over-produced IstA protein, nicked a supercoiled (IS21)2 plasmid precisely at the inner 3' termini of IS21; the resulting staggered cut generated 5' protrusions. The istA gene, but not the istB gene, was required for in vitro cleavage of an IS21-IS21 junction. Because of this cleavage and our previous findings (generation of 4 bp target duplications and loss of the junction sequence after cointegrate formation in vivo) we propose that plasmids with (IS21)2 produce cointegrates by a mechanism which involves joining of the inner 3' ends of IS21 to the 5' ends of the target.

Converting catabolic ornithine carbamoyltransferase to an anabolic enzyme

Pseudomonas aeruginosa has an anabolic and a catabolic ornithine carbamoyltransferase (OTCase). In vitro, these homologous enzymes catalyze the same reaction (ornithine + carbamoyl phosphate (CP) in equilibrium citrulline + Pi), yet in vivo they function unidirectionally owing to specific kinetic properties. The catabolic OTC-ase cannot promote the anabolic reaction (citrulline formation) in vivo because of a sigmoidal CP saturation curve and a high CP concentration for half-maximal velocity. The structural basis for this kinetic specialization was examined. The catabolic OTCase lost most of its homotropic cooperativity and gained anabolic activity when an amino acid residue near the CP binding site, Glu-106, was replaced by alanine or glycine. In the anabolic OTCase of Escherichia coli the glutamine residue corresponding to Glu-106 was exchanged for glutamate; however, in this case no CP cooperativity was acquired. Thus, in catabolic OTCase, sequence features in addition to Glu-106 are important for sigmoidal CP saturation, and such a sequence was identified in the C-terminal part. By an in vivo gene fusion technique the 9 C-terminal amino acids of catabolic OTCase were replaced by the homologous 8 amino acids from anabolic OTCase of E. coli; the hybrid enzyme had a markedly reduced homotropic cooperativity. This gene fusion method should be generally useful for directed enzyme evolution.

The arc operon for anaerobic arginine catabolism in Pseudomonas aeruginosa contains an additional gene, arcD, encoding a membrane protein

The arginine deiminase (ADI) pathway in Pseudomonas aeruginosa serves to generate ATP. The three enzymes involved, ADI, catabolic ornithine carbamoyltransferase and carbamate kinase, are induced by oxygen limitation and encoded by the contiguous arcABC genes. A 1.5-kb region upstream from arcABC was sequenced and found to contain an open reading frame, arcD, coding for a hydrophobic polypeptide of 52 kDa. The content and distribution of hydrophobic amino acids suggest that the arcD gene product may be a transmembrane protein. When arcD was fused to an Escherichia coli promoter, the ArcD protein was synthesized in E. coli maxicells and detected in the membrane fraction. In sodium dodecyl sulfate-polyacrylamide-gel electrophoresis the ArcD protein migrated like a 32-kDa protein; such anomalous electrophoretic mobility is known for other highly hydrophobic proteins. Mutations in arcD rendered the cells unable to utilize extracellular arginine as an energy source. Since anaerobic arginine consumption and ornithine release are coupled in P. aeruginosa, it is proposed that arcD specifies an arginine: ornithine antiporter or a part thereof. Insertions of IS21 or Tn1725 in arcD had a strong polar effect on the expression of the arcAB enzymes, indicating that the arc genes are organized as an arcDABC operon.

Comparison of proC and other housekeeping genes of Pseudomonas aeruginosa with their counterparts in Escherichia coli

In a comparative study of housekeeping genes of Pseudomonas aeruginosa and Escherichia coli, the nucleotide sequence of a proline biosynthetic gene, proC, of P. aeruginosa has been determined. The subunit molecular mass (approximately 29 kDa) and the N-terminal amino acid sequence of purified delta 1-pyrroline 5-carboxylate reductase, the proC gene product, were in agreement with the proC nucleotide sequence. A survey of pairs of isofunctional genes from P. aeruginosa and E. coli reveals that within each pair, translated genes (including proC) have diverged more strongly than have untranslated genes specifying ribosomal or transfer RNAs. The translated genes, but not the untranslated ones, have a G + C content that is typical of the respective genomic G + C contents.

Cyanide production by Pseudomonas fluorescens helps suppress black root rot of tobacco under gnotobiotic conditions

Pseudomonas fluorescens CHA0 suppresses black root rot of tobacco, a disease caused by the fungus Thielaviopsis basicola. Strain CHA0 excretes several metabolites with antifungal properties. The importance of one such metabolite, hydrogen cyanide, was tested in a gnotobiotic system containing an artificial, iron-rich soil. A cyanidenegative (hcn) mutant, CHA5, constructed by a gene replacement technique, protected the tobacco plant less effectively than did the wild-type CHA0. Complementation of strain CHA5 by the cloned wild-type hcn genes restored the strain's ability to suppress disease. An artificial transposon carrying the hcn genes of strain CHA0 (Tnhcn) was constructed and inserted into the genome of another P.fluorescens strain, P3, which naturally does not produce cyanide and gives poor plant protection. The P3::Tnhcn derivative synthesized cyanide and exhibited an improved ability to suppress disease. All bacterial strains colonized the roots similarly and did not influence significantly the survival of T.basicola in soil. We conclude that bacterial cyanide is an important but not the only factor involved in suppression of black root rot.

Genetic structure, function and regulation of the transposable element IS21

The IncP plasmid R68.45 and other plasmids carrying tandem repeats of the insertion sequence IS21 [= (IS21)2] produce replicon fusions via transposition at high frequencies in Escherichia coli and other gram-negative bacteria, whereas plasmids with a single IS21 copy, e.g. R68, give replicon fusions rarely. The 2131 bp nucleotide sequence of IS21 was determined; at the ends there were 11 bp inverted repeats with one mismatch. Two adjacent open reading frames, istA and istB, were located on one DNA strand of IS21. In E. coli maxicells, polypeptides of 46 kDa (the istA gene product) and 30 kDa (the istB gene product) were expressed by (IS21)2 plasmids, but not by IS21 plasmids. Genetic analysis of (IS21)2 plasmids indicates that the IS21-IS21 junctions form a promoter, which initiates transcription of the istAB operon in one of the two IS21 elements. A single IS21 element fused to an inducible external tac promoter expressed both proteins after induction, but did not promote effective replicon fusion, unless an IS21-IS21 junction (the preferred site for IS21 transposase action) was also present on the plasmid carrying the tac-IS21 construct. The sequences located between the IS21 elements in (IS21)2, 3 bp in R68.45 or 2 bp in pME28, were not recovered in the replicon fusion products. Homologous recombination between the directly oriented IS21 elements in the fusion products led to plasmids with a single IS21 insertion. Analysis of the latter showed that IS21 had a low, but not totally random specificity of insertion and created target duplications of 4 bp (occasionally 5 bp).(ABSTRACT TRUNCATED AT 250 WORDS)

ADP-ribosylation of actin causes increase in the rate of ATP exchange and inhibition of ATP hydrolysis

ADP-ribosylation of skeletal muscle actin by Clostridium perfringens iota toxin increased the rate of exchange of actin-bound [gamma-32P]ATP by unlabelled ATP about twofold. Increased exchange rates were observed with ATP and ATP[gamma S], much less with ADP but not with AMP or NAD. ADP-ribosylation of skeletal muscle actin reduced "basal" and Mg2+ (1 mM)-induced ATP hydrolysis by about 80%. Similar inhibition of ATP hydrolysis was observed with liver actin ADP-ribosylated by Clostridium botulinum C2 toxin. The data indicate that ADP-ribosylation of actin at Arg-177 largely affects the ATP-binding and ATPase activity.

Sequence analysis and expression of the arginine-deiminase and carbamate-kinase genes of Pseudomonas aeruginosa

The arcABC operon of Pseudomonas aeruginosa encodes arginine deiminase, catabolic ornithine carbamoyltransferase and carbamate kinase, respectively. We have determined the nucleotide sequences of the arcA and arcC genes. The arcA open reading frame specifies a polypeptide of 46.3 kDa. The same molecular mass was obtained for the subunit of purified arginine deiminase after electrophoresis under denaturing conditions. The N-terminal amino acid sequence of arginine deiminase was in agreement with the corresponding nucleotide sequence. The native arginine deiminase had an estimated molecular mass of 175-180 kDa, suggesting a tetrametric structure. The enzyme was activated by Mg2+ or Mn2+ and strongly inhibited by Zn2+. The apparent Km for L-arginine was 0.04 mM in the presence of Mg2+ and 0.47 mM without Mg2+. The arcC open reading frame codes for a 33-kDa protein, confirming the molecular mass previously reported for the subunit of carbamate kinase. The translation-initiation site of arcC was determined by deletion mapping. Two regions of dyad symmetry found between arcA and arcC might stabilize the putative arcABC transcript in the upstream (arcA) region; this might contribute to the high level of arcA expression as compared to the moderate level of arcC expression. Carbamate kinase had 37% sequence similarity (and 13.5% identity) with the C-terminal part of carbamoyl-phosphate synthetase (large subunit) from Escherichia coli. Arginine deiminase had no apparent similarity with argininosuccinate lyase. Thus, the arcA and arcC genes do not appear to be closely related to arginine biosynthetic genes, whereas it had previously been shown that the arcB gene has a high degree of identity with the arginine biosynthetic argF genes of P. aeruginosa and E. coli.

Complete pathologic maturation and regression of stage IVS neuroblastoma without treatment

Spontaneous maturation of Stage IVS neuroblastoma has been postulated as a mechanism for its favorable prognosis, but this has rarely been documented pathologically. We report on a patient with congenital Stage IVS neuroblastoma who had extensive subcutaneous and bone-marrow involvement. Serial photographs, biopsies, and vanillomandelic acid determinations documented the tumor's initial progression which was followed by spontaneous maturation and involution of the patient's disease over a 6-year period. No cytotoxic therapy was administered. Favorable biologic prognostic factors were documented, including tumor DNA and protein analyses for N-myc amplification or overexpression and analysis for serum neuron-specific enolase and ferritin. Implications for management and therapy of Stage IVS neuroblastoma are discussed with reference to this case and the recent literature.

N2-succinylornithine in ornithine catabolism of Pseudomonas aeruginosa

Most Pseudomonas aeruginosa PAO mutants which were unable to utilize L-arginine as the sole carbon and nitrogen source (aru mutants) under aerobic conditions were also affected in L-ornithine utilization. These aru mutants were impaired in one or several enzymes involved in the conversion of N2-succinylornithine to glutamate and succinate, indicating that the latter steps of the arginine succinyltransferase pathway can be used for ornithine catabolism. Addition of aminooxyacetate, an inhibitor of the N2-succinylornithine 5-aminotransferase, to resting cells of P. aeruginosa in ornithine medium led to the accumulation of N2-succinylornithine. In crude extracts of P. aeruginosa an ornithine succinyltransferase (L-ornithine:succinyl-CoA N2-succinyltransferase) activity could be detected. An aru mutant having reduced arginine succinyltransferase activity also had correspondingly low levels of ornithine succinyltransferase. Thus, in P. aeruginosa, these two activities might be due to the same enzyme, which initiates aerobic arginine and ornithine catabolism.

Integration of replication-defective R68.45-like plasmids into the Pseudomonas aeruginosa chromosome

R68.45 and other similar broad-host-range (IncP) plasmids carrying a tandem repeat of the 2.1 kb insertion element IS21 mobilize the chromosome of many different Gram-negative bacteria. To analyse the structure of R68.45-chromosome cointegrates, whose involvement in the mobilization process had been postulated previously, we selected for the stable integration of R68.45-like plasmids into the Pseudomonas aeruginosa chromosome. Two plasmids were chosen: pME28, a transfer-deficient, mobilizable RP1 derivative with an inactive replication control (trfA) gene, and pME487, an R68.45 derivative with a trfA(ts) mutation causing temperature-sensitive replication. Chromosomally integrated pME28 and pME487 were found to be flanked by single IS21 elements. This structure is in agreement with a 'cut-and-paste' mode of R68.45 transposition. pME28 and pME487 showed a low specificity of insertion but rarely (less than 0.1%) induced auxotrophic mutations. Hfr (high-frequency-of-recombination) donors of P. aeruginosa could be obtained by chromosomal integration of pME487 or pME28; in the latter case, the transfer functions lacking from pME28 had to be provided in trans on an autonomous plasmid. Hfr donors gave higher conjugational linkage and transferred longer stretches of the P. aeruginosa chromosome than did R68.45 donors. This suggests that the integration of R68.45 into the donor chromosome is short-lived in P. aeruginosa.

Anabolic ornithine carbamoyltransferase of Pseudomonas aeruginosa: nucleotide sequence and transcriptional control of the argF structural gene

In Pseudomonas aeruginosa PAO the anabolic ornithine carbamoyltransferase (OTCase, EC 2.1.3.3) is the product of the argF gene and the only arginine biosynthetic enzyme whose synthesis is repressible by arginine. We have determined the complete nucleotide sequence of the argF gene including its promoter-control region. The deduced amino acid sequence of the anabolic OTCase consists of 305 residues (Mr 33,924), and this was confirmed by the N-terminal amino acid sequence, the total amino acid composition, and the subunit Mr of the purified enzyme. The native anabolic OTCase (Mr 110,000 to 125,000) was found to be a trimer by cross-linking experiments. P. aeruginosa also has a catabolic OTCase (the arcB gene product), which catalyzes the reverse reaction of the anabolic conversion. At the nucleotide sequence level, the P. aeruginosa argF gene had 52.4% identity with the arcB gene. The Escherichia coli argF and argI genes, which code for anabolic OTCase isoenzymes, had 47.3 and 44.9% identity, respectively, with the P. aeruginosa argF sequence. This suggests that these four genes have evolved from a common ancestral gene. The arcB gene appears to be more closely related to the E. coli argF gene than to the P. aeruginosa argF gene. Two transcripts (mRNA-1, mRNA-2) of the P. aeruginosa argF gene were identified by S1 mapping. The transcription initiation site for mRNA-1 was preceded by sequences having partial homology with the E. coli -35 and -10 consensus promoter sequences. No sequence similar to consensus promoters of enteric bacteria was found upstream of the 5' end of mRNA-2. E. coli carrying a P. aeruginosa argF+ recombinant plasmid produced mRNA-1 with low efficiency but no (or very little) mRNA-2. Arginine repressed argF transcription in P. aeruginosa. In the argF promoter region no sequence homologous to the "arg box" (arginine operator module) of E. coli was found. The mechanism of arginine repression in P. aeruginosa thus appears to be different from that in E. coli.

The fourth arginine catabolic pathway of Pseudomonas aeruginosa

D-Arginine dehydrogenase activity was discovered in Pseudomonas aeruginosa. This enzyme was inducible by its substrate, D-arginine, as well as by its product, 2-ketoarginine, but not by L-arginine. The enzyme activity was measured in vitro, in the presence of artificial electron acceptore (phenazine methosulphate and iodonitrotetrazolium chloride). 2-ketoarginine was catabolized further to 4-guanidinobutyraldehyde, 4-guanidinobutyrate and 4-aminobutyrate. Two enzymes involved, 4-guanidinobutyraldehyde dehydrogenase and guanidinobutyrase, were inducible by 2-ketoarginine; the latter enzyme was also strongly induced by 4-guanidinobutyrate. An arginine racemase activity was detected by an invivo test. E-Arginine had the potential to be catabolized via the D-arginine dehydrogenase pathway and, after racemization, via the three L-arginine catabolic pathyways previously demonstrated in P. aeruginosa. In mutants blocked in the L-arginine succinyltransferase pathway, but no in the wild-type, L-arginine was channelled partially into the D-arginine dehydrogenase pathway. Mutations in the kauB locus abolished growth of P. aeruginosa on 2-ketoarginine, agmatine and putrescine, and led to loss of 4-guanidinobutyraldehyde dehydrogenase and 4-aminobutyaldehyde dehydrogenase activites. Thus, these two activites appear to be due to one enzyme in P. aeruginosa. The kauB locus was mapped on the chromosome between lysA and argB and was not linked to known genes involved in the three L-arginine catabolic pathways. The existence of four arginine catabolic pathways illustrates the metabolic versatility of P. aeruginosa.

Low- and intermediate-copy-number cloning vectors based on the Pseudomonas plasmid pVS1

The cloning vector pME290 (6.8 kb), which is derived from the Pseudomonas plasmid pVS1 and has about 7 copies, was mutagenized in vitro to provide derivatives with altered copy numbers. Thus, pME292 (about 1-3 copies) and pME294 (about 15-20 copies) were isolated. These vectors were used in the characterization of the P. aeruginosa argF gene encoding ornithine carbamoyltransferase.

Primary and quaternary structure of the catabolic ornithine carbamoyltransferase from Pseudomonas aeruginosa. Extensive sequence homology with the anabolic ornithine carbamoyltransferases of Escherichia coli

We have determined the complete nucleotide sequence of the arcB gene from Pseudomonas aeruginosa strain PAO and we have purified the arcB product, the catabolic ornithine carbamoyltransferase (EC 2.1.3.3), to apparent homogeneity from the same strain. The N-terminal amino acid sequence, the total amino acid composition and the subunit size of the purified enzyme were in agreement with nucleotide sequencing results, which predict a polypeptide of 336 amino acids (Mr 38,108). Crosslinking experiments suggest that the native enzyme (apparent Mr approx. 420,000) basically consists of a trimer aggregating to form nonamers or dodecamers. The arcB gene of P. aeruginosa had strong homology with the argF and argI genes which code for the anabolic ornithine carbamoyltransferase isoenzymes in Escherichia coli; 63% of the nucleotides and 57% of the amino acids were absolutely conserved in arcB and argF. This indicates a close evolutionary relationship between these genes although their products have different physiological functions in the cell. Under conditions of induction (energy depletion) the catabolic ornithine carbamoyltransferase represented greater than or equal to 10% of the total cellular protein. Like other highly expressed Pseudomonas genes, the arcB gene was found not to use seven codons which correspond to minor or weakly interacting tRNA species in E. coli.

Mode of replicon fusion mediated by the duplicated insertion sequence IS21 in Escherichia coli

The insertion sequence IS21 (2.1 kb) originating from the broad-host-range IncP plasmid R68 transposes infrequently; by contrast, the IS21 tandem repeat found on the derivative R68.45 is highly active in transpositional mobilization of other replicons in a variety of Gram-negative bacteria. The mobilized plasmids are joined to R68.45 by single IS21 copies in direct orientation. The formation of IS21 tandem duplications was observed in cointegrates between R68.45 and pBR325::IS21 and also in an RP1::IS21 plasmid derivative in which a segment located between two directly repeated copies of IS21 was deleted spontaneously. We speculate that IS21 tandem repeats can arise when the termini of two IS21 elements are specifically joined in a transposition or deletion event. A resistance gene flanked by two IS21 elements in direct orientation did not behave as a transposon. The omega fragment carrying transcription and translation stop signals was inserted into various sites of the IS21 tandem repeat; in this way it could be shown that the left IS21 element (which is next to the kanamycin resistance gene in R68.45) was 100 times more active in cointegrate formation than was the right-hand element. Cointegrates between the conjugative plasmid R751 and pBR325 derivatives carrying IS21 and IS21::omega in tandem contained a single IS21 at one replicon junction and a single IS21::omega at the other. In the IS21 duplications the inner IS21 ends were preferentially recognized (presumably by IS21 transposase), whereas the outer termini were not required for cointegrate formation. Based on these findings a conservative (simple) pathway of transposition is proposed for R68.45 and other plasmids with an IS21 tandem repeat.(ABSTRACT TRUNCATED AT 250 WORDS)

Deletions in the tetracycline resistance determinant reduce the thermosensitivity of a trfA(Ts) derivative of plasmid RP1 in Pseudomonas aeruginosa

A derivative of the broad-host-range plasmid RP1, pME301, was temperature-sensitive (Ts) at 43 degrees C for maintenance in Pseudomonas aeruginosa, P. mendocina, Klebsiella aerogenes and Escherichia coli. In E. coli, the Ts defect of pME301 could be complemented in trans by the cloned trfA gene, which is known to be essential for RP1 replication in E. coli and P. aeruginosa. Because pME301 expressed a Ts phenotype in P. mendocina and K. aerogenes, we assume that the trfA function is also vital in these organisms. When plasmid-encoded carbenicillin resistance (on transposon Tn801) was selected at non-permissive temperatures in P. aeruginosa strain PAO carrying pME301, we obtained either Tn801 insertions into the chromosome or pME301 derivatives having a deletion (or point mutation) in their tet genes, which determine resistance to tetracycline and are not transposable. From cloning experiments, we infer that the tet gene product(s) destabilize the pME301 replicon in P. aeruginosa at 40-43 degrees C.

The arcABC operon required for fermentative growth of Pseudomonas aeruginosa on arginine: Tn5-751-assisted cloning and localization of structural genes

Pseudomonas aeruginosa is able to utilize L-arginine as the energy source for growth under anaerobic, nitrate-free conditions. Mutations in the chromosomal arcABC gene cluster specifying the inducible arginine deiminase pathway enzymes abolish fermentative growth on arginine. From two different arc::Tn5-751 insertion mutants of P. aeruginosa recombinant plasmids have been derived which carry a resistance marker of transposon Tn5-751 plus flanking parts of the arc region. These recombinant plasmids served to reconstruct in vitro the functional arcABC cluster on a 5.6 kb fragment, which was inserted into the broad-host-range vector pKT240. In P. aeruginosa this 5.6 kb segment complemented arcABC mutations in trans and contained the control region necessary in cis for arc enzyme induction by oxygen limitation and arginine. The results of subcloning experiments and transcriptional lacZ fusions, the polarity of transposon insertions and the effect of external promoters led to the conclusion that the structural genes arcA (for arginine deiminase), arcB (for catabolic ornithine carbamoyltransferase) and arcC (for carbamate kinase) are contiguous and transcribed in the same direction. Thus, the arcABC cluster appears to have the characteristics of an operon. In Escherichia coli the cloned arcABC genes were expressed at low, non-inducible levels; strong vector promoters enhanced arc expression up to 100-fold. This indicates that transcriptional initiation at the arc promoter(s) is poor in E. coli.

Heterologous expression and regulation of the lysA genes of Pseudomonas aeruginosa and Escherichia coli

The Pseudomonas aeruginosa lysA gene encoding diaminopimelate decarboxylase (DAP-decarboxylase) was cloned into a broad host range vector. This gene complemented a lys mutation at the lys-12 locus of P. aeruginosa and a lysA defect in Escherichia coli. The P. aeruginosa DAP-decarboxylase was synthesized constitutively in P. aeruginosa as well as in E. coli, where the Pseudomonas lysA gene was poorly expressed. By contrast, the E. coli lysA gene was expressed well in P. aeruginosa and subject to lysine regulation when the E. coli LysR activator protein was provided. This indicates that the mechanism of transcriptional activation for the E. coli lysA gene is effective in the heterologous host.

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.

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.

IncP-1 R plasmids decrease the serum resistance and the virulence of Pseudomonas aeruginosa

Pseudomonas aeruginosa strain PAO1 was compared to PAO1 strains containing an IncP-1 R plasmid (RP1, R68, or R68.45) in an experimental mouse burn infection model. All R plasmids tested caused a 10- to 400-fold increase in mean lethal dose (LD50). The decrease in virulence produced by plasmids R68 and R68.45 was significantly greater than the decrease caused by the closely related plasmid RP1. All plasmids also led to an increased sensitivity of strain PAO1 to human serum bactericidal activity. Virulence and serum resistance of strain PAO1 were restored by curing of the entire plasmid R68.45 but not by deletions in the plasmid's transfer gene regions.

Altered control of glutamate dehydrogenases in ornithine utilization mutants of Pseudomonas aeruginosa

Two classes of ornithine-nonutilizing (oru) mutants of Pseudomonas aeruginosa PAO were investigated. Strains carrying the oru-310 mutation were entirely unable to grow on L-ornithine as the only carbon and nitrogen source and were affected in the assimilation of a variety of nitrogen sources (e.g., amino acids, nitrate). The oru-310 mutation caused changes in the regulation of the catabolic NAD-dependent glutamate dehydrogenase; this enzyme was no longer inducible by glutamate but instead could be induced by ammonia. The oru-310 locus was cotransducible with car-9 and tolA in the 10 min region of the chromosome. An oru-314 mutant was severely handicapped in ornithine medium but could grow when a good carbon source was added; the mutant also showed pleiotropic growth effects related to nitrogen metabolism. The oru-314 mutation affected the regulation of the anabolic NADP-dependent glutamate dehydrogenase, which was no longer repressed by glutamate but showed normal derepression in the presence of ammonia. The oru-314 locus was mapped by transduction near met-9011 at 55 min. Both oru mutants could grow on L-glutamate, L-proline, or L-ornithine amended with 2-oxoglutarate, albeit slowly. We speculate that insufficient 2-oxoglutarate concentrations might account, at least in part, for the Oru- phenotype of the mutants.

Cloning vectors derived from the Pseudomonas plasmid pVS1

The Pseudomonas plasmid pVS1, which has about seven copies, was reduced to a minimal replicon and used to construct stable gene-cloning vehicles. The host for all cloning experiments was P. aeruginosa strain PAO. Two nonmobilizable plasmids, pME260 and pME290, and one RP1-mobilizable plasmid, pME285, were constructed. The vectors pME260 (6.3 kb) and pME290 (6.8 kb) carry the Tn801 bla gene specifying carbenicillin (Cb) resistance, a good selective marker in Pseudomonas, and the Tn903 aph gene encoding kanamycin (Km) resistance, with useful restriction sites for insertional inactivation. The Mob+ vector pME285 (10.6 kb) carries the aph gene and the Tn501-derived merRTCA genes coding for mercuric ion resistance, another good selective marker in Pseudomonas. The hypothetical merD gene, which may follow the merA gene in Tn501 but is absent from pME285, appeared to be dispensable for mercuric ion resistance in P. aeruginosa. The Mob- vector pME290 could be introduced by transformation and maintained in strains of P. aeruginosa, P. fluorescens, P. putida, P. acidovorans, P. stutzeri, P. mendocina, P. cepacia, and P. syringae. The plasmid was compatible with IncP-1 and IncP-4 replicons.

Transposon insertion mutagenesis of Pseudomonas aeruginosa with a Tn5 derivative: application to physical mapping of the arc gene cluster

For insertional mutagenesis of Pseudomonas aeruginosa, a derivative of the kanamycin-resistance (KmR) transposon Tn5 was constructed (Tn5-751) that carried the trimethoprim-resistance (TpR) determinant from plasmid R751 as an additional marker. Double selection for KmR and TpR avoided the isolation of spontaneous aminoglycoside-resistant mutants which occur at high frequencies in P. aeruginosa. As a delivery system for the recombinant transposon, plasmid pME305, a derivative of the broad-host-range plasma RP1, proved effective; pME305 is temperature-sensitive at 43 degrees C for maintenance in Escherichia coli and P. aeruginosa and deleted for IS21 and the KmR and primase genes. In matings with an E. coli donor carrying pME9(= pME305::Tn5-751), transposon insertion mutants of P. aeruginosa PAO were recovered at approx. 5 X 10(-7)/donor at 43 degrees C. Among Tn5-751 insertional mutants 0.9% were auxotrophs. A thr::Tn5-751 mutation near the recA-like locus rec-102 is useful for the construction of recombination-deficient strains. Several arc::Tn5-751 mutants could be isolated that were defective in anaerobic utilization of arginine as an energy source. From three of these mutants the arc gene region was cloned into an E. coli vector plasmid. Since Tn5-751 has a single EcoRI site between the TpR and KmR genes, EcoRI-generated fragments carrying either resistance determinant plus adjacent chromosomal DNA could be selected separately in E. coli. Thus, a restriction map of the arc region was constructed and verified by hybridization experiments. The arc genes were tightly clustered, confirming earlier genetic evidence.

Lipemic diabetic retinopathy

A study group of eight patients with diabetic retinopathy and marked accumulation of hard exudates in the fundi is described. There was a significant increase in serum triglyceride levels (P less than 0.05) in the study group as compared to a control group of 23 consecutive patients with diabetic retinopathy. This exudative disorder is visually disabling and is associated with legal blindness in 50% of eyes. The authors believe that the term most appropriate to describe such a severe type of exudative response is lipemic diabetic retinopathy.

Pseudomonas aeruginosa mutants affected in anaerobic growth on arginine: evidence for a four-gene cluster encoding the arginine deiminase pathway

Pseudomonas aeruginosa PAO was able to grow in the absence of exogenous terminal electron acceptors, provided that the medium contained 30 to 40 mM L-arginine and 0.4% yeast extract. Under strictly anaerobic conditions (O2 at less than 1 ppm), growth could be measured as an increase in protein and proceeded in a non-exponential way; arginine was largely converted to ornithine but not entirely consumed at the end of growth. In the GasPak anaerobic jar (Becton Dickinson and Co.), the wild-type strain PAO1 grew on arginine-yeast extract medium in 3 to 5 days; mutants could be isolated that were unable to grow under these conditions. All mutants (except one) were defective in at least one of the three enzymes of the arginine deiminase pathway (arcA, arcB, and arcC mutants) or in a novel function that might be involved in anaerobic arginine uptake (arcD mutants). The mutations arcA (arginine deiminase), arcB (catabolic ornithine carbamoyltransferase), arcC (carbamate kinase), and arcD were highly cotransducible and mapped in the 17-min chromosome region. Some mutations in the arc cluster led to low, noninducible levels of all three arginine deiminase pathway enzymes and thus may affect control elements required for induction of the postulated arc operon. Two fluorescent pseudomonads (P. putida and P. fluorescens) and P. mendocina, as well as one PAO mutant, possessed an inducible arginine deiminase pathway and yet were unable to grow fermentatively on arginine. The ability to use arginine-derived ATP for growth may provide P. aeruginosa with a selective advantage when oxygen and nitrate are scarce.

Production of short pulses in semiconductor lasers by external laser excitation through chi((3))

It is shown that parametric mixing through chi((3)) of two injected laser lines can provide index modulation sufficient for the mode locking of the semiconductor laser. Numerical estimates indicate that picosecond pulses with 100-GHz repetition rates should be possible with a few watts of external laser power.

Genetic and molecular characterization of the Pseudomonas plasmid pVS1

A restriction map of the 30-kb nonconjugative Pseudomonas plasmid pVS1 was constructed. Derivatives of pVS1 obtained in vitro by successive deletions were used to localize on the physical map the determinant for resistance to mercuric ions (carried by transposon Tn501), the gene(s) encoding sulfonamide resistance, a 1.6-kb region affecting plasmid stability and establishment in P. fluorescens ATCC 13525, and a segment required for mobilization of pVS1 by plasmid RP1. The sulfonamide resistance determinant of pVS1 appeared to be closely related to that of transposon Tn21. A mini-pVS1 replicon, pME259, consisting of an essential 1.55-kb segment (designated rep and thought to carry the origin of replication) and a mercury resistance determinant was able to replicate P. aeruginosa PAO but selective pressure was needed for plasmid maintenance. The copy number of pVS1 derivatives was estimated to be 6-8 per chromosome equivalent. Plasmids possessing the essential rep segment plus the adjacent stability region could be established in strains of P. aeruginosa, P. putida, P. fluorescens, P. acidovorans, P. cepacia, P. mendocina, P. stutzeri, P. syringae, Agrobacterium tumefaciens, and Rhizobium leguminosarum.

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.

Arginine degradation in Pseudomonas aeruginosa mutants blocked in two arginine catabolic pathways

Pseudomonas aeruginosa mutants defective in agmatine utilization (agu) were isolated. The genes encoding agmatine deiminase (aguA) and N-carbamoylputrescine amidinohydrolase (aguB) were 98% cotransducible and mapped between gpu and ser-3 in the 30 min region of the chromosome. Constructed agu arc double mutants (blocked in the arginine decarboxylase and arginine deiminase pathways) used arginine efficiently as the sole carbon and nitrogen source. This suggests the existence of a further arginine catabolic pathway in P. aeruginosa. The mapping data of this study confirm that in P. aeruginosa the chromosomal genes with catabolic functions do not show supraoperonic clustering as found in P. putida.

Construction of recombination-deficient strains of Pseudomonas aeruginosa

The rec-102 mutation had pleiotropic effects in Pseudomonas aeruginosa: low recombinational proficiency in conjugation and transduction; high UV sensitivity; inability to induce pyocin R2 by mitomycin C; and increased susceptibility to mitomycin C and nalidixic acid. The rec-102 locus was mapped by R68.45-mediated conjugation in the 45 min region of the PAO chromosome, between argF and thr-9001. By selection for a marker in this region, rec-102 can be introduced into a P. aeruginosa strain of interest using an R68.45 rec-102 donor. The recombination-deficient strains constructed in this way were phenotypically similar to Escherichia coli recA mutants.

Spontaneous deletions of the chromosome-mobilizing plasmid R68.45 in Pseudomonas aeruginosa PAO

In Pseudomonas aeruginosa strain PAO the chromosome-mobilizing IncP-1 plasmid R68.45 was unstable whereas the parent plasmid R68 was stable. The instability of R68.45 was observed in rec+ and rec strains within about 100 generations after conjugal transfer of the plasmid and, to a lesser extent, in established R68.45 donor strains. Two phenotypically distinct classes of R68.45 derivatives were obtained: (i) CbR (carbenicillin-resistant), TcR (tetracycline-resistant), KmR (kanamycin-resistant), Tra+ (transfer proficient), Cma- (chromosome-mobilizing ability), lacking the duplicated IS21 copy typical of R68.45 and indistinguishable from R68 by restriction enzyme analysis; (ii) CbR TcR KmS Tra- Cma-, due to deletion of one IS21 copy, the adjacent KmR gene, and a variable part of the Tra-1 region including, in most cases, the origin of transfer (oriT). Both types of deletion derivatives were stable. R68.45 derivatives lacking the Tra-2 region were not recovered spontaneously, but could be constructed in vitro and were stable in strain PAO. Deletion formation of type ii as well as Cma did not depend on homologous recombination and can be ascribed to functions of the duplicated IS21. Chromosome mobilization does not appear to require obligatory transfer of the entire R68.45 plasmid. Four ClaI restriction sites were mapped on R68 extracted from P. aeruginosa. One of these sites was cryptic, presumably because of methylation, when the plasmid was prepared from Escherichia coli (dam+).

Resistance of Pseudomonas aeruginosa PAO to nalidixic acid and low levels of beta-lactam antibiotics: mapping of chromosomal genes

Resistance to high concentrations of nalidixic acid in Pseudomonas aeruginosa PAO was due to mutations in one locus designated nalA, which was mapped by transduction between hex-9001 and leu-10. The nalA mutants were cross-resistant to pipemidic acid, a nalidixic acid analog, at relatively low concentrations. Replicative DNA synthesis was resistant to both drugs in permeabilized cells of nalA mutants. A locus coding for low-level resistance to nalidixic acid, nalB, was cotransducible with pyrB, proC, and met-28. The nalB mutants were also resistant to low levels of pipemidic acid, novobiocin, and beta-lactam antibiotics (e.g., carbenicillin, azlocillin, and cefsulodin), but not to other drugs, such as gentamicin, rifampin, kanamycin, or tetracycline. In nalB mutants, DNA replication showed wild-type sensitivity to nalidixic acid, whereas carbenicillin-induced filamentation required higher drug levels than in the wild-type strain. Thus, nalB mutations appear to decrease cell permeability to some antibiotics. The sensitivity of replicative DNA synthesis to nalidixic acid and novobiocin was very similar in P. aeruginosa and Escherichia coli; by contrast, the concentrations of these drugs needed to inhibit growth of P. aeruginosa were higher than those reported for E. coli by one or two orders of magnitude.

Mapping of the arginine deiminase gene in Pseudomonas aeruginosa

A mutant of Pseudomonas aeruginosa PAO lacking arginine deiminase activity (arcA) was isolated by screening for a derivative of an arcB mutant (deficient in catabolic ornithine carbamoyltransferase) that did not excrete citrulline under conditions of limited aeration. The arcA mutation was highly cotransducible with arcB.

Isolation of an Hfr donor of Pseudomonas aeruginosa PAO by insertion of the plasmid RP1 into the tryptophan synthase gene

A derivative of the IncP-1 plasmid RP1, temperature-sensitive for maintenance, was inserted into the Pseudomonas aeruginosa chromosome by selection for a plasmid marker (carbenicillin resistance) at non-permissive temperature. In one strain, PAO 1000, the plasmid was stably integrated in the trpA, B gene cluster mapped at 27 min, as shown by the following evidence. (i) Trp+ transductants lost all plasmid markers. (ii) Cleared lysates of PAO 1000 showed no plasmid band typical of the autonomous RP1 in agarose gel electrophoresis. (iii) No transfer of carbenicillin resistance by PAO 1000 was detectable. (iv) PAO 1000 mobilised the chromosome from an origin at, or very near, the plasmid insertion site with high frequency (recovery of proximal markers greater than or equal to 10(-3) per donor). Matings on the plate with and without interruption of conjugation showed that chromosome transfer was unidirectional. (v) Recombinants from PAO 1000-mediated crosses did not inherit plasmid markers or the trpA, B mutation. A derivative of PAO 1000 was obtained which had lost the Hfr property and all plasmid markers except carbenicillin resistance. This strain (PAO 1001), when carrying the autonomous RP1 plasmid, was capable of unidirectional chromosome mobilisation like PAO 1000, but with 50-fold lower efficiency. We propose that integration of the temperature-sensitive RP1 plasmid in PAO 1000 occurred via transposition of Tn1, the element specifying carbenicillin resistance.

Regulation of enzyme synthesis in the arginine deiminase pathway of Pseudomonas aeruginosa

The three enzymes of the arginine deiminase pathway in Pseudomonas aeruginosa strain PAO were induced strongly (50- to 100-fold) by a shift from aerobic growth conditions to very low oxygen tension. Arginine in the culture medium was not essential for induction, but increased the maximum enzyme levels twofold. The induction of the three enzymes arginine deiminase (EC 3.5.3.6), catabolic ornithine carbamoyltransferase (EC 2.1.3.3), and carbamate kinase (EC 2.7.2.3) appeared to be coordinate. Catabolic ornithine carbamoyltransferase was studied in most detail. Nitrate and nitrite, which can replace oxygen as terminal electron acceptors in P. aeruginosa, partially prevented enzyme induction by low oxygen tension in the wild-type strain, but not in nar (nitrate reductase-negative) mutants. Glucose was found to exert catabolite repression of the deiminase pathway. Generally, conditions of stress, such as depletion of the carbon and energy source or the phosphate source, resulted in induced synthesis of catabolic ornithine carbamoyltransferase. The induction of the deiminase pathway is thought to mobilize intra- and extracellular reserves of arginine, which is used as a source of adenosine 5'-triphosphate in the absence of respiration.

Catabolism of L-arginine by Pseudomonas aeruginosa

Pseudomonas aeruginosa is known to break down arginine by the arginine deiminase pathway. An additional pathway has now been found whereby arginine is converted to putrescine with agmatine and N-carbamoylputrescine as intermediates. The following enzyme activities belonging to this pathway were detected in crude extracts: arginine decarboxylase (EC 4.1.1.19), which catalyses the release of CO2 from arginine to give agmatine; agmatine deiminase (EC 3.5.3.12), which degrades agmatine to N-carbamoylputrescine; and N-carbamoylputrescine amidinohydrolase (EC 3.5.3.-), which then removes the ureido group of carbamoylputrescine. In crude extracts, arginine decarboxylase activity was stimulated by pyridoxal phosphate, Mg2+ and by the products of the catabolic pathway, putrescine and spermidine. Growth of P. aeruginosa on arginine as the sole carbon and nitrogen source markedly increased the activity of arginine decarboxylase. Agmatine and N-carbamoylputrescine induced the synthesis of agmatine deiminase and N-carbamoylputrescine hydrolase. Addition of succinate or citrate to medium containing arginine or agmatine led to repression of the enzymes involved in the arginine decarboxylase pathway. Moreover, the repression of agmatine deiminase and N-carbamoylputrescine hydrolase was further increased when P. aeruginosa was grown in media with agmatine plus glutamine or agmatine plus succinate and ammonia. This suggests that the expression of the agmatine pathway may be regulated by carbon catabolite repression as well as nitrogen catabolite repression.