Chromosome mapping in Pseudomonas aeruginosa

Pseudomonas aeruginosa Strains from Both Clinical and Environmental Origins Readily Adopt a Stable Small-Colony-Variant Phenotype Resulting from Single Mutations in c-di-GMP Pathways

A subpopulation of small-colony variants (SCVs) is a frequently observed feature of Pseudomonas aeruginosa isolates obtained from colonized cystic fibrosis lungs. Since most SCVs have until now been isolated from clinical samples, it remains unclear how widespread the ability of P. aeruginosa strains to develop this phenotype is and what the genetic mechanism(s) behind the emergence of SCVs are according to the origin of the isolate. In the present work, we investigated the ability of 22 P. aeruginosa isolates from various environmental origins to spontaneously adopt an SCV-like smaller alternative morphotype distinguishable from that of the ancestral parent strain under laboratory culture conditions. We found that all the P. aeruginosa strains tested could adopt an SCV phenotype, regardless of their origin. Whole-genome sequencing of SCVs obtained from clinical and environmental sources revealed single mutations exclusively in two distinct c-di-GMP signaling pathways, the Wsp and YfiBNR pathways. We conclude that the ability to switch to an SCV phenotype is a conserved feature of P. aeruginosa and results from the acquisition of a stable genetic mutation, regardless of the origin of the strain. IMPORTANCE P. aeruginosa is an opportunistic pathogen that thrives in many environments. It poses a significant health concern, notably because this bacterium is the most prevalent pathogen found in the lungs of people with cystic fibrosis. In infected hosts, its persistence is considered related to the emergence of an alternative small-colony-variant (SCV) phenotype. By reporting the distribution of P. aeruginosa SCVs in various nonclinical environments and the involvement of c-di-GMP in SCV emergence from both clinical and environmental strains, this work contributes to understanding a conserved adaptation mechanism used by P. aeruginosa to adapt readily in all environments. Hindering this adaptation strategy could help control persistent infection by P. aeruginosa.

Location of genes for the utilization of acetamide, histidine and proline on the chromosome ofPseudomonas aeruginosa

Interrupted mating methods were used to map the positions on thechromosomeof genes for the utilization of acetamide, histidine and proline. An entry time of 22 min was found for aputmarker determining the utilization of proline. Two groups ofhutmutants were studied. Mutationhut-109 was located at 18 min and mutationhutU108, which results in a defect in urocanase activity, mapped at 28 min.hutUwas shown by transduction with bacteriophage F116 to be linked toser-3 but not tomet-28 andilv-202, giving a map order ofhutU-ser-3-ilv-202-met-28.

The amidase genes were assigned an entry time of 65–75 min. A method is described for examining late entry markers by interrupted mating.

Properties of R plasmids determining gentamicin resistance by acetylation in Pseudomonas aeruginosa

Two clinical isolates of Pseudomonas aeruginosa, one a pyocin type 5 strain from Atlanta, could transfer gentamicin resistance by conjugation. Donor and recipient strains inactivated gentamicin by acetylation. The R plasmids, pMG1 and pMG2, also determined resistance to sisomicin, another substrate of gentamicin acetyltransferase I, sulfonamides, and streptomycin, but not resistance to kanamycin, neomycin, tobramycin, butirosin, or BB-K 8. They were transmissible to many strains of P. aeruginosa, including a Rec(-) strain, but not to Escherichia coli or other enterobacteriaceae. These R plasmids were compatible with R plasmids transmissible to P. aeruginosa from E. coli, including members of C, N, P, and W incompatibility groups. From a strain carrying pMG1 and a compatible plasmid, pMG1 was transferred independently but transfer of the second plasmid often resulted in cotransfer of pMG1. In contrast, pMG1 and pMG2 were incompatible with pseudomonas R plasmids R931 and R3108, and with R931 they readily formed recombinant plasmids. The four plasmids in this incompatibility group determine additional biological properties, including resistance to inorganic and organic mercury compounds, to ultraviolet light, and to certain deoxyribonucleic acid phages. pMG1 and pMG2 also phenotypically inhibited pyocin production. Consequently such R plasmids alter the phage and pyocin types of their host strains.

Carbapenems as inhibitors of OXA-13, a novel, integron-encoded beta-lactamase in Pseudomonas aeruginosa

A clinical Pseudomonas aeruginosa strain, PAe391, was found to be resistant to a number of antibiotics including ticarcillin, piperacillin, cefsulodin and amikacin, and a disk diffusion assay showed evidence of pronounced synergy between imipenem and various beta-lactam antibiotics. Cloning and nucleotide sequence analysis revealed the dicistronic arrangement of an aac(6')-Ib variant and a novel blaOXA-type gene between the intI and qacE delta 1 genes typical of integrons, in PAe391, this integron was apparently chromosome-borne. The beta-lactamase, named OXA-13, displayed nine amino acid changes with respect to OXA-10:I in position 10 of OXA-10 to T (I10T), G20S, D55N, N73S, T107S, Y174F, E229G, S245N and E259A, OXA-13 (pIapp = 8.0) showed poor catalytic activity against penicillins as well as cephalosporins, but was efficient in hydrolysing some penicillinase-resistant beta-lactams, such as cefotaxime and aztreonam. It was efficiently inhibited by imipenem (KIapp = 11 nM), and formed a stable complex. While the KIapp value of meropenem was similar (16 nM), the corresponding complex was less stable.

Aminoglycoside 6'-N-acetyltransferase variants of the Ib type with altered substrate profile in clinical isolates of Enterobacter cloacae and Citrobacter freundii

Three clinical isolates, Enterobacter cloacae EC1562 and EC1563 and Citrobacter freundii CFr564, displayed an aminoglycoside resistance profile evocative of low-level 6'-N acetyltransferase type II [AAC(6')-II] production, which conferred reduced susceptibility to gentamicin but not to amikacin or isepamicin. Aminoglycoside acetyltransferase assays suggested the synthesis in the three strains of an AAC(6') which acetylated amikacin practically as well as it acetylated gentamicin in vitro. Both compounds, however, as well as isepamicin, retained good bactericidal activity against the three strains. The aac genes were borne by conjugative plasmids (pLMM562 and pLMM564 of ca. 100 kb and pLMM563 of ca. 20 kb). By PCR mapping and nucleotide sequence analysis, an aac(6')-Ib gene was found in each strain upstream of an ant(3")-I gene in a sulI-type integron. The size of the AAC(6')-Ib variant encoded by pLMM562 and pLMM564, AAC(6')-Ib7, was deduced to be 184 (or 177) amino acids long, whereas in pLMM563 a 21-bp duplication allowing the recruitment of a start codon resulted in the translation of a variant, AAC(6')-Ib8, of 196 amino acids, in agreement with size estimates obtained by Western blot analysis. Both variants had at position 119 a serine instead of the leucine typical for the AAC(6')-Ib variants conferring resistance to amikacin. By using methods that predict the secondary structure, these two amino acids appear to condition an alpha-helical structure within a putative aminoglycoside binding domain of AAC(6')-Ib variants.

Isolation, characterization, and DNA sequence analysis of an AAC(6')-II gene from Pseudomonas aeruginosa

The gene encoding a 6'-N-acetyltransferase, AAC(6')-II, was cloned from Pseudomonas aeruginosa plasmid pSCH884. This gene mediates resistance to gentamicin, tobramycin, and netilmicin but not amikacin or isepamicin. The DNA sequence of the gene and flanking regions was determined. The 5'- and 3'-flanking sequences showed near identity to sequences found abutting a variety of different genes encoding resistance determinants. It is likely that the current structure arose by the integration of the 572-base-pair sequence containing the AAC(6')-II gene into a Tn21-related sequence at the recombinational hot spot, AAAGTT. We have compared the sequence of the AAC(6')-II gene to genes of other 6'-N-acetyltransferases. An AAC(6')-Ib protein (encoded by the aacA4 gene; G. Tran Van Nhieu and E. Collatz, J. Bacteriol. 169:5708-5714, 1987) that results in resistance to amikacin but not gentamicin was found to share 82% sequence similarity with the AAC(6')-II protein. We speculate that these two genes arose from a common ancestor and that the processes of selection and dissemination have led to the observed differences in the spectrum of aminoglycoside resistance.

Tobramycin iontophoresis into corneas infected with drug-resistant Pseudomonas aeruginosa

Iontophoretic application of tobramycin was used to deliver drug to the cornea of rabbit eyes infected with a tobramycin-resistant strain of Pseudomonas aeruginosa (MIC = 31.25 micrograms/ml). Corneas infected with P. aeruginosa 27853/pMG6 were treated 22 hours after infection with tobramycin delivered by either iontophoresis, mock iontophoresis (eye cup without current), or application of fortified topical drops. Corneal iontophoresis of tobramycin at 25 mg/ml caused more than a three log reduction in bacteria; yielding a significantly lower number of bacteria compared to untreated controls and all other treatments (P less than or equal to 0.0001). Corneal iontophoresis of tobramycin at 10 mg/ml showed a one log reduction in the number of bacteria per cornea, yielding a significantly lower number of bacteria compared to untreated controls (P less than or equal to 0.0001), corneas treated with nine topical applications of 1.36% tobramycin drops (P less than or equal to 0.0001), and corneas treated with mock iontophoresis (P less than or equal to 0.02). These results suggest that iontophoresis is a powerful ocular delivery system for tobramycin and may be suitable for use with other chemotherapeutic agents.

Cloning of genes from mucoid Pseudomonas aeruginosa which control spontaneous conversion to the alginate production phenotype

Strains of Pseudomonas aeruginosa causing chronic pulmonary infections in patients with cystic fibrosis are known to convert to a mucoid form in vivo characterized by the production of the exopolysaccharide alginate. The alginate production trait is not stable, and mucoid strains frequently convert back to the nonmucoid form in vitro. The DNA involved in these spontaneous alginate conversions, referred to as algS, was shown here to map near hisI and pru markers on the chromosome of strain FRD, an isolate from a cystic fibrosis patient. Although cloning algS+ by trans-complementation was not possible, a clone (pJF5) was isolated that caused algS mutants to convert to the Alg+ phenotype at detectable frequencies (approximately 0.1%) in vitro. Gene replacement with transposon-marked pJF5 followed by mapping studies showed that pJF5 contained DNA transducibly close to algS in the chromosome. Another clone was identified called pJF15 which did contain algS+ from mucoid P. aeruginosa. The plasmid-borne algS+ locus could not complement spontaneous algS mutations in trans, but its cis-acting activity was readily observed after gene replacement with the algS mutant chromosome by using an adjacent transposon as the selectable marker. pJF15 also contained a trans-active gene called algT+ in addition to the cis-active gene algS+. The algT gene was localized on pJF15 by using deletion mapping and transposon mutagenesis. By using gene replacement, algT::Tn501 mutants of P. aeruginosa were constructed which were shown to be complemented in trans by pJF15. Both algS and algT were located on a DNA fragment approximately 3 kilobases in size. The algS gene may be a genetic switch which regulates the process of alginate conversion.

Transcriptional and translational analyses of recA mutant alleles in Pseudomonas aeruginosa

Recombinant plasmids containing the recA gene from Pseudomonas aeruginosa were used in complementation, transcriptional, and translational studies to examine the nature of rec-102 and rec-2, mutations which confer a recA-like mutant phenotype on P. aeruginosa PAO strains. For comparison, recA7::Tn501 mutants of strain PAO were constructed by gene replacement. The rec-2 and rec-102 alleles were shown to be recA alleles; plasmids containing the recA gene complemented the three rec mutant strains for defects associated with recA mutation. Northern blot analyses indicated that the recA gene in P. aeruginosa was transcribed as two distinct mRNAs of approximately 1.2 and 1.4 kilobases (kb). A plasmid encoding both transcripts of recA complemented all defects associated with the three recA mutations rec-2, rec-102, and recA7. However, a 2.4-kb subclone (pJH13) encoding only the smaller transcript of the recA gene was expressed differently in the three recA allele backgrounds and served as a tool to distinguish the nature of the rec-2 and rec-102 mutations in recA. A minicell analysis showed that a plasmid expressing both of the recA gene transcripts or one that expressed only the smaller transcript both produced the same 42-kilodalton recA protein. A chloramphenicol acetyltransferase gene fusion in the 3' end of the recA transcript showed that the recA gene of P. aeruginosa was induced following treatment with a DNA-damaging agent (methyl methanesulfonate). The recA7 mutant constructed here showed no recA-related transcript or protein under inducing conditions, and pJH13 in this host produced only low levels of the smaller recA transcript and low levels of recA protein. The rec-2 mutant produced a detectable transcript but no recA protein following induction. The presence of low levels of activated recA protein encoded by pJH13 in the rec-2 mutant resulted in wild-type transcriptional levels of chromosomally encoded recA, but no recA protein was detectable. Thus, the rec-2 allele of recA was normal with respect to induction of mRNA, but these transcripts were defective in either translation or synthesis of a stable protein. The rec-102 mutant also produced a detectable transcript and no recA protein following induction, but having pJH13 in the cell to produce low levels of activated recA protein resulted in overproduction of chromosomally encoded recA transcripts and active recA protein. Thus, the recA defect in the rec-102 mutant is apparently in the interaction between recA and a lexA-like repressor.

Specialized transduction of Pseudomonas aeruginosa PAO by bacteriophage D3

D3, a temperate bacteriophage of Pseudomonas aeruginosa PAO, was found to specifically transduce the alleles met-49 and met-117. Induction of established lysogens with UV light was necessary for the production of transducing lysates. Transduced cells were immune to superinfection by phage D3 and could give rise to high-frequency transducing lysates. Cotransduction of these two alleles could not be demonstrated. met-117 was mapped to 26 min on the PAO genetic map. Complementation studies using the generalized transducing phage F116L indicated that met-49 is an allele of met-9011 which maps at 55 min. The integrated D3 prophage was shown to be coinherited with met-117 and with met-49.

High frequency FP2 donor of Pseudomonas aeruginosa PAO

After NG mutagenesis an FP2 donor was isolated which exhibited an enhanced conjugational capacity for chromosomal genes. The recombination frequency was increased by two orders of magnitude as compared to the parental strain. In plate matings recombinants arose at a frequency up to 5 X 10(-1) per donor cell. Late markers also recombined efficiently. An Hfr state of the donor strain was supported by (i) the high recombination frequency, (ii) the incompatibility reaction with plasmid pRO271 (= FP2::Tn401) and (iii) the clearcut transfer kinetics in interrupted matings, even for a late marker.

Mapping of cysteine genes on the chromosome of Pseudomonas aeruginosa PAO

Three loci coding for different steps in the pathway of cysteine biosynthesis have been mapped by R68.45-mediated coconjugation analysis. The cysteine auxotrophic mutants could be subdivided into sulfite and sulfide-requiring mutants. Sulfide-requiring mutants (cysIV group) were localized at a single position between pyrF and pur-67, while sulfite-requiring mutants (cysI and cysII) mapped at two different regions. The cysI group was also localized between pyrF and pur-67, although more distal to pyrF than the cysIV group. This group included the cys-54 marker, which has been mapped previously. The second group of sulfite-requiring mutants, designated as cysII, was cotransducible with hisI and localized at the end of the PAO chromosomal map. This location was also confirmed for the marker cys-59. The marker cys-59 (which was cotransducible with hisI) was cotransferred by R68.45-mediated conjugations with both the late marker pur-67 and the early marker ilv-226. As the late marker hisI was positioned at about 60-65 min (Herrmann and Günther, in press) the length of the PAO chromosome was estimated to be about 70 min.

Tn501 insertion mutagenesis in Pseudomonas aeruginosa PAO

Transposon insertion mutagenesis of the Pseudomonas aeruginosa PAO chromosome with Tn1 and Tn501 was carried out using a mutant plasmid of R68::Tn501 temperature-sensitive for replication and maintenance. This method consists of three steps. Firstly, the temperature-independent, drug-resistant clones were selected from the strain carrying this plasmid. In the temperature-independent clones, the plasmid was integrated into the chromosome by Tn1- or Tn501-mediated cointegrate formation. Secondly, such clones were cultivated at a permissive temperature to provoke the excision of the integrated plasmid from the chromosome. Excision occurred by the reciprocal recombination between the two copies of Tn1 or Tn501 flanking the integrated plasmid, leaving one Tn1 or Tn501 insertion on the chromosome. Thirdly, the excised plasmid was cured by cultivating these isolates at a non-permissive temperature without selection for the drug resistance. Using this method, we isolated 1 Tn1-induced and 43 Tn501-induced auxotrophic mutations in this organism. Genetic mapping allowed us to identify two new genes, pur-8001 and met-8003. The Tn501-induced auxotrophic mutations were distributed non-randomly among auxotrophic genes, and the reversion of the mutations by precise excision of the Tn501 insertion occurred very rarely.

Genetic mapping and characterization of Pseudomonas aeruginosa mutants defective in the formation of extracellular proteins

We isolated 15 mutants of Pseudomonas aeruginosa PAO which were defective in the formation of certain extracellular proteins, such as elastase, staphylolytic enzyme, and lipase ( Xcp mutants). The mutations were mapped on the chromosome by conjugation and transduction. The locations were xcp -1 near 0', with the gene order cys-59- xcp -1- proB , and loci xcp -2, xcp -3, and xcp -31 at 35', with the gene order trpC , D- xcp -3/ xcp -31- xcp -2- argC . Loci xcp -4 and xcp -41 through xcp -44 were cotransducible with proA at 40'; loci xcp -5, xcp -51, xcp -52, and xcp53 were located at 55', with the gene order leu-10- trpF -met-9010- xcp -53- xcp -5/ xcp -51/ xcp+ ++-52, and xcp -6 was located at 65' to 70', between catA and mtu-9002. Nine mutations ( xcp -2, xcp -3, xcp -31, xcp -4, and xcp -41 through xcp -45) caused decreased production of extracellular enzymes. Six strains with mutations xcp -1, xcp -5, xcp -51, xcp -52, xcp -53, and xcp -6 produced cell-bound exoproteins and had defective release mechanisms. The regulation of production of alkaline phosphatase and phospholipase C is different from other exoproteins , such as elastase, but they all seem to share a common release mechanism. Alkaline protease had separate mechanisms for regulation and release, since this protease was found in culture supernatants of all but one of the mutants, and none of the strains had cell-bound enzyme.

Characterization of a TOL-like plasmid from Alcaligenes eutrophus that controls expression of a chromosomally encoded p-cresol pathway

Alcaligenes eutrophus wild-type strain 345 metabolizes m- and p-toluate via a catechol meta-cleavage pathway. DNA analysis, curing studies, and transfer of this phenotype by conjugation and transformation showed that the degradative genes are encoded on a self-transmissible 85-kilobase plasmid, pRA1000. HindIII and XhoI restriction endonuclease analysis of pRA1000 showed it to be similar to the archetypal TOL plasmid, pWWO, differing in the case of HindIII only by the absence of fragments B and D present in pWWO. In strain 345, the presence of pRA1000 prevented the expression of chromosomally encoded enzymes required for the degradation of p-cresol, whereas these enzymes were expressed in strains cured of pRA1000. On the basis of studies with an R68.45-pRA1000 cointegrate plasmid, pRA1001, we conclude that the gene(s) responsible for the effect of p-cresol degradation resides within or near the m- and p-toluate degradative region on pRA1000.

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.

Identification of Pseudomonas plasmids able to suppress the lysogeny-establishment-deficiency (Les-) phenotype

A suppressor of the mutations which inhibit the establishment of lysogeny in Pseudomonas aeruginosa has been found to be encoded by P. aeruginosa plasmids of four separate incompatibility groups. The wide distribution of this phenotype (designated Sly for suppressor of lysogeny establishment deficiency) indicates that these plasmids are able to enhance or replace host functions involved in the stable establishment of extrachromosomal DNA.

Properties of IncP-2 plasmids of Pseudomonas spp

Thirty IncP-2 R plasmids from isolates of Pseudomonas spp. of diverse geographical origins were examined for the production of resistance properties. All the plasmids determined resistance to tellurite and all inhibited the propagation of certain DNA phages, although several patterns of phage inhibition were detected. Of the 30 plasmids, 29 determined resistance to streptomycin, 28 determined resistance to mercuric ion, and 24 determined resistance to sulfonamide. Resistance to other antibiotics, to compounds of arsenic, boron, or chromium, and to UV irradiation was less common. The degradative plasmid CAM also belonged to this group. When CAM was introduced into recipients carrying an IncP-2 R plasmid, recombinant plasmids were often formed in which antibiotic resistance and the ability to grow on camphor were transferred together to further recipients or were lost together in a strain in which IncP-2 plasmids were unstable. Such hybrid plasmid formation was rec dependent. CAM and other IncP-2 plasmids that determine UV light resistance demonstrated UV-enhanced, nonpolarized transfer of the Pseudomonas aeruginosa chromosome. By agarose gel electrophoresis, all IncP-2 R plasmids and CAM were ca. 300 X 10(6) in molecular weight.

Amikacin resistance mediated by multiresistance transposon Tn2424

Tn2424, a multiresistance transposon 25 kilobases long, was isolated from IncFII plasmid NR79. Tn2424 transposed resistance to sulfonamides, streptomycin and spectinomycin, mercuric chloride, chloramphenicol, and amikacin with a frequency of 6 X 10(-5). Resistance to amikacin was mediated by a 6'-N-acetyltransferase, which conferred higher levels of resistance in Pseudomonas aeruginosa than in Escherichia coli. A restriction analysis and cloning experiments resulted in a physical and functional map of Tn2424. Comparison by a heteroduplex technique revealed that Tn2424 includes the total sequence of Tn21 and two additional DNA fragments that are 1.8 and 4 kilobases long.

Amikacin, gentamicin and tobramycin resistant Pseudomonas aeruginosa in a leukaemic ward. Epidemiology and genetic studies

Four patients in a leukaemic ward were infected with multi-resistant Pseudomonas aeruginosa. Similar organisms were found in the environment and it appeared that lapses in aseptic routine contributed to the outbreak. Serological, bacteriophage and pyocin-typing revealed that a fifth patient was infected with a distinct strain, but agarose gel electrophoresis indicated that all patient and environmental strains carried the same plasmid. The plasmid had a molecular weight of 47 (s.d. +/- 2) X 10(6) dal and was transfer deficient. It conferred resistance to carbenicillin, gentamicin, kanamycin, streptomycin, sulphonamide, tetracycline and tobramycin and determined an aminoglycoside adenylyltransferase active against amikacin in-vitro and not in-vivo. Spread of this non-transferable plasmid to a different Ps. aeruginosa strain and dissemination of multi-resistant organisms led to serious infections.

Cloning the gentamicin resistance gene from a Pseudomonas aeruginosa plasmid in Escherichia coli enhances detection of aminoglycoside modification

Cloning the gene for gentamicin resistance from Pseudomonas aeruginosa plasmid pMG35 on the high-copy-number Escherichia coli cloning vehicle pMK20 allowed detection of 6'-N-acetyltransferase activity that was not readily detected when the parent plasmid was present either in P. aeruginosa or E. coli.

A chromosomally located transposon in Pseudomonas aeruginosa

A new transposon, Tn2521, coding for carbenicillin, streptomycin, spectinomycin, and sulfanilamide resistance, has been identified in Pseudomonas aeruginosa. The transposon occurs naturally in the chromosome of clinical strains of P. aeruginosa isolated in geographically separated hospitals. This has been demonstrated by its transductional linkage to the pur-136 marker and also by Southern hybridization. Tn2521 is 6.8 kilobases, can transpose from the chromosome to both IncP-1 and IncP-2 plasmid genomes, and has a pattern of restriction endonuclease sites unlike that of any previously described transposon. The carbenicillin resistance carried by Tn2521 is due to the PSE-4 type of beta-lactamase.

Isolation and characterization of a Pseudomonas aeruginosa PAO mutant defective in the structural gene for the LIVAT-binding protein

A mutant of Pseudomonas aeruginosa PAO which has a defect in the structural gene for a binding protein for leucine, isoleucine, valine, alanine, and threonine (LIVAT-binding protein) was isolated and characterized. DL-4-azaleucine was taken up via the high-affinity branched-chain amino acid transport system (LIV-I), but not via the low affinity system (LIV-II), and then inhibited the growth of P. aeruginosa cells. This finding enabled us to select mutants defective in the LIV-I transport system alone. Among such mutants, strain PAO3530 was found to produce an altered LIVAT-binding protein. The shock fluid of this strain contained a normal level of the protein which corresponded to the wild-type LIVAT-binding protein as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by an immunological test. However, the shock fluid showed almost no binding activity for branched-chain amino acids, suggesting that strain PAO3530 has a defect in the structural gene for the LIVAT-binding protein. The mutation locus (bra-310) was mapped in a region between cnu-9001 and oru-325 on the chromosome of P. aeruginosa PAO by conjugation mediated by plasmid FP5 or R68.45.

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.

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.

Isolation and characterization of Pseudomonas aeruginosa R' plasmids constructed by interspecific mating

Plasmid R68.45 was used to construct R' plasmids carrying a maximum of 4 to 5 map minutes of the Pseudomonas aeruginosa PAO chromosome by interspecific mating, using P. putida PPN as the recipient. These R' plasmids were used to determine the map location of the amiE locus and to identify tentatively a number of P. putida auxotrophic mutations. Some of these R' plasmids could not be maintained in recombination-deficient P. aeruginosa strains.

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.

Mobilization of the non-conjugative IncQ plasmid RSF1010

The broad host-range non-conjugative IncQ plasmid RSF1010 was mobilised with 100% efficiency in membrane filter matings, both inE. coliK12 andP. aeruginosaPAO, by broad host-range conjugative IncP plasmids. No homology between RSF1010 and an IncP plasmid could be detected. InE. coli, IncIα and IncX plasmids, but not IncF, IncN or IncW plasmids, were also relatively efficient at mobilising RSF1010, while inP. aeruginosa, R91–5 (IncP-10) was highly efficient, but pMG5 (IncP-2) and FP2 (IncP-8) were very inefficient. IncP plasmids also mobilised several plasmids derived from RSF1010 for use as in vectors inin vitrorecombination experiments very efficiently, and pSC101 quite efficiently: this reduces the level of biological containment possible with these plasmids.

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.

Relationship between R and FP plasmids in Pseudomonas aeruginosa

The plasmid FP110 possessing chromosome mobilizing ability for Pseudomonas aeruginosa but carrying no determinants for antibiotic resistance, is found to be related by incompatibility, entry exclusion, and other criteria to the independently isolated R plasmids R18-1 and R56Be which carry resistance determinants for carbenicillin. The frequency of FP plasmid appearance in clinical isolates of P. aeruginosa suggests the possibility that they may be a source of R plasmids in this bacterium.

[Investigations on the aminoglycoside inactivating enzyme AAC-(6') IV (author's transl)]

In Serratia marcescens and Pseudomonas aeruginosa from clinical specimen acetyltransferase AAC-(6') IV leads to varying phaenotypically expressed resistance to aminoglycoside antibiotics. The substrate profile and the rate of inactivation of the enzymes investigated are almost identical with each other and with the enzyme of P. aeruginosa GN 315. The enzymes cannot be associated with R factors by the standard methods for conjugation, transformation, density gradient centrifugation and agarose gel electrophoresis.

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

Genetic mapping of the genes (puu) that encode the enzymes catalysing degradation of purines in Pseudomonas aeruginosa strain PAO has been carried out. Mutants that are deficient in adenine deaminase (puuA), guanine deaminase (puuB), xanthine dehydrogenase (puuC), uricase (puuD), allantoinase (puuE), and/or allantoicase (puuF) were isolated and used for the genetic study. Conjugation by FP5 factor and generalized transduction by phage G101 gave the following map locations of these six genes on the chromosome: hisI--puuB--hisII; trpA,B--puuA--ilv202; met9011--catA1--tyu--nar9011--(puuC, puuD, puuE)--puuF. A close linkage among the puuC, puuD and puuE was demonstrated by the transduction.

Linkage map of Pseudomonas aeruginosa PAT

The locations of new markers relative to markers previously mapped on the chromosome of Pseudomonas aeruginosa strain PAT were defined by generalized transduction with phage F116L and F1083. Although the marker orders of the various marker groups were deduced mainly from the results of two-factor crosses, the locations of a number of markers were confirmed by three-factor crosses. A linkage map of the chromosome of P. aeruginosa PAT was constructed which shows the relative locations of 50 genes. From the available data, the linkage maps of P. aeruginosa strains PAO and PAT appear to be similar.

Characterization of Pseudomonas aeruginosa mutants deficient in the establishment of lysogeny

Mutants of Pseudomonas aeruginosa with impaired ability to establish a lysogenic relationship with temperate bacteriophage (Les-) have been isolated. These les mutations map to two areas of the P. aeruginosa chromosomal map as determined by conjugational and transductional analyses. Two phenotypic classes of Les- mutants were identified. One class of mutations has pleiotropic effects on DNA metabolism. These mutants are unable to recombine genetic material acquired as a result of either conjugation or transduction (Rec-). In addition, the ability of these Les- Rec- mutants to repair UV-induced damage to bacteriophage is reduced (host-cell reactivation deficient, Hcr-). Mutants of the second class are Les-, Rec+, and Hcr+.

Isolation of TOL and RP4 recombinants by integrative suppression

We obtained genetic and molecular evidence of non-thermosensitive recombinants of RP4 (Kmr Tcr Cbr/Apr) and the thermosensitive TOL plasmid. As first isolated in Pseudomonas aeruginosa PAO, the recombinant plasmid pTN1 specified noninducible synthesis of TOL enzymes and was transmissible to Escherichia coli on selection for the transfer of kanamycin resistance. The phenotypic expression of TOL genes of pTN1 in E. coli was low and also noninducible. A spontaneous segregant, pTN2, appearing from pTN1, conferred inducible synthesis of TOL enzymes. These plasmids carry all of the TOL determinants as evidenced by the ability of Pseudomonas putida carrying recombinant plasmids to grow on toluene, xylene, and m-toluate. In E. coli the expression of TOL genes with normal regulation (pTN2) appears to be extremely low without induction, and the induced expression is comparable to that with defective regulation (pTN1). The measurement of the molecular weight of pTN2 by electron microscopy gave a value of about 74 X 10(6).

TOL plasmid in Pseudomonas aeruginosa PAO: thermosensitivity of self-maintenance and inhibition of host cell growth

The TOL plasmid originally isolated in Pseudomonas putida (arvilla) mt-2 was transmissible to strains of the fluorescens group of Pseudomonas, i.e., P. putida, P. fluorescens, and P. aeruginosa, except for a strain of P. aeruginosa, strain PAO. The same strain, however, could accept the plasmid when its restriction and modification abilities were lost by mutations or by growing at high temperature. In addition, the transmissibility of the TOL plasmid from strain PAO to P. putida was low when the plasmid was modified by the donor. By using P. aeruginosa PAO carrying the TOL plasmid, the stability and genetic expression of the plasmid as well as its effect on the host cell growth were examined. Thus the self-maintenance of the plasmid was found to be thermosensitive. Furthermore, the TOL plasmid inhibited the growth of strain PAO at high temperature, accompanied by the formation of some filamentous cells. These thermosensitive properties of the TOL plasmid were host dependent and not exhibited in another strain of P. aeruginosa.

Chromosome mobilization by the R plasmid R68.45: a tool in Pseudomonas genetics

The conjugative plasmid R68.45 mobilizes the chromosome of Pseudomonas aeruginosa strain PAO from multiple sites located in different chromosome regions. In interrupted matings on the plate, selection for any single marker tested resulted in entry times of 3-5 min. When selection was imposed for two markers linked in R68.45-mediated conjugation, double recombinants appeared after a delay which corresponded approximately to the map distance between the two markers as measured by the sex factor FP2. Thus, R68.45 and FP2 appear to promote chromosome transfer at similar rates, but R68.45, unlike FP2, seems to give non-polarized transfer. R68.45 may be used to estimate map distances between linked markers located in those chromosome regions where other sex factors do not produce enough recombinants to permit accurate measurement of entry times. In R68.45 matings on the plate, most recombinants inherited short donor chromosome fragments (usually less than 10 min long) and lost the R plasmid during purification. Used like a "large" generalized transducing phage, R68.45 has proved valuable in construction of PAO strains with desired genotypes.

The genetic organization of arginine biosynthesis in Pseudomonas aeruginosa

Six loci coding for arginine biosynthetic enzymes in Pseudomonas aeruginosa strain PAO were identified by enzyme assay: argA (N-acetylglutamate synthase), argB (N-acetylglutamate 5-phosphotransferase), argC (N-acetylglutamate 5-semialdehyde dehydrogenase), argF (anabolic ornithine carbamoyl-transferase), argG (argininosuccinate synthetase), and argH (argininosuccinase). One-step mutants which had a requirement for arginine and uracil were defective in carbamoylphosphate synthase, specified by a locus designated car. To map these mutations we used the sex factor FP2 in an improved interrupted mating technique as well as the generalized transducing phages F116L and G101. We confirmed earlier studies, and found no clustering of arg and car loci. However, argA, argH, and argB were mapped on a short chromosome segment (approx. 3 min long), and argF and argG were cotransducible, but not contiguous. N-Acetylglutamate synthase, the enzyme which replenishes the cycle of acetylated intermediates in ornithine synthesis of Pseudomonas, appears to be essential for arginine synthesis since argA mutants showed no growth on unsupplemented minimal medium.

Characterization of Pseudomonas aeruginosa derepressed R-plasmids

A genetic study of conjugal transmissibility of two R-plasmids was undertaken in Pseudomonas aeruginosa. Conjugally derepressed mutants of the R-plasmids were isolated, and examination of 11 independent mutants revealed that 10 were recessive to the wild-type transfer repressor, whereas 1 mutant was cis dominant. Cross-repression was observed between the two R-plasmids, suggesting that they have functionally equivalent systems for regulating the expression of tra loci. The derepressed R-plasmid mutants exhibited several characteristics, in addition to derepressed transfer, that were not expressed by the parental plasmids. These included sensitivity to certain donor-specific phages, inhibition of multiplication of a transducing phage, and, in the one case examined, a high degree of entry exclusion. The coexpression of these different functions suggests that their respective genetic loci are controlled by the same regulatory system as that of tra, or else that they are part of the tra complex.

R factor variants with enhanced sex factor activity in Pseudomonas aeruginosa

The R factor R68 readily promotes chromosome transfer in Pseudomonas aeruginosa strain PAT, but shows little such sex factor activity in strain PAO. A variant of this plasmid, R68.45, has been isolated which produces recombinants in PAO plate matings at frequencies of 10(-3)--10(-5) per donor cell for markers in the 0-60 min region of the chromosome. Little or nor chromosome transfer was shown in liquid media. The kinetics of chromosome transfer were studied by interrupting matings on solid media with nalidixic acid. Five chromosomal markers, mapping in widely spaced regions of the chromosome all entered 3-5 min after initiation of mating. These results, combined with linkage studies, indicated that R68.45, unlike the Pseudomonas sex factors FP2 and FP39, promotes chromosome transfer from a range of origin sites and can thus be used for mapping the region of the P. aeruginosa chromosome later than 40 min. R68.45 and other similar variants were isolated from rare chromosomal recombinants appearing in crosses between PAO(R68) donors and PAO recipients in which selection for ARGB+ was made. Selection for other chromosomal markers did not result in such variants suggesting that plasmides of the R68.45 type arise by recombination of genetic material between the R68 plasmid and certain regions of the bacterial chromosome.

Chromosomal location of prophage J51 in Pseudomonas aeruginosa strain PAO

The UV-inducible prophage J51 has been mapped late on the chromosome ofP. aeruginosastrain PAO, relative to the entry point of the sex factor FP2. This was determined following the analysis of the segregation of unselected markers in conjugational crosses between appropriately marked donor and recipient strains. A more precise location of about 50 min was obtained from the kinetics of increase in infectious centres due to zygotic induction during interrupted mating experiments.

Size of the chromosome of Pseudomonas aeruginosa PAO

Electron microscope examination and velocity sedimentation analysis of the deoxyribonucleic acid released from Pseudomonas aeruginosa spheroplasts indicate that this organism carries the bulk of its genetic determinants in a single duplex deoxyribonucleic acid molecule having a molecular mass of 2.1 x 10(9) daltons.

Location of prophage H90 on the chromosome of Pseudomonas aeruginosa strain PAO

Prophage H90 has been found to undergo a phenomenon similar to zygotic induction, during conjugal transfer from a lysogenic donor to a non-lysogenic recipient.

It has not been possible to demonstrate that the level of infectious centres increases concomitantly with transfer of the prophage. However, the genetic consequence of zygotic induction was observed with regard to decreased recombinant yield of markers distal to the prophage. This latter fact has been exploited in interrupted mating experiments, to locate the prophage at between 5 and 7 min on thePseudomonas aeruginosastrain PAO map. It was further shown by transduction experiments that the prophage does not appear to be linked to clusters of co-transductional markers at the 5 and 7 min locations.

The order of replication of chromosomal markers in Pseudomonas aeruginosa strain 1. I. Marker frequency analysis by transduction

The generalized transducing phage F116 has been used to prepare lysates from fast- and slow-growing cultures ofPseudomonas aeruginosastrain 1. These lysates have been used to transduce a number of auxotrophic markers to prototrophy and the ratios of the numbers of transductants obtained with each lysate have been determined. Since the markers are those which have been mapped by conjugation in previous studies it has been possible to compare the ratios obtained for each marker with the relative position of the marker on the chromosome map. If the assumption is made that there is only one circular chromosome inP. aeruginosastrain 1 it is possible to suggest a way in which two apparently unlinked segments might be joined together. It is also possible to suggest that the chromosome replicates sequentially in two directions from a fixed origin.