Translocation of a discrete piece of deoxyribonucleic acid carrying an amp gene between replicons in Eschericha coli

THE EVOLUTION OF TRANSPOSABLE ELEMENTS: CONDITIONS FOR ESTABLISHMENT IN BACTERIAL POPULATIONS

Previous theoretical studies have shown that bacterial transposons can become established in populations by infectious transfer, even if they reduce the fitness of their host cells. Conditions for the persistence of "parasitic" transposons are, however, restrictive: i) transposition must be replicative, rather than conservative; ii) the rate of transposition must be greater than the loss in host fitness caused by the transposon; and iii) cells must exchange plasmids at rates greater than the fitness cost of the transposon. I sought to test the validity of the model underlying this theory by performing experiments with laboratory populations of the bacterium Escherichia coli, the conjugative plasmid R100, and the transposons Tn3 and Tn5. A plasmid-borne transposon was introduced at low frequency into a population of bacteria carrying the same plasmid without the transposon in a habitat where the transposon offered no benefit to its host. The fate of the invading transposon was followed by tracking the various bacterial populations appearing in the cultures. Using independent estimates of the parameters of the model, predicted population changes were generated with numerical solutions of the model, and these were compared to experimental results. Plasmids transferred into new hosts as predicted by the model, and the resulting transconjugant populations either maintained a steady low density or rose slowly in abundance. Transposition appeared to play no role in population changes. Abundance of all cell types fit theoretical predictions of a system with no transposition, despite evidence that transposition was taking place. This is exactly what the model predicted. It thus appears unlikely that deleterious or neutral transposons have much impact on the genetics of bacterial populations. This is consistent with the hypothesis that most bacterial transposons are not parasitic DNA, but rather invade and persist in populations by providing a fitness advantage to cells carrying them.

Gene flow, mobile genetic elements and the recruitment of antibiotic resistance genes into Gram-negative pathogens

Antibiotics were one of the great discoveries of the 20th century. However, resistance appeared even in the earliest years of the antibiotic era. Antibiotic resistance continues to become worse, despite the ever-increasing resources devoted to combat the problem. One of the most important factors in the development of resistance to antibiotics is the remarkable ability of bacteria to share genetic resources via Lateral Gene Transfer (LGT). LGT occurs on a global scale, such that in theory, any gene in any organism anywhere in the microbial biosphere might be mobilized and spread. With sufficiently strong selection, any gene may spread to a point where it establishes a global presence. From an antibiotic resistance perspective, this means that a resistance phenotype can appear in a diverse range of infections around the globe nearly simultaneously. We discuss the forces and agents that make this LGT possible and argue that the problem of resistance can ultimately only be managed by understanding the problem from a broad ecological and evolutionary perspective. We also argue that human activities are exacerbating the problem by increasing the tempo of LGT and bacterial evolution for many traits that are important to humans.

bla(IMP-9) and its association with large plasmids carried by Pseudomonas aeruginosa isolates from the People's Republic of China

A novel plasmid-mediated metallo-beta-lactamase (IMP-9) is described in seven isolates of Pseudomonas aeruginosa from Guangzhou, China, isolated in 2000. The gene was carried on a large (approximately 450-kb) IncP-2 conjugative plasmid. This is the first report of carriage of bla(IMP) genes on such large plasmids.

Occurrence of a new metallo-beta-lactamase IMP-4 carried on a conjugative plasmid in Citrobacter youngae from the People's Republic of China

During the course of an antimicrobial resistance surveillance programme in Guangzhou, the People's Republic of China, single strains of Citrobacter youngae and Pseudomonas aeruginosa were identified which were resistant to imipenem and found to carry the carbapenemase gene bla(IMP). PCR screening of the citrobacter strain with specific primers for the bla(IMP) type genes gave a 587-bp product which when sequenced gave 100% homology with the bla(IMP-4) sequence reported recently from Acinetobacter spp. The determinant in the C. youngae strain was found to be located on a 156-kb plasmid capable of transfer to Escherichia coli UB1637 by conjugation. Sequencing of the bla(IMP-4) open reading frame in the C. youngae strain and adjacent sequences not only confirmed the presence of bla(IMP-4) but also identified that a conserved core site found within the 59-bp element of integrons was present and the same as the one described in the only other occurrence of bla(IMP-4) in Acinetobacter spp. isolated from an intensive care unit in Hong Kong. This is the second report of transferable carbapenemase genes in Enterobacteriaciae outside of Japan and the first in the People's Republic of China. Under the selective pressure of carbapenems and extended spectrum cephalosporins use we might expect this gene to spread and widespread surveillance should be instituted.

pUB2380: characterization of a ColD-like resistance plasmid

A detailed analysis of the mobilizable, ColE1-like resistance plasmid, pUB2380, is reported. The 8.5-kb genome encodes six (possibly seven) major functions: (1) a ColD-like origin of replication, oriV, with associated replication functions, RNAI and RNAII; (2) a set of active mobilization functions highly homologous to that of ColE1, including the origin of transfer, oriT; (3) a ColE1-like multimer resolution site (cer); (4) a kanamycin-resistance determinant, aph, encoding an aminoglycoside-3'-phosphotransferase type 1; (5) an insertion sequence, IS1294; and (6) two genes, probably cotranscribed, of unknown function(s). The GC content of the various parts of the genome indicates that the plasmid is a hybrid structure assembled from DNA from at least three different sources, of which the replication region, the mobilization functions, and the resistance gene are likely to have originated in the enterobacteriaceae.

IS1294, a DNA element that transposes by RC transposition

IS1294, found on the ColD-like resistance plasmid pUB2380, is IS91-like. It is an active 1.7-kb insertion sequence that lacks terminal inverted repeats, displays insertion-site specificity, and does not generate direct repeats of the target site. The element has one large open reading frame, tnp(1294), encoding a transposase of 351 amino acids, related to members of the REP family of replication proteins used by RC-plasmids of gram-positive bacteria. IS1294 transposes using rolling-circle replication, initiated at one end of the element, oriIS, and terminated at the other, terIS. oriIS and terIS are highly conserved among like IS elements. oriIS resembles the leading strand replication origins of RC-plasmids; terIS resembles a rho-independent transcription terminator. IS1294 mediates not only its own transposition, but also sequences adjacent to terIS. A transposition model for IS1294 and related elements, involving rolling-circle replication and single-strand DNA intermediates, is presented.

Identification of the plasmid-mobilization potential of the strain Klebsiella pneumoniae ozenae KIIIA isolated from a polluted aquatic environment

The Klebsiella pneumoniae ozenae KIIIA strain was isolated from the River Rhine soon after a serious mercury pollution episode and was selected for mercury resistance as well as for intergeneric DNA mobilization helper potential. This transfer helper capacity was shown to be related to the presence of a Tn3-like transposable element, Tn5403. Because transposon-mediated fusion was found to be involved in the mobilization potential of KIIIA, the visualization and the identification of the conjugative element, responsible for the transfer, were necessary. Our results show that, in addition to the four nonconjugative plasmids visualized in a previous study, K. pneumoniae ozenae KIIIA harbors two other plasmids, pK130 and pK45, of respective sizes of 130 and 45 kb, but none of these plasmids is involved in the mobilization mechanism. The presence of yet another extrachromosomal element pK225, with a size of 225 kb, was established by indirect methods, since yields of pK225 isolated from KIIIA were low and the plasmid was difficult to visualize directly. However, the integration of this plasmid into the chromosome was not detected. The present paper highlights the problem of detecting some plasmids in bacteria which have been isolated from the environment. For these plasmids, indirect approaches, that detect conjugative functions, constitute a feasible alternative for the investigation of the plasmid content of bacteria, if the direct approach fails. An analysis of the different types of transconjugants indicated that the mercury-resistance marker as well as the mobilization potentials, expressed by KIIIA, are linked to pK225. This plasmid could not be assigned to a described Inc group either by DNA hybridization or by PCR amplification.

Recombinant plasmid mobilization between E. coli strains in seven sterile microcosms

Transfer by mobilization of a pBR derivative recombinant plasmid lacking transfer functions (oriT+, tra-, mob-) from one E. coli K12 strain to another was investigated in seven sterile microcosms corresponding to different environments. These microcosms were chosen as representative of environments that genetically engineered microorganisms (GEMOs) encounter after accidental release, namely attached biomass in aquatic environments (biofilm), soil, seawater, freshwater, wastewater, mouse gut, and mussel gut, GEMOs survived in the same way as the host strains in all microcosms. Recombinant DNA mobilization occurred in the mouse gut, in sterile soil, and in biofilm. The plasmid transfer rates principally reflected the environmental conditions encountered in each microcosm.

Identification of a new transposon Tn5403 in a Klebsiella pneumoniae strain isolated from a polluted aquatic environment

A Klebsiella pneumoniae strain having mobilization "helper" potential has been isolated from the river Rhine. Analysis of the transconjugants resulting from the mobilization of non-conjugative pBR-type plasmids and RSF1010 derivatives showed that the transfer-helper capacity of the K. pneumoniae strain is related to the presence of a Tn3-like transposable element, Tn5403. This element has been identified and localized in a plasmid.

Transposition of the gene encoding a TEM-12 extended-spectrum beta-lactamase

An isolate of Klebsiella oxytoca from the blood culture of a child with leukemia was found to produce two beta-lactamases, at least one of which conferred resistance to ceftazidime. Genes encoding both enzymes were located on a single self-transmissible 100-kb plasmid, pOZ201. This plasmid was introduced into Escherichia coli UB5201 (pACYC184), and the gene encoding one beta-lactamase was transposed onto plasmid pACYC184 by exploiting a gene dosage effect. The transposable gene was found to encode a TEM-12 enzyme as determined by nucleotide sequencing. This gene was subsequently transposed onto plasmid pUB307. The transposable element encoding the TEM-12 enzyme has been designated Tn841. Both plasmids pACYC184::Tn841 and pUB307::Tn841 were shown to encode a beta-lactamase with the same isoelectric point and substrate profile as the TEM-12 beta-lactamase. Transposon Tn841, at approximately 7 kb, is larger than TnA (4.8 kb) and transposes at a lower frequency. Although it produced a resolvase which can complement the resolvase of Tn3, its transposase function was not able to complement the transposition of a TnA element which lacked transposase. The occurrence of a gene encoding an extended-spectrum beta-lactamase on a transposable element in a clinically significant bacterium is potentially a cause for concern for the spread of resistance to the extended-spectrum cephalosporins.

The dehalogenase gene dehI from Pseudomonas putida PP3 is carried on an unusual mobile genetic element designated DEH

As a result of the production of two dehalogenases (DehI and DehII), Pseudomonas putida PP3 utilized halogenated alkanoic acids, such as 2-monochloropropionic acid (2MCPA), as sole sources of carbon and energy. The DehI gene (dehI) was carried on a mobile genetic element (DEH) located on the chromosome of strain PP3. DEH recombined with target plasmid DNAs at high frequencies (e.g. 3.8 x 10(-4) per RP4.5 plasmid transferred). The regulated expression of dehI was detected in P. putida, Pseudomonas aeruginosa, and Escherichia coli strains containing derivative plasmids of RP4.5 and pWW0 recombined with DEH. Movement of DEH from the unstable RP4 derivatives pNJ5000 and pMR5 resulted in the insertion of DEH into the chromosome of RecA+ strains of P. putida but not in RecA+ nor RecA- strains of E. coli. Rescue of DEH from the chromosome of P. putida KT2441 onto plasmid RP4 involved recombination at a frequency (2.7 x 10(-4) per RP4 plasmid transferred) comparable to that observed in strain PP3. The DEH element was not classified as a conventional transposon because it did not move as a discrete DNA fragment: dehI-containing inserts in plasmid DNA targets varied in size between 6 and 13 kb. In addition, DEH exhibited a marked preference for insertion into a specific site on the plasmid pWW0, but its transposition, independent of host recombinational systems, remains to be demonstrated. However, the transposonlike characteristics of DEH included the conservation of restriction endonuclease sites, high-frequency recombination with different target replicons (plasmid and chromosomal DNA), and promiscuous insertion into plasmid RP4-based replicons. Therefore, it is proposed that DEH is an unusual mobile genetic element.

Serum bactericidal resistance of faecal Escherichia coli and bactericidal competence of serum from patients with ulcerative colitis

A microtitre method was developed to screen Escherichia coli from 48 patients with ulcerative colitis and 25 controls for serum resistance. Bactericidal resistance was indicated by a change in colour of indicator due to acid production by viable organisms and quantitated by a change in absorbance. The method clearly differentiated between organisms confirmed as resistant or sensitive by conventional techniques. Twenty four (50%) disease and 14 (56%) control E coli specimens showed serum resistance. Bactericidal competence of sera from patients with ulcerative colitis was assessed by incubating sensitive E coli with sera from 10 patients with ulcerative colitis and pooled normal serum. All sera effectively reduced viable counts to less than 6% of original inoculum. This study shows that serum samples from patients with ulcerative colitis are bactericidally competent and that there is no increase in the number of serum resistant E coli in patients with ulcerative colitis.

Nucleotide sequences required for Tn3 transposition immunity

The Tn3 transposon inserts at a reduced frequency into a plasmid already containing a copy of Tn3, a phenomenon known as transposition immunity. The cis-acting site on Tn3 responsible for immunity was mapped by deletions from each side to be within the terminal 38-base-pair sequence that is inversely repeated at the ends of Tn3. Two palindromic sequences are present in the essential part of this region. Some deletions conferred only partial immunity, and others conferred negative immunity. Multiple copies of partially immune ends conferred additional immunity. No other part of Tn3 was necessary for immunity.

Composite IS1-tetracycline resistance elements in aerobactin-encoding FIme plasmids from epidemic Salmonella wien

Class B tetracycline resistance determinants have been identified in two aerobactin-encoding FIme plasmids representative of those isolated from epidemic Salmonella wien. Genetic data, restriction enzyme analysis of recombinant and mutant plasmids, and Southern blot hybridizations indicate that in both plasmids the class B determinant so far found and described only on Tn10-like transposons is part of a different genetic element. This composite insertion sequence element is about 7 kilobases long and has copies of insertion sequence IS1 at the ends.

Behaviour of a replicating mitochondrial DNA sequence from Aspergillus amstelodami in Saccharomyces cerevisiae and Aspergillus nidulans

An amplified sequence of mitochondrial DNA from a ragged (rgd) mutant of Aspergillus amstelodami has been shown to exist in multimeric circular form, suggesting that it is excised from the genome and can exist independently of it. This sequence has replicative (ARS) activity in Saccharomyces cerevisiae, and a subfragment responsible for this activity has been identified and sequenced. A homologous sequence from Aspergillus nidulans mtDNA also has ARS activity in S. cerevisiae. Both A. amstelodami and A. nidulans ARS elements have been incorporated into the integrative transformation vector pDJB1 and the derived vectors used to transform A. nidulans. Inclusion of the A. nidulans ARS element enhanced the transformation frequency 5-fold relative to pDJB1. No increase in transformation frequency was evident with the ARS element from A. amstelodami. The stability of transformants was variable but in comparison to pDJB1, ARS-containing plasmids were mitotically unstable in A. nidulans. Although plasmid DNAs could be rescued in Escherichia coli from undigested transformant DNA, no freely replicating plasmids were detected by Southern hybridisation.

Identification and expression of a copy number control gene in the IncFIII hemolytic plasmid pSU316

A DNA fragment carrying both the IncFIII determinant and a copy number control gene of the hemolytic plasmid pSU316 has been cloned in pBR322. Deletion derivatives of the hybrid plasmid generated by Bal 31 digestion, which no longer exhibit the IncFIII phenotype, fall into two complementation groups when tested against a pSU316 miniplasmid derivative. Type 1 mutants exhibit the copy number control (Cop+) phenotype whereas type 2 mutants do not. Restriction analysis of type 1 and type 2 mutants allowed us to locate the cop gene of pSU316 in a 700-base-pair fragment adjacent to the IncFIII determinant. Plasmid expression in a minicell system suggests that the product of the cop gene of pSU316 could be a 13,000-dalton protein.

Resistance in Escherichia coli after single dose ampicillin to treat gonorrhoea

Patients with uncomplicated gonorrhoea were treated with a single dose of either ampicillin 3 g orally or procaine penicillin 2.4 MIU by injection, both with probenecid 1 g orally. The proportion of faecal Escherichia coli resistant to ampicillin before and a week after treatment was assessed. Of 55 patients treated with ampicillin who initially possessed sensitive flora, 25 (45.5%) became colonised subsequently by resistant E coli. Resistance to ampicillin, together with resistance to some other antimicrobials, was transferable in vitro. Penicillin, however, selected resistant E coli in only four (14.3%) out of 28 patients with initially sensitive flora. There was no difference in therapeutic response between the two agents. Intramuscular penicillin appeared to offer appreciably greater microbiological benefits than oral ampicillin in treating gonorrhoea.

Structural and functional analyses of the fosfomycin resistance transposon Tn2921

The fosfomycin resistance transposon Tn2921 is flanked by directly repeated sequences homologous to the Tn10-related insertion sequence IS10. The nonrepeated DNA sequences of Tn2921 can be deleted without affecting the transposition ability of the element, showing that at least one of the direct repeats is an active insertion sequence. Transposition of Tn2921 seems to occur through direct transposition, since cointegrates have not been observed. The evolutionary relatedness of Tn2921 and IS10 is discussed.

Characterization of Tn3926, a new mercury-resistance transposon from Yersinia enterocolitica

A new transposon coding for mercury resistance (HgR), Tn3926, has been found in a strain of Yersinia enterocolitica, YE138A14. The element has a size of 7.8 kb and transposes to conjugative plasmids belonging to different incompatibility groups. A restriction map has been established. DNA-DNA hybridization indicates that Tn3926 displays homology with both Tn501 and Tn21; the greatest homology is shown with the regions of these transposons that encode HgR. Weaker homology is observed between Tn3926 sequences and those regions of Tn501 and Tn21 that encode transposition functions. Complementation experiments indicate that the Tn3926 transposase mediates transposition of Tn21, albeit somewhat inefficiently, but not of Tn501, while the resolvase mediates resolution of transposition cointegrates formed via Tn21, Tn501, or Tn1721.

Stability of plasmid content in Salmonella wien in late phases of the epidemic history

Prevalence, genetic characteristics, and EcoRI cleavage analysis of plasmids identified in clinical strains of Salmonella wien isolated in recent years showed that the plasmid content in this serotype has remained uniform and stable over more than a decade and also late in the epidemic history. No correlation between decrease in S. wien isolations and naturally occurring systematic changes in the DNA of its most common FIme plasmid was structurally detectable.

Location of a function on RP1 that fertility inhibits Inc W plasmids

Two fertility inhibition (Fi+) functions which reduce R388 (Inc W) transfer were detected on RP1 (Inc P). Neither function affected R388 -mediated surface exclusion but they could be distinguished by their effect on pilus production. One of the functions was located in the 6.5-kb Pst1 -C region of RP1, part or all of which also occurs on six Fi+ but not two Fi- Inc P plasmids studied.

Plasmid pattern analysis of natural bacterial isolates and its epidemiological implication

Natural isolates of Escherichia coli, Salmonella typhimurium, Klebsiella pneumoniae, and Providencia stuartii were analysed to determine their plasmid content. This data allowed the identification of nosocomial strains of K. pneumoniae and P. stuartii and helped in the differentiation of epidemic strains of E. coli 0111 and S. typhimurium. Phenotypically similar isolates of S. typhimurium could be shown to be of independent origin using plasmid pattern analysis. The dissemination of a particular plasmid through different strains of S. typhimurium resulted in a simulation of a very widely distributed epidemic strain, because the plasmid interfered with the phage type of its host strain in addition to determining resistance properties. Plasmid pattern analysis disclosed two independently existing but interacting epidemic processes: a bacterial 'epidemic' strain may become disseminated over a large territory and may predominate there for a long time; a single plasmid, however, may also become distributed through many different bacterial strains and may spread over a large territory. Plasmid pattern analysis provides a valuable and universal epidemiological laboratory method.

R46 encodes a site-specific recombination system interchangeable with the resolution function of TnA

Transposition of Tn4 onto the IncN plasmic R46 generates unstable DNA molecules. The R46::TnA recombinant plasmids undergo further DNA rearrangements which depend on the orientation in which the TnA element is inserted into the plasmid, and deletions and inversions of R46 and TnA sequences have been observed. Both types of rearrangement have the same specific endpoints, one within TnA and one located between the R46 coordinates, 36.0 and 37.0. The results are consistent with the operation of a recA-independent, site-specific recombination system utilizing, at least in part, the transposon cointegrate resolution system of TnA, together with R46-encoded functions. Data are presented that indicate that R46 encodes analogs of both the res site of TnA and its tnpR gene, although little homology between this element and the plasmid is apparent. Models for the TnA-induced generation of site-specific deletions and inversions upon transposition of TnA to R46 are presented.

Purification of genomic sequences from bacteriophage libraries by recombination and selection in vivo

Cloned genes have been purified from recombinant DNA bacteriophage libraries by a method exploiting homologous reciprocal recombination in vivo. In this method 'probe' sequences are inserted in a very small plasmid vector and introduced into recombination-proficient bacterial cells. Genomic bacteriophage libraries are propagated on the cells, and phage bearing sequences homologous to the probe acquire an integrated copy of the plasmid by reciprocal recombination. Phage bearing integrated plasmids can be purified from the larger pool of phage lacking plasmid integrates by growth under the appropriate selective conditions.

Tn2610, a transposon involved in the spread of the carbenicillin-hydrolyzing beta-lactamase gene

We have found a new transposon, Tn2610, on pCS200 in clinical isolates of Escherichia coli, which encodes the carbenicillin-hydrolyzing beta-lactamase gene in combination with the resistance determinants to streptomycin and sulfonamide. Tn2610 has a molecular size of 24 kilobase pairs and is flanked by long inverted repeat sequences of 3 kilobase pairs in length. Genetical and physical analyses indicate that Tn2610 is a single transposable unit encoding the multiple resistance determinants and that is different from any previously described transposon. The characteristic DNA structure observed in various complex resistance transposons involved in the transposition of the carbenicillin-hydrolyzing beta-lactamase gene is discussed.

Tn2011, a new transposon encoding oxacillin-hydrolyzing beta-lactamase

The type II penicillinase (oxacillin-hydrolyzing beta-lactamase, OXA-1) gene on plasmid Rms213 was transposed to various plasmids or to the host chromosome. The transposon bearing this gene, designated Tn2011, conferred resistance to ampicillin, streptomycin, sulfonamide, and mercuric chloride. By restriction endonuclease digestion and agarose gel electrophoresis, the molecular weight of Tn2011 was estimated to be 12.5 X 10(6). The transposition frequency of Tn2011 was about 10(-4) to 10(-5). The activity of type II penicillinase is related to the copy number of the replicon bearing Tn2011.

Heat curing of a sym plasmid in a fast-growing Rhizobium sp. that is able to nodulate legumes and the nonlegume Parasponia sp

Genes involved in nodulation of both legumes and the nonlegume Parasponia sp., as well as nitrogenase genes, reside on a large plasmid in a fast-growing Rhizobium sp. from Lablab purpureus. This plasmid can be cured by incubation at elevated temperatures and can be mobilized by the P1 group plasmid RP1::Tn501.

Expression of a chemically synthesized human alpha 1 interferon gene

Cells of Escherichia coli containing a chemically synthesized human alpha 1 interferon (IFN-alpha 1) gene, under control of the lac promoter, make a product with biological properties indistinguishable from those of the natural IFN-alpha 1 [antiviral activity, acid stability, species crossreactivity, inactivation by antisera directed against leukocyte or Namalwa cell interferon, and stimulation of (2'-5')oligoadenylate synthetase activity]. Similar levels of IFN synthesis were obtained when the expression unit (lac promoter plus synthetic IFN-alpha 1 gene) was transplanted into the obligate methylotroph Methylophilus methylotrophus.

Genetic and molecular characterization of Tn21, a multiple resistance transposon from R100.1

Tge transposon Tn21 has been transposed from R100.1 to plasmid pACYC184 and, from the resulting recombinants, to plasmid R388. The sites of insertion and the orientation of the element in several pACYC184::Tn21 recombinants have been examined. Restriction enzyme analysis of these recombinants has resulted in a detailed map of Tn21; this is compared with the published maps of the relevant part of R100.1. Heteroduplex analysis has shown short inverted repeat sequences at the ends of the element. With various in vitro-generated deletion mutants of Tn21, the internal gene necessary for transposition (tnpA) was localized within the terminal 4.3 kilobases of the right-hand end of the element. Genetic analysis of transposition of Tn21 suggests that the process proceeds via cointegrates. Since the end products of transposition are simple recombinants of the element and the recipient replicon, Tn21 must contain a gene that codes for a resolvase type of activity (tnpR gene).

Molecular nature of a plasmid specifying beta-lactamase production in Haemophilus ducreyi

We characterized pJB1, the plasmid previously reported to mediate beta-lactamase production in Haemophilus ducreyi. We studied its relationship to pMR0360 and RSF0885, the plasmids responsible for beta-lactamase production in Neisseria gonorrhoeae and Haemophilus parainfluenzae, respectively. Although pJB1 was maintained as a multicopy pool in Escherichia coli, it was not stably maintained in the absence of antibiotic selection. Electron microscope heteroduplex studies showed that it carried 100% of the transposable ampicillin resistance sequence TnA. This sequence was transposed to plasmid pUB307 at a low rate. Heteroduplexes between pMR0360 and pJB1 showed that they contained 3.3 megadaltons of homologous sequences. Two sets of nonhomologous sequences, one a TnA sequence and the other a non-TnA sequence, took the form of insertion loops. For plasmids pMR0360 and RSF0885, previously shown to be highly related, the nonhomologous sequences took the form of a substitution loop. We concluded that all three plasmids shared major portions of their sequences but differed in discrete segments. pJB1 was the first such plasmid to have a physically and functionally intact TnA sequence.

The tnpR gene product of TnA is required for transposition immunity

A mutant of TnA no longer recognizing immune plasmids had been isolated. The mutation is complemented in trans by a functional tnpR gene. The requirement for wild type tnpR gene product for the establishment of transposition immunity was confirmed by the use of a derivative of transposon Tn3 in which both the tnpA and the tnpR genes are partly deleted. This deleted Tn3 was shown to transpose onto an immune plasmid in the presence of a wild type tnpA gene but not in the presence of both tnpA and tnpR genes.

Transposition of a DNA fragment flanked by two inverted Tn1 sequences

The 32 Md fragment (derived from plasmid RP4::Tn1) carrying the Kmr gene and flanked by two inverted Tn1 elements is capable of recA-independent translocation to other plasmids. We designated this new transposon Tn1755. In various crosses, frequencies of Tn1755 transposition to plasmids Co1B-R3, R15 and F'Co1VBtrp varied from 2.5 to 90% of the frequencies of Tn1 transposition. Tn1755 can integrate into various sites of the recipient plasmids. We failed to observe transposition of another RP4::Tn1 fragment flanked by two opposingly oriented Tn1 transposons and harboring the Tcr gene. Presumably, to form a new transposable structure, other features must also be of importance.

Molecular nature of a streptomycin and sulfonamide resistance plasmid (pBP1) prevalent in clinical Escherichia coli strains and integration of an ampicillin resistance transposon (TnA)

A small, nonconjugative plasmid, designated pBP1, was originally found in different fecal Escherichia coli serotypes isolated from a healthy proband. Of a total number of 130 hospital strains of E. coli subsequently studied, 8.5% yielded plasmid of the pBP1 type. This R plasmid specifies resistance to streptomycin (Sm) and sulfonamides (Su) and has a mass of 4.0 megadaltons. Inactivation of streptomycin is due to the aminoglycoside phosphotransferase APH-(3 "). A physical map was constructed by analysis with restriction endonucleases. Another small plasmid, pBP1-1, was isolated from one of the hospital strains and characterized as an enlarged pBP1 replicon containing an additional deoxyribonucleic acid sequence identified as a transposable element for ampicillin resistance (TnA). Plasmid pBP1-1 was cleaved by restriction enzymes for identification of the transposon sequence which codes for a TEM 1 beta-lactamase. The sequence organizations in the Sm Su plasmids RSF1010 and pBP1 were shown to be identical for regions specifying streptomycin and sulfonamide resistance, but different for the region containing the origin of replication and genes for replicative functions. Thus, RSF1010, which has been considered as the prototype of Sm Su plasmids, and pBP1, which is at least as frequent in clinical isolates as RSF1010, do not have a single common ancestor.

Insertions of the transposon Tn1 into the Pseudomonas aeruginosa chromosome

The transposon Tn1 has been translocated to the chromosome of Pseudomonas aeruginosa from plasmid R18, following hydroxylamine mutagenesis of the plasmid. Twelve insertions were mapped to six distinct sites distal to 55 min of the origin of chromosome transfer by the plasmid FP2. These map locations were confirmed by host chromosome mobilization tests mediated by plasmids R18 or R91-5, due to Tn1 homology between plasmid and host chromosome. All the Tn1 chromosomal inserts were retransposable to other plasmids (Sa, R931 and R38). The behavior of Tn1 in P. aeruginosa was very similar to its behavior in Escherichia coli with respect to regional specificity, orientation of insertion and in serving as regions of homology for host chromosome mobilization by plasmids. This last property has permitted the demonstration that Tn1 on R18 and R91-5 is in opposite orientation with respect to the origin of transfer (oriT) of the two plasmids.

Formation of Escherichia coli Hfr strains by integrative suppression with the P group plasmid RP1

Hfr strains of Escherichia coli were obtained by integrative suppression of a dnaA(Ts) mutation by the Inc P-1 plasmid RP1 without prior creation of an unnatural homology between the plasmid and the E. coli chromosome. Unmodified RP1 mobilized the polarized transfer of the chromosome in a counterclock-wise direction from a distinct origin between 81 min (pyrE) and 82 min (dnaA) with pyrE as a leading marker. Inheritance of RP1-Hfr chromosomal and antibiotic resistance genes was due to recombination with the recipient chromosome, as shown by the need for a functional recA system. The acquisition of temperature resistance and donor ability was accompanied by the disappearance of free plasmid when the selection pressure for integration was maintained (growth at 41 degrees C); the loss of temperature resistance and donor ability was accompanied by the reappearance of autonomous RP1 when the selection pressure was removed (growth at 30 degrees C).

Characterization of beta-lactamase-deficient (bla) mutants of the R plasmid R1 in Escherichia coli K-12 and comparison with similar mutants of RP1

Thirty-eight mutants of R1, an R plasmid specifying the type IIIa (TEM) beta-lactamase, were isolated; these mutants are partially or totally unable to synthesize the type IIIa beta-lactamase. The loss of beta-lactamase activity was associated with a reduction in the level of penicillin resistance conferred by the mutants upon their host strain. At least two of the mutants synthesized a beta-lactamase with altered substrate specificity. These properties are compared with those of two beta-lactamase-deficient mutants of plasmid RP1. The results suggest that, for both R plasmids, penicillin resistance is entirely attributable to the presence of beta-lactamase activity. The properties of two R1 derivatives, pUB251 and pUB252, which have phenotypes similar to that of RP1, support this conclusion.

Persistence and spread of a chloramphenicol resistance-mediating plasmid in antigenic types of Escherichia coli, pathogenic for piglets

All chloramphenicol-resistant Escherichia coli strains isolated from piglets in the State veterinary Serum Laboratory, Copenhagen, in 1974-1975 harbored plasmids of IncFII group with largely the same resistance markers. Two strains from 1978 carried plasmids with similar characters. Restriction enzyme analysis of DNA from these plasmids with restriction endonucleases EcoRI, BglII, and PstI shows that the Cm plasmids are extremely closely related; but the patterns obtained (particularly from PstI digests) enable the classification of the plasmids into groups. These bear a strong relation to time and place of isolation so that plasmids isolated on the same farm belong to the same group even when their host strains are of different antigenic types. It is concluded that these plasmids have evolved from a single plasmid.

Tn2301, a transposon construct carrying the entire transfer region of the F plasmid

The largest R . BamHI fragment of the plasmid F, which carries the entire F conjugation system, has been cloned into the single R . BamHI site of the ampicillin (Ap) resistance transposon TN1. pDS1106 (ColE1 mob::Tn1) was the vector plasmid, and the resultant conjugative plasmid, pED830, was characterized both genetically and by restriction enzyme analysis. The transposon construct, denoted Tn2301, was transposable at frequencies similar to Tn1 to small nonconjugative plasmids or to the Escherichia coli host chromosome. In the former case, Apr conjugative plasmids were obtained, whereas in the latter case, Hfr strains resulted. Representative Hfr strains were characterized by quantitative and interrupted mating experiments. Extension of this technique for Hfvr formation should aid chromosome mapping both in E. coli and in other bacterial genera.