[Transmissible formaldehyde resistance in Serratia marcescens]

It was possible to isolate a strain of Serratia marcescens from fresh clinical bacterial isolates which was 4-6 times more resistant against formaldehyde than other strains. It was shown that the strain harbours two plasmids with molecular sizes of 58- and 90 Mdal. It was demonstrated by conjugation-, transformation- and plasmid-curing experiments that the formaldehyderesistance is plasmid mediated and transferable to E. coli. It was shown by labelling with 14C-formaldehyde that the resistant strains bind much more formaldehyde than the sensible strains.

Effect of Ca2+ ions on plasmid transformation of Streptococcus lactis protoplasts

The effects of Mg2+ and Ca2+ ions on the efficiency of the plasmid transformation of lysozyme-treated Streptococcus lactis protoplasts were compared. A 33-megadalton plasmid, pLP712, coding for lactose fermentation and a 6.5-megadalton plasmid, pGB301, coding for erythromycin and chloramphenicol resistance were used as model plasmids, and S. lactis MG1614 was the recipient. Replacing Mg2+ with Ca2+ in the transformation buffer was found to increase transformant frequency more than 10-fold with both plasmids.

Polyethylene glycol-facilitated transformation of Bacteroides fragilis with plasmid DNA

A method for the transformation of Bacteroides fragilis with plasmid DNA was developed by using the clindamycin resistance plasmid pBFTM10 as the source of transforming DNA. The method was technically simple to perform and resulted in an average of 4.2 X 10(3) transformants per microgram of pBFTM10 added. A method for the preparation of frozen competent cells is also described.

[Genetic control and the mechanism of the spread of gentamycin resistance among Enterobacteriaceae strains in a hospital]

Strains of K. pneumoniae belonging to serowars K10, K3, K16 and K62 and two strains of E. coli with multiple drug resistance including newly detected resistance to gentamicin were isolated in succession within the 2-year period of microbiological survey of a hospital department for premature infants. Resistance to gentamicin in the first isolate of K. pneumoniae was due to the non-conjugated plasmid pP12140 with a molecular weight of 15 MD. This plasmid also controlled resistance to streptomycin and sulfanilamides and was physically independent of the other large (about 80 MD) conjugative R plasmid controlling resistance to kanamycin, tetracycline, chloramphenicol and ampicillin. In the strains of K. pneumoniae and E. coli isolated within the following 2 years the marker of gentamicin resistance was included into large (80-120 MD) conjugative R plasmids controlling 6-7 resistance types. DNA of such plasmids was used for transformation of the recipient strain C600 of E. coli. In addition to the transformants with the acquired R plasmids possessing all the resistance markers there were isolated transformants carrying plasmids with the molecular weight of 15 MD controlling resistance to gentamicin, streptomycin and sulfanilamides and capable of self-replication. Analysis of the plasmids with the help of endonucleases EcoR1 and Pst1 revealed complete identity of plasmid pP12140 and similar plasmids of the transformants isolated with the use of DNA of the plasmids of the other K. pneumoniae strains. Marked relation with the plasmids of the transformants isolated with the use of the plasmid DNA of E. coli was also revealed.(ABSTRACT TRUNCATED AT 250 WORDS)

[Biological activity of thiophosphamide-alkylated DNA in the transformation system of Bacillus subtilis]

DNA treated with thiophosphamide was studied for changes in its biological activity in transformation system of Bac. subtilis. DNA alkylation by this three-functional alkylating agent is shown to be followed by the reduction of transforming activity, changes in the competitive ability as well as by a decrease of the cotransfer coefficient for linked markers of transforming DNA. The observed changes in the transforming and cotransforming activities may be explained by variations in the DNA structure.

Transformation of Salmonella typhimurium with plasmid DNA: differences between rough and smooth strains

Lipopolysaccharide-defective mutants of Salmonella typhimurium were transformed by plasmid DNA with a Ca2+ treatment method. Only those mutants with an Rc or Rd2 chemotype, due to galE or rfaF mutations, respectively, gave efficiencies greater than 10(5) transformants per microgram of DNA, frequencies 8- to 630-fold higher than with smooth strains or other rough mutants.

[Effect of O-hydroxylamine on the transforming DNA from Bacillus subtilis. Correlation of chemical modifications with genetic consequences]

The action of methoxyamine (MA) on B. subtilis transforming DNA (50 degrees C, pH 4,5 and 6,0, 1 M MA) was studied. The rate of cytosine residues modification in DNA is 250 times less than in monomer (rate constants for DNA are 1,5 X 10(-1) min-1 at pH 4,5, and 2,5 X 10(-6) min-1 in the first 300 hours of treatment at pH 6,0). At pH 4,5 the rates of cytosine (I) conversion into N4-methoxycytosine (II) and into 6-methoxyamino-5,6-dihydro-N4-methoxycytosine (III) are constant (II/III ratio is about 2,1). At pH 6,0 the II/III ratio smoothly increases from 1,0 to 1,6 (200 and 900 hours of treatment) due to a decrease in the product III accumulation rate. The frequency of MA-induced mutations shows a bell-shaped dependence on time with maxima (approximately 10%) at 80 (pH 4,5) and 500 (pH 6,0) hours of treatment. In both cases approximately 10% of cytosine residues are modified. These results suggest that either compound III is efficiently removed from the transforming DNA, or its presence does not arrest the DNA replication.

[Action of dicaine on the efficiency of plasmid transformation and transfection in Escherichia coli K12]

The action of tetracaine hydrochloride, a local anesthetic, on the effectiveness of plasmid transformation and transfection in variants of E. coli K-12 has been studied. The concentrations of tetracaine hydrochloride used in the experiment (0.002 M) affect the level of the synthesis of most proteins in the outer membrane of these bacteria. This seems to be one of the causes of changes in the effectiveness of plasmid transformation and transfection in E. coli K-12.

Effect of polycations on the transforming activity of various markers of Bacillus subtilis

Polycations interact with DNA and form DNA-polycation complexes. The soluble and insoluble fractions of the DNA-polycation complexes were fractionated by centrifugation. The effect of polycations on the transforming activity of genetic markers of B. subtilis (single and double) have been tested. These markers are tryptophan, histidine, adenine, arginine and lysine. It is found that both parts of DNA in the supernatant and the precipitate of DNA-polycation complexes are biologically active. This means that the activity of the precipitated genetic markers by the different polycations was reserved.

Characterization of non-beta-lactamase-mediated ampicillin resistance in Haemophilus influenzae

Ampicillin resistance in Haemophilus influenzae is most often due to the plasmid-mediated production of TEM beta-lactamase. We studied four strains with high-level ampicillin resistance (MIC of 32 micrograms/ml with an inoculum of 10(5) CFU on solid media) which did not produce detectable beta-lactamase activity with two different detection methods. Two of the four strains contained extrachromosomal DNA by agarose gel electrophoresis. Conjugation failed to transfer ampicillin resistance; in contrast, transformation yielded ampicillin-resistant transformants in three of the four strains. These transformants did not contain detectable extrachromosomal DNA. In addition, mobilization of the resistance determinant by transformation to, or conjugation with, recombination-deficient strains was unsuccessful. DNA-DNA hybridization experiments revealed no homology of the DNA of these strains with two R plasmids (one coding for ampicillin resistance, the other for chloramphenicol and tetracycline resistance). We conclude that the genetic basis of the non-beta-lactamase ampicillin resistance in these strains appears to be chromosomally mediated. We investigated the mechanism of resistance in these strains. Enzymatic modification of penicillin was not detected by autoradiography of a thin-layer chromatogram of cell sonic extracts of three ampicillin-resistant transformant strains incubated with [14C]penicillin. To assess changes in permeability of the cell envelope, a plasmid coding for beta-lactamase was conjugated into these strains, and the hydrolysis of penicillin by intact cells and cell sonic extracts was compared. Only one of three transformant strains had significantly diminished permeability. Outer membrane proteins of these strains analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed apparent differences in comparison with the isogenic ampicillin-susceptible recipient strain. Autofluorography of a sodium dodecyl sulfate-polyacrylamide gel electrophoresis of Sarkosyl-solubilized crude membrane (the putative inner membranes) from these ampicillin-resistant transformant strains incubated with [3H]penicillin compared with the isogenic ampicillin-susceptible recipient strain revealed reduced binding to PBP 3 and 6, 3 and 4, or 4. In addition, affinity binding studies revealed decreased affinity of PBP 4 for ampicillin of all four transformants tested. We conclude that the major mechanism of resistance in these strains is altered penicillin-binding proteins; however, other mechanisms, including permeability, may also play a role.

[Cloning of the purA16 locus in Rec+ cells of Bacillus subtilis]

A portion of purA16 chromosomal locus of Bacillus subtilis was cloned into Rec+ cells of this microorganism with pBD12 plasmid (carrying chloramphenicol and kanamycin resistance determinants) serving as a vector. The hybrid plasmids were stably maintained in cells grown on media supplemented with antibiotics and were lost from cells in the absence of drugs. The cloned fragment could incorporate into the chromosome some with a frequency of 10(-2) per cell per generation. A clone carrying the hybrid plasmid inserted into the chromosome was detected.

[Induced mutagenesis of plasmid and chromosomal genes inserted into plasmid DNA. I. The mutagenic action of radiation]

This paper describes the results of treating plasmid DNA in vitro with mutagens, to obtain mutations both in plasmid genes and chromosomal genes comprised within the plasmid, thus avoiding disorganization characteristic of in vivo mutagenesis. The model system is represented by DNA of RSF2124 responsible for colicine E1 synthesis and resistance to ampicillin. Col- mutants were looked for after exposure to UV- and gamma-irradiation. The lethal effect was estimated as inactivation of the ampicillin resistance marker. After reisolation from mutant transformant of the plasmid DNA, the novel character and resistance to ampicillin proved to retain in the course of subsequent transformations and passages of transformed colonies, suggesting the mutational nature of the changes. Exposure of RSF2124 to short-wave UV-irradiation (lambda = 254 nm) produced a pronounced mutagenic effect: the relative quantity of Col- mutants under optimal conditions of mutagenesis increased about 10 times. In the case of W-reactivation (additional UV-irradiation of C600 wild type cells) of lethal lesions, a 95% reliable increase in mutagenic effect was observed. Significant enhancement of mutagenesis (about 4-fold) was detected when only recipient cells were exposed to low doses of UV (the so-called indirect UV mutagenesis). Thus, with regard to W- and indirect UV mutagenesis, the plasmid DNA behaves like DNA of temperate phages which suggests their evolutionary relationship. Treatment of plasmid DNA with acridine orange prior to UV, only protected from lethal lesions. Gamma-irradiation (60Co) at the dose producing 100-fold inactivation, increased the yield of Col- mutants by one order of magnitude. The presence of RSF2124 plasmid in a cell does not affect its UV sensitivity.

pBR322 plasmid DNA modified with 2-acetylaminofluorene derivatives: transforming activity and in vitro strand cleavage by the Escherichia coli uvrABC endonuclease

Covalently closed circular plasmid DNA was treated with three reactive derivatives of 2-acetylaminofluorene: N-acetoxy-N-2-acetylaminofluorene (N-Aco-AAF), its 7-iodo derivative (N-Aco- AAIF ) and N-hydroxy-N-2-aminofluorene (N-OH-AF), and tested as substrates for the Escherichia coli uvrABC endonuclease and for transformation frequencies on wild-type, uvrA, recA, uvrArecA and polA mutant strains. The uvrABC endonuclease reacted with all three substrates with high efficiency, implicating this enzyme in the repair of DNA containing all three types of adducts. However, only AAF- and AAIF -DNA showed greatly reduced survival on uvrA mutants (five adducts/lethal hit) relative to wild-type (20 adducts/lethal hit). AF-DNA survived equally well on uvrA mutant and wild-type cells, and at a much higher level of modification (60 adducts/lethal hit). A mutation in recA had only a minor effect on the survival of either DNA. The polA mutation reduced the survival of the AAF-treated DNA to the same extent as the uvrA mutation (five adducts/lethal hit). Also AF-DNA showed reduced survival on polA mutant cells versus wild-type. However, many more adducts (20/lethal hit) were tolerated than for AAF-DNA, indicating that AF lesions in the template do not efficiently block replication of DNA.

Role of the electrochemical proton gradient in genetic transformation of Haemophilus influenzae

The uptake of homologous DNA by Haemophilus influenzae was studied as a function of the proton motive force in completely competent cultures in the pH range of 6 to 8. The composition and magnitude of the proton motive force were varied by using the ionophores valinomycin and nigericin (in the presence of various potassium ion concentrations) and by using protonophores. No interaction of the ionophores with the DNA transformation system itself was observed. Either component of the proton motive force, the electrical potential or the pH gradient, can drive the uptake of DNA, and the extent of the uptake of DNA is ultimately determined by the total proton motive force. The transformation frequency increases with the proton motive force, which reaches a maximum value at around -130 mV. These results are consistent with an electrogenic proton-DNA symport mechanism, but direct evidence for such a system is not available. The proton motive force was followed during competence development of H. influenzae at pH 8. In the initial phase (up to 50 min), the proton motive force remained constant at about -90 mV, whereas the transformation frequency rose steeply. In the second phase, the proton motive force increased. The transformation frequency in this phase increased with the proton motive force, as in completely competent cultures. These observations and the observed inhibition by NAD of both the proton motive force and the transformation frequency indicate that structural components of the competent state are formed in the initial phase of competence development, whereas the second phase is characterized by an increase of the proton motive force.

Induced plasmid-genome rearrangements in Rhizobium japonicum

The P group resistance plasmids RP1 and RP4 were introduced into Rhizobium japonicum by polyethylene-glycol-induced transformation of spheroplasts. After cell wall regeneration, transformants were recovered by selecting for plasmid determinants. Plant nodulation, nitrogen fixation, serological, and bacterial genetics studies revealed that the transformants were derived from the parental strains and possessed the introduced plasmid genetic markers. Agarose gel electrophoresis, restriction enzyme analysis, and DNA hybridization studies showed that many of the transformant strains had undergone genome rearrangements. In the RP1 transformants, chromosomal DNA was found to have transposed into a large indigenous plasmid of R. japonicum, producing an even larger plasmid, and the introduced R plasmid DNA was found to be chromosomally integrated rather than replicating autonomously or integrated into the endogenous plasmid. Seemingly, a similar section of chromosomal DNA was involved in all the genomic rearrangements observed in the R. japonicum RP1 and RP4 transformant strains.

Cloning of the kanamycin resistance gene from a kanamycin-producing Streptomyces species

A kanamycin-producing strain, Streptomyces kanamyceticus ISP5500, is resistant to kanamycin. A kanamycin resistance determinant was cloned from S. kanamyceticus into Streptomyces lividans 1326, using the plasmid vector pIJ702. The resulting plasmid, pMCP5, could also transform Streptomyces lavendulae S985 and Streptomyces parvulus 2283 to kanamycin resistance. Transformants carrying pMCP5 were markedly more resistant than S. kanamyceticus to the aminoglycoside antibiotics sisomicin, tobramycin, amikacin, and gentamicin. Studies in vitro polyphenylalanine synthesis showed that strains carrying pMCP5 contained kanamycin-resistant ribosomes. However, growing S. kanamyceticus contained kanamycin-sensitive ribosomes. Ribosomes from S. kanamyceticus grown under kanamycin-producing conditions were kanamycin resistant.

[Physicochemical properties of the pKMR plasmids controlling antibiotic resistance and the capacity to produce colonization antigen]

KMR plasmids controlling antibiotic resistance and the capacity for production of the colonization antigen were identified in wild strains of E. coli (026, 0126, 0124) and S. sonnei isolated from patients with acute intestinal diseases. The strains of E. coli 026 and E. coli 0126 carried p KMR207-1 plasmid determining resistance to chloramphenicol and tetracycline and the adhesive properties. The molecular weight of the plasmid is 98 mD. The strain of S. sonnei carried p KMR 208-1 plasmid responsible for resistance to streptomycin, chloramphenicol and tetracycline and the adhesive properties. The molecular weight of this plasmid is 98 mD. The resistance to streptomycin and tetracycline and the capacity for the synthesis of the colonization antigen in E. coli 0214 was controlled by p KMR209 plasmid with the molecular weight of 2.66 mD. The restriction analysis suggests that p KMR207a-1 and p KMR 207b-1 plasmids detected in E. coli of different serotypes were identical, since they could be broken with BamH1 endonuclease into equal numbers of fragments similar by their molecular weights. p KMR207-1 and p KMR208-1 plasmids differed in their sensitivity to BamH-1 endonuclease. However, they were broken into 6 fragments similar by their molecular weights. p KMR207-1 and p KMR208-1 plasmids are probably closely related but not identical.

Isolation and characterization of Bacillus subtilis mutants altered in competence

We isolated and characterized four Bacillus subtilis competence-deficient mutants. The mutants were obtained by nitrosoguanidine mutagenesis and by screening for mutants unable to be transformed both on solid and in liquid medium. Most of the mutants obtained in this way were tested for their sensitivity to the DNA-damaging agents methyl methanesulfonate, mitomycin C, and UV light. Among the mutants which did not show an increased sensitivity to these agents, four were chosen for further characterization. Data were obtained which indicate that the mutants are reduced in chromosomal and plasmid transformation and in transfection, whereas they are not altered in transduction and in protoplast transformation. Transformation experiments carried out by mixing a culture of a mutant with a culture of a wild-type strain gave some complementation for competence with one of the strains. The mutants were also characterized for their capacity to bind, take up, and break down transforming DNA; furthermore, the four competence mutations were mapped, and the results indicate that they belong to four different genes.

Differences in transformation of repair-deficient mutants of E. coli with BPDE- or chlorozotocin-modified plasmid DNA

Plasmid pBR322 was alkylated with either chlorozotocin or with r-7,t-8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo-[a]pyrene (BPDE) before it was transformed into various strains of Escherichia coli. Plasmid survival was determined as ability to convert the bacteria to tetracycline and ampicillin resistance. Increased levels of alkylation caused a decrease in transforming activity in all strains studied. This decrease did not seem to be a result of alkylation induced strand scission, but rather some other biochemical or conformational change induced by the alkylating event. In E. coli AB1157 transformation was decreased by 50% with 6 alkylations/plasmid molecule for BPDE and 8-9 alkylations for chlorozotocin. At these levels of alkylation the loss in supercoiled DNA due to strand scission was less than 5%. Alkylated pBR322 was also transformed into repair-deficient strains of E. coli. In strain JC2924 (recA6) the survival of both BPDE- and chlorozotocin-modified DNA was similar to survival in the repair proficient strain AB1157, which would indicate that postreplicational repair of BPDE- or chlorozotocin-modified plasmid DNA was not significant under these conditions. Chlorozotocin-modified pBR322 did not seem to be repaired by the bacterial uvr-endonucleases as determined by plasmid survival in strains AB1884 (uvrC34), AB1885 (uvrB5) and AB1886 (uvrA6). With BPDE-alkylated plasmid DNA the results were strikingly different. Strains AB1884 and AB1886 were more sensitive to BPDE modified DNA than the wild type strain AB1157. Strain AB1885 was similar to AB1157 in sensitivity to BPDE-alkylated plasmid. These findings suggest that bacterial uvr-endonucleases may be able to recognize and repair BPDE-alkylated pBR322. The role of the uvrB protein in repair of alkylated DNA needs to be further investigated.

Concurrent transfer and recombination between plasmids encoding for heat-stable enterotoxin and drug resistance in porcine enterotoxigenic Escherichia coli

The frequency of and genetic mechanisms for simultaneous transfer of genes encoding for tetracycline and sulpha-streptomycin resistance, heat-labile (LT) and heat-stable (ST-mouse) enterotoxin production in porcine enterotoxigenic Escherichia coli to Escherichia coli K12 were investigated. Seven E. coli strains of 0-group 149 were studied by conjugation and transformation experiments. All strains transferred tetracycline-resistance plasmids at a high frequency. No interaction was observed between these plasmids and those encoding for LT production. However, most tetracycline-resistant recipient cells were ST-mouse+ following recombination events between plasmids encoding for colicin B and ST-mouse production and plasmids encoding for tetracycline resistance. Alternatively, when selecting for sulpha or streptomycin resistance a majority of the transconjugants were also ST-mouse+, as plasmids coding for sulpha and streptomycin were mobilized by the colicin B and ST-mouse encoding plasmid. Since the simultaneous transfer of genes encoding for drug resistance, colicin B and ST-mouse production are common events in vitro, they might also occur frequently in vivo during antibiotic selective pressure.

Local anesthetics block transient expression of inducible functions for transformation in Streptococcus sanguis

Procaine and tetracaine reversibly inhibit transformation by preventing the transient expression of competence-specific, inducible functions, which are usually triggered in response to cellular stimulation with competence protein. Affinity studies with 14C-labeled procaine showed that the anesthetic bound to cell surface macromolecules specifically in the initiation phases of competence-specific events and blocked transfer of information imparted by cellular membrane receptor(s) upon interaction with competence protein.

[Mutagenic action of O-methlhydroxylamide on transforming DNA]

The mutagenic effect of O-methylhydroxylamine (OMHA) on transforming DNA of Bacillus subtilis was studied. In accordance with the earlier reported chemical and functional data, the mutagenic effect was observed at 4.5 and 6.0 pH. An increase in pH caused a decrease in the rate of mutagenesis, though the maximal level of mutagenesis was equal at both values of pH. The results obtained with recipients defective in the system of UV-repair revealed that both products of reaction of OMHA with the cytosine-base of DNA, N4-metoxycytidine and N4-metoxy-6-metoxyamino-5,6-dihydrocytidine, are effectively eliminated through the system of UV repair.