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V N Krylov

Publications and source records attributed to V N Krylov.

At least 37 records · Page 2Linked to original sources
PubMed1999

[x811--mutation of the Pseudomonas aeruginosa transposable phage D3112 with a pleiotropic effect].

Characteristics of Pseudomonas aeruginosa Transposable Phage D3112 carrying mutation x811 are described. x811 is a recessive mutation with pleiotropic effect. It determines a deteriorated lysis of infected or induced bacteria, a delayed replication, and a considerably decreased replication rate. In addition, the x811 mutation is expressed as the Kil phenotype, since high-temperature induction of prophage D3112 cts15 x811 does not cause an immediate decrease in the ability of bacteria to form colonies at 42 degrees C. Restriction analysis of DNA of D3112 cts15 x811 and its segregants has not revealed extended insertions or deletions. The characteristics of segregants of the D3112 cts15 x811 phage agree with the suggestion that the x811 mutation has emerged in a regulatory element (a gene or a site) that controls both expression of the entire early operon, including the "pre-early" function Kil, and the regulation of the repressor synthesis.

DNA Transposable Elements↗
PubMed1999

[Comparison of the frequency of imi-r resistant Pseudomonas aeruginosa mutants generated by infection of the bacteria with various bacteriophage-transposons].

We compared the frequencies of imipenem-resistant (imi-r) mutants of a Pseudomonas aeruginosa laboratory strain PAO1 infected by the phages-transposons (PT) specific for this pseudomonad species. The frequency of imi-r mutants among the lysogenic bacteria that appeared after infection reflects the frequency of integrative (conserved) PT transposition into ompD2 gene responsible for synthesis of porin, the protein required for the passage of antibiotic through the cell membrane. After infection by either PT the proportion of imi-r mutants among the lysogenic bacteria was higher than that of spontaneous mutants. The imi-r mutants induced by PT infection form colonies that differ in morphology when grown on different media. The frequencies of imi-r mutants induced by all PT are similar, except for HW12, PM57, and PM62 assigned to a species of the group B3. The phages of this species induce imi-r mutants at a high frequency. Variations in frequencies and colony morphology of imi-r mutants are discussed.

Bacteriophages↗
PubMed1999

[Natural interspecific hybrids of transposable phages of Pseudomonas aeruginosa].

Bacterial viruses of Pseudomonas aeruginosa assigned to two groups, D3112 and B3, recombine with very low frequencies. Previous study of the genome structure of intergroup hybrids suggested the incompatibility of some genetic modules of these bacteriophages. In this work, several natural hybrid transposable phages that had the genomes largely consisting of modules of phages from group D3112 and B3, were described. The discovery of these phages suggests the continuous genetic exchange in nature of these viruses belonging to different species. This model is considered as promising from the viewpoint of monitoring virus evolution.

DNA Transposable Elements↗
PubMed1998

[Recombinational origin of natural transposable phages of related species belonging to group B3, active in Pseudomonas aeruginosa species].

A heteroduplex analysis of four related transposable phages--B3, PM57, PM62, and Hw12--of the Pseudomonas aeruginosa B3 group was performed. Heteroduplex structures, restriction maps, and data on DNA-DNA hybridization obtained upon hybridization of phage DNA restriction fragments with labeled probes representing different regions of the phage genomes are in good agreement. The data obtained strongly confirmed the recombinational origin of the analyzed phages. Thus, all natural transposable phages of P. aeruginosa, including phages from both group B3 and species D3112, were shown to have a recombinational origin.

DNA Transposable Elements↗
PubMed1998

[Role of divergence in evolution of group B3 Pseudomonas aeruginosa transposable phage evolution].

A heteroduplex analysis was performed to identify and map divergent DNA sequences in the genomes of the P. aeruginosa transposable phages (TPs) of group B3 using different formamide concentrations (30, 50, and 70%). Six PTs were classified into three related species--B3, PM681, and PM57. The role of DNA divergence in the evolution of TPs within one species is insignificant: the genomes of phages pM105 and PM681 (species PM681) and phages Hw12 and pM57 (species pM57) were shown to contain either homologous (98%) or nonhomologous DNA (2%). Homologous, divergent, and nonhomologous DNA regions (modules) were identified in the genomes of the TP of different species. Homologous modules with a level of DNA homology higher than 86% constitute approximately 30% of the phage genome; they are located at the left (1-5 kb) and right (29-38 kb) ends of the phage genome. Divergent modules with a DNA homology level between 50 and 67% and nonhomologous modules represent 30 to 35% and 25 to 30% of the phage genome, respectively. These regions form a mosaic structure in a 5-29-kb region. Thus, the key role of DNA divergence in the evolution of the natural TPs of three related species of group B3 was shown. A single region containing a 5-11-kb divergent DNA sequence was detected in the pM62 phage genome (species pM57). As shown by our previous data, this region was integrated into phage pM62 via interspecific recombination with a phage of species B3.

DNA Transposable Elements↗
PubMed1997

[Comparison of localizations of insertions of phage-transposons D3112 and B3 into the Pseudomonas aeruginosa chromosome].

Preferential chromosomal integration sites (sites of conservative transposition) of transposable phage D3112 were identified by means of pulsed-field gel electrophoresis and separation of restriction fragments of the Pseudomonas aeruginosa chromosome. Phase B3 was shown to differ from D3112 with respect to this trait. High site-specificity and regional specificity, typical for conservative transposition of D3112, can partially explain the absence of mutations in biosynthetic P. aeruginosa genes upon cell lysogenization with D3112 phage (unlike B3 phage).

Chromosome Mapping↗
PubMed1996

[Introduction of mutator phage D3112 of Pseudomonas aeruginosa into Alcaligenes eutrophus var. metallotollerans (Strain CH34)].

It is demonstrated that the intact genome of a D3112 tranposable phage (TP) of Pseudomonas aeruginosa, integrated into a recombinant plasmid RP4 :: D3112, can be transferred by means of conjugation from P. putida PpG1 (RP4npt :: D3112) donor cells into Alcaligenes eutrophus var. metallotollerans cells. P. aeruginosa strains are unacceptable as donors because they have a bactericidal effect on A. eutrophus. RP4npt :: D3112 plasmid is stably inherited by A. eutrophus with D3112 being expressed and successfully reproduced. However, TP loses the induction ability after UV irradiation or mitomycin C treatment. It is suggested that D3112 TP and its miniderivatives could be used in manipulations with A. eutrophus var. metallotolerans.

Alcaligenes↗
PubMed1996

[Selection and properties of totally phage-resistant mutant Pseudomonas putida PpG1].

The efficiency of using bacteria in open systems to degrade different anthropogenic toxic pollutants can depend strongly on the interaction between these bacteria and natural bacteriophages. The possibility of selecting bacterial Pseudomonas putida mutants resistant to all bacteriophages of this species known so far was tested (in our work, these mutants were designated totally phage-resistant mutants). In a model experiment, changes in the composition of a population upon prolonged growth of bacteria in the presence of one of the virulent phages were examined. On the basis of the results obtained, it is postulated that: (1) Mutants differing in resistance to various phages accumulate in a population; relative numbers of different mutants can undergo alterations over the course of time; mutants selected in the presence of a given virulent phage do not often manifest complete resistance to this phage. (2) It is possible to isolate totally phage-resistant mutants of P. putida PpG1. These mutants carry up to three different mutations simultaneously; however, these mutants regain sensitivity to many phages upon pseudoreversion occurrence.

Bacteriophages↗
PubMed1996

[Interaction between Pseudomonas aeruginosa phages-transposons: genetic analysis of the trait of inhibition by prophage D3112 of phage B39 development].

A novel, previously unknown cip gene of Pseudomonas aeruginosa phage D3112 was discovered. The cip gene is responsible for inhibiting the intracellular growth of the related heteroimmune phage B39 of P. aeruginosa. It was shown that the cip gene product inhibits replication of the B39 genome, interacting, apparently, with the definite s+ site in the phage B39 genome. Mutants cip- of phage D3112, incapable of inhibiting the growth of phage B39, and B39 mutants, insensitive to the action of the cip gene product of phage D3112, were isolated.

DNA Transposable Elements↗
PubMed1996

[Cloning and study of the expression of Pseudomonas aeruginosa cip1 gene by phage-transposon D3112 in a homologous host and in Escherichia coli].

Regulatory gene cipl of Pseudomonas aeruginosa transposable phage D3112 was cloned, and its expression was studied in P. aeruginosa and Escherichia coli. Overexpression of the cipl gene prevents transcription and replication of phage D3112 DNA and also lysogenization of bacteria P. aeruginosa PAO1 by phage D3112. The direction of cipl gene transcription within the vector was determined in the study of cipl gene expression, dependent on its orientation toward the gene lacZ promoter. The expression of the cloned cipl gene inhibited the specific TCS phenotype of E. coli (RP4 :: D3112) cells. The functional homology of the cipl gene of phage D3112 and the negative regulator ner of E. coli Mul phage was discussed.

Bacteriophages↗
PubMed1995

[Origin and properties of Pseudomonas aeruginosa PAO1 clones surviving after induction of prophages-transposons].

Various mutations cancelling the lethal effect of phage lytic development and simultaneous phenotypic modifications were found in rare clones surviving after incubation at 42 degrees C of Pseudomonas aeruginosa (D3112 cts 15), lysogenic for thermoinducible mutant cts 15 of the transposable prophage (TP) D3112. All mutations arose prior to thermal induction. Temperature induction of other bacteriophages (nontransposable) did not lead to selection of bacterial morphological mutants. Therefore, it was concluded that mutagenesis occurred upon the partial (reversible) TP derepression accompanied by coupled replication-transposition of TP, the latter being the direct cause of the mutator effect. Isolation of the P. aeruginosa PAO1 mutant R10 (this mutant is resistant to infection with TP at 42 degrees C) allowed the proper selection and examination of numerous survivors. Comparison of their types derived from lysogens with different prophage location indicated that the number of secondary sites where TP integration is possible without the loss of cell viability is limited. Several transposition events occurred in the history of some survivors (during a repeated or single derepression event). Type D clones, which produce small colonies, are of special interest, because mechanisms underlying the survival of such clones are extremely diverse, and their phenotypes indicate the possibility of stable chromosomal rearrangements in the genome of P. aeruginosa.

Cloning, Molecular↗
PubMed1995

[Mucoid clones of Pseudomonas aeruginosa PAO1, surviving after induction of prophage transposons].

The origin and properties of mucoid clones were studied. The clones were selected with high frequency after thermo-induction of Pseudomonas aeruginosa lysogenic for phage transposons (PT). The production of alginate does not promote the survival of lysogenic bacteria at 42 degrees C. Mucoid clones were shown to appear before thermo-induction; the frequency of their formation does not depend on the specificity of the mutator effect intrinsic to different PT. Phenotypic differences typical of mucoid clones can be mediated by different mutations promoting clone survival at 42 degrees C and by simultaneously arising additional mutations. The SL21 mucoid clone selected among clones of P. aeruginosa PAO1 resistant to PT of B3 possesses an additional trait of phage resistance at 42 degrees C. The presence of D3112 cts 15 prophage has no significant effect on the frequency of SL21 reversion to nonmucoidness. This means that the mutator effect of PT has made a slight contribution to this process. The appearance of mutations promoting the survival of the thermoinducible lysogen SL21 (D3112 cts 15) does not affect the frequency of the loss of mucoidness. Nonmucoid derivatives of SL21 were shown to differ in phage resistance at 42 degrees C and in the extent of the residual mucoidness manifested under specific conditions. Consequently, nonmucoid clones appear as a result of pseudo-reversions. Because some of these pseudo-revertants cannot again be converted to the mucoid form, it is concluded that they carry mutations in genes whose functions are obligatory for the production of alginate.

Alginates↗
PubMed1995

[Cryptic transposable phages of Pseudomonas aeruginosa].

Frequencies of nucleotide sequences homologous to phage transposons (PT) of two species, D3112 and B3, were assessed in genomes of natural Pseudomonas aeruginosa strains by the dot-blot hybridization method. These strains were incapable of liberating viable phages on a lawn of the PA01 standard indicator strain of P. aeruginosa. It was shown that the homologies detected belong to two groups, high and intermediate, with respect to homology level. Homology patterns were classified as high when they provided signals comparable to those for hybridization in a positive control; they were classified as intermediate when the hybridization level higher than the background level, but lower than in the positive control. Homologous PT sequences were designated as cryptic PT. Intact cryptic PT prophages were shown to exist in genomes of particular natural strains manifesting a high level of hybridization. However, the growth of these phages was limited by the restriction system of strain PA01. It is possible to isolate strains maintaining the growth of a portion of cryptic PT. These strains differed from P. aeruginosa with respect to the specificity of the restriction and modification system. Nevertheless, in most cases, the attempt to identify a novel host capable of maintaining growth of a cryptic PT failed. Natural strains often carry cryptic PT related to both known PT species, D3112 and B3. The frequency of cryptic PT is extremely high, reaching 30% in only strains with a high level of homology and up to 50% in all strains exhibiting homology. This high PT frequency is assumed to be associated with the considerable variation of P. aeruginosa.

DNA Transposable Elements↗
PubMed1994

[The phenotype of rpi mutant of Pseudomonas aeruginosa phage-transposon D3112 expressed in a heterologous Escherichia coli host].

A clone of Escherichia coli II-16 with unique properties was isolated upon incorporation of hybrid plasmid RP4::D3112 with an integrated genome of phage-transposon D3112 Pseudomonas aeruginosa into E. coli C600 cells. The cells of this clone produce viable phage and are not sensitive to growth under low temperatures, which is characteristic of the majority of E. coli (RP4::D3112) clones with the genome of wild type phage. The clone E. coli II-16 contains phage genome both in an integrated state within the chromosome and in plasmid RP4. The properties of phage D3112 in the clone II-16 demonstrated that the phage carried a mutation. The mutation was designated RP4-phage interaction (rpi). The phenotypic effect of this mutation is expressed as phage inability to replicate in response to the presence of plasmid RP4 at 30 C (Tcs phenotype). The mutant rpi differs in its characters from the previously described mutants in the early regulator gene cip, the analog of the ner gene of E. coli phage Mu1, and from the known mutations in the A gene. Plasmid RP4::D3112 rpi exerts an inhibitory effect on the burst size of RP4::D3112 in E. coli.

Clone Cells↗
PubMed1993

DNA homology in species of bacteriophages active on Pseudomonas aeruginosa.

Using electron microscopy and DNA-DNA-hybridization, 113 virulent and temperate bacteriophages specific for P. aeruginosa have been assigned to 23 species. In most cases, especially in virulent phages, both particle morphology and DNA homology types were in good correlation and their use was sufficient for clear-cut definition of phage species. No virulent phages of different species had any DNA homology. DNA homology was detected between temperate phages of several species. Temperate phages formed two large groups of two and seven species, respectively. The first group included all transposable bacteriophages. The extent of interspecies DNA homology of phages belonging to each group was not more than 10-15% (except for 25% for phages D 3 and KF 1). No DNA homology was between phages of different groups. The possible origin and function of homologous sequences (genetic modules, linkers, occasional insertional sequences) are discussed. One of the phages (phi C 15) may be considered as the result of recombination between phages belonging to two different species, 295 and SM.

DNA, Viral↗
PubMed1993

[Some developmental features of Escherichia coli Mu phage in Pseudomonas aeruginosa cells].

In order to determine the replication-transposition (RT) efficiency of Escherichia coli phage Mu in Pseudomonas aeruginosa cells, the change of Mu DNA copy number after transfer of P. aeruginosa (RP4::Mu) from 42 (the condition of RP4::Mu plasmid stability and low phage production level in P. aeruginosa) to 30 degrees C (the condition of RP4::Mu plasmid instability and higher phage production level in P. aeruginosa) was analysed. It was shown that the temperature shift causes no increase in Mu DNA copy number, although free phage DNA is revealed after transfer of the cells at 30 degrees C. Considering that the studied cells contained also a linear RP4 DNA and the free Mu DNA hybridized with the RP4 DNA, we proposed that the mature Mu DNA arises as a result of Mu genome packaging from the original plasmid. So, the Mu genome RT is uneffective in P. aeruginosa and all of the phage particles released from P. aeruginosa (RP4::Mu) cells contain Mu DNA apparently originated from the DNA of hybrid plasmid RP4::Mu. Moreover, these results suggest that the Mu DNA packaging is not effective in P. aeruginosa (taking into account that the P. aeruginosa (RP4::Mu) cells release about 10(-2) p.f.u./cell and that originally the copy number of RP4::Mu > or = 1).

Bacteriophage mu↗