Stimulation of the lysogenization of Pseudomonas aeruginosa cells by phage transposon B39 induced by plasmid Rms163

The influence of Rms163 plasmid on lysogenization of Pseudomonas aeruginosa cells by B39 phage was studied. Plasmid Rms163 was shown to increase the frequency of lysogenization of PAO1 cells 7-8 times. C-mutants of B39 phage were isolated. According to complementation test, c-mutants were distributed into two groups--cI and cII/III. The product of cI is essential for establishment and maintenance of lysogenic state, cII/cIII product being only necessary for establishment of lysogenization. The mutants with special characteristics were isolated: B39cx1 phage carries a mutation which seems to be located on a regulatory site essential for establishment of lysogenic state. The region of the B39 genome responsible for interaction with Rms163 plasmid was mapped. Possible mechanisms of Rms163 plasmid interference with transposable B39 phage are discussed.     

The Influence of Changes in Magnetic Variations and Light–Dark Cycle on Life-History Traits of Daphnia magna

Day–night cycle is the main zeitgeber (time giver) for biological circadian rhythms. Recently, it was suggested that natural diurnal geomagnetic variation may also be utilized by organisms for the synchronization of these rhythms. In this study, life-history traits in Daphnia magna were evaluated after short-term and multigenerational exposure to 16 h day/8 h night cycle, 32 h day/16 h night cycle, diurnal geomagnetic variation of 24 h, simulated magnetic variation of 48 h, and combinations of these conditions. With short-term exposure, the lighting mode substantially influenced the brood to brood period and the lifespan in daphnids. The brood to brood period, brood size, and body length of crustaceans similarly depended on the lighting mode during the multigenerational exposure. At the same time, an interaction of lighting mode and magnetic variations affected to a lesser extent brood to brood period, brood size, and newborn's body length. The influence of simulated diurnal variation on life-history traits in daphnids appeared distinctly as effects of synchronization between periods of lighting mode and magnetic variations during the multigenerational exposure. Newborn's body length significantly depended on the lighting regime when the periods of both studied zeitgebers were unsynchronized, or on the interaction of light regime with magnetic variations when the periods were synchronized. These results confirm the hypothesis that diurnal geomagnetic variation is an additional zeitgeber for biological circadian rhythms. Possible mechanisms for these observed effects are discussed. Bioelectromagnetics. © 2020 Bioelectromagnetics Society     

Integration of phage Mu into the RP4::D3112A-plasmid in Escherichia coli cells

Hybrid plasmids obtained as a result of Mu phage insertions into the RP4::D3112 plasmid in Escherichia coli cells were studied. Stable maintenance of RP4::D3112 plasmid in E. coli cells was provided by using the D3112 phage genome with a point polar mutation in the A gene which prevented early genes' expression. The presence of D3112A- in the RP4 plasmid has been shown to have no effect on efficiency of phage Mu transposition into this plasmid. Moreover, RP4 and D3112 genomes were equivalent targets for Mu integration. The integration of transposable phage into genome of nonrelated phage can be used as one of the approaches to construct recombinant phage genomes in vivo in the absence of DNA homology.     

Differences in the allele state of genes controlling the specificity of adsorption in transposable phages of Pseudomonas aeruginosa

To reveal possible differences in adsorptional specificities of transposable phages of Pseudomonas aeruginosa and to study the genetical control of this character, we isolated a group of phage-resistant P. aeruginosa mutants using some temperate and virulent phages. The study of resistance of the mutants to all the phages permitted us to find some types of mutants and to build a formal scheme of distribution of adsorptional receptors on the surface of P. aeurginosa cell. According to the results obtained, there are two main "receptor chains", where the receptors for all phages under study are grouped. For the majority of phages, just a single adsorptional receptor is obligatory, and at least two essential receptors are needed for adsorption of virulent phage E79. Two receptors were found also for another virulent phage, phi 11, one of them only being essential. Transposable phages can be grouped into three types, according to their adsorptional specificities. No correlations of adsorptional specificity types and all other characteristics of transposable phages studied (including the sub-groups of transposable phages belonging to different DNA homology types) were found. Genes of natural transposable phages controlling the differences in adsorptional specificities revealed can recombine in phage crosses.     

Phage-transposon interaction: the cip locus of prophage D3112 responsible for the inhibition of integration and transposition of related phage B39 of Pseudomonas aeruginosa

Bacterial cells lysogenic for D3112, a transposable Pseudomonas aeruginosa phage restrict the growth of a related heteroimmune B39 phage. The lysogens are divided into two different types PAO(D3112). In the lysogens of the type I the efficiency of B39 growth only decreases slightly, the lysogens of the type II restricting completely the growth of this phage (e.o.p. is less than 10(-7). As shown by the results of Southern hybridization experiments, lysogens of the type I are monolysogens, while those of the type II are double or polylysogens. Restriction of B39 in PAO(D3112) is caused by expression of a locus in the D3112 genome. The locus has been termed as cip (control of interaction of phages). The cip locus was mapped at the interval 1.3-2.45 kb of the D3112 physical map using different deletion derivatives of D3112. Expression of cip only takes place in the prophage state and not during the phage lytic development. When expressed, cip affects the early steps in the growth of B39 lowering the level of integration and transposition processes; the effect is not dependent on the way of initiation of the lytic cycle (through prophage induction or infection).     

Role of the body in primary signal processing by the electroreceptor system of the skate

Using a mathematical modeling technique, possible spatial mechanisms of processing information by the ampullae of Lorenzini were investigated in the skate during detection of the dipole electric field corresponding in the first approximation to the bioelectric fields of marine vertebrates and invertebrates. Stationary voltage distribution in the inhomogeneous environment was calculated numerically. An unlimited volume of seawater was used as the environment into which a slim disk was placed simulating the body of the fish, which served to create inhomogeneity. When the dipole axis was on the same plane as the disk, distortion in the voltage distribution was negligible. On occasions when the dipole was perpendicular to the plane of the disk, the electrical field energy absorbed by ampullary groups decreased significantly. Calculations suggested that by reorienting its body the fish is able to phase out signals coming from dipoles with their axes on different planes from that of the skate's body.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 660–665, September–October, 1985.     

Pseudomonas bacteriophage phi KZ contains an inner body in its capsid

Electron microscopical examination of the new virulent bacteriophage phi KZ, specific for Pseudomonas aeruginosa, has revealed an unusual structure in its capsid. In the center of the phage head is a cylinder of low electron density ("inner body"), surrounded by fibrous material which is packed around the inner body in a spoollike manner. The inner body itself has a springlike appearance. These structures disappear after adsorption of phage particles to bacteria. Various morphological forms, which can be interpreted as intermediate steps in phi KZ DNA condensation, have been seen in ultrathin sections of phi KZ-infected cells.     

Multiplicity of the integration sites of Mu-like bacteriophages into Pseudomonas aeruginosa chromosome and plasmids

It has been shown that D3112 prophage can be integrated into different chromosomal sites of Pseudomonas aeruginosa. The other Mu-like phages (B3, B39, PM69) are capable to insert their genomes during infection process into the plasmids RPL11, RMS148, RMS163. Their integration is occasionally accompanied by formation of mutations in plasmid genes. The certain types of auxotrophic and morphological mutants (thi, met, pigmented, met - pigmented) can be found at a frequency about 10% among survivors after a long (48 h) incubation at 42 degrees C of PAO (D3112cts15) or PAO (B39cts1) lysogens. The spectrum of mutants might depend on the time of heat induction. After a short exposure (10-20 min), arg and pigmented mutants can be found. Accumulation of certain kinds of mutants after heat induction is quite a specific phenomenon for Mu-like phages; heat induction of PAO (F116ts245) does not lead to selection of these specific bacterial mutants (F116 is unrelated to Mu-like phages and has extrachromosomal location).     

Transposition of the phage D3112 genome in Escherichia coli cells

It has been demonstrated that the genome of phage D3112 of Preudomonas aeruginosa can be transposed into Escherichia coli chromosome as a component of the hybrid plasmid RP4 TcrKms::D3112. Also, transposition of D3112 from E. coli (D3112) chromosome into RP4 plasmid occurs. The phage stimulates the chromosome mobilizing activity of RP4 plasmid, similar to other transposons. E. coli (RP4::D3112) cells were previously shown to form no colonies at 30 degrees C. Auxotrophic mutants and mutants incapable of utilizing different carbohydrates were found among E. coli clones survived after a long incubation at 30 degrees C (at frequencies approximately 10(-3) - 10(-4). These mutants inherited stably the capability to produce D3112 phage. E. coli auxotrophic mutants have arisen indeed as a consequence of phage integration into the E. coli chromosome, since prototrophic transductants derived from these mutants after their treatment with generalized transducing P1 phage have lost the ability to produce D3112 phage. Clones with mutations in Km or Tc genes of RP4 plasmid, occurring at high frequencies (about 3%) were found after introduction of RP4 into E. coli (D3112). These mutant RP4 plasmids carry insertions of D3112 genomes. Clones of E. coli which lost mutant plasmids still produce D3112 and retain their initial auxotrophic mutations.