Discriminative effect of rifampin of RNA replication of various RNA bacteriophages.

Rifampin interferes exclusively with RNA replication in vivo of the group I phages MS2, f2, and R17, whereas QbetaRNA replication is unaffected by the drug. In addition, rifampin has a discriminative effect of group I phage RNA replication. In the experimental system employed by us the antibiotic differentially interferes with the synthesis of minus RNA strands in f2, whereas it has almost no effect on the synthesis of progeny plus strands. In MS2, the drug differentially arrests the synthesis of progeny plus strands and almost fails to affect the synthesis of minus RNA strands. In R17 both steps of its RNA replication are affected by rifampin, although each step is only partially (approximately 50%) inhibited. The relation of the present results to the possible role of bacterial proteins and tertiary structure of phage RNA in the process of template recognition is discussed.     

Packaging of genomes in bacteriophages: a comparison of ssRNA bacteriophages and dsDNA bacteriophages.

In complex DNA bacteriophages like lambda, T4, T7, P22, P2, the DNA is packaged into a preformed precursor particle which sometimes has a smaller size and often a shape different from that of the phage head. This packaging mechanism is different from the one suggested for the RNA phages, according to which RNA nucleates the shell formation. The different mechanisms could be understood by comparing the genomes to be packaged: single stranded fII RNA has a very compact structure with high helix content. It might easily form quasispherical structures in solution (as seen in the electron microscope by Thach & Thach (1973)) around which the capsid could assemble. Double stranded phage DNA, on the other hand, is a rigid molecule which occupies a large volume in solution and has to be concentrated 15-fold during packaging into the preformed capsid, and the change in the capsid structure observed hereby might provide the necessary DNA condensation energy.     

Effect of 1,3,5-triazines on various bacteriophages and their hosts]

In the agar diffusion test 24 triazines were investigated with regard to their action on the mulplication of DNA phages (lambda and LPP-1) and RNA phages (M12 and Qbeta). In several cases the amount of plaques was diminished or increased depending on the kind of triazine and virus. The investigations demonstrate the triazines to be able to interfere with the formation of plaques by virulent and temperate viruses of procaryotes.     

Recombination of uracil-containing lambda bacteriophages.

Controlled incorporation of uracil into the deoxyribonucleic acid (DNA) of lambda bacteriophages was achieved by growth on dut ung thy mutants of Escherichia coli. The frequency of substitution of uracil for thymine, estimated by alkaline sucrose sedimentation of phage DNA treated in vitro with uracil DNA glycosylase, ranged from 0.17 to 1.9%. The corresponding ratio between the plating efficiencies on wild-type (Ung+) and glycosylase-deficient (Ung-) bacteria ranged from 0.70 to 0.05. If a single-hit dependence of plating efficiency on uracil content is assumed, the probability that any given uracil residue is lethal is approximately 1% (about one-fifth the probability for a pyrimidine dimer). The effect of uracil on recombination was studied in experiments with lambda tandem duplication phages (ethylenediaminetetraacetic acid [EDTA] sensitive), which are converted to single-copy phages (EDTA resistant) by general recombination. For repressed infections (of homoimmune lysogens), recombination was measured by a two-stage assay (DNA extraction, transfection of spheroplasts, and EDTA treatment). The frequencies observed for uracil-containing phages (2 to 4%) were 5 to 10 times higher than control values. However, comparisons with ultraviolet irradiated phages indicated that uracil residues promoted recombination less than 1/100 as efficiently as ultraviolet-induced lesions. Recombination of uracil-containing phages during repressed infections was negligible in recA and partially reduced in recB bacteria. Recombination was very low in ung cells, suggesting that excision repair was responsible for the stimulation. Interestingly, uracil-stimulated recombination was elevated about twofold in xth bacteria.     

Characterization of Streptococcus bovis bacteriophages.

About 25 Streptococcus bovis bacteriophages were isolated from abattoir wastes, bovine rumen fluid, and lysogenic strains of S. bovis. Eight phages were selected and characterized by morphology, stability, rate of adsorption, single-step growth curve, serum neutralization, and antigenic relationship. Two distinct morphological phage types were found, one of which has not been previously reported for group D streptococci.     

Characterization of some pneumococcal bacteriophages.

The growth of pneumococcal phages at high cell and phage densities is enhanced strongly by the substitution of potassium for sodium in the medium. Initial titers of 2 X 10(10) to 4 X 10(10) PFU/ml are readily obtained, and concentrated stocks are stable in a storage buffer described here. The mechanism of the cation effect is obscure. Phages omega3 and omega8 each have linear double-stranded DNA of 33 X 10(6) daltons per particle, with an apparent guanine plus cytosine content of 47 to 49 mol%, as determined by buoyancy and melting temperature, but with an unusual absorbance spectrum. Efficiency of plating is high if sufficient time is allowed for a relatively slow adsorption, which differs several-fold in rate between the two phages. Morphologically, these and other pneumococcal phages are similar to coliphage lambda but with a longer tail and tail fiber. Upon UV inactivation, omega3 and omega8 have D37 values of 33 and 55 J/m2, respectively, and each shows multiplicity reactivation. A total of 13 ts mutants have been isolated from the two phages, representing only two complementation groups; complementation and recombination occur between omega3 and omega8 mutants. Both phages provoke high-titer antisera with extensive cross-reactivity against a number of newly isolated pneumococcal phages.     

Lysogenic pneumococci and their bacteriophages.

About half of pneumococci recovered from pediatric patients and one-third of isolates from adult patients yielded bacteriophages active against one or more of four noncapsulated indicator strains of pneumococcus. Strains of capsular types most frequently causing pediatric infections were associated with lysogeny. Classical restriction-modification phenomena have been demonstrated in vivo with some of the temperate phages, and correlation of restriction with the presence of one or the other of the two known pneumococcal restriction endonucleases has been established. The temperate phages differ serologically and in several other characteristics from virulent pneumococcal phages previously described. All pneumococcal phages so far studied can be classified into a minimum of three serological groups.     

Sporulation-converting bacteriophages for Bacillus pumilus.

Thirty-three sporulation-converting bacteriophages for Bacillus pumilus NRS576 were assigned to two apparently unrelated groups on the basis of morphology and antiserum neutralization. Bacterial sporulation mutants responded similarly (conversion or nonconversion) to representatives of both phage groups. Evidence is presented indicating that PMB1 and related phages specify a restriction and/or modification system.     

Inducible bacteriophages from ruminal bacteria.

The incidence of temperate bacteriophage in a wide range of ruminal bacteria was investigated by means of induction with mitomycin C. Supernatant liquid from treated cultures was examined for phagelike particles by using transmission electron microscopy. Of 38 ruminal bacteria studied, nine organisms (23.7%) representing five genera (Eubacteria, Bacteroides, Butyrivibrio, Ruminococcus, and Streptococcus) produced phagelike particles. Filamentous particles from Butyrivibrio fibrisolvens are the first of this morphological type reported from ruminal bacteria. All of the other particles obtained possessed polyhedral heads and long, noncontractile tails (group B-type phage). The limited range of morphological types produced by mitomycin C induction cannot yet account for the much wider range of types found in ruminal contents by direct examination. The presence of viral genetic material in a significant percentage of the bacteria tested, as well as in a range of different genera, indicates that viral genetic material may be a normal constituent of the genome of appreciable numbers of ruminal bacteria.