The following Bacillus subtilis phages: SP8*, SP82, @e, SPO1,2C and SP50, were studied and compared for morphological characteristics as well as for physico-chemical properties of their DNA. All the determinations were efiected under identical conditions for the six different phages. The aspect and variety of plaques formed by them with susceptible strain B. subtilis 168-2 (as indicator host), on Difco nutrient agar plates, are slightly different from phage to phage, but do not allow differenciation.As shown by electron microscopy measurements, the five phages SP8*, SP82, SPO1, @e, and 2C are morphologically identical and easily distinguishable from SP50, but not from each other.As for the physico-chemical properties of their DNA, the first five phages are clearly different from SP50 DNA which was taken as a reference: (a) their analytical base composition is consistently the same, all of them containing hydroxymethyluracil instead of thymine in their DNA, and the analyzed percentage guanine plus cytosine is 390/,, as compared to 41.6O/, for SP50 DNA which has no unusual bases; (b) sedimentation coefficients for all the DNA (including SP50 DNA) are about 51 S, a t a concentration of 20 p.g/ml ( $ 2 0 ,~) ; (c) the melting point in 0.15 M NaCI, 0.015M Na citrate is 77.5", without any significant variation among the first group (as compared to 87.3", for SPBO, which is approximately the same as the host Bacillus subtilis 168-2); (d) in a cesium chloride gradient, the buoyant densities of the native DNA of the first group are all 1.742 g/cm3. Since the complementary strands differ in average base composition, two bands of buoyant density 1.752 and 1.762 g/cm3 are obtained following denaturation; (e) all denatured DNA become associated with polyriboguanylic acid [poly(G)], which is preferentially bound to the heavy component, although a slight binding to the light component also occured.Preparative centrifugation in CsCl density gradients in the presence of poly G results in good separation of the two components; (f) the extent of homologous base sequence among the six phages has been determined by DNA/DNA hybridization : hybridization of 2C DNA, SPOl DNA and SP82 DNA with 2C DNA is experimentally identical and assumed to represent 100°/, homology. However for SP8 DNA/2C DNA and @e DNA/2C DNA, the percentage is lower, amounting t o 92O/, and 83O/,, respectively. With SP50 and B. subtilis DNA it is only 7O/,.On the whole, there are no apparent properties, peculiar to one of the 2C, SP8*, SP82, @e, and SPOl phages, allowing its differentiation from the others, whereas SP50 is morphologically distinct, particularly by the length of its tail. It also differs by diverse physical and biological properties. All the common characteristics possessed by the first group of phages, particularly the high extent of DNA/DNA hybridization among them, and the fact that the phages and their DNA are serologically related, demonstrate their close relationship.Parmi les bacteriophages de Bacillus subtilis, certains ont la particularit6 ...

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(Rep le 30 septembre/6 d6cembre 1969)Bacillus subtilis phage 2 C DNA is double-stranded, with a high molecular weight (about 100 million), a low T, (77.8"), and a high buoyant density (1.742 g/cm3) in a CsCl densitygradient.Denatured DNA centrifuged in a CsCl gradient reveals two bands (1.752 and 1.762 g/cm3) corresponding to the complementary strands.I n this communication, we report preparative separation of two strands from denatured DNA, either by chromatography on a methylated albumin-kieselguhr column, or by density-gradient centrifugation in the presence of poly G. The melting curves of native and denatured DNA, and of isolated fractions before and after mixing and annealing, are compared. As shown by spectrophotometry, and by buoyant density, a good renaturation was obtained by mixing and annealing the "light" and ('heavy') fractions ; each isolated fraction cannot be renatured alone.Poly G strongly binds to the heavy fraction, increasing its density in a CsCl gradient by about 48 mg/cm3; there is also some binding to the light fraction (density increase under the same conditions, 6 mg/cm3). The resulting density difference between the two fractions is more pronounced than the natural one: 52 mg/cm3 instead of 10 mg/cm3. Poly C only interacts with the light fraction and host ribosomal RNA with the heavy one.Native DNA, and both fractions isolated by centrifugation in the presence of poly G, were analysed for base composition using 32P-labelled DNA. Native DNA had a (G + C) content of 39.1As for the isolated fractions, there are more pyrimidines (cytosine, and hydroxymethyluracil replacing thymine) in the "heavier" fraction, which preferentially interacts with poly G.Both strands from infectious DNA were assayed for infectivity with negative results. The "renatured" DNA also gave negative results, probably owing to some natural or accidental breakage.Le