MORPHOLOGICAL HETEROGENEITY OF TEMPERATE ERWINIOPHAGE 59

This paper is devoted to the phenomenon of morphological heterogeneity within the population of the temperate erwiniophage 59, which does not have analogies among other bacterial viruses.

To investigate the basic properties of erwiniophage 59 heteroge- neous population obtained from different isogenic strains of amilovora-like bacterium Erwinia "horticola" (Eho).

Erwiniophage 59 was obtained by propagation on its traditional host Eho 450, as well as on its three isogenic strains and a related bacterium E. "horticola" 60. Physical and chemical properties of the phage particles were studied using centrifugation in CsCl-gradients, electrophoresis in agarose gels, electron micros- copy, restriction analysis ofDNA and SDS-PA GE of the virion polypeptides.

It was shown that the pool oftemperatephage 59 is a heterogeneous population consisting of two phage types when propagated on the mentioned hosts. These types are discrete and have buoyant-density difference of 0.02 g/cm3, that allowed to separate subpopulations for a de- tailed investigation. The subpopulation with the higher density was determined as the au- thentic bacteriophage 59 (subpopulation II with capsid diameter of55.36 nm). The capsid diameter of the subpopulation Iparticles equals 51.16 nm. Both types ofparticles do not differ by DNA size and have identical restriction patterns. Based on the SmaI-restriction analysis it may be concluded that the DNA packaging remains unchangeable and is carried out according to the headfull packaging mechanism. However; the subpopulation I differs from the original one by a relative content of some polypeptides. Curiously, the subpopulations I and II have different values of lysogenization and spontaneous induction frequencies.

An unusual type of morphological heterogeneity ofthe phage 59 particles was observedfor thefirst time; this heterogeneity is associated with the presence of two equimolar subpopulations with different physical and chemical parametrs of the virions. Morphological heterogeneity of temperate erwiniophage 59 significantly differs from such of the classical coliphages as T4, P1 and the phage system P2-P4.