X-ray inactivation, Weigle reactivation, and Weigle mutagenesis of the lysogenic Vibrio kappa phage.

Vibrio cholerae lysogenic kappa phage was inactivated by X-ray (60 kV) in a dose-dependent manner, the inactivation dose leading to 37% survival (D37) in phosphate-buffered saline (PBS), pH 7.4, being 0.36 kGy. The phages were significantly protected against X-ray irradiation when histidine or cysteine or both were present in PBS or when phages were irradiated in nutrient broth. Maximum protection was offered when both histidine (10.0 mM) and cysteine (10.0 mM) were present in PBS (dose enhancement factor being 4.17). The X-irradiated kappa phages also underwent a small but significant Weigle reactivation and also Weigle mutagenesis in the UV-irradiated V. cholerae host H218Smr. The Weigle factor or the frequency of clear-plaque mutants increased with increasing UV dose, attained a maximum at a UV dose of 2.4 J m-2, and thereafter decreased gradually with a further increase of the UV dose. The X-ray dose (D)--survival (S) curves could be empirically described by the equation S = exp[-(aD + bD2)], where a and b are constants depending on the irradiation conditions, and a good agreement between the theoretical curves and experimental data was obtained.

Ultraviolet inactivation and photoreactivation of the cholera phage 'kappa'.

The lysogenic cholera phage, 'Kappa' is some ten to twenty folds more resistant to UV (254 nm) than are most of the T. phages of E. coli, or the cholera phage PL 163/10, or the host V. cholerae strain H218 Smr, the 37% (D37) and 10% (D10) survival doses being 255.8 J/m2 and 633.6 J/m2 respectively. The UV-irradiated 'Kappa' phages could be photoreactivated in the host V. cholerae strain H218 Smr to a maximum extent of 40%. The removal of the number of lethal hits per phage by the survival-enhancement treatment (photoreactivation) with time followed an exponential relation, the constant probability of removal of lethal hit per unit time being 2.8 x 10(-2)min-1. The UV-irradiated phages could also be Weigle reactivated in the host strain H218 Smr by a small degree, the maximum reactivation factor (ratio of survivals in UV-irradiated and non-irradiated hosts) being 1.50.