EXPERIMENTS ON PHOTOREACTIVATION OF BACTERIOPHAGES INACTIVATED WITH ULTRAVIOLET RADIATION

Abstract

The photoreactivation (PHTR) of the 7 bacteriophages active on Escherichia coli B inactivated with u.-v. light has been studied. PHTR occurs only if the inactivated bacteriophage is adsorbed on bacteria when exposed to the light; illumination of either phage or bacteria prior to adsorption is without effect. Bacterial extracts can not be substituted for bacteria. The survival curve of a phage obtained from PHTR has the same shape as the survival curve obtained in darkness, but it tends toward a straight line with different slopes. Ratio of the slope of the survival curve after PHTR to the slope of the curve in darkness measures the non photoreactivable sector of the cross section of a phage particle to u.-v. After adsorption of an inactive phage on metabolizing bacteria the max. amount of PHTR obtainable with a long exposure to light decreases with the time interval between adsorption and beginning of the illumination; if the phage is adsorbed on resting bacteria this decrease does not take place. PHTR as a function of the time of exposure to a constant light is a one-hit process; PHTR rate is independent of the dose of u.-v. used for inactivation, but depends on light intensity and on temp. When the intensity of the reactivating light increases, PHTR increases and tends to a max. Varying the temp. during the illumination modifies the PHTR rate: the Q10 of this modification increases at low temps. The action spectrum of the photoreactivating light shows a band with max. around 3650 A, extending from 3300 to 4800 A; in this range there is a slight absorption in the unmodified phage, but an absorption band appears in it after long u.-v. radiation. A working hypothesis is proposed, according to which PHTR consists in a photo dissociation of an inhibitor produced by u.-v. treatment on the phage; the dissociation is reversible and can be rendered permanent when the inhibitor is captured by a bacterial receptor. A photosensitive pigment must be involved of unknown nature.