PHOTOREACTIVATION 



475 



The action spectrum for E. coli (Fig. 12-7) is similar to that of photo- 

 reactivation of phage T2 adsorbed on the same bacterium (see Sect. 3-8), 

 the peak being more accurately determined at 3750 A. An unexpected 

 result is the finding that the action spectrum for S. griseus spores extends 

 considerably farther into the longer wave lengths, the peak being at 4360 

 A. The difference between the two spectra is undoubtedly substantial; 

 possible artifacts are discussed by the author, who also discusses the possi- 

 bihty that the photosensitive pigment of S. griseus spores is a porphyrin. 



6 - 



X) 



o 



>- 



o 2 



_i_L 



I I . 



3600 4000 4500 5000 5500 6000 6500 7000 

 WAVE LENGTH , A 



Fig. 12-7. The action spectra of photoreactivation of Streptomyces griseus and of 

 Escherichia coli B/r. The activity of each wave length, proportional to the reciprocal 

 of the dose of light, expressed in quanta per unit area, required for obtaining a stand- 

 ard degree of photoreactivation is plotted versus wave length. (From Kelner, 1951.) 



5-6. CHEMICAL ACTIONS CONNECTED WITH PHOTOREACTIVATION 



Monod d al. (1949) have observed that bacteria of the strain E. coli K12 

 irradiated with ultraviolet in citrate buffer and plated on a synthetic agar 

 medium are not photoreactivable, and that photoreactivability appears, 

 together with a considerable dark reactivation, if catalase or ferrous sul- 

 fate is added to the medium. Latarjet and Caldas (1952) showed that the 

 phenomenon is lather erratic and presumably finely dependent on the 

 physiological state of the bacteria. They found that catalase restoi'ation 

 can take place occasionally in th(> absence of light, but usually re(iuires 

 illumination; that it is absent in other strains of the same species, E. coli B 



