Photobiological behaviour of bacteria and phages supplemented with aza-analogues of nucleic acid bases

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Abstract
The photochemical stability of anomalous nucleic acid bases of the azatype, 5-azacytosine (I), 5-azacytidine (II), 6-azacytosine (III), 6-azacytidine (IV), 6-azathymine (V), 6-azauracil (VI), and 8-aza-adenine (VII) to U. V. light of the wavelength 254 nm differs from the U. V. stability of the normal constituents. Changes of the U.V. inactivation of Escherichia coli K12 C600, E. coli B, Bacillus cereus, as well as E. coli phages gamma cb2 and gamma b2b5 supplemented with azaderivatives prior to irradiation were investigated. It was found that I, II, III, IV, and VII are more, V and VI less sensitive to U. V. light compared with corresponding natural nucleic acid bases. Their changed U. V. sensitivities are reflected in the survival curves after U. V. -irradiation in as far as azabases are incorporated into the nucleic acids in vivo. This explains the increase in U.V. sensitivity of E. coli K12 C600, E. coli B, and B. cereus supplemented with I, II, III, IV, and VII and the decrease in U.V. sensitivity of Streptococcus faecalis supplemented with V (the latter information was taken from Gunther and Prusoff 1967). The lack of any significant influence on inactivation curves of E. coli K12 C600 by V and VI, and on E. coli phages gamma cb2 and gamma c2b5 by II, is discussed in terms of too small incorporation rates. No discrimination was put forward with respect to DNA and RNA incorporation.