Radiosensitization of microorganisms by radical anions. II. Streptococcus faecalis

The inactivation of Streptococcus faecalis by radiolytically generated selective inorganic radical anions was investigated. The Br-2 radical, but not (CNS)-2, had a pronounced radiosensitizing action. In gamma-irradiated solutions at pH 7.0, the radiosensitization of a variety of scavenging systems was studied. Among these the D10 for N2/Br- was 0.082 kGy while N2O/CNS- = 0.35 kGy, N2O = 0.25 kGy, N2 = 0.47, and O2 = 0.16 kGy. As shown previously, inactivation in N2O/Br- systems is due mainly to Br2 and HOBr. From the variation of the inactivation with pH by Br-2 and (CNS)-2 it was deduced that tyrosine is crucial for the survival of S. faecalis via inactivation of enzymes with essential tyrosine residues such as aldolase and lipoyl dehydrogenase which are presumably needed to make energy available for DNA repair. Studies with a variety of scavengers also revealed that the t-butanol radical produced some radiosensitization of S. faecalis while the damaging effect of e-aq was much less than OH as shown by the D10 at pH 7.0; N2/t-butanol = 0.32 and N2/ethanol = 0.71. The radiosensitizing action of Br-2 in a natural environment containing sewage sludge was also determined, using the faecal streptococcal group as test organisms.