Radioresistance of Bacteria as a Function of p-Hydroxymercuribenzoate Binding

A linear relationship exists between the LDo0 of bacteria and the binding of p-hydroxymercuribenzoate (HMB). The radiation response of twelve strains representing four families and eight genera exhibited a range of LDgo from 4.5 to 450 kR with a variety of shapes. HMB binding varied from 2.7 X 10-19 to 4.6 X 10-17 mole per colony-forming unit (CFU). A similar relationship exists between the Do and the HMB binding per cell. This agent saturates its binding sites (sulfhydryl groups) in the intact cell in about 30 minutes and is located in the cell surface and in soluble intracellular fractions of both high and low molecular weight. Exceptions to the relationship include Escherichia coli Bs-, and mutants of Micrococcus radiodurans, which have a lower survival than their HMB binding would predict. Of the four strains of E. coli tested, all bind approximately the same amount of HMB; while their LD90's vary from 4.5 to 37 kR. Similarly, the mutants of M. radiodurans all contain the same sulfhydryl content, while their LDgo's vary from 105 to 735 kR (12). These data suggest that radioresistance is determined primarily by the presence of a functional repair system in the cells. The radioresistance of this repair system is in turn determined by the sulfhydryl content of the cell.