Liquid holding recovery in E. coli K12. II. Role of cellular multiplication

When UV-irradiated, wild-type E. coli cells are incubated in buffer before plating, consequent survival increases cannot be explained by repair mechanisms alone. Regardless of UV-dose, survival after 48-hours incubation reaches a "plateau" at 10(-1) survival level. An important fraction of the irradiated cells is capable of multiplying during buffer incubation, and the same phenomenon is observed with unirradiated E. coli whenever culture concentration is lower than 10(7) cells/ml. Protein contents per viable cell decreases significantly during buffer incubation. A similar phenomenon was observed in an excision deficient strain. Macromolecule biosynthesis was also observed during buffer incubation. We conclude that, under most experimental conditions, cellular multiplication plays a very important role in liquid holding recovery experiments.