The Production of Stable Populations of Color Variants of Serratia marcescens , # 274 in Rapidly Growing Cultures

Abstract

Tubes containing a synthetic ammonium citrate-glycerol broth were inoculated with colonies of different color types (dark red, bright pink, pale pink, and white), and the resulting cultures were kept growing logarithmically over prolonged periods by frequent transfers. At intervals the cultures were plated on synthetic agar and counts were made of the relative number of colonies of each color type which developed. In every case the populations eventually came to equilibrium with about 97% dark red and 3% bright pink colony-forming cells (at 30[degree]C). There was no evidence that the dark red type cells reproduced more rapidly than those of the paler color types; the observed changes in the compositions of the cultures were evidently due to the greater stability of the dark red type. About 0.01% of the dark red cells produced bright pink variants every 2 days, under these conditions of growth; in the same length of time about 0.32% of the bright pink cells produced dark red variants. The pale pink and white type cells appeared to be even less stable. There was no evidence that the pH or the oxidation-reduction potential affected the rates of variation, but temp, did seem to influence stability.