Studies on pigmentation of Serratia marcescens. V. Accumulation of pigment fractions with respect to length of incubation time.

In 1930 Amako reported that as cultures of Serratia marcescens grew old their color changed from red to dark violet. He postulated that the change was associated with the pathway of pigment formation in the microorganism. Weiss (1949) observed a similar color change. Colonies growing on agar were orange-red in color at the end of 24 to 48 hr, but as they grew older the color changed to red-purple. He attributed the color change to certain pigment components which accumulated in the cells with age, and which, together with what he termed the major pigment fraction, contributed to the altered color. We have observed similar color changes, and have demonstrated that the pigment of 5-day-old cultures of S. marcescens may be separated into a blue fraction and a red fraction, the latter composed of three components (Green, Rappoport, and Williams, 1956). Chemical data presented in the report suggested that the blue pigment might be formed by aggregation of the red fractions. The combined blue and red pigments could account for the dark violet and red-purple colors of older colonies described by Amako (1930) and Weiss (1949). The experiments now reported were undertaken to determine whether the blue pigment fraction increased with the age of the cultures, and thus could contribute to the color change of older colonies. In addition, if the blue component were demonstrated to develop later than the red fraction, this fact would suggest that the blue pigment might be produced from the red.