STUDIES ON PIGMENTATION OF SERRATIA MARCESCENS V

Abstract

Cultures of S. marcescens change in color as they grow old. The change has been attributed to different pigment components which accumulated in the cells at different time intervals. Pigment was extracted from the Nima strain of S. marcescens by acetone treatment, and separated into blue and red fractions by chromatography. Quantitative measurement of the pigments are carried out by using their absorption coefficients. Red pigment could be demonstrated in 16-hr.-old cells, and this fraction comprised the major portion of total pigment until 144 hr. Blue pigment first appeared at 24 hr, when it comprised about 5% of total pigment. Maximal increase in both pigments occurred between 24 and 120 hr. During this interval the blue fraction increased at almost 10 times the rate of the red. At 144 hr the weight of the two fractions was almost equal. From this time to the termination of the experiment the blue fraction was the major component. After 288 hr it comprised about 55% of the total weight of pigment. Comparison between the rate of pigment accumulation and the population increase curve demonstrated that the maximal rate of cellular growth occurred before maximal pigment production. When visible pigment first appeared, cell growth had already slackened. The time of maximal pigment production coincided with the stationary phase of the growth cycle. Increase in pigment did not cease until after 288 hr when the culture was well into its phase of decline. Pigmentation increased during the latter phase although the viable count decreased. ,During the later culture phases, the amount of pigment in the cells paralleled the total cell mass rather than the viable count. The results substantiated the postulation that the pigment composition of S. marcescens varies with the age of the culture, and that the color change of colonies is the. result of the admixture of the pigment fractions.