LIGHT AS A FACTOR IN THE PRODUCTION OF PIGMENT BY CERTAIN BACTERIA

Abstract

Pigment formation is a phenomenon common in bacteria. Some workers have attempted to show that pigmentation serves a useful purpose, but, except for the purple bacteria, there is little evidence to indicate that pigments are really of value to the organisms that possess them. The bacteriologist makes use of them, it is true, for purposes of identification, but this can hardly be said to serve the organism. Pigments are often variable and not infrequently the ability to form pigment is permanently lost without altering other metabolic activities in any noticeable way. That the presence of molecular oxygen is necessary for pigment formation has long been known. Obligatory anaerobes, therefore, are never pig-mented. It is also well known that high incubation temperatures are unfavorable for pigment formation, and that continuous incubation at body temperature will often permanently deprive many of the saprophytic chromogens of their color-forming habits. The pH of the culture medium has an influence in many cases and also the presence of certain chemical substances in the culture medium. Recently, while studying a group of acid-fast bacteria, an organism was observed which developed a rich pigment when grown in the presence of light but which was wholly unpigmented when incubated in darkness. The examination of a rather large collection of acid-fast organisms, most of which were pigment-forming, revealed an additional strain exhibiting this peculiar action toward light.