120 CAROTINOIDS AND RELATED PIGMENTS 



ditions under which they develop, has already been pointed out. The 

 work upon which our present knowledge of carotinoids in bacteria is 

 based will now be reviewed. Bacteria are at present classified as 

 Schizomycetes, and arc best considered as algae. Their morphology 

 and reproduction most nearly resemble the Cyanophyceae. In fact, 

 bacteria are considered by some as having "degenerated" from the 

 blue-green algae. They do not, however, contain chlorophyll, and it 

 is this fact, especially, which enhances the interest in the possibility 

 of carotinoids being normal constituents of these organisms. 



As in the case of non-chlorophyll bearing fungi, it is not to be 

 assumed that all yellow, orange and red tinted bacterial colonies owe 

 their color to carotinoids. The pigments of B. prodigiosus and B. 

 xanthinum Ehren. first described by Schroeter (1875) are obviously 

 not carotinoids, although color alone would suggest that this is the 

 case. Griffiths (1892) ascribes the formula C 38 H 56 N0 5 to the red 

 pigment of B. prodigiosus, but the empirical relation between the car- 

 bon and hydrogen suggests, rather than negatives a relation of the 

 pigment to carotin. Schroeter described the change of color of the 

 colonies of this bacteria from red to orange to yellow and ascribed it 

 to the formation of an alkaline substance in the course of the growth 

 of the bacteria. This variation in color of B. prodigiosus is probably 

 well known to bacteriologists and might be thought to be due either 

 to a variation in concentration of the same pigment or to the presence 

 of distinct yellow (possibly carotinoid) and red pigments, the latter, 

 when present, masking the former. Schroeter supported his explana- 

 tion of the change in color, however, by showing that the orange-red 

 alcoholic extract of the bacteria turns red with acid and yellow with 

 alkali. 



Aside from the brief observation of Schrotter (1895) that the pig- 

 ments of Sarcina aurantiaca and M. (Staph.) pyrogenes aureus show 

 the solubility properties and color reaction (with H 2 S0 4 ) of "lipo- 

 xanthin" (carotinoid) our knowledge regarding carotinoid producing 

 species of bacteria is due apparently solely to Zopf (1889, a, c; 1891; 

 1892b) who has described the chromolipoids in eight species of bac- 

 teria. The descriptions as given by Zopf point with certainty to caro- 

 tinoids in the case of four species only, namely, B. egregium, B. Chry- 

 sogloia, M. (Staph.) aureus and Sphaerotilus roseus. The first three 

 of these bacteria form yellow colonies, but the last mentioned species 

 is red. The evidence for carotinoids is as follows: 



B. egregium. Forms intensely yellow colonies on gelatin or beef- 



