BACTERIAL PIGMENTS 127 



colored about the portions most exposed to air. Since pigment-form- 

 ing bacteria produce pigments only under certain conditions, and can 

 grow abundantly without producing any pigment, it is evident that 

 the pigment formation is no very essential part of their metabolism. 

 It is possible to modify pigment production almost at will, and even 

 to develop races of bacteria that do not produce pigment at all from 

 races that ordinarily are pigment-producers. 



Of numerous classifications of pigment-forming bacteria, all faulty 

 because of our slight knowledge of the chemistry of the process, that 

 of Migula seems the best; it is based on the solubility of the pigments 

 formed, as follows: 



(1) Pigments Soluble in Water. — This includes the pigm-ents of all fluorescent 

 bacteria, as well as those giving a red or brown color to gelatin media. Most 

 important among these is Bacillus -pyocyane^is, whose pigments have been consider- 

 ably studied. There seem to be two pigments, one, pyocyanin, characteristic for 

 this organism ; and a fluorescent pigment which numerous other organisms also pro- 

 duce. Pyocyanin has been analyzed by Ledderhose, who found it to be a ptomain- 

 like body, a derivative of the aromatic series, probabh'^ related to the anthracenes. 

 It can be reduced to a colorless leuco-base, in which form it is probably produced by 

 the bacteria, and then is oxidized in the air into the pigment. Its composition is 

 ChHhN20 (the sulphur-containing pyocj'anin which has been described is probably 

 impure).^* The fluorescent pigment is insoluble in alcohol and chloroform, and 

 can thus be separated from pyocyanin, which is soluble in chloroform. Although 

 related to the ptomains, pyocyanin seems to be altogether non-poisonous to ani- 

 mals. 



Jordan^^ and Sullivan"" have studied the conditions under which pigments are 

 formed, and found that pvocyauin can he produced in protein-froe media, and 

 without the presence of either phosphates or sulphates; but both sulphur and 

 phosphorus must be present to produce the fluorescent pigment. As pigments 

 can be produced on media containing only ammonium salts of succinic, lactic, or 

 aspartic acid, or asparagin, they are evidentlj^ formed synthetically, and not by 

 cleavage of the media. 



(2) Pigments Soluble in Alcohol and Insoluble in Water. — The most important 

 bacteria of this group are the Slaphylococcus pyogenes aureus and citreus. Their 

 pigment is of a fatty nature, a lipochrome, which lies among thebacteria in the form 

 of dendritic crystals. Being a fat, it can be saponified, and when decomposed it 

 gives the acrolein reactions and odor, from the breaking down of the glycerol 

 of the fat molecule. Acted upon by strong sulphuric acid, the yeUow pigment 

 changes into blue granules and crystals {iipocyanin reaction). The lipochromes 

 are soluble in the usual fat solvents, and form fat spots on paper. 



(3) Pigments Insoluble in Water and in Alcohol. — The pigment of Micrococcus 

 cereus flavus belongs to this class; its nature is quite unknown. 



"* Analysis of pyocj'anin-HCl by Madinaveitia (Anales soc. espan. fis. quim., 

 1916 (14), 26.3) gave CsoHBsNiuCioOs, but the phj-sical properties indicated a 

 lower molecular weight. 



«' Jour. Exper. Med., 1899 (4), 627. 



