IQ4 BIOLOGY OF SPECIALIZED GROUPS 



Bacterial pigments are secreted as colorless compounds, 

 which, in the majority of cases, are waste products of the 

 bacterial cell. These compounds are of the nature of leuco- 

 bases, which assume color only when oxidized by the air. The 

 yellow and black pigments are distinct oxidation products. 

 Chromogenic bacteria can be grown under certain conditions, 

 as, for example, at high temperatures, and no pigment will 

 be produced. Non-chromogenic forms can be produced from 

 ordinarily chromogenic forms, etc. There can be no doubt 

 that pigment formation is an unessential metabolic process to 

 the bacterial cell except, as mentioned before, in the chromato- 

 phorous bacteria. Very few chromogenic bacteria are patho- 

 genic to animals. Pseudomonas pyocyanea and the various 

 pyogenic micrococci are among the common forms. Chro- 

 mogenic bacteria among the plant pathogens are not un- 

 common. 



Migula has arranged the chromogenic bacteria into three 

 classes, as follows. Those producing 



(1) Pigments soluble in water. 



(2) Pigments insoluble in water, soluble in alcohol. 



(3) Pigments insoluble in water and alcohol. 

 Pigments Soluble in Water. Chromogenic bacteria which 



produce fluorescent pigments, which are soluble in the culture 

 media and diffuse through it, belong to this class. Pseudo- 

 monas pyocyanea, Pseudomonas fluorescens, and Pseudomo- 

 nas syncyanea are typical organisms of this group. Pseudo- 

 monas pyocyanea and Pseudomonas fluorescens, referred to 



