B~IJ~n~CK (1918)
reported that the yeast Candida pulcherrima forms a red pigment when growing in media to which iron salts have been added. If the organism is grown on plates of iron-poor media, pigment is not produced but, upon addition of a ferric salt solution to the growth on these plates, both the colonies and the agar medium surrounding them turn red. BwiJV,~mcK postulated that the organism excretes a colorless precursor ("chromog~ne incolore") which reacts with the iron present in the medium to form pigment, and concluded, on the basis of other experiments, that this reaction occurs only in the presence of 0~.
RO]~E~TS (1946) confirmed BEIJ]~R~CK'S observations on the indispensability of 02 for pigment production and reported that a precursor of the pigment, but not the pigment, is produced by the ceils during anaerobic growth in media containing iron. Upon exposure to air the precursor reacts with iron present in the medium and forms the red pigment.
An extensive investigation of the red pigment produced by C. pulcherrima was later conducted by VAN I)~ WALT (1952). According to this author, cells growing aerobically in iron-poor media do not excrete a precursor which yields pigment upon addition of iron, an observation conflicting with BwiJ~I~cK's conclusions. Furthermore, vA~ ])~ WALT found that cells growing anaerobically in the presence of iron do not produce a precursor from which the pigment originates upon exposure to 02. He concluded that the presence of both iron and 02 during growth affects cell metabolism by directing it toward pigment production. In other words, both iron and O 2 act as regulatory or controlling factors for the synthesis of pigment. VA~ ])E~ ~u investigated the chemical structure of the pigment, which he named pulcherrimin. Through his work and that of other investigators (KLvYv]~ et al., 1953 ; Cook and SLATWR, 1954, 1956) the pigment was characterized as a ferric complex of pulcherriminic acid (2,5-dfisobutyl-3,4-dihydro-4,6-dihydroxy-3-oxopyrazine 1-oxide). More recently MACDONALD (1963 and1966), as the