The yeast PhafJia rhodozyma, a promising microbial producer of the carotenoid astaxanthin, was cultivated in batch and continuous processes in an agitated and aerated fermenter using an acid peat extract -based culture medium. For the accelerated growth phase, the mean specific growth rate and doubling time were found to be 0.038 h-', and 18.24 hours, respectively. The production of astaxanthin was found to be basically growth associated, the maximum concentrations of the pigment produced in batch culture and continuous cultivation being similar.
Phafia rhodozyma is a basidiomycetous yeast that synthesizes the carotenoid astaxanthin, 3,3'-dihydroxy-P,P-carotene-4,4'-dione (JOHNSON and LEWIS 1979). This is the principal carotenoid found in the flesh of salmon (KARRER and JUCKER 1950, KANEMITSU and AOE 1958a, b, ANDREWES et al. 1974, SIMPSON et al. 198 1). It is also the most costly component of commercial salmonid feeds (TORRISSEN et al. 1989). l? rhodozyma was isolated in the 1970's from exudates of deciduous trees in Japan, Alaska, and the former Soviet Union (PHAFF et al. 1972, MILLER et al. 1976).
Although astaxanthin is rarely found in fungi, it has been isolated from the Basidiomycetes Peniophora aurantiaca, I! hydnoides andl? quercina of theAphyllophorales (GOOD-WIN 1972). When compared with Haematococcus, another possible biological source of astaxanthin, I! rhodozyma is more desirable for use as an industrial pigment source due to its heterotrophic metabolism, relatively rapid growth rate, ability to achieve high cell densities in industrial fermenters, nutritional quality, and safety as a food additive (AN et al. 1991). Potential industrial use is, however, limited by the relatively low quantities of astaxanthin in certain strains of the yeast.
Unlike the yeast Rhodotorula rubra, in which carotenoid biosynthesis occurs mainly after