Phytases (myoinositol hexaphosphate phosphohydrolase EC 3.1.3.8 and 3.1.3.26) belong to a group of acid phosphatases which hydrolyse phytate to a series of lower phosphate esters of myo-inositol and phosphate (Jareonkitmongkolet al. 1997, Kim et al. 1998). Phytic acid is the major storage form of phosphate in plant seeds that are used as animal feed ingredients (Maga 1982). Phytase supplementation to poultry and swine diets is of growing interest as it has the potential both to improve feed efficiency and growth rate of the animals, and to mitigate against environmental pollution (Pen et al. 1993). There are reports on the supplementation of animal feed with yeast phytase to improve the nutritional status of feed (Stahl et al. 2000). An enzyme to be used in supplementing animal feeds must retain activity when exposed to 80–85◦C for a few seconds during pelleting. Among yeasts, extracellular phytases are produced by Schwanniomyces castellii (Segueilha et al. 1992) and Arxula adeninivorans (Sano et al. 1999), and an intracellular phytase occurs in Saccharomyces cerevisiae (Nayini & Markakis 1984). The present investigation deals with phytase production by the yeast, Pichia anomala. A high activity of intracellular phytase was detected although the extracellular phytase
activity was not significant (7 mU ml−1), and therefore, we have concentrated on the cell bound fraction, since yeast cells can be used as such to supplement animal feeds (Stahl et al. 2000). We report here our findings on the improvement of phytase production by P. anomala.