To develop an effective fermentation system for producing Escherichia coli phytase AppA2, we expressed the enzyme in three inducible yeast systems: Saccharomyces cerevisiae ( pYES2), Schizosaccharomyces pombe ( pDS472a), and Pichia pastoris ( pPICZ alpha A), and one constitutive system: P. pastoris ( pGAPZ alpha A). All four systems produced an extracellular functional AppA2 phytase with apparent molecular masses ranging from 51.5 to 56 kDa. During 8-day batch fermentation in shaking. asks, the inducible Pichia system produced the highest activity (272 units ml(-1) medium), whereas the Schizo. pombe system produced the lowest activity (2.8 units ml(-1)). The AppA2 phytase expressed in Schizo. pombe had 60-75% lower K-m for sodium phytate and 28% higher heat-stability at 65 degrees C than that expressed in other three systems. However, all four recombinant AppA2 phytases had pH optimum at 3.5 and temperature optimum at 55 degrees C and similar e. cacy in hydrolyzing phytate - phosphate from soybean meal.