A phytase gene from Aspergillus niger was isolated and two Escherichia coli expression systems, based on T7 RNA polymerase promoter and tac promoter, were used for its recombinant expression. Co-expression of molecular chaperone, GroES/EL, aided functional cytosolic expression of the phytase in E. coli BL21 (DE3). Untagged and maltose-binding protein-tagged recombinant phytase showed an activity band of similar to 49 and 92 kDa, respectively, on a zymogram. Heterologously-expressed phytase was fractionated from endogenous E. coli phytase by (NH4)(2)SO4 precipitation. The enzyme had optimum activity at 50 A degrees C and pH 6.5.