The resembling values of dry cell weight (i.e., 8.65 and 9.15 g L1) and specific growth rate (0.25 h1) were observed during the growth phase in fermentation I and II. Acetic acid recorded at the end of growth phase was 0.66 and 0.69 g L1, respectively. However, it was reduced to 0.08 g L1 after a centrifugation-resuspension step in fermentation III. A significant improvement of expressed phytase activity from 306 to 1204.3 U mL1, specific activity from 112.29 to 498.47 U mg1 as well as a 3.7-fold increase in phytase yield was noted. The higherproductivity for two-stage operation was attributed to the removal of acetate in the cell broth and resuspension of cell paste in a refreshed medium with yeast extract. It was found that phytase expression in the flask culture was strongly restrained in the presence of 2 g L1 acetate. Many studies have reported that the presence of growth inhibitors like acetic acid could limit the activity of recombinant strains during fermentation (13,29). Evidently, similar phenomenon was observed in the present study.