185 Phytate Utilization by Tetrahymena

Abstract

Phytate, myo‐inositol hexakisphosphate, is the storage form of phosphate in seeds and grains and a major form of environmental phosphate loading from fertilizer inputs and agricultural runoff. Little is known about the effects of phytate on heterotrophic protozoa. Members of the genus Tetrahymena were chosen as the model organisms for this study because of their wide geographic distribution and adaptability. We found that Tetrahymena can use phytate as their sole phosphate source and that growth is comparable to that for cells grown in media containing orthophosphate. The internal phytate concentration increases dramatically during the logarithmic phase of growth and then decreases during the stationary phase. These internal levels in T. vorax are as much as 10‐fold greater than those for cells grown in phosphate without phytate, suggesting diet as a main source of accumulation. In T. thermophila, the internal phytate level also decreases during stationary phase, but the levels during both logarithmic and stationary phase of growth are similar whether cells are grown in phytate or phosphate. Tetrahymena thermophila possesses several nonspecific acid phosphatases capable of using phytate as a substrate including one associated with the pellicle. We are examining the properties of this phytase.