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When living in nature Tetrahymena pyriformis is highly phagotrophic. The cell cytoplasm contains food vacuoles formed by the engulfment ot large molecular weight materials, including particulate matter, through the well developed buccal apparatus. However, no food vacuoles are formed when the organism is cultured axenically in chemically defined media containing only low molecular weight constituents; nourishment is apparently obtained by passage of nutrients across the cell membrane rather than by an engulfment or phagotrophic [phagocytic] process. In a more crude medium containing soluble materials of large molecular weight, such as the peptone-yeast extract broth, axenically grown cells contain large numbers of fluid vacuoles; phagotrophic activity of cells grown in this medium is demonstrated by the cell ability to incorporate the non-permeable dye, trypan blue (1). The phagotrophic activity of peptone-yeast cultured cells is lost after extensive washing with distilled water, phosphate buffer, or even with the defined synthetic growth medium. Addition of small amounts of peptone-yeast extract broth to washed cells, or to cells cultured in synthetic medium, rapidly stimulates phagotrophic activity, indicating the presence in the mixture of a phagotrophic inducer (unpublished observations). A similar requirement for a protein inducer has been shown for pinocytosis in amoebae (see for example, 2, 3). Novokoff has reported (4) that in Amoeba proteus acid phosphatase activity increases at the plasma membrane immediately prior to engulfment. Similar effects have been observed in pinocytic vacuoles of several higher animal tissues (5, 6). Since, as pointed out by Karrer (7), phagocytosis and pinocytosis are so closely related that they may be considered essentially the same process, it was of interest to ascertain if acid phosphatase activity is also associated with the phagotrophic (phagocytic) process in the ciliate.

ACID PHOSPHATASE ACTIVITY ASSOCIATED WITH PHAGOTROPHY IN THE CILIATE, TETRAHYMENA