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In the polymorphic ciliate Tetrahymena vorax, the non-selective phagocytosis seen in microstomes changes to a highly selective process in macrostomes

Heidi K. Grønlien^*, Trond Berg and Arne M. Løvlie

Department of Biology, University of Oslo, PO Box 1051 Blindern, N-0316 Oslo, Norway

View larger version (29K): [in a new window]   Fig. 1. The distribution of latex beads in the pouch of macrostomes. Macrostomes were allowed to prey on latex beads with a diameter of (A) 20.3 µm and (B) 30.0 µm. The macrostomes did not differentiate between these two sizes. The macrostomes did not capture latex beads with a diameter of 3.0 and 41.3 µm. In all experiments, the concentration of beads was 106 ml-1. The experiment was repeated three times, and 50 cells are counted in each experiment. Values are expressed as the mean + S.E.M.

View larger version (18K): [in a new window]   Fig. 2. The percentage of macrostome cells that captured either deciliated Tetrahymena thermophila (grey columns) or latex beads with a diameter of 30 µm (stippled columns) in a medium containing (A) only deciliated T. thermophila, (B) only latex beads and (C) both deciliated T. thermophila and latex beads. The macrostomes consistently selected the cells rather than the beads. In all experiments, the concentration of the prey was 106 ml-1. The experiment was repeated three times, and 100 cells were counted in each experiment. Values are expressed as the mean + S.E.M.

View larger version (71K): [in a new window]   Fig. 3. (A) A macrostomal Tetrahymena vorax that has captured a latex bead with a diameter of 30 µm. The picture was taken 30 min after capture of the bead; there was no sign of phagocytosis of the latex bead. Scale bar, 20 µm. (B) A macrostomal cell Tetrahymena vorax that has phagocytosed a latex bead together with a T. thermophila cell. The picture was taken 10 min after adding T. thermophila cells and latex beads to the medium. Scale bar, 20 µm.

View larger version (27K): [in a new window]   Fig. 4. Diagram of the behavioural response of a macrostomal cell of Tetrahymena vorax after capturing a T. thermophila cell. The macrostome selects a T. thermophila (1) and captures it (2). The macrostome continues to swim in the same direction for 1.7±0.6 s (mean ± S.E.M., N=8) (3) before briefly swimming backwards and the anterior part starts to contract (4); this is followed by cell rotation (5). The total duration of the chain of events depicted (1-5) was 28.3±5.2 s (mean ± S.E.M., N=8). The cell then swims forward again, the prey is in a digestive vacuole (DV) (6). It normally takes 10-13 min before phagocytosis restarts.

View larger version (62K): [in a new window]   Fig. 5. The effect of cytochalasin B (10 µg ml-1) on phagocytosis in a macrostomal cell of Tetrahymena vorax. Both pictures are taken 30 min after the addition of T. thermophila to the medium. In the control cell (A), phagocytosis of three T. thermophila cells has occurred. In the cytochalasin-B-treated cell (B), the T. thermophila has been captured but no phagocytosis has taken place. DVs, digestive vacuoles. Scale bar, 20 µm.

View larger version (20K): [in a new window]   Fig. 6. The distribution of digestive vacuoles (A) in untreated microstomes (control) and (B) in cells treated with 5 µmol l-1 nocodazole. No significant differences were observed between the control and treated cells. In all experiments, the concentration of T. thermophila was 105 cells ml-1. The experiment was repeated three times, and 100 microstomal cells were counted in each experiment. Values are expressed as the mean + S.E.M.

View larger version (16K): [in a new window]   Fig. 7. The distribution of digestive vacuoles in macrostomes in untreated microstomes (A) (control) and in cells treated with 0.3 µmol l-1 (B), 3.0 µmol l-1 (C) and 30.0 µmol l-1 (D) nocodazole. Nocodazole largely prevented macrostomes from forming more than one digestive vacuole. In all experiments, the concentration of T. thermophila was 105 cells ml-1. The experiment was repeated three times, and 100 microstomal cells were counted in each experiment. Values are expressed as the mean + S.E.M.