FIGURE 3.

The Δtggt1 mutant can replicate without exogenous glutamine even though it is vital to establish the parasite infection. A, schematized lytic cycle of T. gondii tachyzoites showing the consecutive events of invasion, replication, and egress. B and C, plaque assays. Tachyzoites were cultured with or without glutamine (2 mm) in medium containing 10% dialyzed serum or treated without or with DON (2 μm) in standard culture medium (37 °C, 7 days, 5% CO₂). Parasites added into the wells were allowed to sediment onto host cells by natural floating (sedimented) or centrifuged at 400 × g for 10 min immediately after adding parasites (centrifuged). DON was added at the time of (0 h) or after (4 h) infection of host-cell monolayers. Plaques were stained by crystal violet and analyzed using the ImageJ suite. Plaque numbers (B) and sizes (C) from three assays are shown (mean ± S.E.). Supplemental Fig. S7 shows the corresponding plaque images. Statistics (Student's t test) in panels B and C were done with respect to the parental strain grown under control condition (*, p < 0.05; **, p < 0.01; ***, p < 0.001). n.d., not detectable ; p.i., post-infection.