FIG. 2.

Confocal micrographs of the interaction of Tetrahymena SSU with S. enterica serovar Thompson and L. monocytogenes. Staining with the green fluorescent DNA stain SYTO 9 revealed that (A) serovar Thompson was maintained at high density within the food vacu-oles of Tetrahymena while (B) L. monocytogenes cells were mostly digested (white arrows). The inset in panel B shows that grazing on L. monocytogenes pNF8 resulted in the presence of vacuoles that appeared fluorescent but with few bacterial cells (blue arrows) due to the release of GFP from digested cells. (C) Single optical slice through a large vesicle secreted by Tetrahymena and containing GFP-labeled serovar Thompson cells, only a few of which appeared nonviable by PI staining (yellow arrow), is shown. The micrographs were acquired by using a confocal laser scanning microscope (Leica Microsystems). Bars, 10 μm.