4.2. Cell Viability Assay—Propidium Iodide (PI) Staining

Propidium Iodide (PI) is a fluorescent dye that can pass through damaged membranes of dead cells and intercalate within the DNA staining dead cells which can be detected with a fluorescence microscope or flow cytometer. Logarithmic phase cell culture of W303-1A and rho⁰ strains in SD medium were treated with 3-BP. After treatment OD600 of samples was adjusted to 1.0 and 1 mL of cells was centrifuged (1 min, 10,000× g), the medium was removed, and the cell pellet was resuspended in 1 mL of PBS. Propidium Iodide (Sigma-Aldrich, St. Louis MO, USA) was added to a final concentration of 2 μg/mL and samples were incubated for 15 min in the dark. Samples were centrifuged (1 min, 10,000× g), the supernatant was removed and cells were resuspended in 1 mL of PBS (Phosphate Buffered Saline). Fluorescence was detected with Axio Imager M1 epifluorescence microscope (Carl Zeiss, Jena, Germany) using a CFP filter set. Percent of PI-positive cells was calculated.