Direct Evidence of Intracellular Alkalinization in Saccharomyces cerevisiae KNU5377 Exposed to Inorganic Sulfuric Acid

The toxicity of inorganic sulfuric acid as a stressor was characterized in Saccharomyces cerevisiae KNU5377. In this work, we examined physiological responses to low extracellular pH $(pH_{ex})$ caused by inorganic $H_2SO_4$, which could not affect cell growth after pH was adjusted to an optimum with Trizma base. The major toxicity of sulfuric and was found to be reduction of environmental pH, resulting in stimulation of plasma membrane ${H^+}-ATPase$, which in turn contributed to intracellular alkalinization. Using a pH-dependent fluorescence probe, 5-(and-6)-carboxy SNARF-1, acetoxymethyl ester, acetate (carboxy SNARF-1 AM acetate), to determine $pH_{in}$, we found that color was dependent on the changes of intracellular pH which coincided with calculated $pH_{in}$ of alkalinization up to approximately pH 7.3. This alkalinization did not seem to affect survival of these cells exposed to 30 mM sulfuric acid, which lowered the $pH_{ex}$ of the glucose containing growth media up to approximately pH 3.0; however, the cells could grow only up to 70% of the maximum growth in the same media, when 30 mM sulfuric acid was added.