Antimutagenesis in Yeast by Sodium Chloride, Potassium Chloride, and Sodium Saccharin

Abstract

Aqueous salt solutions containing NaCl, KCl, MgCl₂, Na₂SO₄, CaCl₂, NH₄Cl, or sodium saccharin are mutagenic in yeast when logarithmic growth of cells is interrupted by exposure to a 0.5–2.0 M salt solution. Stationary-phase cells are not mutated by this treatment. When placed in an enriched medium with the salt, the stationary-phase cells grow after a prolonged lag period. The compounds tested (NaCl, KCl, and sodium saccharin), under conditions in which growth in medium can take place, exhibit an antimutagenic response as measured by the compartmentalization test.

The antimutagenic action of salt solutions in yeast is concentration-dependent. Unlike the mutagenic action of these compounds, which approximates an osmolality-dependent response, the antimutagenic action seems to be correlated with toxicity as measured by growth rate reduction at increasing concentrations of the compounds. For example, sodium saccharin and NaCl exhibit almost identical osmolalities; however, 0.3 M sodium saccharin reduces the growth rate much more than does 0.3 M NaCl. At these same molar concentrations, the spontaneous mutation rate for histidine prototrophy is, for the control, 6.2 × 10⁻⁸ mutations/cell/-generation, 3.5 × 10⁻⁸ with 0.3 M NaCl, and 1.7 × 10⁻⁸ with 0.3 M sodium saccharin.