FIG. 4.

(A) Growth curves under hyperosmotic stress conditions (black symbols, 1.8 M sorbitol; gray symbols, 1.8 M KCl) of the K. lactis MW278-20C strains harboring pGM-GAM and either the empty vector p426SD11 (squares) or the pKlSOD1 plasmid (triangles) on YKK medium supplemented with 0.1 mM CuCl₂ and 0.1 mM ZnCl₂. (B) Cell viability after H₂O₂ exposure: the above-mentioned strains grown on YKK medium supplemented with 0.1 mM CuCl₂ and 0.1 mM ZnCl₂ for 48 h were challenged with 50 mM H₂O₂ for 15 min. The viability was evaluated by plating the samples on YPD medium and was expressed as the CFU percentage of the corresponding untreated cultures. The values are the means of three independent experiments and show an SD of <10%.