Fig. 6.

Fine-tuning the lactose/NPN ratio modulates physiological parameters including OP and stress tolerance. Data from the “Results” section were used to establish a correlation between the lactose/NPN ratio and the physiological parameters. The lactose/NPN ratio of growth media was plotted as a function of trehalose/NPN (A), the trehalose accumulation as a function of lactose concentration in growth media (B), and the GB accumulation as a function of NPN concentration in growth media. The lactose/NPN ratio was also plotted as a function of heat tolerance (D), of oxidative tolerance (E), of acid tolerance (F), and of bile salt tolerance (G). This suggests that the lactose/NPN ratio is correlated with the trehalose/GB ratio and that an optimal lactose/NPN ratio exists for each stress challenge