Time course of adaptation to elevated salt by Saccharomyces rouxii

Cells from a 24-h preculture of Saccharomyces rouxii grew without lag on a medium containing yeast extract, neopeptone, and glucose. Additions of 0.3 M KCl or 0.6 M pentaerythritol, which increased the osmolality of the medium 10-fold, still allowed immediate growth, whereas addition of 0.3 M NaCl resulted in a lag of 23 h (after which the growth rate was normal). The time course of growth in this elevated-sodium medium of 0.3 M was studied under defined conditions for inoculum history as well as experimental culture. S. rouxii cells with single exposure to elevated-sodium medium for 23 h exhibited a shorter lag (12 h) on fresh elevated-sodium medium; even with an intervening washing step. Elevated-sodium medium that had received the standard inoculum became conditioned during the lag so that it then supported growth of new, untrained cells with only 2 h lag; even with an intervening filter- or heat-sterilization treatment. The lag period on elevated-sodium medium could also be decreased by (1) using younger cells for inoculum, (2) increasing the amount of the inoculum, or (3) adding extra glucose to the medium. The results indicate that a diffusible, heat-stable factor is synthesized by cells during adaptation to elevated sodium, and that a threshold concentration of the factor is a prerequisite for the normal growth that eventually ensues. A change in retentivity for the factor with cellular age may explain the different growth kinetics with younger or older inocula.