FIG. 1.

Growth and acidification of monocultures and mixed cultures grown in 10% reconstituted skim milk at 42°C. (A) CFU per ml of S. thermophilus in monoculture (▪) and mixed culture (□) and L. bulgaricus in monoculture (▴) and mixed culture (▵), and the OD₆₀₀ of the mixed culture (○). Error bars indicate the standard deviations of triplicate measurements. Gray and white boxes indicate the five distinct growth phases of the mixed culture. Arrows indicate sampling points for transcription profiling. (B) pH (black lines) and acidification (mM lactic acid/h) (gray lines) of typical milk fermentations of S. thermophilus (dashed lines), L. bulgaricus (dotted lines), and the mixed culture (solid lines). In the S. thermophilus and mixed culture, the two exponential phases display a maximal acidification rate (1st and 2nd max). In between, at the transition phase at t = 4.5 h, there is a point at which the acidification rate drops almost to zero.