Fig. 4.

(a) Effect of lactic acid on NZ131 during the lag and exponential phases of growth. (a) A bacterial culture grown overnight in THY was diluted to OD₆₀₀ ~0.02 in fresh THY medium or in THY medium acidified with 1 M lactic acid to a pH of either 6.35 or 5.3. Samples were taken 2 h after the start of the culture, every 1 h during the exponential phase and for 2 h after the end of the exponential phase. Each time, OD₆₀₀ values were determined. The initial pH values are given at the end of each curve. (b) Effect of acidification of a NZ131 culture at the beginning of the exponential phase. An overnight bacterial culture was diluted to OD₆₀₀ ~0.02 and grown to OD₆₀₀ 0.3. At that point, the culture was split into two and one half was acidified to pH 5.41 with 1 M lactic acid. Samples from both cultures were taken every 15 min or at multiples of 15 min, and OD₆₀₀ and pH values (numbers in parentheses) were determined.