<p>Cultures in the mid-exponential phase (OD<sub>600</sub> = 0.6) were harvested and divided into two. Half of the cells were cultured for 2 h in the original medium, serving as the control group, and the other half of the cells wereculturedat pH 4.5 for 2 h, serving as the pre-stressed group. Then, the cells from both groups were harvested and challengedat a lethal pH 3.5 for 2 h. The resulting cells served as the control-pH 3.5 group and the pre-stressed-pH 3.5 group. ATR, response to pH 4.5; ASR, response to pH 3.5 of the cells in the control group; ASR, response to pH 3.5 of the cells in the pre-stressed group.</p
