Acid stress survival by histidine decarboxylation in L. lactis.
A, L. lactis NZ9000 harboring pNZ-PhdcAPB (HDC+) or the empty vector pNZ8048 (HDC-) was grown in GM17 to stationary phase and washed and resuspended in GM17 adjusted to pH 3 with or without 25 mm histidine (His+ or His-, respectively). After 2-h incubation, 10 μl of droplets of serial dilutions were put on GM17 agar plates to determine colony-forming units (CFU)/ml. Dilution factors are indicated at the top. B, survival of L. lactis NZ9000 expressing the active (pNZ-hdcAPB, ■) or inactive pathway (pNZ-hdcA-S82S-PB, □) resuspended in GM17 containing 10 mm histidine adjusted to pH 3. At the indicated times, CFU/ml were determined as described above.