FIG. 2.

Kinetics of induction of the proU and kdp operons by osmotic shock with 0.3 M NaCl. Strain TL3353 (kdp⁺ proV⁺ proW⁺ proX-phoA/proV⁺pro W⁺ proX-lacZ) was grown in K medium and shocked with 0.3 M NaCl at 0 min. The accumulation of the kdpA, proV, phoA, and lacZ mRNAs was determined by Q-RT-PCR. The synthesis of alkaline phosphatase and β-galactosidase activities were measured at the indicated time points as described in Materials and Methods. The mRNA levels are normalized to the level of 16S rRNA, and the enzyme activities are in nanomoles of substrate consumed per minute per milligram of protein. (A and B) Normalized mRNA levels displayed for the first 15 min (A) and for 60 min (B); panel A shows an expanded version of the same data as panel B. For the sake of clarity, the mRNA data for kdpA and lacZ are plotted on different scales than for proV and phoA; the normalized mRNA levels were multiplied by 2 for kdpA and by 10 for lacZ. (C) Alkaline phosphatase and β-galactosidase specific activities. The levels of the phoA and lacZ mRNAs from panel B are also included in this panel. The threshold times of induction and times of peak expression were determined by ANOVA, as described in Materials and Methods. The threshold induction times of proV and kdpA were at 4 and 9 min, respectively (P < 0.0001). Mean peak value expression of proV was at 14 min (t = 17.3) and of kdpA was at 20 min 20 min (t = 15.5) (P < 0.0001 for both).