Fig. 3.

Influence of external K⁺ on kdpDE transcription. (A and B) Influence of K⁺ stimuli on the transcription of kdpDE. The transcript levels of kdpD and kdpDE in the WT were tested when the cells were grown under different K conditions for different times. Three groups of wild-type bacteria were initially cultivated in CDM with 0.2 mM K⁺ to an OD₆₀₀ of 0.3, and then K⁺ was added to two groups of these until final concentrations of 4 mM and 100 mM were reached. Each group was divided into three parts on average, and the three parts of the cells were harvested after cultivation for 10 min, 40 min, and a longer time (about 3 h to reach an OD₆₀₀ of 0.5). (C) Experiments to explore whether or not the K⁺ stimuli in the environment influenced the transcription of kdpDE through KdpE. The transcript levels of kdpD in SX10 (kdpE mutant) were tested with cells grown under different K⁺ conditions for different times. (D) Comparison of the transcript levels of kdpD between WT and SX10 (kdpE mutant) under different K⁺ conditions. All the real-time PCR assays were repeated four times with similar results. Error bars indicate standard deviations.