Figure 3. FIGURE 3: Effects of alkaline pH stress on phosphate metabolism.

(A) Depletion of intracellular PolyP stocks upon alkalinization of the medium. Strains BY4741 (wild type, closed circles) and its isogenic derivative DCS30 (ppn1 ppx1, open circles) were grown up to OD₆₀₀ 0.6 and subjected to alkaline stress (pH 8.0) as in 82. For comparison, in parallel experiments the wild type strain was subjected to phosphate limitation (0.1 mM Pi) as in 126. Samples of the culture were taken at the indicated times and polyP content determined as in 126. Data is expressed as percentage relative to the levels just prior initiation of the stress and are mean ± SEM from 3 independent experiments.

(B) Reversible cytosolic-nuclear transfer of Pho4 upon modification of the extracellular pH. Wild type strain DBY746 was transformed with plasmid Pho84-GFP, carrying a C-terminally GFP-tagged version of PHO4, and grown until OD₆₆₀ 0.6 in Verduyn medium 127. Aliquots were injected into a CellASIC^® ONIX Y04C-02 microfluidics chamber and the pH of the medium changed with time as indicated in the figure. Images were collected with a Nikon Eclipse TE2000-E microscope using a FITC filter and a Hamamatsu ORCA-ER camera.