Live Cell Measurement of the Intracellular pH of Yeast by Flow Cytometry Using a Genetically-Encoded Fluorescent Reporter

The intracellular pH of yeast is a tightly regulated physiological cue that changes in response to growth state and environmental conditions. Fluorescent reporters, which have altered fluorescence in response to local pH changes, can be used to measure intracellular pH. While microscopy is often used to make such measurements, it is relatively low-throughput such that collecting enough data to fully characterize populations of cells is challenging. Flow cytometry avoids this drawback, and is a powerful tool that allows for rapid, high-throughput measurement of fluorescent readouts in individual cells. When combined with pH-sensitive fluorescent reporters, it can be used to characterize the intracellular pH of large populations of cells at the single-cell level. We adapted microscopy and flow-cytometry based methods to measure the intracellular pH of yeast. Cells can be grown under near-native conditions up until the point of measurement, and the protocol can be adapted to single-point or dynamic (time-resolved) measurements during changing environmental conditions.