[Measurement of intracellular pH in long-chain dicarboxylic acid-producing yeast Candida tropicalis and its growth activity].

Intracellular pH (pHi) has an important influence on the metabolic activity of cells or cellular processes. The intracellular pH (pHi) of long-chain alpha,omega-dicarboxylic acid-producing Candida tropicalis was determined by fluorescence technique using a pH-sensitive fluorescent probe 5(6)-carboxyfluorescein diacetate. Optimal loading conditions of the fluorescent probe into the cells were experimentally determined. Effects of extracellular pH and carbon sources for growth on pHi in the cell grown in a flask were studied; the results indicated that extracellular pH has a slight influence on pHi, whereas carbon sources such as sucrose, glucose, acetic acid, and n-tridecane showed moderate influences. Further work on the relationship between the cell growth activity and pHi was carried out in a 5 L bioreactor. The time course of specific rates of the cell growth, glucose consumption, CO2 production, and pH gradients across cell plasma membrane were plotted, where the cell growth was improved by the higher pHi at 8 - 12 h. The measured pHi values were varied from 5.72 to 6.15 at medium pH 6.0 in which glucose and sodium acetate were used together as carbon source. The investigation of pHi can be helpful for understanding its effects on the kinetics of the metabolic steps involved in the synthesis rate of alpha,omega-dicarboxylic acid and alpha,omega-dicarboxylic acid transport across plasma membranes.