Measurement of cytoplasmic pH of the alkaliphile Bacillus lentus C-125 with a fluorescent pH probe.

A method was established to measure the cytoplasmic pH of the facultative alkaliphilic strain, Bacillus lentus C-125. The bacterium was loaded with a pH-sensitive fluorescent probe, 2',7'-bis-(2-carboxyethyl)-5 (and -6)-carboxyfluorescein (BCECF), and cytoplasmic pH was determined from the intensity of fluorescence of the intracellular BCECF. The activity of the organism to maintain neutral cytoplasmic pH was assessed by measuring the cytoplasmic pH of the cells exposed to various pH conditions. The cytoplasmic pH maintenance activity of C-125 increased with increasing culture pH, indicating that the activity was regulated in response to the culture pH.