Continuous intracellular pH measurement: Escherichia coli culture medium pH dependence

Abstract

E. coli is the most used host microorganism to high-valuable compounds production in current industry. Cells pH homeostasis is a crucial factor to grow in different environment maintaining an intracellular pH control, however, to our knowledge, there is not a study about E. coli continuous intracellular pH growing in a culture. In this study the intracellular E. coli pH has been determined for cultures growing with glucose or glycerol as carbon sources. To determine intracellular E. coli pH, a novel, simple and accurate method based on pGFPR01 plasmid (kindly provided by Dr. Joan Slonczewski) was employed (1). This vector expressed ratiometric pHluorin. Thus, fluorescence ratio 410/470 showed a perfect lineal dependence with intracellular pH between 5.5 and 9. The results showed a surprising high intracellular pH for E. coli glucose cultures, which raised values of 8.5-9 at exponential growth phase. However, glycerol cultures showed a major regulation of intracellular pH, keeping the values at 6.5-7.5 in exponential and stationary stages. These differences show the dependence between the intracellular pH and the carbon source. In addition, the measurement method developed is a very useful tool for the control of bioprocesses.