Growth and proton exchange in recombinant Escherichia coli BL21

We have quantified the processes responsible for exchange of protons in batch cultures of Escherichia coli BL21 and a recombinant strain growing on glucose or glycerol as carbon substrates and ammonium as nitrogen source. Ammonium uptake was quantitatively the most important process accounting for 70±3 and 94±6% of overall proton production when glucose and glycerol were used as carbon sources, respectively. Formation of bicarbonate accounted for 11±1 and 6±1%, respectively, while acetic acid contributed with 19±2% of overall proton exchange when glucose was the carbon source. The amount of basic titrant added to maintain constant pH corresponded to the sum of the proton generating processes and could be used to estimate biomass concentration and specific growth rate of the cultures. Induction of recombinant protein production did not markedly change the stoichiometry between biomass formation and proton production though the specific growth rate decreased. Because of the conserved relationship between biomass formation and proton production, titrant additions were suited for indirect on-line estimation of biomass concentration and specific growth rate during recombinant protein production processes in E. coli BL21.