Differential inactivation of glucose- and glutamate dependent acid resistance of Escherichia coli TMW 2.497 by high-pressure treatments

The inactivation by 200-400 MPa and post-pressure survival at acid conditions of E. coli TMW 2.497 was characterized by the measurement of intracellular pH (pHin), viable cell counts, glutamate (Glu) and arginine (Arg) consumption, and the influence of mild adaptation to mild acid stress prior to pressure treatment. Glutamate and arginine did not affect viable cell counts or the pHin during pressure application but improved the ability to maintain a high pHin after pressure treatment. In pH 4.0 buffer without arg and glu, a 3 log reduction of cell counts occurred after 24 h of incubation, whereas little or no loss of viability was observed after 24 h incubation in the presence of glu and arg. During post-pressure incubation at pH 4.0, 10 mM glutamate were metabolized but only 2 mM arginine were used, indicating that glutamate rather than arginine was responsible for the protective effect on pHin and survival. In conclusion, the pressure induced, irreversible loss of the transmembrane ΔpH correlates to cell death and glu stabilizes the pHin of E. coli during post-pressure incubation.