FIG. 5.

A specific internal pH is not the only requirement for acid stress survival. Cells (EK227) were grown in LBG to stationary phase. A 1-ml aliquot of the culture was harvested and resuspended in 200 μl of EG pH 2.3 medium with 40 mM sodium glutamate or pH 2.7 medium without exogenous glutamate. (A) Internal pH measurements were made at 0, 30, and 60 min after acid challenge. (B) ΔpH (inset) and survival were measured in the presence (hatched bars) and absence (solid bars) of glutamate. ΔpH was calculated by subtracting the internal pH from the external pH.