In this paper, we report on the analysis of acid formation in an E. coli pyk mutant. The results demonstrate that acid formation is insignificant for both the wild-type and the mutant at low glucose concentrations. However, at relatively high glucose concentrations, acid formation remains very low for the mutant but is significant for the wild-type. This substantial reduction in acids is accompanied by an increase in CO2 production. Moreover, unlike the B. subtilis pyk mutant, the E. coli pyk mutant did not show a substantial increase in the PEP pool.