Effect of growth rate reduction and genetic modifications on acetate accumulation and biomass yields in Escherichia coli

Although acetate biosynthesis in Escherichia coli provides an important int ermediary for ATP synthesis, its accumulation inhibits both cell growth and protein production. Since pyruvate provides the largest flux to acetate an d is central to the problem of acetate production, acetate accumulation cou ld be reduced or abolished if the pyruvate pool for the TCA cycle was reduc ed. To examine this possibility, various pyruvate kinase (pyk) and phosphot ransferase system (pts) mutants were tested for acetate production in batch cultures with glucose as the only carbon source. The pykA pyk mutant exhib ited significant reductions in the specific growth rate and acetate product ion compared with the wild-type strain. Interestingly, in the ease of pts a nd pts pyk mutants in which increased biomass yields were observed in compa rison with the wild-type strain, no acetate production was detected. Theref ore, these mutants are potentially useful for higher production of recombin ant proteins. The results from the continuous cultivation performed using t he wild-type strain at various dilution rates, suggest acetate reduction as a consequence of both genetic changes and growth rate diminutions.