Effects of mutations in acetate metabolism on high-cell-density growth of Escherichia coli

To study the role played by acetate metabolism during high-cell-density gro wth of Escherichia coli cells, we constructed isogenic null mutants of stra in W3100 deficient for several genes involved either in acetate metabolism or the transition to stationary phase. We grew these strains under identica l fed-batch conditions to the highest cell densities achievable in 8 h usin g a predictive-plus-feedback-controlled computer algorithm that maintained glucose at a set-point of 0.5 g/l, as previously described. Wild-type strai ns, as well as mutants lacking the sigma(s) subunit of RNA polymerase (rpoS ), grew reproducibly to high cell densities (44-50 g/l dry cell weights, DC Ws). In contrast, a strain lacking acetate kinase (ackA) failed to reach de nsities greater than 8 g/l. Strains lacking other acetate metabolism genes (pta, acs, poxB, iciR, and fadR) achieved only medium cell densities (15-21 g/l DCWs). Complementation of either the acs or the ackA mutant restored w ild-type high-cell-density growth, On a dry weight basis, poxB and fadR str ains produced approximately threefold more acetate than did the wild-type s train. In contrast, the pta, acs, or rpoS strains produced significantly le ss acetate per cell dry weight than did the wild-type strain. Our results s how that acetate metabolism plays a critical role during growth of E. coli cultures to high cell densities. They also demonstrate that cells do not re quire the sigma(s) regulon to grow to high cell densities, at least not und er the conditions tested.