Altered acetate metabolism and biomass production in several Escherichia coli mutants lacking rpoS-dependent metabolic pathway genes.

The stress responsive sigma factor RpoS regulates the expression of tktB and talAgenes of the non-oxidative pentose phosphate (PP) pathway, and fumCand acnA genes of the TCA cycle at the stationary phase of growth. In the present study, batch cultivations were performed using tktB, talA, fumC or acnA-knockout mutants of Escherichia coli to observe the metabolic changes at different phases of growth compared to the wild type strain. Although the specific growth rates of the mutants were similar to the wild type, acetate yield was nearly half in all mutants except the acnA mutant. Altered acetate yield in the mutants was also accompanied by variations in the biomass yield. While the biomass yield in both the tktB and talA mutants was increased by 13.8%, biomass was 5.5% and 13.8% lower in the fumC and acnA mutants, respectively. Upregulation of global regulators such as rpoS and soxRS, the acs, aceA, aceB genes, and several TCA cycle genes such as fumC, acnA and sucA, is consistent with higher acetate consumption and biomass yield in the tktB and talA mutants. On the other hand, the fumC and acnA mutants, with their impaired TCA cycles, were unable to utilize acetate for biomass production in spite of the higher expression of rpoS and soxRS.