Metabolic pathways and ΔpH regulation in Escherichia coli during the fermentation of glucose and glycerol in the presence of formate at pH 6.5: the role of FhlA transcriptional activator

Abstract

Escherichia coli is able to ferment mixed carbon sources and produce various fermentation end products. In this study, the function of FhlA protein in the specific growth rate (µ), metabolism, regulation of ΔpH and proton ATPase activity was investigated. It was shown reduced µ in fhlA mutant by ∼25% suggesting the role of FhlA in the growth process. The utilization rate of glycerol is decreased in fhlA ∼ 2 fold depending on the ORP values. Bacteria regulate Hyd enzymes activity during the growth depending on the external pH, which manifests the lack of H2 generation during the glycerol utilization at pH below 5.9. It is suggested that cells maintain ΔpH during the fermentative growth via formate-lactate-succinate exchange. The decrement of the value of pHin, but not pHex in mutant cells is regulating ΔpH and consequently proton motive force generation.