Current knowledge of the Escherichia coli phosphoenolpyruvate-carbohydrate phosphotransferase system: peculiarities of regulation and impact on growth and product formation.

In Escherichia coli, the phosphoenolpyruvate-carbohydrate phosphotransferase system (PTS) is responsible for the transport and phosphorylation of sugars, such as glucose. PTS activity has a crucial role in the global signaling system that controls the preferential consumption of glucose over other carbon sources. When the cell is exposed to carbohydrate mixtures, the PTS prevents the expression of catabolic genes and activity of non-PTS sugars transport systems by carbon catabolite repression (CCR). This process defines some metabolic and physiological constraints that must be considered during the development of production strains. In this review, we summarize the importance of the PTS in controlling and influencing both PTS and non-PTS sugar transport processes as well as the mechanisms of transcriptional control involved in the expression of catabolic genes of non-PTS sugars in E. coli. We discuss three main approaches applied efficiently to avoid these constraints resulting in obtaining PTS(-) glc(+) mutants useful for production purposes: (1) adaptive selection in chemostat culture system of PTS(-) mutants, resulting in the selection of strains that recovered the ability to grow in glucose, along with the simultaneous consumption of two carbon sources and reduced acetate production; (2) replacement in PTS(-) strains of the native GalP promoter by strong promoters or the substitution of this permease by recombinant glucose transport system; and (3) enhancement of Crp (crp+) in mgsA, pgi, and ptsG mutants, resulting in derivative strains that abolished CCR, allowing the simultaneous consumption of mixtures of sugars with low acetate production.