Coutilization of glucose and glycerol enhances the production of aromatic compounds in an Escherichia coli strain lacking the phosphoenolpyruvate:: carbohydrate phosphotransferase system

Background: Escherichia coli strains lacking the phosphoenolpyruvate: carbohydrate phosphotransferase system (PTS) are capable of coutilizing glucose and other carbon sources due to the absence of catabolite repression by glucose. In these strains, the lack of this important regulatory and transport system allows the coexistence of glycolytic and gluconeogenic pathways. Strains lacking PTS have been constructed with the goal of canalizing part of the phosphoenolpyruvate ( PEP) not consumed in glucose transport to the aromatic pathway. The deletion of the ptsHIcrr operon inactivates PTS causing poor growth on this sugar; nonetheless, fast growing mutants on glucose have been isolated (PB12 strain). However, there are no reported studies concerning the growth potential of a PTS-strain in mixtures of different carbon sources to enhance the production of aromatics compounds. Results: PB12 strain is capable of coutilizing mixtures of glucose-arabinose, glucose-gluconate and glucose-glycerol. This capacity increases its specific growth rate (mu) given that this strain metabolizes more moles of carbon source per unit time. The presence of plasmids pRW300aroG(fbr) and pCLtktA reduces the mu of strain PB12 in all mixtures of carbon sources, but enhances the productivity and yield of aromatic compounds, especially in the glucose-glycerol mixture, as compared to glucose or glycerol cultures. No acetate was detected in the glycerol and the glucose-glycerol batch fermentations. Conclusion: Due to the lack of catabolite repression, PB12 strain carrying multicopy plasmids containing tktA and aroG(fbr) genes is capable of coutilizing glucose and other carbon sources; this capacity, reduces its mu but increases the production of aromatic compounds.