Johann Then

Production of L-phenylalanine from phenylpyruvate using resting cells of Escherichia coli

SummaryWe describe the production of L-phenylalanine from phenylpyruvate using resting cells of a genetically modified strain of Escherichia coli. Fermentations were carried out by continuously raising the feeding rate of D-glucose. We reached a biomass of 10 g/l dry weight and an aminotransferase activity of 14000 U/l The maximum phenylalanine concentration achieved was 173 mmol/l with a phenylpyruvate molar conversion yield of 95%.

Cloning of the gene coding for aromatic amino acid aminotransferase from anE. Coli B strain

SummaryAnE. coli B strain showing high activity in the transamination of phenylpyruvate to phenylalanine was used as the DNA source for the construction of a cosmid library inE. coli DG30, a strain which is known to be defective in all three major transaminase genes (aspC, ilvE andtyrB). By complementation analysis, cosmid clones could be identified with inserts carrying atyrB gene. The DNA inserts were further subcloned into pAT153 and thetyrB gene fromE. coli B was found to be similar to the gene reported forE. coli K12. Plasmids containing theE. coli BtyrB gene were transformed into the originalE. coli B strain and the recombinant strains assayed for transaminase activity and plasmid stability.