Fed‐batch production of l‐tryptophan from glycerol using recombinant Escherichia coli

Abstract

l-tryptophan is an essential amino acid of high industrial interest that is routinely produced by microbial processes from glucose as carbon source. Glycerol is an alternative substrate providing a variety of economic and metabolic advantages. Process performance of the recombinant l-tryptophan producer Escherichia coli NT367 was studied in controlled fed-batch processes. The chromosome of the recombinant l-tryptophan producer was equipped with additional genes coding for enzymes of the aromatic amino acids biosynthetic pathway and l-serine biosynthesis, including genes for feedback-resistant enzyme variants ( trpE fbr , aroFBL, and serA fbr ), deletions of enzymatic steps for the degradation of precursors or the product l-tryptophan ( sdaB and tnaA), and alterations in the regulation of l-tryptophan metabolism (deletion of trpL and trpR). The impact of glycerol supply rates as well as the application of a multicopy plasmid (pF112- aroFBL -kan) were investigated in fully controlled stirred-tank bioreactors on a 15 L scale. The combination of E. coli NT367 carrying pF112- aroFBL -kan and an appropriate biomass-specific glycerol supply-rate resulted in the highest final product concentration of 12.5 g L -1 l-tryptophan with the lowest concentrations of other aromatic amino acids. Fed-batch production of l-tryptophan from glycerol was shown for the first time with recombinant E. coli.