Hyperproduction of tryptophan by Escherichia coli: genetic manipulation of the pathways leading to tryptophan formation

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Abstract
Conversion of glucose and ammonium salts into trytophan by mutants of E. coli was examined as part of a feasibility study on the manufacture of tryptophan. This involved construction, largely by transduction, of a variety of multiple-mutation strains with defined genotypes. By comparing the properties of these strains, several changes that significantly enhance process productivity were defined in biochemical terms: release of the 1st enzyme of the common pathway of aromatic biosynthesis and the 1st enzyme of the tryptophan pathway (3-deoxy-D-arabino-heptulosonate 7-phosphate synthase and the anthranilate aggregate, respectively) from inhibition by end products; blockage of the diversion of chorismate to phenylalanine and tyrosine biosynthesis; and presence of highly elevated tryptophan pathway enzyme levels, such as result from interference with both repression and attenuation, combined with gene amplification. Using strains carrying appropriate mutations to effect all of these changes, high values of specific productivity were obtained in bath culture (about 80 mg/g [dry wt] per h). A pronounced decay in the level of 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase activity was implicated as a cause of declining process productivity during stationary phase, emphasizing the value of having derepressed levels of this enzyme.