Patent ID: 7687253

Claim:
An isolated E. coli strain producing between about 95 and about 150 g/L, of L-threonine by about 48 hours of growth in culture produced by a process comprising: (a) inserting into the chromosome of an E. coli cell at least one threonine operon operably linked to a non-native promoter to produce a parent strain; (b) performing at least one cycle of mutagenesis on the parent strain; (c) screening the mutagenized parent cells to identify mutagenized parent strains which produce between about 95 and about 150 g/L, of L-threonine by about 48 hours of growth in culture; (d) culturing said mutagenized parent strains in a medium containing at least 0.2% threonine raffinate based on ammonium sulfate content wherein said threonine raffinate is the broth effluent waste stream product generated during the ion-exchange chromatographic purification of L-threonine; and (e) selecting at least one threonine raffinate-resistant mutagenized E. coli strain that overproduces L-threonine compared to an unmodified E. coli strain, wherein said mutagenized threonine raffinate-resistant E. coli strain produces between about 95 and about 150 g/L of L-threonine by about 48 hours of growth in culture.