L-Isoleucine synthesis

An advantageous fermentation method for production of L-isoleucine is the use of chemically synthesized substrates that only require a few steps to be converted to L-isoleucine. Among these the natural precursors 2-ketobutyrate or D,L-2-hydroxybutyrate have been used for the production with Corynebacterium glutamicum. A leucine requiring mutant of Corynebacterium glutamicum, with increased D-lactate utilization and consuming D,L-2-hydroxybutyrate, accumulates 13.4 g/L L-isoleucine. However, exploitation of this process is hampered by formation of byproducts. Sugar based L-isoleucine processes have been developed with strains of Corynebacterium glutamicum Serratia marcescens, and Escherichia coli. The mutant Escherichia coli H- 8285, being resistant to thiaisoleucine, arginine hydroxamate, and D,L-ethionine accumulates 26 g/L L-isoleucine in 45 h in a fed-batch process. Introduction of resistance to 6-dimethylaminopurine in strain H-8285 resulted in a mutant Escherichia coli H-8461 that increased L-isoleucine accumulation to 30.2 g/L. The biosynthesis of L-isoleucine has been investigated in detail on the level of involved genes, thus recombinant strains are being constructed with high productivity and selectivity. An appropriate balance of homoserine dehydrogenase and threonine dehydratase activities in the construct Corynebacterium glutamicum DR17/pECM3::ilvA (V323A) with feedback-resistant aspartate kinase create a specific productivity of 0.052 g L-isoleucine per gram dry biomass per hour. The recombinant strain Escherichia coli AJ13100 produces L-isoleucine from glucose with high selectivity in 30% yield.