Fermentation of 10% (w/v) sugar to D: (-)-lactate by engineered Escherichia coli B.

Derivatives of ethanologenic Escherichia coli K011 were constructed for D: (-)-lactate production by deleting genes encoding competing pathways followed by metabolic evolution, a growth-based selection for mutants with improved performance. Resulting strains, SZ132 and SZ186, contain native genes for sucrose utilization. No foreign genes are present in SZ186. Strain SZ132 also contains a chromosomally integrated endoglucanase gene (Erwinia chrysanthemi celY). Strain SZ132 produced over 1 mol lactate per liter of complex medium containing 10% (w/v) sugar (fermentation times of 48 h for glucose, 120 h for sucrose). Both strains produced 667-700 mmol lactate per liter of mineral salts medium. Yields for metabolized sugar ranged from 88% to 95% in both media.