Aerobic production of alanine by Escherichia coli aceF ldhA mutants expressing the Bacillus sphaericus alaD gene

Alanine was produced from glucose in an Escherichia coli aceF ldhA double mutant strain that contained the pTrc99A-alaD plasmid expressing Bacillus sphaericus alanine dehydrogenase. The aceF gene encodes one of the proteins of the pyruvate dehydrogenase complex, and therefore this strain required acetate as an additional carbon source. The ldhA gene encodes fermentative lactate dehydrogenase, a competitor of alanine dehydrogenase for the substrate pyruvate. Fermentations included an oxygenated growth phase followed by an oxygen-limited alanine production phase. The lowest value for the mass transfer coefficient (kLa) studied during the production phase yielded the greatest alanine. With feeding of glucose and NH4Cl, 32 g/l alanine accumulated in 27 h with a yield of 0.63 g alanine generated per gram glucose consumed.