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L-Alanine has important applications in food, pharmaceutical and veterinary and is used as a substrate for production of engineered thermoplastics. Microbial fermentation could reduce the production cost and promote the application of L-alanine. However, the presence of L-alanine significantly inhibit cell growth rate and cause a decrease in the ultimate L-alanine productivity. For efficient L-alanine production, a thermo-regulated genetic switch was designed to dynamically control the expression of L-alanine dehydrogenase (alaD) from Geobacillus stearothermophilus on the Escherichia coli B0016-060BC chromosome. The optimal cultivation conditions for the genetically switched alanine production using B0016-060BC were the following: an aerobic growth phase at 33 °C with a 1-h thermo-induction at 42 °C followed by an oxygen-limited phase at 42 °C. In a bioreactor experiment using the scaled-up conditions optimized in a shake flask, B0016-060BC accumulated 50.3 g biomass/100 g glucose during the aerobic growth phase and 96 g alanine/100 g glucose during the oxygen-limited phase, respectively. The L-alanine titer reached 120.8 g/l with higher overall and oxygen-limited volumetric productivities of 3.09 and 4.18 g/l h, respectively, using glucose as the sole carbon source. Efficient cell growth and L-alanine production were reached separately, by switching cultivation temperature. The results revealed the application of a thermo-regulated strategy for heterologous metabolic production and pointed to strategies for improving L-alanine production.

D-lactate is an important chiral intermediate and a substrate for polylactic acid (PLA) production. Escherichia coli accumulate D-lactate as the primary fermentative product, and synthesis is directly controlled by the activity of lactate dehydrogenase, the efficiency of the carbon resource utilization, and the redox state. D-lactate accumulation is complicated by the flux through the competing metabolic routes and the indirect regulation of energymetabolism, aswell as by the unexpected interconnectivities of the cellular components in the remote metabolic routes. These effects have been extensively studied, and a number of metabolic engineering strategies have been applied to overproduce D-lactate with high titers, yields and productivities in E. coli that have been able to reduce the production costs and precisely control the fermentation process. This review summarizes the related strategiesandsuggestsdirections for further study; these directions provide guidelines for the development of other metabolic products using E. coli as an industrial platform. [ABSTRACT FROM AUTHOR]