1,3-Butanediol (1,3-BDO) is an important
C4 platform chemical widely
used as a solvent in cosmetics and a key intermediate for the synthesis
of fragrances, pheromones, and pharmaceuticals. The development of
sustainable bioprocesses to produce enantiopure 1,3-BDO from renewable
bioresources by fermentation is a promising alternative to conventional
chemical routes and has aroused great interest in recent years. Although
two metabolic pathways have been previously established for the biosynthesis
of (R)-1,3-PDO, the reported titer and yield are
too low for cost-competitive production. In this study, we report
the combination of different metabolic engineering strategies to improve
the production of (R)-1,3-BDO by Escherichia
coli, including (1) screening of key pathway enzymes; (2)
increasing NADPH supply by cofactor engineering; (3) optimization
of fermentation conditions to divert more flux into 1,3-BDO pathway;
(4) reduction of byproducts formation by pathway engineering. With
these efforts, the best engineered E. coli strain
can efficiently produce (R)-1,3-BDO with a yield
of 0.6 mol/mol glucose, corresponding to 60% of the theoretical yield.
Besides, we also showed the feasibility of aerobically producing 1,3-BDO
via a new pathway using 3-hydroxybutyrate as an intermediate.