Merging of a chemical reaction with microbial metabolism via inverse phase transfer catalysis for efficient production of red Monascus pigments

Both chemical catalysis and microbial fermentation are essential ways to produce small molecules related to our everyday lives. The apparent mismatch between the approaches used in synthetic organic chemistry and the culture conditions required to support living micro-organisms remains one of the largest challenges in combining chemical catalysis with microbial fermentation in a one-pot procedure. In the present work, microbial fermentation of red Monascus pigments, which involves biosynthesis of orange Monascus pigments and non-enzymatic chemical conversion of hydrophobic orange Monascus pigments into red ones, was set up as a model. Inverse phase transfer catalysis (IPTC) consisting of a water–tetradecane two-phase system with hydroxypropyl-β-cyclodextrin as an inverse phase transfer catalyst was exploited to accelerate the chemical modification of hydrophobic orange Monascus pigments. At the same time, Monascus aurantiacus exhibited excellent biocompatibility in this system. Thus, microbial fermentation and further chemical modification of orange Monascus pigments had been merged successfully in one-pot by IPTC, where the shift of the microbial metabolic flux to orange Monascus pigments (almost undetectable yellow Monascus pigments) and efficient production of red Monascus pigments (corresponding to nearly 2 g l−1) were achieved. This is the first report about exploitation of IPTC as a biocompatible medium for merging of a chemical reaction with microbial metabolism.