Enzyme cascades for the bioproduction of (R)-mandelic acid from L-Phe, glucose or glycerol. a The five-enzyme artificial cascade containing PAL, PAD, SMO, StEH, and AldO for the conversion of L-Phe to (R)-MA. b Biotransformation of glycerol or glucose to (R)-MA by combining L-Phe biosynthesis pathway with five-enzyme artificial cascade