Preparation of Bilirubin Through the Biotransformation of Biliverdin Using Whole Cells of Recombinant Yeast

Bilirubin is a key component in the preparation of two traditional Chinese medicines: Calculus bovis sativus and Calculus bovis artifactus. Currently, industrial-scale production of bilirubin is limited to extraction from pig bile in a very low yield and its market price is very high, so it is important to develop an alternative method for producing bilirubin. This study developed a potential process for bilirubin production through biotransformation of biliverdin. The codon-optimized gene for biliverdin reductase (BVR) from Synechocystis PCC6803 was recombinantly expressed in Komagataella phaffii GS115, resulting in the genetically modified strain GS115-bvdR, which successfully expressed BVR with intracellular activity. Whole cells of GS115-bvdR were capable of transforming biliverdin to bilirubin in vitro. The overexpression conditions were optimized to enhance BVR production by GS115-bvdR, and the optimal conditions for the biotransformation of biliverdin into bilirubin using resting GS115-bvdR cells were established (pH 5.0 buffer, at 30 °C for 24 h, with 200 mg/L biliverdin). Under these conditions, a bilirubin concentration of 153 mg/L was achieved, with a conversion of 76.2% from biliverdin. These findings provide valuable insights for future studies on the biosynthesis of bilirubin through metabolic engineering.