Enantioselective Oxidation of Racemic Citronellol with an Interface Bioreactor

Abstract

Microbial oxidation of racemic citronellol was done on the interface between a nutrient agar plate and decane (interface bioreactor). While Rhodococcus accumulated (R)-citronellal (21-80% e.e.), many yeasts accumulated (S)-citronellic acid (20–68% e.e.) as the oxidation product. For the production of (R)-citronellal and (S)-citronellic acid, Rhodococcus equi IFO 3730 and Hansenula anomala IFO 0147 were the best strains, respectively. While citronellol-oxidation in R. equi IFO 3730 was (S)-selective, citronellal-oxidation was (S)-selective. Although H. anomala had also both (S-selective alcohol and aldehyde dehydrogenases (constitutive, NAD+-dependent), the equilibrium of the alcohol dehydrogenase shifted to reduction of citronellal. Geotrichum candidum JCM 01747 accumulated very high concentrations of citronellic acid (conversion yield 90% in 5 days or accumulation 65 mg/ml in 13 days) in spite of the strong toxicity of the acid, although the optical purity was low. For the alleviation of the toxicity of ...