Conversion of chenodeoxycholic acid to ursodeoxycholic acid by Clostridium absonum in culture and by immobilized cells

Abstract

The bioconversion of chenodeoxycholic acid (CDCA) to ursodeoxycholic acid (UDCA) was observed in growing cultures of Clostridium absonum. Using carboxyl-[14C]chenodeoxycholic acid, we could measure the conversion of approx. 80% of the CDCA to UDCA. Concentrations of CDCA greater than 5 × 10−4 M decreased bacterial growth and bioconversion of CDCA to UDCA. Experiments were conducted with immobilized bacterial cells to measure the conversion of CDCA to UDCA in phosphate buffer solution. CDCA was converted to UDCA in 2 days of incubation, if the bacteria were grown in the presence of CDCA before immobilization. When grown in the absence of CDCA prior to immobilization, cells converted CDCA to the 3α-7-keto product. Transformation of CDCA to UDCA by immobilized cells was increased when the cells were maintained under anaerobic conditions. The activity of the immobilized cells was stable up to 10 days, but then decreased quickly. When the immobilized cells were activated with 0.5% peptone for 24 h prior to adding CDCA the activity and stability of cells increased by 30%.