Immobilization of Mycobacterium sp. NRRL B-3805 Cells onto Radiation Crosslinked PVA/PVP Hydrogels for Production of Androstenones from β-Sitosterol

The use of hydrophilic supports, as an immobilization matrix for mycobacterial cells, in a bioconversion system where hydrophobic species are present, such as sterols and mycobacterial cells, was evaluated. Several homo- and co-polymers prepared by y-irradiation were tested for cells surface adhesion. Immobilized mycobacterial cells onto poly (vinyl alcohol) (PVA)/ poly (vinyl pyrrolidone) (PVP) copolymer hydrogel led to the best bioconversion estimates. The highest yield of AD was observed using PVA/PVP copolymer of composition (8:2, w/w) polymerized at 20kGy y-irradiation dose. Under these conditions, almost the same product yield was obtained after only 24h incubation period compared with 48h in case of the free cells. Moreover, PVA/PVP mycobacterial beads could be used for 10 successive biotransformation cycles with a maximum product output of about 82%, which was of higher magnitude than that obtained by the free mycobacterial cells (76.5%). This work clearly highlights the ability of hydrogels to serve as an efficient immobilization matrix for mycobacterial cells to convert P-sitosterol to AD