Conversion of beta-sitosterol by Mycobacterium sp, NRRL B-3805 cells immobilized on Celite supports

Mycobacterium sp. NRRL B-3805 cells immobilized on Celite were effectively used for the selective side-chain cleavage of sitosterol to androstenedione (AD) in organic media (phthalate derivatives). Kinetic studies were perfor med with sitosterol concentrations up to 24 mM, with different Celite mater ials and particle sizes. Higher activity levels were observed when a larger pore size Celite was used as immobilization matrix. Substrate inhibition w as observed for sitosterol concentrations above 6 mM. Toxicity effects were not apparently correlated with the high log P solvents (> 9) here used as bioconversion media. The use of immobilized cells in repeated batch biotran sformations did not prove effective, mainly due to biocatalyst desorption d uring the periodical, aqueous washing steps used for nutrient delivery to t he cells. (C) 2001 Elsevier Science B.V. All rights reserved.