Immobilized cells of Actinoplanes teichomyceticus ATCC 31121 were used to selectively cleave the acyl group of A40926 yielding the deacylated form of the molecule. The feasibility of this particular biotransformation in a series of three perfectly mixed airlift bioreactors with immobilized cells was examined. A continuously operated airlift cascade was designed using a model for a series of reactors with immobilized biocatalyst beads obeying Michaelis-Menten kinetics. In independent experimental runs the cascade bioreactor system was operated continuously for 56 days with an overall conversion of 99%. Model estimates for reactor volumes and relative conversions were found to be in a good agreement with the experimental results. (c) 2005 Elsevier Inc. All rights reserved.