A thermophilic Bacillus spp. capable of transforming aliphatic nitriles, cyclic nitriles and dinitriles was used as a free cell suspension and immobilized in alginate beads to study the utilization of acetonitrile and acrylonitrile in a buffered biotransformation medium. The cells grew optimally at 65 degrees C and contained a nitrile hydratase-amidase enzyme system that transformed nitrile compounds stoichiometrically to the corresponding carboxylic acids. In the presence of urea or chloroacetone, amidase activity was inhibited and the amide intermediate was accumulated. Mass transfer limitation of nitrile utilization rates was observed with immobilized cells, but the alginate afforded the cells some degree of additional thermal stability and potential advantage in re-use. In vitro inhibition of the partially purified amidase was confirmed and the use of whole cells of this organism in a continuous bioreactor to generate amide products from nitrile substrates was demonstrated. (C) 2000 Elsevier Science Inc. All rights reserved.