Rhodococcus sp. AJ270, a nitrile hydratase/amidase-containing microorganism, were immobilized in alginate capsules. The influences of the bead size and the crosslinking agent on morphology and the biocatalytic activity of the cells were examined. In the presence of an organic co-solvent, such as methanol or acetone (5%), the encapsulated Rhodococcus sp. AJ270 has been found to catalyze efficiently the biotransformation of racemic trans-2-methyl-3-phenyl-oxiranecarbonitrile and its amide to yield highly enantiopure 2R,3S-(-)-2-methyl-3-phenyl-oxiranecarboxamide in at least seven runs. (c) 2005 Elsevier Inc. All rights reserved.