A whole-cell epoxide-hydrolyzing biocatalyst designed as uniform polyelectrolyte complex capsules was developed. Nocardia tartaricans bacterial cells with cis-epoxysuccinate (CES) hydrolase activity were used as a model microbial strain. Stereospecific hydrolysis of CES catalyzed by CES hydrolase in encapsulated cells yields enantiomerically pure L-(+)-tartrate. An air-stripping device with multiloop reactor was used for controlled production of capsules containing bacterial cells with the standard deviation in diameter below 4% and in membrane thickness below 7%. Capsules formed by polyelectrolyte complexation of sodium alginate and cellulose sulfate as polyanions, poly(methylene-co-guanidine) as polycation, CaCl2 and NaCl (SA-CS/PMCG) provide a favorable microenvironment for encapsulated cells. Biotransformation was monitored by RP-HPLC, electrospray ionization mass spectrometry and optical rotation. The results are discussed in view of data previously obtained by cell entrapment in hardened calcium pectate gelled beads (CPG). Encapsulation of the whole-cell biocatalyst in SA-CS/PMCG capsules leads to (i) about two-fold increase, from 91.5 to 208.2 U/mg, in the CES hydrolase activity, (ii) a decreased time required for total biotransformation, from 5.5 to 3 h, and (iii) a significantly improved relative increase in CES hydrolase activity during 51 days of storage, from about 3-fold to about 20-fold, compared to the CPG beads. (C) 2004 Elsevier Inc. All rights reserved.