Cell microencapsulation is one of the promising biotechnological processes for immobilized cell culture. In this work, Escherichia coli and Saccharomyces cerevisiae cells were entrapped in alginate-chitosan-alginate (ACA) microcapsules. The behavior of microencapsulated and nonencapsulated free cells were studied and simulated by mathematical models. The Gompertz and Richards function were modified and compared to describe the growth and metabolism of microencapsulated and free microbial cells for a better understanding of the growth and its optimization. The results showed that both of the modified Gumpertz and Richards model could be used to describe the growth and metabolic process in ACA encapsulated culture as well as in free culture. Particularly, the modified Richards model was more suitable in describing the consumption of the controlling substrate due to the additional parameter, In, which described the shape of the three-parameter functions. The experimental data and the models highlighted that ACA microencapsulated culture could reach a higher maximum biomass concentration and a higher maximum biomass growth rate than in free culture. It is indicated that the ACA microcapsule could be used in immobilized microorganism culture, which offered favorable microenvironment for cell growth. The effects of status of ACA microcapsule cores on the cell growth and metabolism were further investigated. The results showed that there was no significant difference in the growth and metabolism of microencapsulated cells whether the cores of the microcapsules were solid or liquefied. And the optimized initial cell density was 3 x 106 cells mL(-1) of microcapsule based on the models. (c) 2005 Elsevier Inc. All rights reserved.