Resting cells of Rhodococcus sp. G20 were used for the transformation of beta-aminopropionitrile to beta-alanine, an important beta amino acid. A 2(3) central composite experimental design was performed with the purpose of optimizing the beta-alanine production in a bubble column reactor with 200 mL working volume using response surface methodology (RSM). The individual and interactive effects of three independent variables (cells loading, substrate concentration, airflow rate) on beta-alanine production were investigated. A quadratic polynomial predictive model was obtained after statistical analysis to predict the optimum biotransformation conditions. The optimum bioconversion conditions of beta-aminopropionitrile in a batch operation for beta-alanine production were as follows: cells loading of 16.50 g(ww)/200 mL, substrate concentration of 1.29% (v/v), and airflow rate of 86.56 L/h, under which an overall 40.6% increase in productivity of beta-alanine was obtained. The influences of the temperature and pH on the conversion were also studied, and the optimums were 30 degrees C and pH 7.5. The measured activation energy (E(a)) was found to be 22,199 J/mol, thus indicating the presence of diffusional resistance. (C) 2008 Elsevier Ltd. All rights reserved.