The purpose of this study was to investigate the effect of medium additives on the secretion of recombinant a-cyclodextrin glucosyltransferase (alpha-CGTase) into the culture media of Escherichia coli. It is found that supplementation of the E. coli culture with SDS, glycine, Ca2+ or Na+, individually, facilitated the secretion of alpha-CGTase. Orthogonal experiment showed that the optimal condition to achieve maximal secretion of alpha-CGTase was the supplementation with 0.03% SDS, 400 mM Na+, 0.3% glycine and 10 mM Ca2+ together. Under this condition, extracellular enzyme activity reached 12.89 U/ml, which is 15 times higher than that of the culture without any additives. Further analysis showed that the permeability, fluidity and phosphatidylglycerol content of the E. coli cell membrane under the optimized condition were significantly increased in comparison to those under the control condition. These might be the potential mechanisms for the increased secretion of alpha-CGTase from the periplasmic compartment into the culture medium. (C) 2010 Elsevier Ltd. All rights reserved.