The removal kinetic characteristic and mechanism of cadmium by growing Rhodobacter sphaeroides were investigated. The removal data were fitted to the second-order equation, with a correlation coefficient, R-2 = 0.9790-0.9916. Furthermore, it was found that the removal mechanism of cadmium was predominantly governed by bioprecipitation as cadmium sulfide with biosorption contributing to a minor extent. Also, the results revealed that the activities of cysteine desulfhydrase in strains grown in the presence of 10 and 20 mg/l of cadmium were higher than in the control, while the activities in the presence of 30 and 40 mg/l of cadmium were lower than in the control. Content analysis of subcellular fractionation showed that cadmium was mostly removed and transformed by precipitation on the cell wall. (C) 2008 Elsevier Ltd. All rights reserved.