In real environmental applications, such as heavy metal bioremediation, microorganisms are generally not kept at their optimum growth conditions; therefore, it is imperative to investigate their heavy metal removal performance under diverse environmental conditions. The present study aims to investigate the effects of pH, temperature and growth phases on the removal of Cu2+ and Cr6+ by two environmental isolates identified as Ochrobactrum intermedium LBr and Cupriavidus metallidurans CH34. Results showed that cells in logarithmic phase presented better biosorption capacity than cells in stationary phase for both isolates. The Cr6+ metal was removed more efficiently by live O. intermedium LBr than dead cells; while dead C. metallidurans CH34 biosorbed better than live ones. It was also found that the pH and temperature affected the biosorption capacity. The optimum temperatures were determined to be 37 C and 27 degrees C, and the optimum pH values were 6 and 7 for O. intermedium LBr and C metallidurans CH34, respectively. Additionally, both microorganisms preferentially adsorbed Cu2+ in Cu2+/Cr6+ mixtures. The main mechanism of adsorption was determined to be through carboxylic, hydroxyl, and amino functional groups. (C 2014 Elsevier B.V. All rights reserved.