The microbial growth and simultaneous bioaccumulation of Cu(II) and Ni(II) ions during the growth of Rhizopus delemar in molasses medium was investigated in a batch system. The level of Cu(II) and Ni(II) bioaccumulation and microbial growth was dependent on pH, molasses sucrose concentration and initial Cu(II) and Ni(II) ion concentrations. An increase in initial total metal ion concentration inhibited both the growth rate of fungus and the bioaccumulation capacity. Lineweaver-Burk plot of Monod equation was used to study the inhibition kinetics of bioaccumulation of Cu(II) and Ni(II) and the intrinsic and apparent model parameters were evaluated in metals-free and metals-contaminated fermentation media. The maximum specific growth rate (mu(m)) and the Monod constant (K-s) of microorganism in metals-free media were found as 0.405 L/h and 3.977 g/L, respectively. As mu(m) remained constant in the presence of increasing concentrations of Cu(II) and Ni(II) ions, the combined inhibition of Cu(II) and Ni(II) ions on the growth rate of R. delemar was found to be a competitive inhibition. The inhibition constants for Cu(II) and Ni(II) ions were determined as 56.71 mg Cu(II)/L and 47.44 mg Ni(II)/L. As the bioaccumulation of Cu(II) and Ni(II) ions was reduced by the presence of increasing concentrations of the other metal ion, compared with the single-metal systems, the individual action of Cu(II) and Ni(II) ions on the bioaccumulation of R. delemar was generally found to be antagonistic. On the other hand, the total combined effects of Cu(II) and Ni(II) ions on the bioaccumulation of R. delemar are thought to be synergistic since the total bioaccumulated metal ion quantities per unit mass of biomass were higher than those obtained in the growth media containing Cu(II) and Ni(II) ions alone at the same concentrations. (C) 2009 Elsevier B.V. All rights reserved.