The growth of A.niger and A.terreus were markedly decreased with increasing Cr ion concentrations in the growth medium up to 2000 mg/L. Whereas, A.niger tolerated Ag up to 800mg/L and A.terreus tolerated it up to 200 mg/L. The conidiophores of A.niger and A.terreus exhibited a constrictions and distortion in the conidial heads and phialides with elevated Cr in the growth medium. Except that at 2000mgCr/L, A.terreus failed to form conidiophores and the mycelia seemed to be distorted with appearance of intercalary spores. A constriction in the conidiophores and distortions in the conidial heads and phialides were also observed when A.niger and A.terreus were grown in elevated concentrations of silver. Electron microscopic study of A.niger and A.terreus cells grown with elevated Cr and Ag concentrations, revealed that the cytoplasm of both organisms aggregated in the form of black dense area inside the cells and also the cell wall increased in its diameter and appeared electron dense black, which may be due to deposition of metals in the form of granules or crystals on the cell wall or in the vacuoles. |
