Production of Cadmium-binding Protein in Chlorella ellipsoidea

Abstract

The uptake of cadmium (Cd) and the production of cadmium binding protein (Cd-BP) in Chlorella ellipsoidea were examined. To the medium in which chlorella was growing to the stationary phase CdCl₂ (2 mg Cd/l) was added and the cultivation in the presence of CdCl₂ was run for 0-120 h under light intensity of 4 kLx at 25°C with bubbling 5% CO₂ gas. An aliquot of chlorella was harvested every 24 h from the culture medium and its Cd concentration was estimated by atomic absorption spectrophotometry. Cadmium taken up by the cells increased with increasing the cultivation period and the concentration of CdCl₂ added to the medium. Cadmium in the cells was detected in the cytosol fraction and estimated to bind to the protein. The Cd-BP produced in the cytosol was eluted at the position of Ve/Vo 2.3 on a Sephadex G-75 column. The production of Cd-BP was found to be dependent on the concentration of Cd in chlorella cells. Moreover, the production of Cd-BP was not stimulated by ZnSO₄ (5.36×10^-5 mol in the medium). Cadmium bound to the protein was partly substituted by Cu when 1.07×10^-5 mol CuSO₄ was added to the medium.