Copper tolerance in the green alga, Chlorella vulgaris

Abstract. The effect of sub-lethal concentrations of copper upon tolerant and non-tolerant strains of Chlorella vulgaris was investigated. Copper concentrations of 0.2 and 0.4 mg dm⁻³ increased the lag phase of both strains, the effect being greater in the non-tolerant strain. No difference was observed in the toxicity of copper to the photosynthetic rates of the isolated chloroplasts of either strain. However, significant differences were shown at the whole cell level.
Lower copper uptake was shown by the tolerant cells. In both strains initial uptake of copper was followed by a phase of desorption before cell division occurred. In cultures of both strains the concentration of ionic copper was decreased by complexation with extracellular organic material. Over a 14 day growth period more organic material was produced by the tolerant cells. The organic material produced by the tolerant cell formed organo-copper complexes which had a higher conditional stability constant.
It is proposed that the cell wall acts as a barrier to copper in the tolerant cells and prevents copper from affecting cell metabolism. Organo-copper complexation occurs at this barrier and this complex is then released into the medium.