Cadmium-binding polypeptides in microalgal strains with laboratory-induced cadmium tolerance

Abstract

[Strains of 5 algal species that have been induced to develop tolerance to previously toxic cadmium (Cd) concentrations were investigated for production of the Cd-binding polypeptides, poly(yglutamylcysteinyl)glycines, (ϒ-EC)nG. Liquid chromatography using Sephadex G-50, ICP analysis of Cd in Chromatographie fractions, and amino acid analysis provided clear evidence of (ϒ-EC)nG production in the 2 most tolerant species, Phaeodactylum trícornutum and Dunaliella tertiolecta. Production of Cdbinding peptide in P. trícornutum was positively correlated with cellular Cd content, on a dry-weight basis. In contrast, Cd-tolerant strains of Isochrysis galbana, Pavlova lutherí, and Tetraselmis maculata did not produce detectable (ϒ-EC)nG. Although Cd-tolerant I. galbana differed from the control strain in some aspects of polypeptide content, as seen by the production of thiol-rich compounds, the specific mechanism for enhanced Cd tolerance in the 3 species that do not produce (ϒ-EC)nG remains unknown.]