Antagonistic effect of manganese to cadmium toxicity in the alga Dunaliella salina

Abstract

The unicellular halotolerant alga Dunaliella salina was exposed to different concentrations of cadmium in the range 9 to 135 μM. Chlorosis was observed at 25 μM cadmium, and inhibition of cell division was established at 45 μM cadmium. Biosynthesis of the cellular osmoregulator, glycerol, was not affected by cadmium toxicity throughout the concentration range. Cadmium toxicity was found to be antagonized by low concentrations of manganese. Michaelis-Menten analysis of substrate (Mn²⁺)–inhibitor (Cd²⁺) interactions showed competitive inhibition with the following Ks values at the various concentrations of Cd²⁺: Ks [Cd = 0] = 0.175, Ks [Cd = 45 μM] = 0.175, Ks [Cd = 90 μM] = 0.126, Ks [Cd = 135 μM] = 0.10. Ki of cadmium was 0.01. Results indicate a specific hyperbolic competitive cadmium–manganese interaction on one or both of 2 possible sites: on the cell membrane, or intracellularly on a specific metalo-enzyme. Results imply a possible protection of primary phytoplankton producers by nutrient trace metals against toxic heavy metals present in the oceans.