Copper requirement of a copper-tolerant isolate of Scenedesmus and the effect of copper depletion on tolerance

Abstract

A copper-tolerant isolate of Scenedesmus from Sudbury, Ontario, cultured in medium completely lacking copper, lost its ability to grow at high copper concentrations after 10 generations. The change was sudden in onset and relatively rapid. The algae had previously been maintained on medium with micronutrient levels of copper and had retained their tolerance over 7 years of laboratory culture.The tolerance of the copper depleted cells to nickel and cobalt also decreased. Their tolerance to cadmium and silver was unchanged by copper depletion. The situation for zinc tolerance was less clear, but there was no significant decrease over the range tested.When copper-depleted cells were cultured in complete medium with micronutrient levels of copper, copper tolerance increased after four divisions and recovered to the original state after eight divisions. Plate assays indicated that all of the cells in the culture were recovering i.e., this was not a reselection of a few tolerant cells.The results are discussed in terms of possible tolerance mechanisms, and their implications for the occurrence of multiple or cotolerance.