ADAPTATION OF A SACCHAROMYCES-CEREVISIAE STRAIN TO HIGH COPPER CONCENTRATIONS

A strain of Saccharomyces cerevisiae has been adapted to increasing co ncentrations of copper at two different pH values. The growth curve at pH 5.5 is characterized by a time generation increasing with the amou nt of added copper. A significant decrease of cell volume as compared with the control is also observed. At pH 3 the cells grow faster than at pH 5.5 and resist higher copper concentrations (3.8 against 1.2 mM) . Experimental evidence indicates that, after copper treatment, the me tal is not bound to the cell wall, but is localized intracellularly. A significant precipitation of copper salts in the medium was observed only at pH 5.5. Increased levels of superoxide dismutase (SOD) activit y were observed in copper-treated cells and which persisted after 20 s ubsequent inocula in a medium without added metal. On the contrary, ca talase activity was not stimulated by copper treatment and, hence, not correlated with SOD levels. The mechanism of copper resistance, there fore, probably involves a persistent induction of SOD, but not of cata lase, and it is strongly pH-dependent.