Abstract
The physiological importance of magnesium has been established for many years, and the excess cobalt is known to be toxic to organisms.
In this study, interaction of Co and Mg in growth of yeast, Saccharomyces cerevisiae, was investigated by batch culture.
Magnesium stimulated cell growth rate and cell density at equiliblium. On the contrary, cobalt depressed them. Mg and Co were found to react antagonistically to cell growth. Addition of Mg to the medium decreased the inhibition of the cell growth caused by Co toxicity. A hyperbolic relationship between the inhibition rate of cell growth and Co concentration in the medium was obtained under the experimental conditions. The cells on the earlier growth phase were more sensitive to Co toxicity. Yeast cells damaged by Co could be repaired by Mg addition. The extent of repairs in cell growth depended on the concentration of Co in the medium and the amount of Mg supplemented. The linear relationship between the exposed time of cells to Co and the growth rate or cell density was observed, that is, the longer the exposed time to Co, the more the yeast cells were damaged irreversibly in cell growth. However, when the excess Mg was added to the medium compared with Co, the exposed time did not cause the large difference in the cell density. The amount of Mg accumulated in cells was independent on the Mg and Co concentrations in the medium, but that of Co was dependent on the Co concentration in the medium and the high concentration of Mg in the medium depressed Co uptake by yeast.
