Reduced uptake of nickel by a nickel resistant strain of Candida utilis.

A nickel resistant strain of the yeast Candida utilis was obtained by selection of spontaneous mutants on solid medium containing 3 mM Ni2+. In time-course experiments, non-growing suspensions of the mutant strain took up approximately 50% less nickel than the parent strain over 30 min incubation in MES buffer plus glucose at pH 5.5. Efflux of nickel from either strain was negligible. Uptake was reduced by omission of glucose from the uptake buffer in both strains but this was much more marked in the parent strain. Uptake of nickel in the presence of equimolar concentration of Mg2+ was reduced by 80% in both parent and mutant strains. It was concluded that resistance to nickel was due to an alteration in a transport system primarily responsible for uptake of magnesium.