The relationship between soil copper content and copper resistance in yeast of an ultisol in midwestern Nigeria.

Yeast isolates were obtained from the brewer's stock of the Guinness brewery in Benin City, midwestern Nigeria, and from local sources such as mango and sugar cane. The fruits were exposed to the immediate soil environment in eleven selected sites in the Ugbowo and Ikpoba Hill areas of Benin City, Edo State of midwestern Nigeria. A total of twenty-seven yeast isolates were obtained. Fourteen isolates were identified as Saccharomyces cerevisiae and 13 as S. carlsbergensis. Analysis of resistance to copper sulphate revealed that the two brewer's yeast isolates were resistant to 3.5 mM and 4.2 mM CuSO4, respectively, while the local yeasts were resistant to higher concentrations ranging from 6.5 to 16.5 mM. The percentage copper sulphate resistance of yeast isolates obtained from Mangifera inidica ranged from 52.4 to 73.8%, while the percentage copper sulphate resistance of yeast isolates obtained from Saccharum officinarum ranged from 51.8 to 62.6%. The two brewer's yeast isolates (BY2 and BY4) had a percentage CuSO4 resistance of 32.4 and 38.5%, respectively. Comparison of soil copper concentration and copper resistance levels in selected yeast isolates indicated that the soil copper concentrations generally influenced the ability of yeasts to resist copper.