Environmental adaptation factors of two yeasts isolated from the leachate of a uranium mineral heap.

Two yeasts from the effluent of a uranium mineral heap were identified as Candida sorbophila and Rhodotorula mucilaginosa. They are well adapted to such an environment as shown by their tolerance to metals and acid pH. However, different mechanisms could be involved in the adaptation: C. sorbophila could be considered to be more acid-tolerant as a function of its specific growth rate and respiratory behavior at acidic pH in an organic medium. However, R. mucilaginosa was capable of growing by 1 log unit when inoculated in a sterilized leaching effluent or in a ferrous mineral medium, without added organic compounds. Indeed, the ability of R. mucilaginosa to grow in a low-nutrient environment could be as important a factor as its acid tolerance for coping in the isolation habitat. In mixed cultures with sulfide-oxidizing bacteria, no effect was observed on the ferrous oxidation normally carried out by these bacteria. However, a negative effect on both yeasts, especially in C. sorbophila, was observed, when the bacteria were present.