ISOLATION AND TEMPERATURE CHARACTERIZATION OF PSYCHROTROPHIC STRAINS OF THIOBACILLUS FERROOXIDANS FROM THE ENVIRONMENT OF A URANIUM MINE

Abstract

Mine samples enriched for Thiobacillus ferrooxidans at 18, 12 and 6°C, after numerous transfers in medium 9K, yielded average generation times of 23, 44, and 103hr, respectively. Temperature characterization of a natural isolate, over a range of 6 to 35°C, showed that growth occurred at the temperature extremes and that the optimum temperature for growth was 25 to 30°C. A stock culture (commercially available) chosen for comparison showed a similar optimum temperature for growth, but lower growth rates at the lower temperatures examined. Growth studies of the natural isolates in the range of 2 to 35°C revealed that growth rates decreased on either side of 25 to 30°C. This effect was most pronounced in the 2 to 12°C range. These studies revealed the psychrotrophic nature of the natural T. ferrooxidans isolates, and their better growth capabilities at lower temperatures than T. ferrooxidans ATCC 33020. These observations are discussed in the light of their importance in the uranium bioleaching process, as it is currently being used.