THE ABSENCE OF PSYCHROPHILIC THIOBACILLUS-FERROOXIDANS AND ACIDOPHILIC HETEROTROPHIC BACTERIA IN COLD, TAILINGS EFFLUENTS FROM A URANIUM-MINE

Iron-oxidizing autotrophs (mainly Thiobacillus ferrooxidans) and acidophilic heterotrophs were recovered and quantified at an incubation temperature of 18 degrees C, in four tailings-effluent samples obtained from the environment of a uranium mine in Ontario, Canada, The samples were collected during winter when the temperatures of the effluents were in the range 0.5-5.0 degrees C. Iron-oxidizing autotrophs were recovered in the four samples and their numbers ranged from 3 +/- 2 to 185 +/- 18 colony-forming units/mL; acidophilic heterotrophs were recovered in three of the four samples and their numbers ranged from 13 +/- 3 to 2517 +/- 859 colony-forming units/mL. Forty-six of the iron-oxidizer isolates and 63 of the acidophilic heterotrophic isolates were examined for their ability to grow at temperatures of 4, 18, 21, and 37 degrees C. None of the isolates was psychrophilic, although 96% of the iron oxidizers and 54% of the acidophilic heterotrophs were psychrotrophs; less that 5% of the isolates for both nutritional types were capable of growth at 37 degrees C. In addition, the isolates were categorized as 'broader temperature range psychrotrophs,' 'narrower temperature range psychrotrophs,' 'intermediates,' or mesophiles, and the narrower temperature range psychrotrophs were found to be numerically predominant.