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 acido philic heterotrophs were recovered and quantified at an incubation tem perature of 18 degrees C, in four tailings-effluent samples obtained f rom the environment of a uranium mine in Ontario, Canada, The samples were collected during winter when the temperatures of the effluents we re in the range 0.5-5.0 degrees C. Iron-oxidizing autotrophs were reco vered in the four samples and their numbers ranged from 3 +/- 2 to 185 +/- 18 colony-forming units/mL; acidophilic heterotrophs were recover ed 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-oxidiz er isolates and 63 of the acidophilic heterotrophic isolates were exam ined for their ability to grow at temperatures of 4, 18, 21, and 37 de grees C. None of the isolates was psychrophilic, although 96% of the i ron oxidizers and 54% of the acidophilic heterotrophs were psychrotrop hs; less that 5% of the isolates for both nutritional types were capab le of growth at 37 degrees C. In addition, the isolates were categoriz ed as 'broader temperature range psychrotrophs,' 'narrower temperature range psychrotrophs,' 'intermediates,' or mesophiles, and the narrowe r temperature range psychrotrophs were found to be numerically predomi nant.