TEMPERATURE STUDIES OF IRON-OXIDIZING AUTOTROPHS AND ACIDOPHILIC HETEROTROPHS ISOLATED FROM URANIUM MINES

Iron-oxidizing autotrophs and acidophilic heterotrophs were quantified at an incubation temperature of 18-degrees-C in several samples obtai ned from the bioleaching areas of two uranium mines in Ontario, Canada . All samples were minewater samples with temperatures in the range 13 -18-degrees-C. Iron-oxidizing autotrophs ranged from 2683 +/- 377 to 2 45 000 +/- 20 205 colony-forming units.mL-1 and were always numericall y superior to acidophilic heterotrophs, which ranged from 40 +/- 8 to 9650 +/- 161 colony-forming units.mL-1. For each sample, approximately 20 isolates of each nutritional group were examined for the ability t o grow at temperatures of 4, 18, 21, and 37-degrees-C, respectively; o verall, 559 isolates of iron-oxidizing bacteria (predominantly Thiobac illus ferrooxidans) and 252 acidophilic heterotrophic isolates were ex amined and categorized as 'broader temperature range psychrotrophs,' ' narrower temperature range psychrotrophs,' 'intermediates,' or mesophi les. Although psychrotrophic representatives of both groups were abund ant, no psychrophiles were recovered from any of the samples. For the iron oxidizers, the temperature growth profiles of the isolates were s imilar from sample to sample. For the acidophilic heterotrophs, the te mperature growth profiles varied considerably among samples.