Temperature growth response and identification of iron-oxidizing autotrophs and acidophilic heterotrophs isolated from underground uranium mine leachates and tailing effluents

Iron-oxidizing autotrophs and acidophilic heterotrophs from 30 samples obtained from bioleaching areas of two underground uranium mines and from four samples obtained from four tailings effluents in Elliot Lake, Ontario were quantified at an incubation temperature of 18 {dollar}pm{dollar} 0.5{dollar}spcirc{dollar}C. Mine-water sample temperatures ranged from 13-18{dollar}spcirc{dollar}C; tailings effluent sample temperatures ranged from 0.5-5{dollar}spcirc{dollar}C. Iron-oxidizing autotrophs were isolated from all 34 samples and their numbers ranged from 2,683 {dollar}pm{dollar} 377 to 245,000 {dollar}pm{dollar} 20,205 colony-forming units (CFU) mL{dollar}sp{lcub}-1{rcub}{dollar} in mine samples and 3 {dollar}pm{dollar} 2 to 185 {dollar}pm{dollar} 18 CFU mL{dollar}sp{lcub}-1{rcub}{dollar} in tailings samples. The vast majority of iron-oxidizers were identified as Thiobacillus ferrooxidans, although the presence of Leptospirillum ferrooxidans was confirmed in several of the mine samples. Acidophilic heterotroph numbers ranged from 40 {dollar}pm{dollar} 8 to 9,650 {dollar}pm{dollar} 161 CFU mL{dollar}sp{lcub}-1{rcub}{dollar} in mine samples where they were always numerically inferior to iron oxidizers. Acidophilic heterotroph numbers in tailings samples ranged from 13 {dollar}pm{dollar} 3 to 2,517 {dollar}pm{dollar} 859 CFU mL{dollar}sp{lcub}-1{rcub}{dollar} and no consistent dominance of acidophilic heterotrophs or iron oxidizers was observed. Members of the species T. acidophilus and genus Acidophilium were identified. For each sample, approximately 20 isolates of each nutritional group were examined for the ability to grow at temperatures of 4, 18, 21 and 37{dollar}spcirc{dollar}C, respectively; overall 605 iron oxidizers and 315 acidophilic heterotrophs were examined and categorized as 'broader temperature range psychrotrophs,' 'narrower temperature range psychrotrophs,' 'intermediates,' or mesophiles. Although psychrotrophic representatives of both nutritional types were abundant in both sample types, no psychrophiles were recovered from any of the samples.