MICROBIAL COMMUNITIES IN DEEP CANADIAN SHIELD GROUNDWATERS - AN IN-SITU BIOFILM EXPERIMENT

Microbial biofilm communities were cultivated on stainless steel and polypropylene surfaces within brine-filled exploration boreholes in crystalline rocks of the Canadian Shield at Kidd Creek Mine (Timmins, Ontario) and Copper Cliff South Mine (Sudbury, Ontario) at depths of 1402 m and 1219 m, respectively. The calcium-sodium-chloride brines were acidic (pH 3.5-4.8) and had temperatures of 23.4 degrees C to 18.6 degrees C. Direct microscopic counts using DAPI (4',6-diamidino-2-phenylindole) epifluorescent staining revealed coccoid-shaped, vibroid, rod-shaped, and filamentous bacteria in Copper Cliff South biofilms. The same morphological types were observed at Kidd Creek with the addition of a group of large (2-3 mu m in length) vibroid to rad-shaped bacteria. Average total counts were 9 +/- 7 x 10(6) bacteria/cm(2) for Copper Cliff South biofilms and 5 +/- 1 x 10(6) bacteria/cm(2) for Kidd Creek biofilms with a mean biomass value of 131 +/- 35 mu g carbohydrate/cm(2). Transmission electron microscopy revealed slightly vibroid, rod-shaped, gram-negative cells (up to 2.3 mu m in length) at Kidd Creek Mine. At Copper Cliff South Mine, small gram-negative coccoid-shaped bacteria were observed (< 0.5 mu m in diameter). Many of the bacteria contained large polyhydroxybutyrate) rate storage inclusions and were commonly mineralized by amorphous precipitates exhibiting a typical iron oxide morphology. The accumulation of these iron oxide precipitates in the biofilms suggests that Fe2+-oxidizing bacteria are present Copper Cliff South ground-waters contained sufficient concentrations of sulfate and nitrate to support sulfate-reducing and denitrifying bacteria, whereas Kidd Creek groundwaters did not. These results show that diverse populations of biofilm-forming bacteria exist in deep groundwaters at Copper Cliff South and Kidd Creek Mines.