CHARACTERIZATION OF MICROBIAL COMMUNITIES IN DEEP GROUNDWATER FROM GRANITIC ROCK

The microbial characteristics of deep granitic nutrient-poor groundwat er from two boreholes at the Underground Research Laboratory of Atomic Energy of Canada Limited were studied. Scanning electron microscopy o f the groundwater samples revealed significant numbers of bacteria of various sizes and shapes, including spherical, rod, and curved shaped. A few bacteria with appendages were also observed. Significant number s of bacteria (similar to 10(5)/mL) were enumerated using acridine ora nge (AO) staining. An active microbial population was detected with th ree direct methods and it ranged from 1 to 83% of the AO count, depend ing on the method used. Culturable aerobic and anaerobic (including fa cultative) heterotrophic bacteria ranged from 0.06 to 10.2% and 0.008 to 7.35%, respectively, of the AO count. Denitrifying, N-2-fixing, sul phate-reducing, and iron-precipitating bacteria were present, but no i ron-oxidizing bacteria or methanogens could be detected. Tentative ide ntification of 160 isolates using the Biolog(R) system showed a predom inance of three Pseudomonas species, P. fluorescens, P. marginalis, an d P. corrugata. Phospholipid fatty acid analysis showed that the bacte ria in the groundwater samples faced starvation stress. However, labor atory studies showed that these bacteria can efficiently uptake and mi neralize organic substrates when supplied.