BACTERIAL HETEROGENEITY IN DEEP SUBSURFACE TUNNELS AT RAINIER MESA, NEVADA TEST SITE

To characterize the deep subsurface environment of Rainier Mesa, Nevad a Test Site, rock samples were taken from tunnels U 12b, U 12g, U 12p, and U 12n, which varied in depth from 50 m to 450 m and in gravimetri c moisture content from 4% to 27%. Values for total count, viable coun t, biomass, Simpson diversity, equitability, similarity coefficient, a nd number of distinct colony types indicated microbiological variabili ty between samples. Viable counts ranged from less than 1 x 10(1) to 2 .4 x 10(5) CFU g dry wt-1 of rock. Direct counts and enumeration based on phospholipid determination indicated larger numbers of cells g dry wt-1 of rock than viable counts. Simpson diversity indices, equitabil ity, and numbers of distinct colony types varied from 3.00 to 8.05, 0. 21 to 0.89, and 7 to 19, respectively, and indicated heterogeneity bet ween samples. Each distinct morphotype was purified and characterized. Gram reaction, morphology, metal and antibiotic resistances, and meta bolic activities of each isolate confirmed spatial variability among m icrobiota isolated from different locations. Most probable numbers of nitrifying, sulfur oxidizing, and sulfur-reducing bacteria were below the limit of detection in all samples, while the numbers of nitrogen f ixing bacteria ranged from below the level of detection to 7.8 x 10(2) cells g dry wt-1 of rock sample, and the numbers of dentrifying bacte ria ranged from below the level of detection to greater than 1.6 x 10( 3) cells g dry wt-1 of rock sample.