ATP-related specific heterotrophic activity in petroleum contaminated and uncontaminated groundwaters

Bacterial numbers, ATP content, heterotrophic potentials, and thymidine incorporation were determined for petroleum contaminated and uncontaminated groundwaters. ATP measurements and cell counts gave variations of a factor of 7 in values among the sites. The acridine orange direct counting yielded counts 2 to 3 orders of magnitude higher than the plate counts and counts 1 to 2 orders of magnitude higher than counts given by the ATP measurement using a conversion factor of 10⁻⁶ ng ATP/cell. Mean V_max values for ¹⁴C-labled glucose, acetate, and naphthalene were 0.59, 0.17, and 1.14 μg ∙ L⁻¹ ∙ h⁻¹, respectively. Naphthalene was only used as substrate in the contaminated samples. Acetate and naphthalene showed fairly good correlations to ATP contents, 0.94 and 0.95, respectively, as well as with tritiated thymidine incorporation rates, r = 0.94. V_max specific activity indices (SAI) based on ATP content showed very little variation for the selected groundwaters compared with SAI values reported earlier for groundwaters.Key words: groundwater, heterotrophic potential, tritiated thymidine incorporation, ATP.