Growth determinations for unattached bacteria in a contaminated aquifer

Growth rates of unattached bacteria in groundwater contaminated with treated sewage and collected at various distances from the source of contamination were estimated by using frequency of dividing cells and tritiated-thymidine uptake and compared with growth rates obtained with unsupplemented, closed-bottle incubations. Estimates of bacterial generation times [(In 2)/μ] along a 3-km-long transect in oxygen-depleted (0.1 to 0.7 mg of dissolved oxygen liter^-1) groundwater ranged from 16 h at 0.26 km downgradient from an on-land, treated-sewage outfall to 139 h at 1.6 km and correlated with bacterial abundance (r² = 0.88 at P