Sample collection and preparation. We inoculated anaerobic microcosms with
groundwater from the Cr-contaminated Hanford 100H site (WA) and supplemented
them with lactate (10 mM) and the electron acceptors nitrate (4 mM),
sulfate (2.5 mM), amorphous ferric oxyhydroxide (20 mM), and chromate (250
ppb). Microcosms were destructively harvested at various time points during
sequential terminal electron-accepting processes, and 15-ml aliquots were sampled
into 30 ml of RNAlater. After an overnight incubation at 4°C, the samples
were centrifuged (5,000 g for 15 min at 4°C), and the supernatant was discarded.
The pellets were flash frozen in liquid nitrogen and stored at 80°C, and
the DNA and RNA were extracted as detailed below. For this study, samples
taken after 2 days of incubation following complete denitrification were analyzed.