Dataset: bacteria

Samples were processed immediately following collection. Short-term incorporation assays followed procedures described in Ducklow et al. (1992a). Duplicate 30 ml samples were amended with methyl-H-thymidine (New England Nuclear, sp. act. >75 Ci mmol; 10 nM final concl.) and incubated at or near in situ water temperatures in screwtop polycarbonate centrifuge tubes in chilled water bath incubators. Following incubation periods of ca. 1--3 h, the incubation was terminated with the addition of 0.5 % formalin. To measure nonspecific incorporation, these samples were filtered onto Sartorius cellulose nitrate membranes (0.22 um pore size, extracted by rinsing the filters over a vacuum three times with ice-cold 5 % trichloroacetic acid (TCA) and three times with 80 % ethanol, as suggested in Wicks and Robarts (1988). To measure incorporation into DNA only, separate parallel samples were extracted in 0.25 n NaOH (final conc.) and chilled on ice. These samples were stored on ice for up to 48 hours, then neutralized with ice-cold 100 % TCA (final conc. 20 %), and filtered onto 22 mm dia. 0.2 um cellulose nitrate membrane filters. Finally the samples wre extracted on the filter holders by rinsing three times each with 50 % chloroform-phenol (a 1:1 c/c mixture of liquified phenol and chloroform) and with 80 % ethanol to purify the labelled DNA (Wicks and Robarts, 1987). Zero-time controls were subtracted to correct for adsorption and other abiotic effects. The cellulose nitrate filters were packed tightly into 7 ml glass scintillation vials and dissolved in 1.0 ml of ethyl acetate, prior to addition of Ultima Gold biodegradeable scintillation cocktail (Packard). Samples were counted aboard ship on the T.G. Thompson scintillation counter.

H-leucine incorporation was estimated in parallel incubations of samples inoculated with 0.5 nM H-leuchine (New England Nuclear, sp. act. 153 Ci mmol ) and 10 nM unlabeled leucine (Kirchman et al., 1985), for a final leucine concentration (hot plus cold) of 10.5 nM 30 ml leucine samples were filtered onto replicate 22 mm dia. 0.22 um cellulose nitrate filters and extracted with ice cold 5 % TCA and ethanol as described above.