Thymidine incorporation and microbial respiration in the surface sediment of a hypereutrophic lake1

Abstract

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Net autotrophy in an oligotrophic lake rich in dissolved organic carbon and with high benthic primary production

“…This test showed that dilution with equal amount of non-radioactive thymidine shut off the de novo pathway. Analyses of benthic heterotrophic bacterial production were then performed according to Bell & Ahlgren (1987), within 1 h after sampling. In short, triplicates were incubated in situ with 0.2 ml sediment and 2.08 µmol l -1 [methyl- ).…”

“…The incubations were stopped with 5 ml of 80% ethanol and the samples were transported to the laboratory where they were kept at 4°C until further analysis. DNA was extracted and the samples were measured in the scintillation counter according to Bell & Ahlgren (1987). The empirical conversion factor of 2 × 10 18 cells mol -1 incorporated thymidine was used to calculated the production of heterotrophic bacteria (Bell 1993).…”

Evidence against incorporation of exogenous thymidine by sulfate‐reducing bacteria

“…In conclusion, these data suggest that total heterotrophic bacterial activity should not be measured with the [)H]TdR uptake method in environments where SRB are important contributors to total microbial growth, including most estuarine and shallow-water marine sediments (other than surficial sediment floes: Fallon et al 1983;Bell and Ahlgren 1987), anoxic saline waters, and sediments of freshwaters in which SOb2-levels are raised. Use of thymidine uptake in these systems may grossly underestimate bacterial production, depending on the relative amount of S0,2--reducing activity in the sample.…”

Incorporation of thymidine, adenine and leucine into natural bacterial assemblages

“…Thus, any potential overestimation of DNA synthesis (at most by 25 %) is counteracted by the corresponding loss of DNA (20 to 30 % ) during the extraction procedures (Findlay et al 1984, Bell & Ahlgren 1987, Wicks & Robarts 1987. We measured adenine incorporation into protein (hot-TCA-insoluble material) during stationary phase and found that incorporation into pro-tein was 20 to 30 % of total incorporation into DNA + protein.…”