JPR Advance Access published online on September 3, 2004
Journal of Plankton Research, doi:10.1093/plankt/fbh142
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1 Center for Anatomy and Cell Biology, Research Group General Microbiology; Medical University Vienna, Waehringer Strasse 10, A-1090 Vienna, Austria
* To whom correspondence should be addressed. E-mail: alexander.kirschner{at}meduniwien.ac.at.
To assess the variability and predictability of the empirical conversion factor (CF) for converting the uptake of 3H-thymidine (TDR) to bacterial carbon production rates in eutrophic environments, 11 dilution culture experiments were performed and the results related to a set of important concomittantly recorded environmental variables. TdR incorporation data from a field study were then converted to carbon production with the established empirical CF, a theoretical CF and compared to production estimates derived from leucine incorporation. Mean empirical CF varied between 0.5 x 106 and 7.0 x 106 cells (pmol TDR)-1 over the year, and showed highly significant negative correlation with TDR incorporation rate and a highly significant positive correlation to temperature. Values of carbon production derived with the variable empirical CF were lower than the values obtained by the use of the theoretical CF of 1 x 106 cells (pmol TDR)-1. It showed less seasonal variation than values obtained by leucine incorporation and periods of uncoupling were observed. However, when the empirical CF was calculated from the multiple regression equation including TDR incorporation and temperature, the resulting carbon production rates showed a high correspondence with the leucine derived production rates. The results of the analyses were interpreted as an indication that under favourable conditions (resulting in high TDRincorporation) bacteria may be able to optimise DNA duplication over protein synthesis as a possible strategy to persist and to maintain their potential to divide under limiting conditions (e.g. decrease in temperature and substrate availability). At unfavourable conditions (resulting in low incorporation rates) bacteria may then use already produced DNA copies for rapid growth, when the environmental conditions turn favourable again. Thus, an experimental set-up causing nutrient enrichment of the sampled water by autoclaving and filtering, as generally used for dilution culture experiments, does not always reflect in-situ situations, especially during periods with low nutrient concentrations.
Accepted August 23, 2004
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Variability and predictability of the empirical conversion factor for converting TDR-uptake into bacterial carbon production for a eutrophic lake
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