Effects of temperature on the incorporation of leucine and thymidine by bacterioplankton and bacterial isolates

The effect of temperature on the incorporation of H-3-leucine (H-3-Leu) and H-3-thymidine (H-3-TdR) by bacterioplankton and bacterial isolates from marine, estuarine, and freshwater habitats was examined. There was a significant, positive correlation between in situ temperature and molar Leu:TdR incorporation by bacterioplankton in oceanic and lagoonal environments. Temperature manipulation experiments showed that Q(10) values for Leu incorporation by bacterial assemblages and isolates were significantly higher than corresponding Q(10) values for TdR incorporation. Evidence indicated that the temperature-dependence of Leu:TdR ratios was not a function of community composition, unbalanced growth, non-specific labelling of macromolecules, or substrate limitation. Thus, Leu and TdR incorporation appear to be affected by temperature differently. These experiments indicate that Leu and/or TdR conversion factors, for estimating bacterial production, are not constant with respect to temperature.