Temperature-driven adaptation of the bacterial community in peat measured by using thymidine and leucine incorporation

The temperature-driven adaptation of the bacterial community in peat was st udied, by altering temperature to simulate self-heating and a subsequent re turn to mesophilic conditions. The technique used consisted of extracting t he bacterial community from peat using homogenization-centrifugation and me asuring the rates of thymidine (TdR) or leucine (Leu) incorporation by the extracted bacterial community at different temperatures. Increasing the pea t incubation temperature from 25 degreesC to 35, 15, or 55 degreesC resulte d in a selection of bacterial communities whose optimum temperatures for ac tivity correlated to the peat incubation temperatures. Although TdR and Leu incorporations were significantly correlated, the Leu/TdR incorporation ra tios mere affected by temperature. Higher Leu/TdR incorporation ratios were found at higher temperatures of incubation of the extracted bacterial comm unity. Higher Leu/TdR incorporation ratios were also found for bacteria in peat samples incubated at higher temperatures. The reappearance of the meso philic community and disappearance of the thermophilic community when the i ncubation temperature of the peat was shifted down were monitored by measur ing TdR incorporation at 55 degreesC (thermophilic activity) and 25 degrees C (mesophilic activity). Shifting the peat incubation temperature from 55 t o 25 degreesC resulted in a recovery of the mesophilic activity, with a sub sequent disappearance of the thermophilic activity. The availability of sub strate for bacterial growth varied over time and among different peat sampl es. To avoid confounding effects of substrate availability, a temperature a daptation index was calculated. This index consisted of the log,, ratio of TdR incorporation at 55 and 25 degreesC. The temperature index decreased li nearly with time, indicating that no thermophilic activity would be detecte d by the TdR technique 1 month after the temperature downshift. There mere no differences between the slopes of the temperature adaptation indices ove r time for peat samples incubated at 55 degreesC 3 or 11 days before incuba tion at 25 degreesC. Thus, different levels of bacterial activity did not a ffect the temperature-driven adaptation of the bacterial community.