Comparison of leucine uptake methods and a thymidine incorporation method for measuring bacterial activity in sediment

Three [C-14]leucine uptake methods and a [H-3]thymidine method for measuring bacterial activity in sediment were compared. For leucine uptake, a combustion method, in which prior to combustion sediment was washed with ethanol, yielded the most consistent results. The TCA extraction methods with a filtration step yielded very variable and much lower results than the combustion method. A high concentration of leucine was needed to reach the saturation level (13.7 mu M), but that was not found to enhance bacterial activity. No clear saturation level for thymidine incorporation was achieved for two of the four lake sediments tested. Therefore, and because of other weaknesses of the method, the thymidine incorporation underestimated the bacterial carbon production in sediment.