Some observations on the copper tolerance of bacterial communities determined by the (3H)-thymidine incorporation method in heavy metal polluted humus

Changes in pH after filtration of bacterial suspensions are important when applying the radioactive thymidine incorporation method to heavy-metal polluted soils with low microbial activity. In the original method (Baath 1992; Soil Biology and Biochemistry 24, 1157-1165) the blended and centrifuged suspension was filtered through glass wool to remove humus particles from the suspension. When we filtered the bacterial suspension through glass wool the pH increased by 2 units and the thymidine incorporation rate decreased. This made the community copper tolerance measurement ambiguous. When using soil samples with very low activity, we recommend the use of acid-washed glass wool or polyester net filtration which eliminates changes in pH. (C) 2000 Elsevier Science Ltd. All rights reserved.