[ 3H]Leucine incorporation method as a tool to measure secondary production by periphytic bacteria associated to the roots of floating aquatic macrophyte

The present study assessed the application of [ 3H]Leucine incorporation into protein by periphytic bacteria associated with the roots of the floating aquatic macrophyte Eichornia crassipes. Basic assumptions underlying the method, such as linearity of leucine incorporation, saturation level of incorporation rates, incorporation into other macromolecules, specificity of incorporation for bacterial assemblages and [ 3H]Leucine degradation during samples storage were tested, and two procedures for extracting the incorporated leucine were compared. Both methods gave the same results, however, the hot TCA extraction method was less time consuming than the alkaline extraction method. Incorporation of [ 3H]Leucine was linear for up to 40 min. Saturation concentration of [ 3H]Leucine incorporation into protein was 1500 nM. An experiment with prokaryotic and eukaryotic inhibitors showed no significant [ 3H]Leucine incorporation into eukaryotes even in high leucine concentrations. No significant amounts of radiolabel were incorporated into other macromolecules. The maximum time of sample storage after the incubation is 15 days. The leucine incorporation method can be a reliable tool to measure bacterial production in the periphyton root-associated bacteria.