Adenine incorporation into DNA as a measure of microbial production in freshwaters

The use of [3H]adenine incorporation into DNA as a means of estimating total microbial production in freshwaters was assessed with both algal cultures and natural assemblages of microorganisms. By adding [3H]adenine over a wide range of concentrations (10–200 nM), we determined that in mesotrophic and eutrophic environments >50 nM and probably >100 nM of [3H]adenine is required to maximally label the internal precursor pools of both algae and bacteria. With bacterioplankton assemblages the incorporation of [3H]thymidine and [3H]adenine gave equivalent estimates of DNA synthesis. Growth rates of Scenedesmus in turbidostats determined from 14C assimilation and [3H]adenine incorporation (DNA synthesis) also agreed well. Our results suggest that the use of [3H]adenine to measure total microbial (bacteria + algae) production combined with the use of [3H]thymidine to measure “bacterial” production could provide an interesting complement to current procedures.