ABSTRACT

Rates of planktonic bacterial growth may be estimated by measuring the incorporation of various radiolabeled precursors into macromolecules. To calculate bacterial growth from thymidine incorporation requires knowledge of various biochemical parameters that may be difficult to measure, or alternatively, an empirical calibration using bacterioplankton cultures. If bacterioplankton are in balanced growth, rates of incorporation into different macromolecular fractions will give equivalent estimates of growth rate. The use of thymidine as a radiolabeled exogenous precursor of deoxyribonucleic acid synthesis has a long history of use in microbiology and biochemistry. Thymidine is readily degraded within cells, initially by the inducible enzyme thymidine phosphorylase. The rate of thymidine incorporation must always be converted to moles of thymidine per unit volume and time to allow comparisons between studies. M. Simon and P. Azam found that the thymidine conversion factor gave results comparable to bacterial productivity based on the leucine incorporation method.