Limitations of the [3H]thymidine method for estimating bacterial productivity due to thymidine metabolism

Abstract

Thymidine (TdR) was extensively metabolized by bacterioplankton from South San Francisco Bay and Elkhorn Slough, California, USA. Total super(3)H incorporation rate was linear for 2 to 4 h, but macromolecular super(3)H distributions differed depending on whether TdR was supplied as methyl- or 6-( super(3)H)-TdR. Methyl-( super(3)H) was incorporated at rates greater than or equal to 6-( super(3)H). Methyl-( super(3)H) incorporation by South San Francisco Bay bacterioplankton was: 0 to 35% into DNA, 34 to 67% into RNA and 20 to 59% into protein. In the same samples, 6-( super(3)H) incorporation was: 33 to 58% into DNA, 17 to 52% into RNA and 13 to 34% into protein. Tritiated water was produced from both substrates. At high TdR concentrations, methyl-( super(3)H) incorporation into DNA was blocked while incorporation into protein continued.