ESTIMATES OF BACTERIAL-GROWTH RATE CONSTANTS FROM THYMIDINE INCORPORATION AND VARIABLE CONVERSION FACTORS

Thymidine incorporation into DNA is widely used to estimate rates of b acterial growth and secondary production in aquatic systems. The proce dure requires the use of several conversion factors and assumptions to convert rates of thymidine uptake to rates of carbon production. Perh aps the most controversial of the conversion factors is that which con verts rates of incorporation to the rate of cell production. During a year-long study in Lake Arlington, Texas, we empirically determined co nversion factors from bacterial growth in filtered (1.0 mum porosity) and diluted (1:9) lake water. Bacterial growth rate constants determin ed from changes in cell abundance were compared to growth rate constan ts estimated from empirically derived (both instantaneous and annually averaged), theoretical, and modeled conversion factors. Single value conversion factors (i.e., theoretical, or average of 19 empirically de termined conversion factors) did not yield estimates of bacterial grow th rate constants that compared favorably to growth estimates from cha nges in bacterial abundance. Conversion factors, determined from a reg ression model based on empirically determined conversion factors, gave annual growth estimates that were similar to those obtained from chan ges in cell abundance.