Relationship between thymidine metabolism, bacterioplankton community metabolic capabilities, and sources of organic matter.

Numerous investigations have been directed at verifying and calibrating methods for measuring bacterioplankton production, particularly methods based on the incorporation of thymidine (TdR) into DNA. Careful examination of these data can provide insights into other aspects of the ecology of aerobic heterotrophic microbial communities. Once method-specific biases are eliminated, these measurements indicate that there are broad-scale patterns in the metabolic fate of TdR, differences that seem to reflect broad differences in community metabolic capabilities. Based on work conducted primarily in San Francisco and Tomales Bays, California, I suggest that the metabolic fate of TdR in a given environment may reflect the relative importance to bacterioplankton nutrition of detritus versus fresh phytoplankton carbon. This is probably due to differences in community composition that result from growth on qualitatively different carbon sources. If true, the metabolic fate of TdR may provide a broadly applicable, but simple, index that can be used to assess the relative importance of these general sources of organic matter. Such an index could be very useful in characterizing lacustrine, estuarine, and nearshore environments.