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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 6998

Jaap Bloem, Frank M. Ellenbroek, Marie-Jose B. Bar-Gilissen, and Thomas E. Cappenberg; Protozoan Grazing and Bacterial Production in Stratified Lake Vechten Estimated with Fluorescently Labeled Bacteria and by Thymidine Incorporation. Appl.Environ.Microbiol. 55(7):1787-1795, 1989

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In stratified Lake Vechten, The Netherlands, protozoan grazing was estimated on the basis of uptake of fluorescently labeled bacteria and compared with bacterial production estimated on the basis of thymidine incorporation. By using a grazer-free mixed bacteria population from the lake in continuous culture, an empirical relationship between cell production and thymidine incorporation was established. Thymidine incorporation into total cold-trichloroacetic-acid-insoluble macromolecules yielded a relatively constant empirical conversion factor of ca. 10E18 (range, 0.38x10E18 to 1.42x10E18) bacteria mol of thymidine-1 at specific growth rates (µ) ranging from 0.007 to 0.116 hr-1. Although thymidine incorporation has been assumed to measure DNA synthesis, thymidine incorporation appeared to underestimate the independently measured bacterial DNA synthesis by at least 1.5- to 13-fold, even if all incorporated label was assumed to be in DNA. However, incorporation into DNA was found to be in significant as measured by conventional acid-base hydrolysis. Methodological problems of the thymidine technique are discussed. Like the cultures, Lake Vechten bacteria showed considerable thymidine incorporation into total macromolecules, but no significant incorporation into DNA was found by acid-base hydrolysis. This applied not only to the low-oxygen hypo- and metalimnion but also to be aerobic epilimnion. Thus, the established empirical conversion factor for the thymidine incorporation into total macromolecules was used to estimate bacterial production. Maximum production rates (141x10E6 bacteria liter-1 hr-1; µ, 0.012 hr-1) were found in the metalimnion and were 1 order of magnitude higher than in the epi- and hypolimnion. In all three strata, the estimated bacterial production was roughly balanced by the estimated protozoan grazing. Heterotrophic nanoflagellates were the major consumers of the bacterial production and showed maximum numbers (up to 40x10E6 heterotrophic nanoflagellates liter-1) in the microaerobic metalimnion.