Protozoan Grazing and Bacterial Production in Stratified Lake Vechten Estimated with Fluorescently Labeled Bacteria and by Thymidine Incorporation

Abstract

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 bacterial 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. 10 18 (range, 0.38 × 10 18 to 1.42 × 10 18 ) bacteria mol of thymidine −1 at specific growth rates (μ) ranging from 0.007 to 0.116 h −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 insignificant 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 the aerobic epilimnion. Thus, the established empirical conversion factor for thymidine incorporation into total macromolecules was used to estimate bacterial production. Maximum production rates (141 × 10 6 bacteria liter −1 h −1 ; μ, 0.012 h −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 40 × 10 6 heterotrophic nanoflagellates liter −1 ) in the microaerobic metalimnion.

Planktonic community structure determines the fate of bacterial production in a temperate lake

“…The literature data and the Upton Lake data are based on epilimnion communities only. Recent field studies in lakes also provide evidence for slow bacterial turnover times in the epilimnion, metalimnion, and hypolimnion (Sanders et al 1989;Bloem et al 1989). We conclude that community turnover times of planktonic bacteria in Upton Lake and in most systems are considerably > 1 d.…”

“…Previous studies have considered the relationship between bacterial growth and losses due to grazing and have inferred that growth and grazing are in close balance (McManus and Fuhrman 1988;Sanders et al 1989;Bloem et al 1989). On the other hand, Sherr et al (1989) made simultaneous measurements of growth and protozoan grazing and found that growth estimates consistently exceeded grazing estimates in a Georgia estuary.…”

“…Subsamples from the same bags used in the disappearance experiments were taken several times during the first hour of incubation. These samples were preserved with an equal volume of cold 4% glutaraldehyde, which minimizes particle losses from cells (Sanders et al 1989;Bloem et al 1989) and avoids the safety and precipitation problems associated with the fixative containing acrolein, tannic acid, and glutaraldehyde recommended by Sieracki et al (1987).…”

Effects of the Agricultural Pesticides Atrazine, Deethylatrazine, Endosulfan, and Chlorpyrifos on an Estuarine Microbial Food Web

“…Phagotrophic protists in the nannoplankton, flagellates, and 10 to 20 m ciliates are likely to have major roles as consumers of picoplanktonic primary production as well as of the secondary production of heterotrophic bacteria [37]. Phagotrophic protists are also responsible for much of the regenerative flux of nitrogen and phosphorus in the sea [38,39], and they can serve as a vital food resource for metazoans [40].…”

Fate of heterotrophic bacteria in Lake Tanganyika (East Africa)

“…For around two decades, the role of protozoa, in particular HNF, in controlling bacterial production in various types of aquatic systems has been demonstrated by different authors (Azam et al, 1983;Bloem et al, 1989;Servais et al, 2000). By efficiently feeding on bacteria, protozoa can channel up bacterial production to upper trophic levels, provided that metazooplankton actually prey upon them.…”