Estimating bacterial DNA synthesis from [3H] thymidine incorporation : discrepancies among macromolecular extraction procedures

The estimation of bacterial DNA synthesis in trophic studies with [3H] thymidine requires quantitative extraction of labeled DNA. To determine the DNA contribution to total macromolecular labeling in a eutrophic ecosystem, we tested three extraction procedures currently used to estimate DNA labeling from thymidine incorportation : enzymatic fractionation, acid-base hydrolysis, and phenol-chloroform extraction. Because labeled macromolecular fractions are generally defined as DNA, RNA, and proteins, we used incorporation of tritiated thymidine, uridine, and leucine to preferentially label DNA, RNA, and proteins. Our data showed that each fractionation method yielded different apparent macromolecular distributions of the same radiolabeled substrates. Enzymatic digestions of the fractions obtained by acid-base hydrolysis and phenol-chloroform extraction showed that these two procedures are inadequate for estimating bacterial DNA labeling in our ecosystem. Finally, using the enzymatic procedure at different sites, DNA labeling appeared to represent a nearly constant proportion of the labeled macromolecules (20,1%, r=0.952, n=101) over a wide range of incorporations rates. (Résumé d'auteur

Wind induced resuspension in a shallow tropical lagoon (GBR)

In shallow environments, particle resuspension can induce large ecological effects. Under some certain conditions of fetch, wind velocity, bathymetry and bed roughness, resuspension is generated by wind induced waves. During December 1991, a shallow station (1 m depth) in the north shore of a tropical lagoon (Côte d'Ivoire) was investigated in order to study the impact of wind induced resuspension on the ecosystem. In this area, Austral trade winds are dominant almost all year long, and their velocity shows a marked diel pattern. During the survey, three sequences were distinguished : a period of Austral trade winds (with possible resuspension), a period of Borela trade winds. Only Austral trade winds with a speed > 3 m s-1 allowed particle resuspension. For chlorophyll, mineral seston and ammonia, significantly higher values were noted during the windy sequences. Conductivity and water colour varied in relation to tides. Granulometric and mineralogical analyses showed that only the 0-3 cm superficial level of the sediment was involved in resuspension. (D'après résumé d'auteur

Diel fluctuations of bacterial abundance and productivity in a shallow eutrophic tropical lagoon

Abundance and productivity (3H thymidine incorporation) of free-living and attached bacteria from surface waters were studied from hourly samples during typical hydrological conditions (rainy and flood seasons) in three different bays of the Ebrié lagoon (Côte d'Ivoire). Several additional biological variables (particulate organic carbon, phytoplankton biomass, zooplankton density) were also recorded in order to establish possible relation with bacterial parameters. (D'après résumé d'auteur