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

Ecological organization and succession during natural recolonization of a tropical pond

The structure of a planktonic community was studied in April 1990 for 24 days (D1 to D24) during the natural recolonization of a tropical pond (Côte d'Ivoire) made azoic by empting and liming (D0). Abundance of bacterioplankton, phytoplankton, protozoans and zooplankton were studied twice daily, whereas hydrological descriptors (temperature, conductivity, oxygen, pH, dissolved nutrients, sestonic weights) were recorded several times daily. After the pond treatment, the natural refilling from groundwater began immediately. The microheterotrophic (bacteria, flagellates, ciliates), phytoplanktonic (#Coelastrum microsporum) and zooplanktonic (the rotifers #Brachionus plicatilis and #Hexarthra intermedia$) communities were first based on opportunist species favored by the initially large nutritive availability. (D'après résumé d'auteur

Role of bacteria as food for zooplankton in a eutrophic tropical pond (Ivory Coast)

The aim of this study was to determine bacteria could be a substantial source of carbon for zooplankton and whether the grazing pressure of these metazoan filter-feeders could influence the fate of bacterial production. Eight grazing experiments using natural bacteria labelled with 3H thymidine were conducted in a tropical pond (Ivory Coast) during various phases of biological colonization (rotifer-dominated and copepod-dominated phases of the colonization). Higher grazing and clearance rates were observed with rotifers (#Brachionus plicatilis and #Hexarthra intermedia), while very low values where obtained when the cyclopoid copepod #Apocyclops panamensis$was dominant. Less than 1$ consumed up to 36% of this production. However, this consumption of bacteria appeared to contribute only to an insignificant proportion of the daily carbon intake (e.g. 0.9. to 7.1% of body carbon for rotifers). The low contribution of bacteria in the nutrition of zooplankton is discussed in terms of their cell size and their relative abundance in the total amount of seston available. (Résumé d'auteur

In situ spawning rate of the calanoid copepod Acartia clausi in a tropical lagoon (Ebrié, Côte d'Ivoire) : diel variations and effects of environmental factors

rate of the calanoid copepod Acartia clausi in a tropical lagoon (Ebrié, Côte d Ivoire): diel variations and effects of environmental factors. Zoological Studies 43(2): 244-254. Diel changes in the spawning rate of Acartia clausi were studied during several 24 h time series performed between 1993 and 1997 at several sites in Ebrié Lagoon (Côte d Ivoire) at which the morphology and hydrological structures differed. The daily egg production rate ranged from 8 to 60 eggs female-1 d-1 (5 % to 45 % of body carbon) and varied according to stations and periods. A correlation analysis, performed with the present results, revealed no significant effect of either envi-ronmental factors (salinity, temperature, and chlorophyll a biomass) or individual weight of females. However, the roles of salinity and food abundance (chlorophyll a) appeared when grouping the present data (1993-1997) with results from the same sites obtained previously (1981-1982) by Saint-Jean and Pagano (1984). This grouping showed the importance of inter-annual variations as compared to seasonal variations. The rhythm of egg laying was characterized by a night maximum which occurred earlier in the estuarine zone (22:00-01:00) than in the western oligohaline zone (04:00-06:00). These peaks of egg laying always occurred after the peak of gut fluorescence which was consistently observed at the beginning of the night (data from Kouassi et al

Організаційно-структурні основи функціонування Міністерства народного здоров’я та опікування в Українській державі у 1918 р.

Розглядаються нормативно-правові та організаційно-структурні основи функціонування Міністерства народного здоров’я та опікування в Українській державі у 1918 р. Характеризується структура міністерства, функції апарату МНЗтаО, розкривається взаємодія міністерства з органами місцевого самоврядування.Рассматриваются нормативно-правовые и организационно-структурные основы функционирования Министерства народного здоровья и опеки в Украинском государстве в 1918 г. Характеризуется структура министерства, функции аппарата МНЗиО, раскрывается взаимодействие Министерства с органами местного самоуправления.Examined normatively legal and organizationally structural bases of functioning of Ministry of folk health and guardianship in the Ukrainian state in 1918. The structure of ministry, function of vehicle of MNZtaO is characterized, co-operating of ministry opens up with the organs of local self-government

Ages of stellar populations in the low-metallicity star-forming dwarf galaxies

We perform a comprehensive study of ten star-forming (SF) galaxies with the oxygen abundance Z 1 (or ~10 Gyr) just as for low-mass galaxies efficient star formation have been triggered at z ~ 0.2 (or ~2 Gyr)