Short-term bacterial reactivity of nitrogen-enriched seawater of a eutrophic lagoon

We carried out, in September, a 24 h experiment to determine the potential reactivity of bacterial communities found in the sea water in Arcachon Basin (France). To create eutrophic systems, batches of seawater were enriched with 30 mgl^?1 of either ammonium chloride or amino acids. Samples were taken every 3 h. Quantitative measurements were made of direct counts (AODC), biomass and ATP content. The heterotrophic bacterial communities were defined in terms of their catabolic potentialities and ‘specific’ diversity. Bacterial heterotrophic activity was established by measuring heterotrophic uptake and the mineralization percentage of labelled glucose or amino acids. From these data, ratios of AMP/ATP and P/B were calculated where P is the uptake of labelled substrate and B is the biomass.After the nitrogen enrichment an increase of the respiration was seen at first. After 6 h, a biomass peak appeared associated with a continuous increase in the number of cells. Bacterial growth was concurrent with a qualitative modification of the community: UAI increased, and diversity dropped. A less diversified community resulted suggesting an immature ecological state (zymogenous bacterial). Low values of respiration percentage (20%) characterized high growth yields.     

Temporal Variations of Benthic Bacterial Microflora on the Northwestern Mediterranean Continental Shelf and Slope

Abstract. Bacterial (direct and heterotrophic counts, heterotrophic potentials) and organic matter (org C, org N) parameters were studied over 2 years in the surface sediments of 3 stations located on the continental shelf (station A: 15m; station B: 35m) and slope (station C: 910m) in the northwestern Mediterranean Basin.
Although logistic constraints did not allow a satisfactory sampling periodicity in the offshore survey, some seasonal trends were still observable at the deepest station. Variations were quantitatively more important in the two shallow sediments (from 3×10² heterotrophic bacteria – ml^-1 in December 1984 to 10⁷ heterotrophic bacteria-ml^-1 in March 1986). Epifluorcsccncc direct counts were relatively constant (5×10⁸ cells-ml^-1), while heterotrophic potentials (with ¹⁴C labelled glucose and glutamic acid) showed a succession of very short pulses over the year. Different concentrations of organic matter (from 0.2% orgC at 15m to 0.8% orgC at 35m) appeared to sustain very similar bacterial numbers. Nevertheless, a certain relation between the seasonal evolution of bacterial and organic matter parameters was discernable. Although depth apparently had no measurable effect on maximal spring bacterial densities, it seemed to lessen the summer and winter decreases in the two shallow stations.     

Short-term changes of marine bacterioplankton in antarctic coastal environment

Observations of the short-term changes of seawater bacterioplankton were carried out during the summer of 1988 in Antarctic coastal surface waters. The studies were designed to compare the variations of bacterioplankton in freemoving and enclosed seawater. Even when a diurnal cycle is present the data collected from the enclosed seawater experiments remain much more constant than the corresponding data in free-moving seawater. The wide range of parameters used in the two experiments reveals common properties which illustrate the major role of displacements of water masses at a fixed sampling station in the temporal changes observed in free-moving Antarctic coastal seawater.