par Servais, Pierre ;Garnier, Josette
Référence Microbial ecology, 25, 1, page (19-33)
Publication Publié, 1993-01-01
Article révisé par les pairs
Résumé : Bacterial activity was measured in the river Seine by two methods, 3H-thymidine incorporation into DNA and 3H-leucine incorporation into proteins. Both incorporation rates are characterized by low values upstream of Paris,a large increase just downstream of the outfall of the Acheres treatment plant effluents, and then decreasing values further down stream. The covariation of both activities is demonstrated by the constancy of the molar ratio (leucine to thymidine incorporation rate) in the range of 6 to 8 for all the samples,except in the perturbed area where it is higher( 15 to 35). These high values of molar ratio are linked to the introduction in to the river of large sized bacteria(>=1 µm) with higher incorporation rates per cell or biomass u nit than the small autochthonous bacteria(<1 µm). Growth rates of large bacteria were on average 3 .7 times higher than those of small bacteria.B acterial production was calculated with experimentally determined conversion factors(0.5 x 1018 cells per mole of thymidine incorporated and 900 gC per mole of leucine incorporated) and by taking into account the activity of both size classes of bacteria measured through fractionation experiments(post-incubation filtration). Production estimated in the perturbed area downstream of Acheres was very high, up to 60 pgC/liter.h in the summer.Carbon consumption by bacteria in the area perturbed by the Acheres effluents was calculated assuming a growth yield of 0.2 and compared to the load of biodegradable organic matter discharged by the treatment plant.In summer, an additional supply of organic matter is required to account for the intense bacterial activity, suggesting the importance of phytoplankton production in the carbon budget.