Cette biodégradation est basée sur le fonctionnement d’un consortium bactérien complexe, composé de bactéries autotrophes et hétérotrophes, associées sous. Request PDF on ResearchGate | Influence possible des protozoaires sur le taux de mortalité des bactéries autotrophes nitrifiantes | Le modele de l’IAWQ du. Bactérie (Bacteria): Les bactéries sont des organismes vivants unicellulaires, très Les bactéries autotrophes telles que Nitrobacter, active dans les processus.
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By regenerating oxidised forms of nitrogen nitratethe nitrification process plays an important role in the nitrogen cycle of aquatic environments. The measurement of the activity and biomass of nitrifying bacteria is thus essential to understand and quantify the general nitrogen fluxes in those environments.
Different methods of measuring the nitrifying activity exist.
The first methods developed were based on the use of specific nitrification inhibitors: N-serve, allyl thio-urea, acetylene, methylfluoride and dimethyl ether, as most used. They consist in measuring differences of ammonium, nitrite and nitrate dynamics in an inhibited and control sample during time.
These methods can be applied as long as the inhibitors are specific for bacterje bacteria, and activities are high enough to allow the measurement autotrohpe concentration variations during incubation times which are not too long.
At the present time, the most used methods are dealing with isotopic tracers: This factor is considered to be constant in the standard incubation conditions. The most frequently used enumeration methods of nitrifying bacteria are not very satisfactory. Classical culture techniques most probable number and immunofluorescence techniques are known to greatly underestimate the numbers of active organisms.
Recently developed gene-probes techniques work well for the identification of particular strains, but are not yet useful for the numeration.
A good alternative to these methods consists in the measurement of potential nitrifying activity which is correlated to the nitrifying biomass. This work presents a reassessment of the autotrophic nitrifying activity measurement by the 14C-bicarbonate incorporation method and its use to estimate the biomass of nitrifying bacteria.
Several methods were used for our study: Continuous enrichment cultures of nitrifying bacteria were obtained from an inoculum coming from the Seine estuary freshwater section.
Pure cultures of Nitrosomonas europaea and Nitrobacter winogradskyi were obtained from the National Collection of Industrial and Marine Bacteria Aberdeen, Scotland and a continuous enrichment culture of mixed heterotrophic bacteria, without nitrifying organisms, was obtained with a freshwater inoculum by imposing a residence time of 2 hours less than the generation time of nitrifying bacteria.
Nitrifying cell numbers and size in the pure cultures were determined by epifluorescence with a microscope, after Autoteophe staining.
Biovolumes were estimated according to cell size and converted in biomasses according to a conversion factor determined experimentally with a carbon analyser. Ammonium was measured with the indophenol blue method, nitrate was reduced in nitrite bactfrie a cadmium bed and nitrite was measured with the sulfanilamide method.
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Bicarbonate was measured by acid titration in natural water samples, and with the evolution method for culture samples. C incorporation rates are measured by the incubation of samples with 14C-bicarbonate, the samples being filtered on 0.
Autotrophf general validity bacteriee the method was demonstrated by experiments on nitrification inhibitors in enrichment cultures. These experiments consisted in measuring the effect of different combinations of N-serve, ethanol the organic solvent of N-serve and chlorate, on N-oxidation rates and C incorporation rates on samples of the two nitrifying enrichment cultures ammonium- and nitrite-oxidising bacteria.
The inhibitors effects were also determined bzcterie the C incorporation rates of heterotrophic bacteria. However, the ethanolic solution of N-serve had an unwanted result on C incorporation. The organic solvent enhanced heterotrophic incorporation of C which totally masked out the autotrophic contribution of nitrifying bacteria.
Une réévaluation de la methode d’incorporation – Revue des sciences de l’eau – Érudit
For this reason N-serve was added in the empty flask before the sample to allow the evaporation of the solvent. By acting this way, inhibition of autotrophic C incorporation by nitrifying bacteria was also complete, while heterotrophic incorporation was unaffected. To measure potential nitrifying activities, the optimal growth conditions of nitrifying bacteria were determined on enrichment cultures: The determined optimal growth rate was 0. This factors allowed us to establish a relationship between potential nitrifying activity measurements and nitrifying biomass: Our conclusion is that the results presented in this paper allow the validation of the 14C-bicarbonate incorporation method with and without inhibitors to measure the nitrifying activity.
The main differences of our protocol to the original ones is that we propose the use of a combination of 2 inhibitors, N-serve and chlorate, and the elimination by evaporation of the organic solvent of N-serve ethanol to avoid any interference with the heterotrophic populations.
The method can be used in in situ conditions, to allow real nitrifying activities measurements in samples. In this case, carbon incorporation rates can be converted in ammonium oxidation rates with the use of the conversion factor 0. The method can also be used by placing the sample in optimal temperature, pH, oxygen and ammonium conditions for nitrifying bacteria, to allow potential nitrifying activity measurements. This potential activity can be used to estimate the nitrifying biomass by considering a conversion factor of 0.
Download the article in PDF to read it. Nitrifying activity, nitrifying biomass, 14C-bicarbonate incorporation, nitrification inhibitors, N-serve, chlorate. Revue des sciences de l’eau11 2— Revue des sciences de l’eau 11, no.