Evaluation des modifications quantitatives, qualitatives et fonctionnelles induites par la conservation de consortiums bactériens extraits de sols

Conservation of bacterial consortia: functional and genetic consequences. Conservation of bacterial consortia exhibiting a high functional diversity can be useful to study both genetic and functional diversity as well as to exploit functional capacities for example to study biotransformation of different molecules and to analyze chemicals possibly produced. In order to improve bio-tests based on the use of complex microbial community, the possibility to repeat analyses with bacterial consortia exhibiting similar capacities of transformation over time was necessary. That is why consequences of conservation methods, either -80°C freezing in glycerol or lyophilization were studied. Bacterial consortia were characterized according to quantitative, qualitative and functional criteria: i) bacterial density by direct counting using orange acridine staining, ii) genetic structure by Ribosomal Intergenic Spacer Analysis, iii) respiratory activity by Substrate Induced Respiration measurements and iv) capacity to transform various toxic components in bio-tests. Bacterial consortia were extracted from two soils by mechanical dispersion. Culture of extracted consortia after conservation induced a slight decrease of bacterial density especially when they were lyophilized. Changes in respiratory capacities were also observed depending on soil. Although genetic structure of consortia became close after culture whatever the conservation method, differences in biotransformation capacities were observed depending on the toxic component tested. For atrazine, lyophilization induced a decrease in biotransformation capacity compared with frozen consortia. In conclusion, freezing has been shown to be the conservation method which allowed to minimize changes in transformation capacity in bacterial consortia.