TERBUTHYLAZINE DEGRADATION IN A CONTAMINATED AQUIFER: STUDY OF THE HOMEOSTATIC CAPACITY OF THE AUTOCHTONOUS BACTERIAL COMMUNITY

The ability of groundwater to recover from pesticide contamination is primarily dependent on the presence of a microbial community able to degrade them. Neverthless, the study of bacterial population living in groundwater is quite scarce because it is strictly dependent on methods able to identify and characterize their community structure and functioning. In the present work we apply the Fluorescence In situ Hybridization (FISH) method to groundwater samples from a phreatic aquifer, located in the centre of Italy, in order to identify the autochtonous bacterial community. The use of 16S rRNA-targeted oligonucleotide probes, specific for the main phylogenetic levels (Archaea, Eubacteria, Alpha- Beta- Gamma-subdivision of Proteobacteria, Plantomycetes, and Gram-positive bacteria with high a DNA G+C content), and a DAPI stain made it possible to determine the structure of the bacterial community and its response to the addition of the herbicide terbuthylazine in groundwater microcosms treated with it. The biodegradation of the herbicide and the formation of its main metabolites was compared to sterile groundwater samples. The results show that, although at a lower rate compared to soil ecosystems, the groundwater bacterial community has a capability of degrading the herbicide.