The Carnoulès acid mine drainage is characterized by an acidic pH and high metal and arsenic concentrations. Based on the low bacterial biodiversity, molecular approaches allowed the determination of a bacterial community functioning model. The aim of the PhD work was to clariff both the composition andthe functioning of this community, using cultural and functional approaches, focusing on the organic matter recycling. Different media were designed that allowed the isolation of 49 bacterial strains belonging to 19 genera,leading to a 70 o  increase in the bacterial diversity compared with previous metagenomic approaches. Among the 19 genera,3 are new, one of which, a previously uncultured genus frequently detected in acidic environments, has been taxonomically characterized and named Acidiminos cornoulesii.The ability of strain Q8, belonging to the genus Paenibacillus, to degrade starch and xylan over a wide rangeof pH values as well as 4rsenic concentrations allows to assign to Paenibacillus a role in the resilience of the community for these functions. A function-based screening of the Q8-DNA in Escherichia coli led to isolatethe genes encoding the polymer-degrading proteins.Moreover, a function-based screening of 80,000 clones from a Carnoulès metagenomic DNA library led to the detection of 28 positive clones for the amylolyic activity. Two proteins sharing no sequence similarity with known amylases were characterized in vitro, demonstrating that bioprospecting in a priori incongruous sites can lead to unsuspected discoveries.These works show that new informations using cultural and functional approaches can be obtained compared to those gained with molecular approaches. Results confirmed the complementarity between both approachesis crucial to analyze complex ecosystems. Nevertheless, more research efforts still have to be undertaken tounderstand their functioning.
