WHERE DO DEHALOGENASES COME FROM ? A MULTIDISCIPLINARY STUDY HIGHLIGHTS THE PRIMARY ROLE OF HORIZONTAL GENE TRANSFER DURING RECENT FUNCTIONAL ADAPTATION
Résumé
The dehalogenases are enzymes responsible for the degradation of many chlorinated compounds. Most of them appear to be recent additions to the genomes of bacteria capable of xenobiotic compound degradation. To understand where these dehalogenases come from, a multidisciplinary approach was used. First, the proteic and nucleic sequence were analyzed by using bioinformatics techniques and no ancestor sequence was identified from which the dehalogenases could be derived. Another bioinformatics approach was applied which consisted of comparing the dehalogenase sequences between themselves. This approach showed a mosaic structure of these enzymes, suggesting horizontal gene transfer might have occurred. In addition, this approach defined several motifs that are common among the dehalogenases and that might represent functional characteristics. To support this observation, we applied an in vitro genetic shuffling method to try and reproduce the dehalogenases genes. To connect these observations to the potential for soil microbial communities to adapt by using different DNA fragments as defined by the motifs, we pyrosequenced the metagenome of a non-polluted soil in order to find the sources of the motifs among the original sequences of the soil metagenome.