KeywordsBacteria, metals, soils, communities, copper
In the bacterial world, different mechanisms of metal resistance have been described (complexation, efflux, reduction, mineral formation, etc.). All resistance genes are usually grouped in gene clusters that may contain more than 20 coding sequences. However, the function of many genes is not always known and their relative position in different bacterial strains may vary. In addition, these resistance gene clusters may be located on chromosomes, chromids or plasmids of various sizes. The aim of the present project is to understand the origin, the organisation and the function of these resistance genes in one of the most complex copper resistance gene cluster, the cop cluster of Cupriavidus metallidurans CH34. This cluster is composed of 21 plasmidic genes, and many of them (copH, copV, copM, etc.) have no known function. To better understand this cop cluster, new strains of the genus Cupriavidus will be isolated and compared to the model CH34 strain. As the CH34 cop cluster has a supposedly recent origin, several ancient soils, contaminated by copper for more than 400 years (or more) will be examined. Strains of Cupriavidus, possibly in a dormant state, will be isolated from these soils. These strains might indeed contain other versions of the cop cluster, with less genes and other gene dispositions. Ancient copper mines and the soil form Medieval foundries will be sampled in various places in Europe. For each copper resistant Cupriavidus strain obtained, the eventual cop clusters will be seeked and sequenced. The different clusters obtained will then be compared to each other. Knockout mutants will be designed and studied for selected genes in some strains. This dual approach (comparison of gene clusters in different strains and the study of knokout mutants) will improve our understanding of one of the most complex copper resistance system.