Biologie et diversité génétique des souches de Frankia associées aux Casuarinacées

Summary Here we present some methodologies developed for the study of the biology and genetic diversity of Frankia nodulating actinorhizal plants belonging to the Casuarinaceae family. First, the exponential growth was improved for some strains. This permitted to describe their complex proteolytic system, an excretion of exo-proteins and to use some isoenzyms to characterize these strains. We have also studied the preliminary microbial signals that follow exposure of host-plant to flavonoids. In a second part, the genetic diversity of Frankia nodulating Casuarinaceae was studied. The isolation step was avoided by a direct characterization of the endosymbiont inside the nodule. A genetic diversity was shown among Frankia associated to Casuarinaceae in Australia, whereas previous studies on isolated strains had shown an important genetic homogeneity.