Decrypting phytomicrobiome of the neurotoxic actinorhizal species, , and dispersal boundary of cluster 2 in soil outward compatible host rhizosphere.

The actinorhizal plant, is a neurotoxic plant species endemic to the western Mediterranean area, which forms a nitrogen-fixing symbiosis with members of cluster 2. Contrarily to other clusters, the occurrence and mode of dispersal for infective cluster 2 units outside of the host plant rhizosphere remains controversial. The present study was designed to investigate the structure of the microbiomes of phytosphere, rhizosphere, and soil samples extending outward linearly up to 1 km. Results showed that the epiphyte and endophyte communities were not significantly different from each other for most of the plant tissues. The communities associated with the below-ground tissues (nodule and root) were significantly different from those found on the above-ground tissues (fruit, leaves, and stems) and had a higher community richness. phytomicrobiomes were dominated by for leaf, stem, and fruit while and were dominant in the root and nodule organelles. The nodule, a special niche for nitrogen fixation, was mainly inhabited by but contained several non- bacteria. Beside cluster 2, the presence of clusters 1, 4, and large numbers of cluster 3 strains have been detected in nodules, roots, and rhizospheres of . Despite being found in all plots using plant trapping bioassays with seedlings, cluster 2 was not detected in soil metagenomes showing the limits of detection by this approach. This result also suggests that in the absence of appropriate host plant species, cluster 2 has a reduced number of infective units present in the soil outward from the rhizosphere.