AUTHOR=Swanson Erik , Sbissi Imed , Ktari Amir , Cherif-Silini Hafsa , Ghodhbane-Gtari Faten , Tisa Louis S. , Gtari Maher 

TITLE=Decrypting phytomicrobiome of the neurotoxic actinorhizal species, Coriaria myrtifolia, and dispersal boundary of Frankia cluster 2 in soil outward compatible host rhizosphere

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.1027317

DOI=10.3389/fmicb.2022.1027317

ISSN=1664-302X

ABSTRACT=<p>The actinorhizal plant, <italic>Coriaria myrtifolia,</italic> is a neurotoxic plant species endemic to the western Mediterranean area, which forms a nitrogen-fixing symbiosis with members of <italic>Frankia</italic> cluster 2. Contrarily to other <italic>Frankia</italic> 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 <italic>C. myrtifolia</italic> 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. <italic>Coriaria myrtifolia</italic> phytomicrobiomes were dominated by <italic>Cyanobacteria</italic> for leaf, stem, and fruit while <italic>Actinobacteria</italic> and <italic>Proteobacteria</italic> were dominant in the root and nodule organelles. The nodule, a special niche for nitrogen fixation, was mainly inhabited by <italic>Frankia</italic> but contained several non-<italic>Frankia</italic> bacteria. Beside <italic>Frankia</italic> cluster 2, the presence of clusters 1, 4, and large numbers of cluster 3 strains have been detected in nodules, roots, and rhizospheres of <italic>C. myrtifolia</italic>. Despite <italic>Frankia</italic> being found in all plots using plant trapping bioassays with <italic>C. myrtifolia</italic> seedlings, <italic>Frankia</italic> 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, <italic>Frankia</italic> cluster 2 has a reduced number of infective units present in the soil outward from the rhizosphere.</p>