METAGENOMIC ANALYSIS OF THE MICROBIAL COMMUNITY ASSOSCIATED WITH THE ROOT NODULES OF THE ACTINORHIZAL PLANT CASUARINA GLAUCA

The symbiosis between Frankia and actinorhizal plants in the genus Casuarina are intentionally exploited in efforts to reclaim degraded lands and improve agricultural production through the practice of agroforestry, particularly in countries on the continent of Africa. Laboratory investigations have shown that some non-Frankia bacteria isolated from the root nodules of Casuarina plants can play active and positive roles in this symbiosis, but a culture-independent survey of the microbial community in system had not yet been conducted. To fill this knowledge-gap, a metagenomic survey of the endophytic microbial community of Casuarina glauca root nodules was performed at three sites in the country of Tunisia. The sites were chosen to evaluate the difference in community structure across a steep gradient of aridity. To complement this survey, a shotgun metagenomic analysis of the endophytic and epiphytic microbial community of C. glauca root nodules at these sites was also performed. Results of both analyses found a sharp decrease in the abundance of the symbiont Frankia in the semi-arid and arid samples. Other microbial taxa that were known to be active in the system as well as previously unobserved taxa were found in increased abundance in samples with decreased Frankia abundance. These results show a strong effect of climate on the endophytic community associated with C. glauca and provide insights for continued laboratory and field testing of this system

Permanent Draft Genome Sequence for Frankia sp. Strain EI5c, a Single-Spore Isolate of a Nitrogen-Fixing Actinobacterium, Isolated from the Root Nodules of Elaeagnus angustifolia

Frankia sp. strain EI5c is a member of Frankia lineage III, which is able to reinfect plants of the Eleagnaceae, Rhamnaceae, Myricaceae, and Gymnostoma, as well as the genus Alnus. Here, we report the 6.6-Mbp draft genome sequence of Frankia sp. strain EI5c with a G+C content of 72.14 % and 5,458 candidate protein-encoding genes

Permanent Draft Genome Sequence of Frankia sp. Strain BR, a Nitrogen-Fixing Actinobacterium Isolated from the Root Nodules of Casuarina equisetifolia

Frankia sp. strain BR is a member of Frankia lineage Ic and is able to reinfect plants of the Casuarinaceae family. Here, we report a 5.2-Mbp draft genome sequence with a G+C content of 70.0% and 4,777 candidate protein-encoding genes

Alone Yet Not Alone: Frankia Lives Under the Same Roof With Other Bacteria in Actinorhizal Nodules

Actinorhizal plants host mutualistic symbionts of the nitrogen-fixing actinobacterial genus Frankia within nodule structures formed on their roots. Several plant-growth-promoting bacteria have also been isolated from actinorhizal root nodules, but little is known about them. We were interested investigating the in planta microbial community composition of actinorhizal root nodules using culture-independent techniques. To address this knowledge gap, 16S rRNA gene amplicon and shotgun metagenomic sequencing was performed on DNA from the nodules of Casuarina glauca. DNA was extracted from C. glauca nodules collected in three different sampling sites in Tunisia, along a gradient of aridity ranging from humid to arid. Sequencing libraries were prepared using Illumina NextEra technology and the Illumina HiSeq 2500 platform. Genome bins extracted from the metagenome were taxonomically and functionally profiled. Community structure based off preliminary 16S rRNA gene amplicon data was analyzed via the QIIME pipeline. Reconstructed genomes were comprised of members of Frankia, Micromonospora, Bacillus, Paenibacillus, Phyllobacterium, and Afipia. Frankia dominated the nodule community at the humid sampling site, while the absolute and relative prevalence of Frankia decreased at the semi-arid and arid sampling locations. Actinorhizal plants harbor similar non-Frankia plant-growth-promoting-bacteria as legumes and other plants. The data suggests that the prevalence of Frankia in the nodule community is influenced by environmental factors, with being less abundant under more arid environments