Discovering signaling events in the actinorhizal symbiosis

Although the symbiosis between Frankia and actinorhizal host plants has been widely studied, very little is known about the initial molecular interactions. To address this issue, Casuarina cunninghamiana root exudates were collected and tested on Frankia Ccl3. Frankia growth yield was enhanced by root exudates but Frankia could not utilize them as a sole carbon and energy source. Exposure to root exudates caused Frankia hyphal curling and surface property changes in fatty acids and carbohydrates. Pre-exposure to root exudates also decreased the time required for nodule initiation. The results show that root exudates and Frankia physiological changes for symbiosis are involved in the actinrohizal symbiosis. Frankia auxin production in planta was also researched as a possible signaling molecule. Bioinformatics of auxin synthesis genes and expression analysis of putative Frankia genes revealed Frankia can likely produce auxins in mature nodules, suggesting auxins may be a signaling molecule in the actinorhizal symbiosis

Contrasted Reactivity to Oxygen Tensions in Frankia sp. Strain CcI3 throughout Nitrogen Fixation and Assimilation

Reconciling the irreconcilable is a primary struggle in aerobic nitrogen-fixing bacteria. Although nitrogenase is oxygen and reactive oxygen species-labile, oxygen tension is required to sustain respiration. In the nitrogen-fixing Frankia, various strategies have been developed through evolution to control the respiration and nitrogen-fixation balance. Here, we assessed the effect of different oxygen tensions on Frankia sp. strain CcI3 growth, vesicle production, and gene expression under different oxygen tensions. Both biomass and vesicle production were correlated with elevated oxygen levels under both nitrogen-replete and nitrogen-deficient conditions. The mRNA levels for the nitrogenase structural genes (nifHDK) were high under hypoxic and hyperoxic conditions compared to oxic conditions. The mRNA level for the hopanoid biosynthesis genes (sqhC and hpnC) was also elevated under hyperoxic conditions suggesting an increase in the vesicle envelope. Under nitrogen-deficient conditions, the hup2 mRNA levels increased with hyperoxic environment, while hup1 mRNA levels remained relatively constant. Taken together, these results indicate that Frankia protects nitrogenase by the use of multiple mechanisms including the vesicle-hopanoid barrier and increased respiratory protection

Permanent draft genome sequence of Nocardia sp. BMG111209, an actinobacterium isolated from nodules of Casuarina glauca

Nocardia sp. strain BMG111209 is a non-Frankia actinobacterium isolated from root nodules of Casuarina glauca in Tunisia. Here, we report the 9.1-Mbp draft genome sequence of Nocardia sp. strain BMG111209 with a G + C content of 69.19% and 8,122 candidate protein-encoding genes

Permanent improved high-quality draft genome sequence of Nocardia casuarinae strain BMG51109, an endophyte ofactinorhizal root nodules of Casuarina glauca

Here, we report the first genome sequence of aNocardiaplant endophyte, N. casuarinaestrain BMG51109, isolated fromCasu-arina glaucaroot nodules. The improved high-quality draft genome sequence contains 8,787,999 bp with a 68.90% GC contentand 7,307 predicted protein-coding genes

Draft genome sequence of Frankia sp. strain DC12, an atypical, noninfective, ineffective isolate from Datisca cannabina

Frankia sp. strain DC12, isolated from root nodules of Datisca cannabina, is a member of the fourth lineage of Frankia, which is unable to reinfect actinorhizal plants. Here, we report its 6.88-Mbp high-quality draft genome sequence, with a G+C content of 71.92% and 5,858 candidate protein-coding genes

Draft Genome Sequence of Frankia sp. Strain BMG5.12, a Nitrogen-Fixing Actinobacterium Isolated from Tunisian Soils

Members of the actinomycete genus Frankia form a nitrogen-fixing symbiosis with 8 different families of actinorhizal plants. We report a draft genome sequence for Frankia sp. strain BMG5.12, a nitrogen-fixing actinobacterium isolated from Tunisian soils with the ability to infect Elaeagnus angustifolia and Myrica gale

Draft Genome Sequence of Frankia sp. Strain BCU110501, a Nitrogen-Fixing Actinobacterium Isolated from Nodules of Discaria trinevis

Frankia forms a nitrogen-fixing symbiosis with actinorhizal plants. We report a draft genome sequence for Frankia sp. strain BCU110501, a nitrogen-fixing actinobacterium isolated from nodules of Discaria trinevis grown in the Patagonia region of Argentina

Draft Genome Sequence of Frankia sp. Strain QA3, a Nitrogen-Fixing Actinobacterium Isolated from the Root Nodule of Alnus nitida

Members of the actinomycete genus Frankia form a nitrogen-fixing symbiosis with 8 different families of actinorhizal plants. We report a high-quality draft genome sequence for Frankia sp. strain QA3, a nitrogen-fixing actinobacterium isolated from root nodules of Alnus nitida

Draft Genome Sequence of Frankia sp. Strain CN3, an Atypical, Noninfective (Nod–) Ineffective (Fix–) Isolate from Coriaria nepalensis

We report here the genome sequence of Frankia sp. strain CN3, which was isolated from Coriaria nepalensis. This genome sequence is the first from the fourth lineage of Frankia, strains of which are unable to reinfect actinorhizal plants. At 10 Mb, it represents the largest Frankia genome sequenced to date