N2-fixing actinomycetes isolated from Alnus acuminata field nodules able to deficiently interact for nodulation with their original host root

VALDÉS, D; VOBIS, G; WALL, LG

New Hampshire, USA.

Simposio; XIII Symposium on Frankia and Actinorhizal Plants; 2004

As part of a project to isolate novel Frankia strains from nodules of Alnus acuminata harvested at “La Banderita” native forest (Tucumán, Argentina), we have isolated four actinomycetes that fix nitrogen in vitro but do not develop typical Frankia morphotypes as multilocular sporangia or vesicles. We have characterized their growth on different substrate media, BAP+N, BAP-N, with either glucose or propionate as C source, and soil extract agar (Kehe), and evaluated the morphology of filaments, aerial mycelium, substrate mycelium, sporangia or spore disposition, colony morphology and colour. BOX-PCR fingerprints revealed diversity between the isolates and confirmed the identity between single-spore cultures and their parental strains. Two fragments of the expected size were amplified by nested PCR using primers previously reported to be Frankia specific, which suggests that a close relationship exists between these actinomycetes and Frankia. Interestingly, the isolates were able to interact with the original host. Plant reaction to inoculation with the isolates varied between root hair deformation, pre-nodule formation, or ineffective nodulation. Co-inoculation of Alnus acuminata with these nodulation-defective isolates and the non-infective Frankia BCU110501 (originally isolated from Discaria trinervis), resulted in a limited physiological complementation for nodulation. We propose that these actinomicete isolates behave as Frankia nodulation mutants or nodulation defective Frankia that could be used as a tool to understand early interactions leading to recognition and nodulation in actinorhizal symbiosis.