The plant-growth-promoting actinobacteria of the genus Nocardia induces root nodule formation in Casuarina glauca

Abstract

Actinorhizal plants form a symbiotic association with the nitrogen-fixing actinobacteria Frankia. These plants have important economic and ecological benefits including land reclamation, soil stabilization, and reforestation. Recently, many non-Frankia actinobacteria have been isolated from actinorhizal root nodules suggesting that they might contribute to nodulation. Two Nocardia strains, BMG51109 and BMG111209, were isolated from Casuarina glauca nodules, and they induced root nodule-like structures in original host plant promoting seedling growth. The formed root nodule-like structures lacked a nodular root at the apex, were not capable of reducing nitrogen and had their cortical cells occupied with rod-shaped Nocardiae cells. Both Nocardia strains induced root hair deformation on the host plant. BMG111209 strain induced the expression of the ProCgNin:Gus gene, a plant gene involved in the early steps of the infection process and nodulation development. Nocardia strain BMG51109 produced three types of auxins (Indole-3-acetic acid [IAA], Indole-3-Byturic Acid [IBA] and Phenyl Acetic Acid [PAA]), while Nocardia BMG111209 only produced IAA. Analysis of the Nocardia genomes identified several important predicted biosynthetic gene clusters for plant phytohormones, secondary metabolites, and novel natural products. Co-infection studies showed that Nocardia strain BMG51109 plays a role as a "helper bacteria" promoting an earlier onset of nodulation. This study raises many questions on the ecological significance and functionality of Nocardia bacteria in actinorhizal symbioses.

Biodiversity of Culturable Endophytic Actinobacteria Isolated from High Yield Camellia oleifera and Their Plant Growth Promotion Potential

“…Besides, there were other genera such as Actinomadura, Microbiospora, Micromonospora and Nocardia also shared in two or three C. oleifera samples. Studies have reported that these actinobacterial genera showed potential for use as biofertilizers in other crops including chickpea [56], alfalfa [57], Casuarina glauca [58]. These suggested that the endophytic actinobacteria from C. oleifera possessed wide range of application and great development value.…”

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

“…Most of these isolates were ignored or discarded as being irrelevant to the plants. However, these non- Frankia Actinobacteria have consistently been isolated from several actinorhizal plants including Casuarina ( Guillén et al, 1993 ; Niner et al, 1996 ; Valdes et al, 2005 ; Ghodhbane-Gtari et al, 2010 ), and consist of Actinobacteria from Micromonospora ( Valdes et al, 2005 ; Ghodhbane-Gtari et al, 2010 ), Nocardia ( Ghodhbane-Gtari et al, 2010 , 2019 ) and Streptomyces genera ( Ghodhbane-Gtari et al, 2010 ). Similarly, non-symbiotic bacteria, such as Azospirillum , Bacillus , Pseudomonas , and Streptomyces , are known to be auxiliary bacteria in several Rhizobium -legume symbioses ( Iruthayathas et al, 1983 ; Grimes and Mount, 1984 ; Li and Alexander, 1990 ).…”

Stable Transformation of the Actinobacteria Frankia spp

“…Three 2-month-old Casuarina glauca plants were inoculated with 2 ml of a concentrated culture of F. casuarinae strain CcI3(pHKT1) transformant. After 2 months incubation, an average of 35 nodules per plant were collected and sterilized (41). After a week of incubation in LB medium, 6 nodules were crushed with a sterile mortar.…”