LAUSR

Abstract Frankia is a mycelium-forming actinobacterial genus that is found in actinorhizal plants as a nitrogen-fixing facultative endo-symbiont. Frankia has been a commonly uncultured endophytic actinobacteria with very slow growth germination. In the present study, the root nodules from Casuarina spp. were collected at hyper-saline and terrestrial habitats in Tamil Nadu, South India. The root nodules were surface-sterilized, dried, homogenized, and inoculated on the DPM medium with sodium propionate as a carbon source and biotin as a vitamin source. A total of 11 Frankia isolates were obtained from the specified habitats in a solid and liquid medium. The larger number of isolates was recorded in the hyper-saline habitats compared to terrestrial habitats. Finally, 2 predominant growth occurrences of isolates were selected; from each habitat, unique isolates were molecularly characterized and identified as Frankia sp. DDNSF-01 and Frankia casuarinae DDNSF-02. The physico-chemical property analysis of Casuarina rhizosphere soil of hyper-saline habitat showed higher pH, salinity and micro-nutrients like Fe−, Mn−, Cu−, and Zn− than terrestrial habitats, which could be the major factors responsible for the distribution dynamics of Frankia in hyper-saline habitats. Similarly, the biologically active metabolites of Frankia spp. were extracted by the ethyl acetate extraction method and tested by MIC assay, which was performed against emerging multi-host pathogens like Pseudomonas sp. and Candida sp. Likewise, the antibiofilm activity assay was done against the above pathogens. The biofilm inhibition of live/dead cells was confirmed by CLSM microscopic analysis. The F. casuarinae was inhibited the high level of biofilm formation of both pathogens when compared with Frankia sp. The present findings conclude the F. casuarinae is efficient in the control of emerging multi-host pathogens in actinorhizal plants.