Physiological and Genomic Elucidation of Cold-Resilient Rhizobacteria Reveals Plant Growth Promotion by Siderophore Optimization and Enhanced Biocontrol Potential Against Fungal Pathogens

Abstract

Cold stress and fungal pathogens pose significant challenge to high-altitude agriculture, impeding plant growth and metabolism. Siderophore-producing plant growth-promoting (PGP) rhizobacteria offer a promising solution by enhancing iron uptake and engaging in pathogen biocontrol. The current research aims to investigate the potential of siderophore-producing psychrotrophic bacteria to manage fungal phytopathogens effectively for its possible application as a bio-inoculant. In our search for psychrotrophic PGP bacteria with biocontrol potential, we isolated 13 rhizobacterial morphotypes; among these, AMR01 showed excellent biofertilizer characteristics. Taxonomic analysis elucidated AMR01 as a potentially novel Pseudomonas species. At 10 °C, AMR01 produced 33.23% siderophore unit (PSU), increasing to 55.76 PSU through pH, NH₄NO₃, and iron concentration optimization. Furthermore, AMR01 exhibited other PGP attributes, including auxin and ammonia production (13.47 µg/ml and 25.08 mg/l), phosphate solubilization (295.1 µg/ml), nitrogen fixation, potassium solubilization, and hydrogen cyanide (HCN) production. Remarkably, AMR01 demonstrated biocontrol potential, inhibiting three phytopathogens. Seed bacterization with AMR01 enhanced the germination of fungus-infected seeds, as evidenced by increased root and shoot length, compared to uninoculated control, conferring protection against fungal infestation. Genome analysis identified genes involved in pyoverdine synthesis and PGP traits in AMR01. The biosynthetic gene cluster associated with siderophore, HCN, and NRPS further supported AMR01 as a potent biocontrol agent. This research underscores the capacity of a novel, Pseudomonas sp., to improve plant growth by aiding in nutrient uptake and protecting against phytopathogens. Physiological and genomic evidence supports the potential of AMR01 as a bio-inoculant for addressing fungal-induced diseases in crops grown in the Indian Himalayan region.