Comparative genomic insights into a plant-associated Enterobacter adelaidei strain isolated from the taro rhizosphere

Enterobacter adelaidei, an extensively drug resistant strain, was recently described and isolated from hospital wastewater in Australia. However, its distribution in plant-associated environments has not been documented yet. This study presents a whole-genome-based characterization of E. adelaidei strain CELK12, isolated from the rhizosphere of taro (Colocasia esculenta L.) and its plant growth-promoting performance under saline stress conditions.

Genomic analyses confirmed the strain as E. adelaidei (ANI: 96.49%, dDDH: 71.90%). The genome of strain CELK12 (4.68 Mb, 53.5% GC content) was predicted to contain key genes involved in nutrient acquisition (gcd, pqqC, amtB), phytohormone biosynthesis (ipdC, trpE), iron transport (entB, feoB), and stress tolerance (otsA, katG, sodA, oxyR). These genomic features suggest the potential for rhizosphere competence and plant-beneficial activity of strain CELK12. Comparative genomics suggested a trend toward an open pan-genome among the selected strains (Heap's law α = 0.11) and strain-specific divergences in secondary metabolite production, consistent with possible environmental adaptation. Genomic and phenotypic assessments revealed that while CELK12 carries certain chromosomally encoded resistance genes, it lacks plasmids, shows no hemolytic activity, and exhibits broad phenotypic susceptibility to major antibiotic classes. The seed germination and pot investigations confirmed significant enhancement of rice growth under saline conditions (100-150 mM NaCl) following CELK12 treatment.

The findings of this study expand the known ecological range of E. adelaidei to include plant-associated niches and provide the first genomic predictions and experimental evidence of potential plant-beneficial traits within this specific lineage of the species.