Genomic and Phenotypic Characterization of Enterobacter sp. MALB-1 Isolated from Monochamus alternatus for Plant Growth-Promoting Potential and Safety Assessment

초록

In this study, we isolated a plant growth-promoting bacterium, designated Enterobacter sp. MALB-1, from the gut of Monochamus alternatus. A polyphasic taxonomic approach demonstrated that while MALB-1 belongs to the genus Enterobacter, it represents a genetically and phenotypically distinct lineage. Whole-genome analysis revealed average nucleotide identity (ANI) values of 86.7－88.2% and digital DNA-DNA hybridization (dDDH) values of 31.8－34.7% with closely related type strains, which are significantly below the thresholds for species delineation. Genomic functional annotation identified a diverse repertoire of genes involved in nitrogen fixation, phosphate solubilization, and indole-3-acetic acid (IAA) biosynthesis, highlighting its potential as a biofertilizer. Phenotypically, MALB-1 exhibited robust adaptability to agricultural stress conditions, including broad pH (5－9) and salinity tolerance (0－5%), and possessed a versatile metabolic profile capable of utilizing various root exudate components. Importantly, a comprehensive safety assessment was conducted to address concerns regarding the opportunistic pathogenicity of the genus. Although genomic screening detected putative virulence factors and antibiotic resistance genes, phenotypic susceptibility assays confirmed that MALB-1 is susceptible to key therapeutic antibiotics, including ampicillin, kanamycin, and norfloxacin. This distinctive susceptibility profile, in stark contrast to the multidrug-resistant phenotypes of related Enterobacter strains, suggests a manageable safety risk. Collectively, these findings position Enterobacter sp. MALB-1 as a promising, safe, and efficient candidate for agricultural application.

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