Genome characterisation of three mycorrhizal helper bacterial strains isolated from a polycyclic aromatic hydrocarbon polluted site.

The study aimed to explore the genetic and functional potential of mycorrhizal helper bacteria (MHB) strains isolated from polluted soil, focusing on their ability to enhance plant growth and ameliorate the adverse effects of polycyclic aromatic hydrocarbons (PAHs). We sequenced the genomes of three MHB strains isolated from soil contaminated with PAHs and phenol. Moreover, experiments were carried out to check if these bacteria have ability to stimulate the growth of arbuscular mycorrhizal fungi (AMF) and promote plant development. Phylogenomic analysis identified the strains as belonging to the Streptomyces, Pantoea, and Bacillus genera, all exhibiting high tolerance to hydrocarbons. Genome mining revealed genes encoding enzymes for the degradation of aromatic compounds, alongside biosynthetic gene clusters for secondary metabolites such as siderophores and antibiotics. Laboratory experiments confirmed that the studied MHB strains enhance AMF development and spore production while exhibiting plant growth-promoting mechanisms such as siderophore and ammonia production, phosphate solubilization, and cellulolytic enzyme synthesis. These findings highlight the potential application of MHB in microbial-assisted remediation of hydrocarbon-contaminated soils through the tripartite plant-MHB-AMF system.