Aerobic Bacterium ‘achromobacter Sp. B10c’ Having Traits to Degrade Phenanthrene and Can Improve Physiology of Alfalfa Plant

Environmental pollution from polycyclic aromatic hydrocarbons (PAHs) poses a significant threat to ecosystems due to their mutagenic and carcinogenic properties. This study focused on the isolation and characterization of a novel bacterial strain, Achromobacter sp. B10c’ from contaminated agricultural soil in Chengdu, China, to evaluate its phenanthrene-degrading potential and its effect on alfalfa ( Medicago Sativa ) plant growth. The 16S rRNA gene sequencing identified the strain with 99.42% identity to other Achromobacter species. Under optimized environmental conditions (pH 7.0 and 30–35°C), Achromobacter sp. B10c’ achieved a maximum phenanthrene degradation rate of 88.33% within 72 hours. Metabolic analysis using GC-MS identified tetrachloroethane and phthalic acid as the primary degradation intermediates. In vivo plant studies revealed that phenanthrene stress (up to 200 mg/L) significantly reduced alfalfa growth parameters, including shoot and root length, biomass, and chlorophyll content. However, inoculation with Achromobacter sp. B10c significantly mitigated these toxic effects, increasing root and shoot lengths by 48% and 35%, respectively, in contaminated treatments. Furthermore, the bacterial strain reduced oxidative stress, evidenced by decreased Malondialdehyde (MDA) and hydrogen peroxide (H ₂ O ₂ ) levels, while simultaneously enhancing the activity of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT). These results suggest that Achromobacter sp. B10c is a highly efficient candidate for the bioremediation of PAH-contaminated sites and can serve as a plant growth-promoting agent under environmental stress.