Phylloremediation approach to green air: phenanthrene degrading potential of Bacillus spp. inhabit the phyllosphere of ornamental plants in urban polluted areas

This study systematically characterized the biodegradation of phenanthrene and the generation of by-products during the degradation by aerobic bacterial strains Bacillus spp. inhabited the phyllosphere of ornamental plants grown in urban polluted areas. The HPLC results revealed that four isolated Bacillus spp. ( Bacillus sp . 1—95%, Bacillus velezensis —90%, Bacillus megaterium —91%, Bacillus sp. P 2 B-02—93%) were able to degrade more than 88% of phenanthrene within the first 2 days of incubation with the specific growth rate of 0.0773 day −1 , 0.0993 day −1 , 0.0993 day −1 , and 0.302 day −1 , respectively. The results of the kinetic assay revealed that the isolated four bacterial strains followed the first-order kinetics, and out of them, Bacillus sp. P 2 B-02 had the shortest half-life (2.82 ± 0.07 days) and the highest specific growth rate of phenanthrene degradation (0.302 day −1 ). In addition to the phenanthrene peak, all four bacterial strains showed an additional peak in their chromatograms on the second and third incubation days. Furthermore, GC–MS analysis results revealed that the by-product formation during the phenanthrene degradation in all four Bacillus strains is identified as Phenol, 2-(phenylmethyl) (C 13 H 12 O) (molecular weight 184.0 g mol −1 ). Further HPLC analysis results revealed that nonetheless, that intermediate peak height gradually decreased until the sixth day, when it disappeared, indicating that some bacterial strains had completely degraded the by-products. According to the results, all four Bacillus spp. had greater than 50% of viability, confirming the non-toxicity of the by-products to the degrading bacterial strains. Furthermore, in toxicity assay with Vigna radiata , the appearance of the shoot and root from the seeds within 2 days confirmed that the highest concentration of by-product had no effect on seed growth and that the by-products produced were not harmful to the phyllosphere. Therefore, these phyllosphere Bacillus spp. can be used as efficient bioremediators which can clean phenanthrene-like polyaromatic hydrocarbon pollutants through phylloremediation. Graphical abstract