Biocatalytic Degradation of Burned Engine Oil Hydrocarbons by Marine-Derived Bacillus subtilis AAS1

Burned engine oil is a hazardous pollutant composed of persistent hydrocarbons and toxic compounds. This study investigated the biodegradation potential of the Bacillus subtilis strain AAS1, which was isolated from marine sediments in El-Arish, North Sinai, Egypt. The strain was identified via 16S rRNA gene sequencing (GenBank accession no. PV544895), with phylogenetic analysis indicating more than 98.5% similarity to known B. subtilis strains. AAS1 demonstrated strong lipolytic activity, formed the largest halo zone on Tween 80 agar, and was capable of emulsifying and utilizing burned engine oil as its sole carbon source. Optimal degradation occurred at a 4% oil concentration, pH 7.0, with an inoculum of 60 µl⁻¹ over 10 days of incubation at 37 °C. GC‒MS analysis revealed a total hydrocarbon degradation rate of 58.31%, with the elimination of compounds such as heptadecane and eicosane and high degradation efficiencies for 9-octadecene bis(ethanediyloxy) (61.24%), octadecanoic acid decyl ester (56.30%), and HAHNFETT (58.29%). Lipase activity increased with pH (from 6.81 U/ml at pH 6 to 18.62 U/ml at pH 10) and temperature (from 1.11 U/ml at 10°C to 16.68 U/ml at 60°C). The enzyme yield was greater in the presence of burned engine oil (28.68%) than in the presence of crude engine oil (17.07%), with a molecular weight of 49.9 kDa. Bioinformatics analysis revealed a stable lipase protein (GRAVY score: - 0.705), characterized by a dominant alpha-helix structure (50.76%) and a high-quality 3D model (MolProbity score: 1.14, 96.94% Ramachandran favored). STRING analysis revealed functional associations with related proteins. These findings highlight the potential of AAS1 in future bioremediation applications.