Enhanced phenanthrene biodegradation by Bacillus subtilis strain CYA27 in the presence of dispersant

Pollution by aromatic hydrocarbon compounds is closely associated with oil industry activities and poses significant environmental and human health risks. Biodegradation using hydrocarbon-degrading bacteria, particularly in combination with dispersants, offers a promising approach to mitigate such pollution. In this study, phenanthrene was used as a model compound to evaluate the effect of dispersant addition on the degradation capacity of Bacillus subtilis strain CYA27. Two dispersants were compared: a palm oil-based dispersant (Bio-OSD) and a petroleum-based dispersant (Non-Bio-OSD). The results showed that the presence of Bio-OSD and Non-Bio-OSD enhanced phenanthrene degradation, achieving up to 73.9% and 46.7% after 35 days, respectively. This improvement was attributed to increased substrate bioavailability, the potential use of dispersants as an auxiliary carbon source via a cometabolic mechanism, as supported by the detection of catechol dioxygenase activities (C12O and C23O) and selected metabolic intermediates, which provide preliminary evidence for possible enzymatic involvement in aromatic ring cleavage. Metabolic profiling using LC-MS/MS revealed that the degradation pathways utilised in the presence of dispersants included both the salicylic acid and phthalic acid pathways, which are further metabolised through the tricarboxylic acid (TCA) cycle. In contrast, phenanthrene biodegradation proceeded without a dispersant via the formation of 4-methoxy-1-naphthol, suggesting a methoxylation mechanism that potentially reduces toxicity but does not proceed to the TCA cycle. These findings revealed that dispersants not only enhance substrate bioavailability but also alter bacterial metabolic preferences, highlighting their dual role in oil spill bioremediation strategies. This work provides novel insight into phenanthrene catabolism and the mechanistic effects of dispersants on marine PAH biodegradation.