Phenanthrene-Induced Proteomic Adaptations in Marine Pseudomonas oleovorans: Insights into PAH Biodegradation Mechanisms

Rationale Polycyclic aromatic hydrocarbons (PAHs) are persistent organic contaminants whose chemical stability and toxicity pose risks in marine environments. Phenanthrene is used as a model PAH to elucidate transformation mechanisms relevant to more complex and carcinogenic compounds. While microbial degradation of PAHs is recognised as a key attenuation process, chemically resolved evidence linking enzymatic activity to transformation intermediates in marine systems remains limited. This study investigates phenanthrene degradation by a marine Pseudomonas oleovorans strain, integrating proteomic and metabolite analyses to resolve dominant degradation pathways. Methodology Pseudomonas oleovorans strain NIOSV8 was incubated in Luria–Bertani broth amended with phenanthrene (100 mg L⁻¹) for 48 h. Phenanthrene removal was quantified over time. Protein expression profiles under control and phenanthrene-amended conditions were analysed using LC–MS QToF–based shotgun proteomics. Differentially expressed proteins were used to infer active metabolic pathways. Degradation intermediates were identified using gas chromatography–mass spectrometry (GC–MS) to validate proteomic interpretations. Results Approximately 55% of phenanthrene was degraded within 48 h. Proteomic analysis identified 5,902 proteins across all conditions, with 2,486 proteins detected exclusively in phenanthrene-amended cultures, indicating metabolic reprogramming. Enzymes associated with aromatic hydrocarbon transformation were enriched, particularly salicylate hydroxylase and catechol 2,3-dioxygenase-related proteins, consistent with a salicylate–catechol degradation sequence. Multiple oxidoreductases and dehydrogenases involved in xenobiotic metabolism were also upregulated. GC–MS analysis detected intermediates such as 1-naphthol and 8-methyl-1-naphthoic acid, which support the oxidative transformation of phenanthrene to salicylate-related compounds. Discussion The combined proteomic and metabolite evidence demonstrates that phenanthrene degradation proceeds via a salicylate-mediated pathway. The induction of oxidoreductases highlights oxidative reactions in PAH transformation and the maintenance of redox balance. Changes in energy metabolism indicate that phenanthrene degradation is a metabolically demanding process. These findings provide mechanistic insight into microbial PAH transformation and contaminant fate in marine environments and sediments.