Metabolic and enzymatic insights into n-hexane biodegradation by Rhodococcus qingshengii strain SCJ-1

Abstract

n-Hexane, a neurotoxic volatile organic compound ubiquitously present in industrial emissions, poses environmental and health risks due to its recalcitrance to biodegradation stemming from its hydrophobic nature. The strain Rhodococcus qingshengii strain SCJ-1, isolated from pharmaceutical wastewater sludge through adaptive enrichment and identified via 16S rRNA sequencing, exhibited robust degradation capabilities. Whole-genome sequencing showed that the strain carries a wide array of genes related to alkane degradation. Following optimization using the Haldane growth model, under conditions of pH 7.0 and 30℃, the strain SCJ-1 degraded 82.3 % of n-hexane at a concentration of 200 mg·L⁻¹ within 48 h. Under these conditions, alkane hydroxylase (AlkB: 27.6 nmol·mg⁻¹ prot) catalyzed the initial hydroxylation of n-hexane, while alcohol dehydrogenase and aldehyde dehydrogenase (ADH/ALDH: 37.3 nmol·mg⁻¹ protein) drove its sequential oxidation to aldehydes and carboxylic acids. Concurrently, superoxide dismutase (SOD: 10.9 mmol·mg⁻¹ protein), catalase (CAT: 34.5 mmol·mg⁻¹ protein), and total antioxidant capacity (T-AOC: 42.2 mmol·mg⁻¹ protein) collectively mitigated oxidative stress, enhancing enzyme stability. Gas chromatography-mass spectrometry (GC-MS) analysis detected pentanoic acid and ethyl butyrate, indicating the presence of a Baeyer–Villiger monooxygenases (BVMO)-mediated degradation pathway. To investigate the metabolite selectivity of BVMO and the origin of pentanoic acid and ethyl butyrate, molecular docking confirmed its specificity for 2-hexanone (binding energy of −3.925 kcal·mol⁻¹). These results suggest that the strain SCJ-1 is an effective candidate for bioremediation, utilizing a novel BVMO-driven pathway for the sustainable control of n-hexane pollution.