Comparative Evaluation of Methylorubrum sp. for Crude Oil Degradation in Free and Immobilized Systems: A Functional Enzymatic Approach
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Keywords: Alkane monooxygenase, Methylorubrum sp., Cell immobilization, Cytochrome P450, Lipase,
Abstract :
Crude oil spills and the persistence of hydrocarbon compounds in the environment pose significant threats to both human health and ecological integrity. These pollutants—due to their toxicity, chemical stability, and tendency to accumulate in water and soil—disrupt trophic interactions and exacerbate environmental degradation. Bioremediation using microorganisms offers an effective, cost-efficient, and environmentally sustainable strategy for mitigating such contamination. In this study, the crude oil degradation capacity of Methylorubrum sp. was evaluated under both free-living and sodium alginate–immobilized conditions. The activities of three key enzymes involved in hydrocarbon catabolism—alkane monooxygenase, cytochrome P450, and lipase—were also assessed. Under exposure to 4% (3200 mg/L) crude oil, free cells degraded approximately 50% of the petroleum hydrocarbons, whereas alginate immobilization enhanced degradation efficiency to 70%. Gas chromatography–mass spectrometry (GC–MS) analysis demonstrated complete degradation of light n-alkanes (C4–C9) and up to 74% degradation of long-chain n-alkanes (C14–C28) in the immobilized treatment. Field emission scanning electron microscopy (FE-SEM) confirmed the porous architecture of the alginate beads and uniform entrapment of bacterial cells. On day three, the immobilized cells exhibited peak specific activities of alkane monooxygenase, cytochrome P450, and lipase at 13.55, 9.5, and 9.0 U/mg protein, respectively. Overall, immobilization improved microbial stability, conferred resistance to environmental stress, and significantly enhanced crude oil biodegradation. These findings demonstrate the potential of immobilized Methylorubrum sp. for effective crude oil bioremediation and represent a promising step toward the development of scalable, safe, and environmentally responsible approaches to managing petroleum pollution.