Crude-oil biodegradation by indigenous hydrocarbon-degrading bacteria and their co-culture from port dickson, Malaysia

Crude oil contamination threatens environmental quality due to the persistence and toxicity of petroleum hydrocarbons. Bioremediation using indigenous microorganisms offers an effective and environmentally friendly solution. This study isolated and characterized indigenous hydrocarbon-degrading bacteria from crude oil-contaminated soil collected from a refinery in Port Dickson, Malaysia, and assessed their biodegradation capability individually and as a co-culture. Soil samples were enriched in Bushnell-Haas medium supplemented with crude oil as sole carbon source to isolate potential hydrocarbon-degrading bacteria. Among ten isolates, two superior growth and biosurfactant activity isolates were selected and identified as Klebsiella pneumoniae (isolate OB) and Pseudomonas aeruginosa (isolate SC) using 16S rRNA gene sequencing. Biodegradation efficiency was determined gravimetrically after 21 days, while changes in the residual crude oil profile were examined by GC-MS. Individual degradation efficiencies reached 39.56% for K. pneumoniae and 43.41% for P. aeruginosa, while their mixed co-culture achieved substantially higher efficiency (54.67%), indicating synergistic interactions. GC-MS analysis further supported the crude-oil degradation results, revealing alterations in the residual hydrocarbon profile, including reductions in selected hydrocarbon-associated compounds and changes in the relative abundance of individual components. These findings demonstrate that indigenous biosurfactant-producing bacteria, particularly in co-culture, reveal enhanced crude oil degradation.