Isolation, Characterization and Identification of Bacteria from Crude Oil Contaminated Soil at Obi-Ayagha, Delta State, Nigeria

Abstract

Background: Crude oil contamination can alter soil physicochemical properties and microbial communities, creating environmental and agricultural concerns. Indigenous bacteria occurring in contaminated soils may possess adaptive characteristics that enable survival under hydrocarbon stress and may therefore represent useful candidates for bioremediation. Characterising such bacteria is important for understanding their potential role in restoring petroleum-polluted environments. Aim: This study was carried out to isolate and identify bacteria present in soil from an abandoned artisanal refinery in Obi-Ayagha, Ughelli South Local Government Area of Delta State, Nigeria. Method: The samples were collected in sterile Ziploc bags, kept in a cooler containing ice packs, and transported to the laboratory at the Department of Pharmaceutical Microbiology and Biotechnology, Delta State University. The physicochemical properties of the soils were assessed following standard methods. One (1 g) gram of the soil sample was weighed and placed in nine (9) mL of normal saline, and a 1:10 serial dilution was carried out up to a dilution of 10-7. A 0.1 millilitre aliquot of each of the different dilutions (10-3 - 10-6) was plated onto sterile agar plates containing different media (Nutrient agar (NA), Mannitol salt agar (MSA), MacConkey agar (McC), Cetrimide agar (CET), and Xylose Lysine Deoxycholate agar (XLD)). Colony counts were performed after 24 hours of incubation to determine the colony-forming units per mL (CFU/mL). Bacterial isolates were characterised and tentatively identified using Gram staining and biochemical tests. Results: The results showed that cation exchange capacity (10.12 meq/100g), sulphate (46.18 mg/kg), available phosphate, and total organic carbon (1.9%) were higher in the artisanal soil than in the control soil, whereas total nitrate (97.55 mg/kg), pH (6.0), and moisture (6.0%) were higher in the control soil. Lead (7.11 mg/kg), nickel (13.30 mg/kg), and chromium (10.04 mg/kg) were also higher in the artisanal soil. Bacterial counts in the artisanal soil were 1.85 × 106 CFU/g, 7.5 × 105 CFU/g, 3.6 × 105 CFU/g, 9.1 × 104 CFU/g, and 7.5 × 105 CFU/g on NA, XLD, McC, MSA, and CET, respectively. In the control soil, counts were higher on CET (7.6 × 105 CFU/g), NA (2.61 × 106 CFU/g), and XLD (7.6 × 105 CFU/g). Seventeen bacteria were isolated. Staphylococcus species was the only Gram-positive bacterium identified, whereas Shigella, Salmonella, Proteus, Klebsiella, Acinetobacter, and Pseudomonas species were Gram-negative bacteria. Conclusion: The results showed that some of the bacteria isolated and identified may be beneficial for the bioremediation of contaminated soil.