Microbial Analysis of Soil from Petroleum-Contaminated Sites in Warri, Delta State

Petroleum hydrocarbon contamination of soil in Nigeria's South South oil-producing communities has caused extensive ecological damage and public health concerns, while also generating microenvironments that select for hydrocarbon-degrading microbial communities. This study analyses microbial populations in petroleum-contaminated soil samples from active and former crude oil spill sites in Warri, Delta State. Soil samples were collected from three contaminated sites at varying distances from spill epicentres and compared against uncontaminated control soils from adjacent agricultural land. Total heterotrophic bacteria count, hydrocarbon utiliser count, total fungal count, and total coliform count were determined. Molecular identification of dominant hydrocarbon-utilising isolates was performed using 16S rRNA gene sequencing. Total heterotrophic bacteria counts were significantly lower in heavily contaminated soils, while hydrocarbon utiliser counts were markedly higher at contaminated sites compared to controls. Dominant hydrocarbon utilisers identified included Pseudomonas putida, Bacillus subtilis, Rhodococcus erythropolis, and Alcanivorax borkumensis. Fungal hydrocarbon degraders included Aspergillus niger and Penicillium species. A significant inverse correlation was observed between total petroleum hydrocarbon concentration and species diversity index. The study provides baseline microbial data for bioremediation planning at Warri spill sites and recommends bioaugmentation trials using isolated indigenous hydrocarbon degraders as a cost-effective site remediation strategy. Keywords: petroleum contamination, hydrocarbon-degrading bacteria, bioremediation, Warri, soil microbiology