Isolation and Identification of Some Crude Oil‐Degrading Bacterial From Soil Contaminated With Crude Oil

ABSTRACT Petroleum hydrocarbons represent a major class of organic pollutants that seriously endanger marine and terrestrial ecosystems upon contamination, highlighting the urgent need for cost‐effective remediation methods. Bioremediation, a promising and innovative approach utilizing microorganisms and plants to degrade or stabilize pollutants, has gained increasing attention. This study focused on isolating and identifying crude oil‐degrading bacteria from petroleum‐contaminated soils in five locations within the Kirkuk oil refinery. Soil samples were analyzed for physical and chemical properties, including organic carbon, lime content, total petroleum hydrocarbon levels, and heavy metal concentrations. After enrichment, bacteria capable of thriving in crude oil‐containing media were isolated, resulting in 24 strains selected for molecular identification using DNA extraction and 16S rRNA gene sequencing. The genetic diversity of these strains was assessed, and a phylogenetic tree was created using MEGA version 4 software. The top 10 strains were further evaluated for their degradation capabilities in media with 0.5% crude oil using spectrophotometric and gravimetric techniques. Notable isolates included Rhodococcus jostii , Ochrobactrum intermedium , Achromobacter spanius , and Citrobacter amalonaticus . These bacteria demonstrated significant degradation activity across different oil types, with the highest efficiency recorded in crude oil, followed by heavy and light crude oil, particularly by O. intermedium , C. amalonaticus , and A. spanius . Two microbial consortia, A and B, were formulated based on their degradation performance, with A being optimal for heavy oil and B for crude oil. The bacterial diversity was further analyzed using species diversity indices, confirming a broad range of hydrocarbon‐degrading microbes within the sampled soils. Ultimately, the identified strains show strong potential for use in bioremediation strategies aimed at mitigating petroleum hydrocarbon pollution in affected environments.