Isolation, Molecular Characterization, and Screening for Hydrocarbon-degrading Potential of an Indigenous Enterobacter sp. from Petroleum-contaminated Soil for Bioremediation Applications

Abstract

Petroleum hydrocarbon contamination creates ecological risks and motivates sustainable remediation strategies. This study isolated indigenous oil-degrading bacteria from petroleum-contaminated soils and screened their relative hydrocarbon-degrading potential. Four soil samples were collected from automobile-workshop sites in and around Bengaluru and Chikkaballapur, Karnataka, India. Samples were enriched in Bushnell–Haas minimal salt medium supplemented with 3% (v/v) used engine oil as the sole carbon source. Eight isolates were obtained and screened using an agar well diffusion clearance-zone assay. Morphological and biochemical characterisation was followed by 16S rRNA gene sequencing of the most active isolate. Isolate K2 produced the largest clearance zone (30 mm), followed by C2 (25 mm) and K3 (20 mm), whereas W1 and S1 produced 5 mm zones. BLASTn and phylogenetic analysis placed K2 within the Enterobacter cloacae complex, with 99.93% sequence identity to reference sequences in GenBank. The results indicate that indigenous bacteria from chronically hydrocarbon-contaminated soils can show differing relative activities under the screening conditions, with K2 displaying the strongest response among the isolates tested. Because the agar well diffusion assay does not directly quantify hydrocarbon removal, the observed clearance zones should be interpreted as a relative screening measure. Quantitative gravimetric or chromatographic analyses, together with soil-based validation, are required before the degradation efficiency and bioremediation applicability of K2 can be established.