Characterization and Functional Gene Analyses of Microorganisms in Remediated Sites in Gokana Local Government Area of Rivers State, Nigeria

Abstract

Petroleum hydrocarbon pollution is a severe environmental threat worldwide, and decades of oil exploration in Gokana, Rivers State, have led to extensive soil contamination and affected microbial diversity. This study evaluated the effectiveness of post-remediation measures through the assessment of microbial diversity and the determination of alkane degradation genes (alkB) in the area. Soil samples were collected from four sites: long-term remediated dryland (LRDL), pristine dryland control (PDL), pristine wetland control (PWL), and unremediated wetland (URWL). Total heterotrophic bacteria (THB), hydrocarbon-utilising bacteria (HUB), total fungi (TF), and hydrocarbon-utilising fungi (HUF) were identified based on morphological, biochemical, and molecular characterisation, while alkane degradation genes (alkB) were detected using specific primers. The findings showed that soil microbial counts varied significantly across sites. Pristine dryland (PDL) had the highest THB count at 98.3 × 10⁶ CFU/g, and TF followed a similar pattern. In contrast, HUB was highest in LRDL at 92.8 × 10⁴ CFU/g, while HUF peaked in LRDL at 42.4 × 10² CFU/g. A total of 42 species were identified. Molecular analysis confirmed the presence of Pseudomonas aeruginosa, Bacillus subtilis, Aspergillus niger, and Fusarium solani. The alkB gene occurred in three of five tested bacterial isolates, whereas no fungal isolates carried detectable alkB. Overall, the findings suggest partial but meaningful remediation success in dryland sites in Gokana, with a need to prioritise wetland-specific remediation and longitudinal multi-parameter monitoring.