Detection and Quantification of Sulfate-Reducing and Polycyclic Aromatic Hydrocarbon-Degrading Bacteria in Oilfield Using Functional Markers and Quantitative PCR

Oilfield water samples from injection water treatment facility and soil/sludge samples from Gas Oil Separation Plant (GOSP) at Saudi Aramco were analyzed for the presence of SRB and PAH-degrading bacteria. SRB were detected by targeting a fragment of the apsA gene encoding adenosine-5-phosphosulfate reductase, which is characteristic of all SRB. The PAH-degrading bacteria were detected using a primer pair that amplifies a fragment of the gene encoding the large subunit of the naphthalene dioxygenase gene nahA. The nahA gene was detected in almost half of the soil/sludge samples with the highest copy number of 60540 copies/g soil/sludge. Most of the analyzed water samples contained high copy numbers of nahA gene with the highest copy number 3846 copies/ml. Most of the analyzed water samples revealed the presence of high copy numbers of the apsA gene with the highest copy number of 44 x 106/ml in sample number 2. Only 7 of the soil/sludge samples revealed the presence of the apsA gene with the highest copy number of 107920/g soil/sludge in sample number 11. In contrast to the nahA gene, the highest copy numbers of the apsA gene were detected in the water samples. SRB and PAH-degrading bacteria exist in some Saudi oilfields and appear to play a role in the H2S production and PAH degradation.