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Production Processes Affected Prokaryotic amoA Gene Abundance and Distribution in High-Temperature Petroleum Reservoirs

Although the presence and activity of ammonia-oxidation archaea (AOA) and ammonia-oxidation bacteria (AOB) were observed in thermophilic habitats recently, their existence in the geothermal subterranean oil reservoirs is still not available. This study investigated the abundance and distribution of AOA and AOB in the production waters of high-temperature oil reservoirs by using real-time PCR and phylogenetic analysis based on amoA genes. The results indicated the occurrence of both AOA and AOB in 9 out of totally 17 wells. The AOA-like phylotypes are mainly clustered within two major clades of archaeal amoA sequences known from water columns, sediments and soils: clusters A and B, and a few clones are related to the new genera: Candidatus ‘Nitrosocaldus yellowstonii’. The AOB-like phylotypes mainly belong to Nitrosospira and Nitrosomonas clusters, while two of them are deep-branched in Nitrosospira cluster and showed no substantial alignment to the known cultured AOB, indicating the possibility of new AOB phylotypes. The abundance of AOA and AOB-like amoA genes ranged from 2.92 × 103 to 9.21 × 104 and from 2.91 × 102 to 8.12 × 103 amoA gene copy numbers per ml production water with the ratios of AOA to AOB ranging from 5.10 to 95.5. Statistical analysis showed that amoA gene fell into five groups and the distribution of amoA gene is significantly correlated with the environmental factors, e.g., temperature and recovery process. Our study showed distribution of prokaryotic amoA gene in various oil reservoirs was affected by production processes.