Diversity and abundance of ammonia-oxidizing bacteria (AOB) revealed by PCR amplification of amoA gene in a polyacrylamide transportation system of an oilfield

• Higher abundance of AOB than AOA was associated with the polyacrylamide injection system at oilfield.
• The AOB-like phylotypes were mainly aligned with Nitrosospira briensis while others showed low identity to the known AOB.
• This study shows an active nitrifying microbial community associated with degradation of polyacrylamine.

Microorganisms were detected in the hydrolyzed high-molecular-weight polyacrylamide (HPAM) transportation system. The diversity of both general bacteria and ammonia-oxidizing bacteria (AOB) in the online distribution system was further analyzed using 16S rRNA and the functional amoA genes through PCR amplification and clone library methods together with the physicochemical properties and environmental factors of samples. In total, twenty-four families of bacteria were identified in the system; biofilm sample showed higher diversity and production water showed lower diversity than the other samples. The AOB-like phylotypes in sample S6 mainly showed high alignment to Nitrosospira briensis while others in samples showed low alignment to the known uncultrued AOB, indicative of new AOB phylotypes possibly. The abundance of AOB amoA gene abundance ranged from 3.54 × 102 to 2.04 × 103 copies·ml−1, where were significantly lower than those of bacterial 16S rRNA gene copies from 2.94 × 106 to 6.33 × 108 copies·ml−1 in samples S4–S6. The RDA analysis showed that the AOB amoA gene was positively related to the concentration of NH4+, NO2−, NO3−, SO42− and S2−. The results showed the distribution of bacterial amoA gene for nitrification in this polyacrylamide transporting system and the information enriches our knowledge of microbial community diversity in the nitrogen cycle of the polyacrylamide transportation system.