| Extremely acidic and metal-rich acid mine drainage (AMD) waters can have severe toxicological effects on aquatic ecosystems. AMD has been shown to completely halt nitrification, which plays an important role in transferring nitrogen to higher organisms and in mitigating nitrogen pollution. We evaluated whether AMD differentially impacts three groups of microorganisms involved in nitrification: ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and nitrite-oxidizing bacteria (NOB). Sediment and water samples were collected from AMD-impacted aquatic sites during June and August/September 2013 and 2014 in the Iron Springs Mining District (Ophir, Colorado). Many of the sites were characterized by low pH (<5), low dissolved oxygen concentrations (<6 mg/L), and high metal concentrations. Community 16S rRNA gene sequencing revealed the presence of AOA (Nitrososphaera and Cenarchaeota), AOB (Nitrosomonas), and NOB ( Nitrospira) at multiple AMD-impacted sites. The overall abundance of AOA, AOB and NOB were examined using quantitative PCR (qPCR) amplification of the amoA and nxrB functional genes and 16S rRNA genes. The total gene copy numbers across the 2013 and 2014 samples ranged from 2.0x103--4.9x107 archaeal amoA copies/microg DNA, 1.5x103--5.3x10 5 AOB 16S rRNA copies/microg DNA, and 7.3x105--7.7x10 7 Nitrospira nxrB copies/microg DNA. Overall, Nitrospira nxrB genes were found to be more abundant than AOB 16S rRNA and archaeal amoA genes in most of the sample sites across 2013 and 2014. Archaeal amoA, AOB 16S rRNA, and Nitrospira nxrB genes were quantified in sediments with pH as low as 3.2. Statistical analyses showed a significant correlation between AOB 16S rRNA gene abundance and the surface sediment pH, temperature, and dissolved oxygen. Archaeal amoA gene abundance was significantly correlated with dissolved calcium and sodium concentrations. These findings extend our understanding of the relationship between AMD and nitrifying microbes and provide a platform for further research. |
