Enrichment Of Ammonia Oxidizing Archaea And Their Function In Wastewater Land Treatment System

For over a century, ammonia oxidizing bacteria(AOB) have been considered the key to ammonia oxidation in wastewater treatment systems. Recently, in some extreme environments, including low dissolved oxygen environments, ammonia oxidizing archaea(AOA) have been discovered and confirmed to be capable of oxidizing ammoniato nitrite, which renders thepotential for application of AOA inwastewatertreatment systems. As the history of AOA discovery is short, the knowledge about AOA is still limited. Therefore, in this study, the occurrence and enrichment of AOA,and their function in wastewater land treatment system were studied,in order to understand their characteristics further and lay foundations for the application.The abundance distribution and community structure of AOA in 7 soil samples collected from farmlands in the plateau were analyzed by using the clone library and quantitative polymerase chain reaction(qPCR). The results showed that AOA outnumbered AOB, and the diversities of AOA communitywere affected by total nitrogen and organic matterconcentration in the soils. The microbial community structures in 16 activated sludge samples collected from wastewater treatment systems were characterized by using pyrosequencing. The results showed that Crenarchaeota phylum which AOA belong to accounted for 0.01% to 1.09% of the total microbes. The origins andcharacteristics of the influent wastewater played key rolesin shaping the community structure of AOA. Low dissolved oxygen and high salinitywould favor the occurrence of AOA in wastewater treatment systems.A new strain of AOA, named as SAT1, affiliated with thaumarchaeal group I.1a, was obtained in the enriched culture from both soil and wastewater treatment system. The strain SAT1 was irregular spherical-shaped with a diameter ofapproximately 0.5 to 0.9 μm. The maximum specific growth andammonia oxidation rates of the strain SAT1 were respectively 0.021 h-1 and 0.13 fmol N cell-1 h-1. The whole genome sequencing results indicated that the strain SAT1 has a complete gluconeogenic and glycolysis metabolism pathway which was found for the first time with AOAaffiliated withthaumarchaeal group I.1a. It also revealed that the SAT1 might be capable of hydrolyzing urea for growth and resisting to high salinity, heat shock and oxidative damage.Two land treatment systemswere built and operated for treatingwastewaterunder high and low pollutant loading ratefor about 560 days, with good performance in pollutants removal. Theresults of qPCR and pyrosequencing analysis on the microorganisms indicated thatall the archaea could be AOA in the systems, and AOA outnumbered AOB with abundance stability during the operation period. Based on the results of moving windowanalysis, AOA communitywas determined with a low level variation while AOB community changed at a high level, which supports the assumption that AOA could play an important role to ammonia oxidation in the systems. Based on theanalysis of the specific influent ammonia loadingrates and the results of mathematical model calculation on microbial growthcombined with the data of soil microcosm and DNA-SIP experiments, it was confirmed that AOA did involve in autotrophic ammonia oxidation in the systems.There was thepossibility that AOA utilize heterotrophic metabolism pathway.