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Frontiers of Environmental Science & Engineering >> 2020, Volume 14, Issue 4 doi: 10.1007/s11783-020-1239-8

Insights from metagenomic, metatranscriptomic, and molecular ecological network analyses into the effects of chromium nanoparticles on activated sludge system

1. Beijing Engineering Research Center of Environmental Material for Water Purification, College of Chemical Engineering, Beijing University of Chemical Technology, Beijing 100029, China
2. Key Laboratory of Cleaner Production and Integrated Resource Utilization of China National Light Industry, Beijing Technology and Business University, Beijing 100048, China

Available online: 2020-04-17

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Abstract

Abstract • Cr NPs significantly promoted the denitrifying process and phosphorus removal. • The quantities of denitrifying and phosphorus genes greatly increased. • The transcription of denitrifying and phosphorus genes greatly increased. • The networks associated with nitrogen and phosphorus removal became complicated. • Cr NPs decreased some genera related to GAOs. The objectives of this study were to investigate the influence of chromium nanoparticles (Cr NPs) on the nitrogen and phosphorus removal performance and the bacterial structures of an activated sludge (AS) system. Also, we through molecular ecological networks (MENs) discussed the bacterial interactions. At last we researched the change of the functional genes and their expression patterns related to nitrogen and phosphorus removal in an AS system. The results showed that long-term exposure to 1 mg/L Cr NPs significantly promoted the denitrifying process and phosphorus removal in the AS system. The relative abundance of denitrifying and phosphorus removal microorganisms, such as Denitratisoma, Thauera, Dechloromonas, and Defluviicoccus, increased significantly. Candidatus Accumulibacter, well-known as polyphosphate-accumulating organisms (PAOs), increased significantly; the relative abundance of Candidatus Competibacter, known as glycogen-accumulating organisms (GAOs), decreased significantly. Furthermore, metagenomic and metatranscriptomic analysis revealed that most of the genera related to denitrifying and phosphorus removal had greatly increased, according to the quantities of denitrifying and phosphorus genes, and the corresponding transcription likewise greatly increased. Lastly, MENs analysis showed that although the overall network became smaller and looser in the presence of Cr NPs, the microbial connections among members related to nitrogen and phosphorus removal were enhanced. The abundance increases of denitrifiers and PAOs, and their increased transcription of functional genes, together with the enhanced interactions may be associated with the promotion of the denitrifying process and phosphorus removal.

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