Genome-based insights into the characteristics of anammox bacteria for nitrogen removal from wastewater

Abstract

Anaerobic ammonium-oxidizing (anammox)-based processes for nitrogen removal have attracted increasing attention due to its advantages: less oxygen requirement, no additional carbon matters, and less sludge production. Anammox process uses ammonium as an electron donor and nitrite as an electron acceptor and converts them to dinitrogen gas (N₂). It has been successfully applied for ammonium-rich wastewater treatment, however, the application for mainstream wastewater treatment is still in progress. Till now, anammox bacteria have been analyzed from the genomic level, and an increasing number of anammox genomes was annotated such as Ca. Brocadia fulgida, Ca. Brocadia Sinica JPN1, Ca. Kuenenia stuttgartiensis and Ca. Jettenia caeni etc. The development of molecular biotechnology enables researchers to recover new whole-genome anammox species from various anammox processes and annotate key genes involving in the anammox reaction. However, it is still vital to gain a comprehensive understanding on the potential metabolic pathways in anammox bacteria based on different environmental conditions. This doctoral study was to investigate anammox bacteria enriched in different reactors treating low strength wastewater and explore their potential metabolic mechanisms from whole-genome level. The chapter three of this dissertation rapidly starts up partial nitrification-anaerobic ammonium oxidation fluidized-bed bioreactor to treat low strength ammonium wastewater without inoculating anammox sludge. Of partial interest was to investigate the unique genes in the strain of Ca. Brocadia sp. Subsequently, the observed gene encoding superoxide dismutase, Fe-Mn family (SOD2) in Chapter three indicates anammox bacteria has the potential for oxygen detoxification. Chapter four recovers the potential metabolic pathways for oxygen detoxification and mixotrophic metabolism in anammox bacteria and examine the related genes expression values. To test the feasibility of freshwater anammox for saline wastewater treatment, Chapter five starts up the anammox process with low-strength wastewater containing different seawater proportions and investigates the shift of microbial community structure. In the previous chapter, anammox species affiliated with the genus of Ca. Brocadia was enriched in saline environment. Therefore, it is vital to identify the anammox species and explore its potential metabolic pathways. In Chapter six, a new anammox species was de novo assembled, and its nitrogen transformation and sulfur-dependent pathways were reconstructed. Further, the sodium pump associated with energy conservation in the dominant anammox bacteria was investigated. Finally, Chapter seven draws the conclusions and recommendations during doctoral study.