Nitrogen metabolism in photosynthetic bacteria wastewater treatment: A novel nitrogen transformation pathway

Nitrogen removal from wastewater is a worldwide environmental problem. Photosynthetic bacteria (PSB) were reported to have a great potential in treating varieties of nitrogen-contaminated wastewater. However, their nitrogen metabolic mechanism is still unclear, which was further explored in this work. The results showed that PSB can efficiently utilize NH4+-N, NO3--N and NO2--N. Over 90% nitrogen removal efficiencies were obtained under suitable condition. 35 similar to 51% of removed nitrogen was transformed to N-2 and N2O. In addition, basically no mutual transformation occurred between NH4+-N, NO3--N and NO2--N in PSB, which is different from other biological technologies. Combining with the analysis of functional gene groups, it indicated that there might be a new direct nitrogen transformation pathway, i.e. NH4+ might be directly oxidized to N-2/N2O in nitrogen metabolism of PSB, which breaks the limitations of existing technologies, and proposed a new understanding of nitrogen metabolism in PSB.