To study on autotrophic removal of nitrogen from wastewater containing a high concentration of NH₃-N,a strain of Pseudomonas fluorescens dN13 was isolated,by means of incubation in Skerman's medium for Nitrosomona,from the sequence batch reactor system(SBR)of a wastewater treatment plant in Nanjing.Under aerobic condition,this strain could oxidize NH₃-N into NO₂^--N and grow without organic carbon source;and reduce NO₂^--N and NO₃^--N into NH₃-N with organic carbon source and adequate concentration of NO₂^--N and NO₃^--N,while under anaerobic condition,strain dN13 could still reduce NO₂^--N and NO₃^--N into NH₃-N with sodium acetate as the sole carbon source.In the cells of strain dN13 with such multi-paths of nitrogen metabolism,coupling of nitrification and denitrification is feasible.