Nitrogen assimilation characteristics of strain (Z5) were investigated under both single (organic nitrogen, NH₄-N, or NO₂-N) and mixed nitrogen sources (organic nitrogen and NH₄-N, organic nitrogen and NH₄-N, or NH₄-N, and NO₂-N) Activity of protease, glutamine synthetase, and nitrite reductase, which are all involved in nitrogen metabolism, was also determined. The results showed that both organic and inorganic nitrogen assimilation rates of 2-N assimilation rates under a C/N ratio of 20 were 3.39 and 2.25 times higher, respectively, than those under a C/N ratio of 5. There were no significant differences in the assimilation of NH₄-N and NO₂-N between C/N ratios of 15 and 20 (0.05). -N→bacterial protein, respectively. -N) assimilation rates increased with higher C/N; the protein nitrogen content of the bacteria enriched from NH₄-N and NO₂-N increased from 25.0% and 19.4% under a C/N of 5 to 41.3% and 43.0% under a C/N of 20, respectively. In addition, was significantly regulated by NH₄-N while protease and NiR activity were not regulated significantly by the nitrogen species.