The biological nitrogen removal technology utilizing heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria has shown effectiveness in wastewater treatment. However, the nitrogen removal efficiency of HN-AD bacteria significantly decreases as the salinity increases. To tackle the challenge of treating high-salt and high-nitrogen wastewater, we isolated a moderately halophilic HN-AD strain 5505 from a salt lake in Xinjiang. The strain was identified based on morphological, physiological, and biochemical characteristics and the 16S rRNA gene sequence. Single-factor experiments were carried out with NH₄⁺-N, NO₃^--N, and NO₂^--N as sole or mixed nitrogen sources to study the nitrifying effect, denitrifying effect, and nitrogen metabolism pathway of the strain. The strain was identified as Halomonas sp.. It can grow in the presence of 1%-25% (W/V) NaCl and exhibited efficient nitrogen removal ability in the presence of 3%-8% NaCl. At the optimal NaCl concentration (8%), the strain showed the NH₄⁺-N, NO₃^--N and NO₂^--N removal rates of 100.0%, 94.11% and 74.43%, respectively. Strain 5505 removed inorganic nitrogen mainly by assimilation, which accounted for over 62.68% of total nitrogen removal. In the presence of mixed nitrogen sources, strain 5505 showed a preference for utilizing ammonia, with a potential HN-AD pathway of NH₄⁺→NH₂OH→NO₂^-→NO₃^-→NO₂^-→NO/N₂O/N₂. The findings provide efficient salt-tolerant bacterial resources, enhance our understanding of biological nitrogen removal, and contribute to the nitrogen removal efficiency improvement in the treatment of high-salt and high-nitrogen wastewater.
Halomonas/classification* ; Nitrogen/isolation & purification* ; Denitrification ; Nitrification ; Wastewater/microbiology* ; Aerobiosis ; Biodegradation, Environmental ; Salinity

Studies on NaCl concentration, pH tolerance and selectivity to different concent rations of Na +, K +, Mg 2+ and Ca 2+ of 43 isolates from th e saline soils in XinJiang, HeBei and QingHai Provinces of China and 4 type stra ins were performed in this paper Results showed that halotolerant actinomycete s have extensiv e adaptability to Na +, K + and Mg 2+ and only a few of them can grow in low CaCl 2 concentration Halophilic actinomycetes have extensive adaptability to Na +, and for most halophilic actinomycetes, Na + can be substituted by K + , Mg 2+ , but not for Ca 2+ For some halophilic actinomycetes , it is necessary to have Na + for their growth It also showed that the growth of al l halophilic actinomycetes had se lectivity with different concentration of Na +, K +, Mg 2+ So it is pre sumed that only Kaliumphilic or Magnesiumphilic Actinomycetes maybe exist in hig h salt environments In addition, the growth pH range were 6 0～9 0 and the o ptimum pH were 7 0～8 0 not only for halophilic but also for halotolerant acti nomycetes The dis tribution of halophilic actinomycetes also have some relativity to isolation sit es