A halophilic aerobic-heterotrophic strain Halomonas venusta SND-01: Nitrogen removal by ammonium assimilation and heterotrophic nitrification-aerobic denitrification

Abstract

Nitrogen (N) removal from high-salinity wastewater is a major challenge. The aerobic-heterotrophic nitrogen removal (AHNR) process has been demonstrated to be feasible for treating hypersaline wastewater. In this study, Halomonas venusta SND-01, a halophilic strain capable of performing AHNR, was isolated from saltern sediment. The strain achieved ammonium, nitrite, and nitrate removal efficiencies of 98%, 81%, and 100%, respectively. The N balance experiment suggests that this isolate removes N mainly via assimilation. Various functional genes related to N metabolism were found in the genome of the strain, establishing a complex AHNR pathway that includes ammonium assimilation, heterotrophic nitrification-aerobic denitrification, and assimilatory nitrate reduction. Four key enzymes in the N removal process were successfully expressed. The strain exhibited high-adaptability under C/N ratios of 5-15, salinities of 2%-10% (m/v), and pH of 6.5-9.5. Therefore, the strain shows high potential for treating saline wastewater with different inorganic N compositions.

Keywords: Aerobic-heterotrophic nitrogen removal (AHNR); Ammonium assimilation; Assimilatory nitrate reduction; Complete genome sequencing; Heterotrophic nitrification–aerobic denitrification (HN-AD).