Efficient nitrogen removal performance and mechanism of a novel salt-tolerant bacterium Vreelandella sp. J1-11

Heterotrophic nitrification and aerobic denitrification (HN-AD) showed great potential in biological wastewater treatment. Robust strains still are one of the key limitations to improve the efficiency and stability of HN-AD during wastewater treatment. In this study, a novel salt-tolerant HN-AD bacterium (Vreelandella sp. J1-11) was isolated from the marine sediments. It could efficiently remove nitrogen under high salinity with sole or mixed nitrogen sources. The maximum nitrogen removal rate reached 13.86 mg/L/h, as well as no intermediate accumulation. Especially, the strain was also capable of removing about 100 % of NH₄⁺-N at salinity of 15-90 g/L or when NH₄⁺-N was 100-800 mg/L. Notably, the nitrogen balance analysis showed that above 81 % of nitrogen was assimilated with NH₄⁺-N or NO₃^--N as nitrogen source. Genomic analysis suggested that ammonium assimilation, dissimilated and assimilatory nitrate reduction, nitrification, and denitrification were involved in nitrogen removal. Nevertheless, the absence of certain common nitrogen transformation genes implies the potential existence of unique genes or pathways involved in these processes. The strain J1-11 demonstrated high nitrogen removal efficiency under C/N ratios of 4-12, salinities of 15-100 g/L, and temperature of 15-35 °C. Overall, the strain J1-11 shows great potential for the treatment of wastewater under high ammonium and salinity stresses.