Evaluation and mutagenesis of an assimilatory nitrate reduction bacterium Priestia megaterium BZ-95
Hao Chen Jiang, Xian Cong Fan, Ke Zheng, Yan Zhao, Zi Yan Jin, Yu Cheng, Yan Zou, Xiang Shan JiAbstract
Aims
Excessive NO3−-N and NO2−-N accumulation threatens aquaculture water quality, highlighting the need for aerobic microorganisms capable of converting dissolved inorganic nitrogen into biomass-associated organic nitrogen. This study aimed to characterize the assimilatory NO3−/NO2− reduction mechanism of Priestia megaterium BZ-95 and to evaluate its potential for aquaculture wastewater treatment.
Methods and Results
A NO3−-reducing bacterium, P. megaterium BZ-95, was investigated using whole-genome analysis, gene expression profiling, and nitrogen-removal assays. Genome analysis revealed two nitrogen-assimilation modules, namely a NO3− assimilation cluster (nasC-nirB_2-narT) and a nitrite assimilation operon (nirB_1-nirD-nirC-cysG), where as no denitrification or DNRA genes were detected. In NO3−-N medium, NO3−-N decreased from 72.59 to 8.07 mg/L within 24 h, accompanied by transient NH4+ accumulation. In NO2−-N medium, NO2−-N decreased from 70.00 to 0.009 mg/L within 21 h, with no detectable NH4+ accumulation. In mixed-N medium, NO3−-N and NO2−-N decreased from 30.00 to 3.33 mg/L and from 30.00 to 0.99 mg/L, respectively, within 24 h. Gene expression analysis showed that NO3− mainly induced the nasC-nirB_2-narT module, whereas NO2− strongly induced the nirB_1-nirD-nirC-cysG module. In addition, the mutant BZ-95D4 showed a 61.08% higher NO3−-N removal capacity than the parental strain BZ-95.
Conclusions
P. megaterium BZ-95 possesses a dual-module assimilatory nitrogen-reduction system with distinct responses to NO3− and NO2−. These findings improve understanding of microbial nitrate assimilation and indicate that BZ-95, particularly the improved strain BZ-95D4, is a promising candidate for aquaculture wastewater treatment.