Enrichment of marine microbes to remove nitrogen of urea wastewater under salinity stress

Salinity (NaCl) and urea concentration significantly affect the diversity, structural and physiological function of microbial communities in the biological treatment of wastewater. However, the responses of microbial in high salt and urea wastewater remain elusive. Here, we investigated microbial community function and assembly of four regions using gradient domestication experiment combined with 16S rRNA gene sequencing and statistical methods. The results showed that with the increase of salinity and urea concentration, the consortium Xiamen could still remove most urea, while the other three consortia could not. The alpha diversity of microbial community initially decreased and then increased, showing a recovery trend. After domestication, the consortium Xiamen exhibited high physiological activity and complex network structure, and the community assembly process changed from stochastic to deterministic during the domestication. Furthermore, the keystones with low abundance were associated with urea removal and important for maintain the complexity of the networks, while Arenibacter and Oceanimonas were found to be keystones in maintaining efficient urea removal in harsh environments. To sum up, environmental effects dominated by salinity and urea concentration stress drove the community assembly and species coexistence that underpinned the microbial differentiation pattern at a geographic scale. These results provided new sights for elucidate how microbial response to salinity and urea during wastewater treatment.