Strategy to mitigate salinization of sulfide-autotrophic denitrification: Sodium ion uptake from the environment and mutualistic symbiosis among microorganisms

Sulfolithoautotrophic denitrification metabolic pathways are widely distributed in nitrogen cycling of seawater and saline lakes. Sulfideautotrophic denitrification process (SAD) has been demonstrated a promising method for treating hypersaline nitrogenous wastewater. Meanwhile, the disposal of hypersaline nitrogenous wastewater has always been a problem to be solved. Therefore, it is urgent the clarification of the substrate removal performance of SAD under salinity stress. Furthermore, the response strategy and community interaction mechanism of SAD to salinity invasion are still unexplored. The present work aimed to unravel the salt tolerance of SAD at different substrate concentrations. It was found that the denitrification performance of SAD could reach 55.65 % when the salinity level was below 4.67 wt%, but the denitrification performance of SAD collapsed when the salinity level reached 6.64 wt%. Changes in the physicochemical characteristics of microbial communities in the sludge indicated that microorganisms resisted osmotic stress by taking up Sodium from the environment after salinity invasion, and the large concentration of accumulated Sodium inhibited the SAD behavior of functional microorganisms. However, the results of community succession showed that the functional microorganisms like Thauera and Sulfurimonas, showed resilience to salinity and restored SAD behavior through interactions with other microorganisms in the sludge.