Research progress on nitrogen-removal characteristics and mechanisms in salt-tolerant microorganisms

Nitrogen pollution in wastewater from industrial effluents contains various substances, including salts and organic matter, that pose potential threats to aquatic ecosystems and human health. Denitrification microorganisms therefore play crucial roles in nitrogen bioremediation. This review focuses on salt-tolerant denitrification microorganisms, including their definition and classification. The effects of salinity on three different biological nitrogen-removal processes - nitrification-denitrification, anaerobic ammoxidation, and heterotrophic nitrification-aerobic denitrification - are systematically reviewed from the perspective of microbial communities and their practical applications in wastewater treatment. The salt-tolerance mechanisms of denitrifying microorganisms are clarified based on the relevant genes, synthesis of compatible intracellular solutes, ion transport, and extracellular polymeric substances involved. A comprehensive understanding of the mechanisms underlying salt tolerance in denitrifying microorganisms is essential for accelerating nitrogen-removal rate in saline conditions and could contribute to the development of effective strategies for microbial removal of nitrogen in saline environments.