Biogeochemical sulfur cycling coupling with dissimilatory nitrate reduction processes in freshwater sediments

Dissimilatory nitrate reduction processes including denitrification, anaerobic ammonium oxidation (ANAMMOX), and dissimilatory nitrate reduction to ammonium (DNRA) are crucial nitrogen (N) cycling pathways in freshwater ecosystems. Denitrification has long been considered as the primary pathway of N loss from aquatic environments. Recently, ANAMMOX and DNRA have been gaining more attention in N dynamics at the sediment–water interface. The ubiquitous presence of various sulfur (S) species in sediments makes them an important role on N transport. Interactions between dissimilatory nitrate reduction and the S cycle are mainly embodied by the inhibitory or promoting effects of sulfide on nitrate-reducing pathways, as well as the competition of sulfate with nitrate reduction for substrates. This review summarizes the current progress in the coupling of S cycling with nitrate-reducing pathways in freshwater sediments, the distribution and diversity of related microorganisms, as well as the functional genes encoding related enzymes. Future perspectives of related research are discussed in terms of coupled N cycling with other element cycles and molecular detection of functional bacteria to better understand and manipulate N cycling in freshwater environments.