The rates and players of denitrification, dissimilatory nitrate reduction to ammonia (DNRA) and anaerobic ammonia oxidation (anammox) in mangrove soils

Mangroves are ecosystems located in the transition zone between land and sea, characterized by periodic flooding that confer to its unique characteristics. Little is known about the transformation of nutrients that occur during the organic matter degradation in this system. In this study, we monitor the nitrogen transformations in soils from three mangroves with distinct levels of contamination using labeled 15NO3-. We also screened the mangroves metagenomes for the presence of genes that encode enzymes involved in denitrification (nirS, nirK, nosZ, norB and narG), anaerobic oxidation of ammonia (anammox) (hh, hao and hzo) and dissimilatory nitrate reduction to ammonium (DNRA) (nrfA). The transformations of 15NO3-indicated the balance of denitrification over anammox and DNRA in all three mangroves, with lower rates of processes in the mangrove affected by oil contamination. The metagenomic analysis detected 56 sequences related to denitrification, 19 with anammox and 6 with DNRA. Genes related with denitrification were phylogenetically distributed among several groups of bacteria (mainly Gammaproteobacteria). Anammox and DNRA related sequences were affiliated with Planctomycetes and Gammaproteobacteria, respectively. Thus, metagenomic and functional approaches supported the description of denitrification, anammox and DNRA rates in mangrove soils, and identified the major bacterial groups involved in these processes.