Resumo

Mangrove ecosystem is a coastal tropical biome, located in transition zone between land and sea, characterized by flooding period that gives to this biome unique and specific environment conditions. These places have a large amount of organic matter accumulated, which makes nitrogen decomposition and other nutrients available at the beginning of the trophic chain. One form of nitrogen, nitrate, plays an essential role in nature. For bacteria, nitrate is both a nitrogen source and an electron acceptor in the absence of free oxygen. Thus, some processes may compete for nitrate such as denitrification processes and anaerobic ammonium oxidation (anammox). The comparison of these pathways composes the goals of this study, accessing, additionally, the effect of mangrove contamination related with such transformations. The mangroves sampled in this study are located in the city of Bertioga (São Paulo State, Brazil), with different states of conservation: BrMgv01 (with low oil spill), BrMgv02 (with high oil spill), and BrMgv03 (with anthropogenic action). Therefore, we analyzed the genetic basis for the occurrence of such processes (metagenomics), the expression of such genes analyzed sediments (metatranscriptomics), and the functionality of such processes (incubations with 15N labeled nitrogen), trying to understand the transformations which the nitrogen/nitrate is preferentially in this environment. DNA and RNA analyses showed the presence and expression of genes for the occurrence of such transformations, especially genes related to denitrification (nirS, nirK, nosZ, norB and narG) in metagenomic analysis, and expression of genes related to anammox process in metatrancriptomic analysis (mainly hao genes). Incubations with labeled nitrogen demonstrated higher occurrence of denitrification and low rate of anaerobic ammonium oxidation pathway. These processes were altered according mangroves contamination, and the impacted area with oil showed lower values of denitrification and anammox. These results describe an unprecedented transformation of nitrogen/nitrate in mangroves, and indicate effects of environmental degradation from environment to this important biogeochemical cycle for maintaining the mangrove ecosystem.