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Abstract:
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.
