RESUMO
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.
Assuntos
Amônia/metabolismo , Anaerobiose , Desnitrificação , Nitratos/metabolismo , Oxirredução , Áreas Alagadas , Desnitrificação/genética , Metagenoma/genética , Ciclo do Nitrogênio , Plantas/metabolismo , SoloRESUMO
The mangrove ecosystem is a coastal tropical biome located in the transition zone between land and sea that is characterized by periodic flooding, which confers unique and specific environmental conditions on this biome. In these ecosystems, the vegetation is dominated by a particular group of plant species that provide a unique environment harboring diverse groups of microorganisms, including the endophytic microorganisms that are the focus of this study. Because of their intimate association with plants, endophytic microorganisms could be explored for biotechnologically significant products, such as enzymes, proteins, antibiotics and others. Here, we isolated endophytic microorganisms from two mangrove species, Rhizophora mangle and Avicennia nitida, that are found in streams in two mangrove systems in Bertioga and Cananéia, Brazil. Bacillus was the most frequently isolated genus, comprising 42% of the species isolated from Cananéia and 28% of the species from Bertioga. However, other common endophytic genera such as Pantoea, Curtobacterium and Enterobacter were also found. After identifying the isolates, the bacterial communities were evaluated for enzyme production. Protease activity was observed in 75% of the isolates, while endoglucanase activity occurred in 62% of the isolates. Bacillus showed the highest activity rates for amylase and esterase and endoglucanase. To our knowledge, this is the first reported diversity analysis performed on endophytic bacteria obtained from the branches of mangrove trees and the first overview of the specific enzymes produced by different bacterial genera. This work contributes to our knowledge of the microorganisms and enzymes present in mangrove ecosystems.