Resumo

Rhizophora mangle, known as the red mangrove, is distributed in estuarine ecosystems throughout the tropics. Red mangroves are easily distinguishable through their unique prop roots system and viviparous seeds. While co-occurring with other species of mangrove and subject to many of the same natural and anthropogenic threats, R. mangle remains the dominant species within its range. However, given that mangrove habitats are in decline globally, it is important to monitor the future status of this critical mangrove species. Although microbes play an important role in the cycling of nutrients in the mangrove ecosystem, very little information is available about the types of microbes associated with R. mangle. In this context, the aim of this study was to survey the taxonomic diversity of bacteria in the R. mangle root zones in 8 mangroves (Icapui, Malcozinhado, Cocó, Ceará, Aracatiaçu, Acaraú Coreaú and Timonha) along the coast of Ceará state, Brazil, covering 573 km of mangroves submitted to different human disturbances. The total DNA extracted from sediments was pooled and used for construction of 16S rDNA libraries. After quality analysis, 627 sequences were obtained with an average size of 809bp. All mangroves exhibited high phylum richness and Acidobacteria, Bacteroidetes, Chloroflexi, and Proteobacteria were detected at all locations. Proteobacteria was dominant in all mangroves, and it was mainly represented by Alpha, Delta, and Gammaproteobacteria. Alphaproteobacteria was the most abundant class in five of the eight mangroves, from Icapui (far east coast of the State) up to Aracatiaçu (west coast). The greatest richness was found in the pristine mangrove, Timonha, with 14 phyla while the lowest richness was found in Ceará, an urban mangrove, threated by intense urbanization, with only 7 phyla. The results clearly showed that the taxonomic diversity of bacteria from mangroves subjected to intense urbanization (Ceará) and shrimp farming (Acaraú) have decreased, highlighting the risks of these changes for functioning of nutrient cycles associated with the R. mangle.