Resumo

Mangroves are coastal ecosystems found in tropical and subtropical regions, which are quite productive, however constantly impacted. The typical flora along with the associated microorganisms support the high productivity found in this environment. As microorganisms are essential components of the biogeochemical cycles and are also responsible for the degradation of organic matter and pollutants, it is very important to understand the relationships between microbial communities and the environment and how these communities respond to natural and anthropogenic disturbances, providing subsidies for its conservation and restoration. The aim of this study was to describe the structure of bacterial communities in the rhizosphere of Rhizophora mangle L. over four years in the Pacoti river mangrove, state of Ceará, northeast Brazil. This is the first long-term study on microbial ecology of sediments in this ecosystem. To this end, the mangrove sediments were sampled at three sites (river mouth, in an intermediate location and distant from the sea) along the R. mangle rizosphere, in two seasons (wet and dry), always in the exact same sites for over four years. At each site, five samples were collected, homogenized and some environmental variables were measured (pH, salinity, organic matter content and granulometry). Simultaneously, the total DNA from the samples was extracted and the structure of bacterial communities was accessed by PCR-DGGE of the rDNA 16S V3 region. Considering all the results, it is clear that the structure and composition of bacterial communities respond to the accessed environmental variables. The organic matter had a significant effect (p <0.05) on the community structure of bacteria. In terms of richness, the population throughout the area covered by R. mangle was similar. Despite major differences between the sampling sites according to evaluated environmental variables, still many common ribotypes among the sites were found, indicating the existence of a rhizosphere effect, in which the exudates released by R. mangle influence communities established there. The stability found in the structure and richness of bacteria suggests that communities are in dynamic equilibrium.