Resumo

Microbial activity is essential for the functioning of all ecosystems, however studies on the ecology of microorganisms are still scarce, especially in Northeastern Brazil mangroves. These coastal ecosystems generally occur in urban and/or touristic areas, subjected to impacts that, in turn, might alter the composition and diversity of the microbial communities. Taking this background into account, this study aimed to access and compare the structure of bacterial communities using DGGE for the 16S rRNA gene, in areas in the presence and absence of vegetation at five mangroves (Pacoti, Ceará, Acaraú, Coreaú and Timonha) along the coast of the State of Ceará, during the dry and wet seasons in two consecutive years. Furthermore, we aimed to verify the existence of a correlation by means of redundancy analysis (RDA) between the microbial community structure and the environmental variables (pH, salinity, organic matter and silt-clay contents) measured at each mangrove. The clusters derived from the DGGE profiles for the bacterial communities revealed that the sampling sites on vegetated areas (sites 2 and 3) had a higher similarity when compared to the non-vegetated site (site 1), which clustered separately in all analyzed mangroves. As for the sampling seasons, there was a tendency of seasonal instead of annual clustering. The ribotype richness, i.e. the number of bands in the DGGE gel, ranged from 11 to 38, with the mangrove considered pristine (Timonha) having the lowest average richness. The RDA revealed that the silt-clay content explained most of the variability of the data, significantly influencing (p <0.05) the structure of bacterial communities in the mangrove of Ceará and Coreaú while in the other mangroves any of the evaluated variables reached significance. Thus it can be concluded that the presence and type of vegetation seems to exert a major influence in structuring bacterial communities and, despite differences and the large distance between the studied mangroves, it was possible to find temporal and spatial patterns correlated mainly with the contents of silt-clay in the sediments. These findings constitute a starting point to further characterize these environments, which is fundamental for planning conservation and/or restoration actions of these threatened ecosystems.