Resumo

Recent studies have found that the Archaea domain is widespread and this group plays an important role on ecosystem functioning, especially in mangrove sediments where the extreme conditions imposed by daily tidal variations turn these ecosystems into hot spots for microbial diversity. However studies on the Archaea communities in mangrove sediments in Brazil are still scarce. Thus the aim of this work was to investigate the archaeal structure in 5 different mangroves in the State of Ceará, Northeast Brazil with different types of impacts, i.e. shrimp farming (COR an ACA), urbanization (CEA), river damming (PAC) and we also included a pristine mangrove as a control (TIM). Samples from the bulk sediment and the root zones of Rhizophora mangle and Avicennia shaueriana were collected in 4 sampling expeditions, in the dry and wet seasons from two consecutive years and environmental variables such as pH, salinity, organic matter and silt-clay percentages were measured. DNA was extracted, the V3 region of the gene encoding the 16S rRNA was amplified and the amplicons were separated by DGGE. Results showed that bulk sediment clustered separately from root zones in all mangroves, indicating that the roots exert an effect on the structure of the archaeal communities. Also, Archaea in all mangroves exhibited a tendency of annual rather than seasonal clustering. When analyzing ribotype richness the pristine mangrove had the highest values, followed by the urbanized (CEA), the shrimp farm mangroves (COR and ACA, respectively) and by the river damming mangrove (PAC). Redundancy Analysis (RDA) was used to correlate community structure with the environmental variables and results showed that silt-clay percentage was the only analyzed variable that significantly (p<0.05) influenced the archaeal community structure in CEA, COR and ACA, while in PAC and TIM none of the variables reached significant values. It appears that the impacts are altering the structure of archaeal communities and decreasing their richness in mangrove sediments.