Ecologia microbiana de sedimentos de manguezal do Estado do Ceará

Abstract

Mangroves are highly productive coastal ecosystems found in tropical and subtropical climates, with Brazil having the second largest mangrove area in the world and the largest in the Americas. Although the macro ecology of these environments is well known, little is known about the microbial community. The objective of this study was to contribute to the knowledge of the microbial ecology of mangrove sediments investigating mangroves of the state of Ceará (Pacoti, Ceará, Coreaú and Acaraú) subjected to different types of impacts, having a pristine mangrove (Timonha) as a reference. One of the studies involved a five-year monitoring of the microbial community structure in the sediment in the root zones of Rhizophora mangle in Pacoti mangrove. A second approach comprised a biogeographic study of microbial communities in sediments without vegetation and in the root zones of R. mangle and Avicennia shaueriana in five mangroves. These two studies were performed using PCR- DGGE and analyses of environmental variables and their correlations. The last approach sought to characterize the taxonomic diversity of the five mangroves using high-throughput sequencing. The results of the five-year monitoring of bacteria and archaea showed variation in the structure of these communities, and this variation was mostly explained by the silt-clay contents. The ribotype richness for Bacteria and Archaea ranged from 10-29 and 14-38, respectively, and the site most distant to the sea presented the lowest average richness for both domains. In the biogeographic study the structure of bacterial and archaeal communities was largely explained by the silt-clay contents, but also by the mangrove species, since the sediments of vegetated areas were more similar to each other than with the unvegetated sediments. The five mangroves differed regarding to the microorganism richness, with Pacoti having the second highest richness of bacteria and the lowest of archaea. By analyzing the richness in the habitats, the unvegetated area showed lower bacterial richness, especially in the mangroves impacted by shrimp farming. Regarding the taxonomic diversity the predominance of the phylum Proteobacteria in the mangroves was detected, with the exception of Pacoti, which showed higher abundance of Firmicutes. Among the most abundant phyla Bacteroidetes, Actinobacteria, Acidobacteria, Chloroflexi and Planctomycetes were also detected. The most abundant classes of Proteobacteria in the five mangroves were Gamma, Delta, Alpha and Epsilonproteobacteria. Only two phyla of Archaea were detected in the five mangroves, Crenarchaeota and Euryarchaeota. Interestingly, Ceará mangrove exhibited some unique genera of archaea, including Halobacterium, Natrococcus and Thermogymnomonas. This first dataset for northeast Brazil mangroves clearly demonstrates the existence of structural patterns of the communities of Bacteria and Archaea and these patterns were molded primarily by the silt-clay contents and habitat type. Seven phyla of Bacteria and two of Archaea dominate these mangroves. This basal phyla composition comprises a wide range of genera that distinguishes each mangrove and signals for a high functional redundancy. This complex microbial diversity is responsible for the mangrove functioning and contributes to the resilience of these ecosystems, emphasizing the importance of their conservation.