Diversidade de micro-organismos associados a zoantídeos (cnidaria, zoanthidae)

Abstract

Coral reefs are ecosystems of great biological diversity and ecological relevance. Some animals on coral reefs have a dynamic association between the animal host and a diversity of associated micro-organisms. These micro-organisms are directly envolved on their fisiology, generating benefits as the exchange of nutrients and production of bioactive compounds used in defense against predation and competition for space. The importance of coral–microbial interactions is increasingly being recognized, with studies demonstrating the active role that the associated microbial communities play in maintaining coral health and resilience. The limited knowledge on the diversity of zoanthids´ symbionts and the hypothesis that symbiotic micro-organisms are involved in competitive strategies of defense to adverse factors justify the relevance of this study, which aimed to access the diversity and community structure of bactéria and zooxanthellae associated with Palythoa caribaeorum, Zoanthus sociatus and Protopalythoa variabilis, commonly found on the northeast coast of Brazil. The structure of the communities was assessed by denaturing gel gradient electrophoresis (DGGE) and 16S cloning library. Tissues from corals and seawater were collected and used for extraction and amplification of 16S or 28S rDNA genes by polymerase chain reaction. The results showed diverse microbial communitie associated with the zoanthid species and sea water. The microbiota appears to be species-specific. According to the 16S rDNA libraries, the phyla Proteobacteria, Bacteriodetes and Cyanobacteria were predominant. The class Gammaproteobacteria was characteristically found associated to P. caribaeorum whereas Alphaproteobacteria was dominant in Z. sociatus and P. variabilis, which were also the most diverse hosts. Most of the identified bactéria were related to bioactive compound production which can be benefic to the host. The presence of exclusive bacteria in the zoanthids suggests that some species might be transmitted vertically to the host. The study of zooxanthellae diversity indicates the occurrence of the clades A and C of Symbiodinium in the studied zoanthids. The clade A was identified only in Z. sociatus whereas the clade C was present in all studied zoanthids. These clades are related to bleaching resistance and can confer more resistance to adverse environmental factors. This is the first study to examine the diversity and community structure of bactéria and zooxanthellae of Brazilian zoanthids. These data indicate that symbiont diversity is high and must be considered regarding the conservation of marine habitats.