Estudo da diversidade dos micro-organismos associados a ascídias coloniais (Tunicata, Ascidiacea)

Abstract

The symbiosis with microorganisms is well known for many marine invertebrate taxa. Despite that, information about these interactions along the Brazilian coast are scanty or even nonexistent. Microorganisms have also recognized as the real producers of interesting natural compounds extracted from marine invertebrates, such as ascidians. With that in mind, the goal of the present study was to evaluate the microbiota associated to colonial ascidians, focusing on symbiotic cyanobacterias, then classifying, estimating the community diversity, and identifying specific interactions between the microbiota and its hosts. This study assessed two ascidians species Didemnum galacteum and Cystodytes sp. collected in the west coast of Ceara state (Brazil), at Dois Coqueiros beach and port of Pecém, respectively. The microbiota was analyzed initially through optical microscopy and subsequently by molecular techniques such as denaturing gradient gel electrophoresis (DGGE) and 16S rRNA library. The microscopic analysis showed a community comprising cyanobacteria and diatoms. DGGE results presented the community profile in terms of Operational Taxonomic Units (OTUs), pointing out Didemnum galacteum as the most diverse. The microbiota in the seawater where specimens were collected was compared to that from the ascidians’ tunic surfaces, and results showed higher number of OTUs in the water, and a more specific microbiota in ascidians. The microbiota community studied by 16S rRNA library revealed dominance of bacteria in both libraries assessed, in which Proteobacteria taxon prevailed with either Alphaproteobaccteria in Didemnum galacteum, and Gammaproteobacteria in Cystodytes sp. Others, such as Bacteroidetes, Planctomycetes, Actinobacteria, Cyanobacteria and uncultured bacteria were evident in Didemnum galacteum, but in a lesser proportion