Estudo comparativo de cianobactérias simbiontes em colônias de ascídias do Atlântico e Pacífico

Abstract

The symbiosis between marine invertebrates and cyanobacteria is well documented for many taxa, such as Porifera and Ascidiacea. Within the Ascidiacea this association often occurs with cyanobacteria from the genus Prochloron. Many studies have been conducted concerning the hosts and morphological and molecular aspects of the symbionts. Nevertheless, most of these studies were developed for organisms from the Pacific, while the South Atlantic is still ignored, especially as to the true identity of the symbionts. Therefore, the purpose of the present study was to identify the symbiont using 16S rDNA sequences, and also verify his phylogenetic affinity. In order to achieve these goals, specimens of ascidians form the species Didemnum ligulum, Didemnum galacteum and Cystodytes sp. with a visible biofilm were collected. The biofilm was washed, examined under optical microscopy and then total DNA was extracted. Using the purified DNA a 16S rDNA fragment with 1,148 b.p. was obtained through PCR for the species Cystodytes sp. The sequence showed 98% similarity with Prochloron sequences from the GenBank. The phylogenetic analysis revealed a well supported clade for Prochloron containing the Brazilian lineage. Despite the geographically distant locations, the Brazilian lineage seems not to differ from the Pacific (Japan, Australia, USA) os North Atlantic (Panama) ones. This is the first study concerning the identification of the cyanobacteria Prochloron in symbiosis with the colonial ascidian Cystodytes sp. using molecular tools, and also the first account for the South Atlantic.