Antarctic Cyanobacteria Biodiversity Based on ITS and Trn L Sequencing and Its Ecological Implication

Abstract

Antarctic\rcyanobacteria biodiversity was investigated by simultaneous sequencing of the nuclear ribosomal internal transcribed spacer (ITS flanked by partial 16S and 23S), and Chloroplast tRNALeu UAA intron (TrnL),\rexploring whether such morphotypes constitute distinct species and explaining\rtheir current distribution. We identified Nostocales, Chrococcales and Oscillatoriales species, collected in different habitats (soil, algal\rmats, lake sediments, ice-water) after their growth in cultures. By comparative sequence\ranalyses available in Genbank, our results proved to be mostly in agreement\rwith both TrnL and ITS, in the identification of the strains,\rparticularly for Nostocales. Although\rITS demonstrated more usefully than TrnL\rdid in identifying Oscillatoriales and Chroococcales, due to the\rfrequent lack of the intron in these groups, our results lead us to support an\rindependent phylogenetic dataset of ITS and TrnL (the latter based on\rconserved regions) producing not only concordant clusters but also a secondary\rstructure. Specific assignments of the secondary structure evidenced by different cyanobacteria groups,\respecially the D1-D1’ region of ITS and the P6b region of TrnL. For the latter region, the sequences analyzed for Nostoc species could be divided into the two classes previously\ridentified, on the basis of different heptanucleotide repeats in P6b which were\rnot foun