Molecular identification, typing and traceability of cyanobacteria from freshwater reservoirs

Abstract

In order to assess the potential of several molecular targets for the identification, typing and traceability of cyanobacteria in freshwater reservoirs, molecular techniques were applied to 118 cyanobacterial isolates mostly sourced from Portuguese freshwater reservoirs and representative of three orders of cyanobacteria: Chroococcales (54), Oscillatoriales (15) and Nostocales (49). The isolates were previously identified by morphological methods and subsequently characterized by composite hierarchical cluster analysis of STRR and LTRR (short and long tandemly repeated repetitive sequences) PCR fingerprinting profiles. Representative isolates were selected from each cluster and their molecular identification, at the species level, was obtained or confirmed by phylogenetic positioning using 16S rRNA gene and rpoC1 phylogenies. A highly congruent association was observed between STTR- and LTRR-based clusters and taxonomic affiliation, revealing the usefulness of such PCR fingerprinting profiles for the identification of cyanobacteria. Composite analysis of hierarchical clustering of M13 and ERIC PCR fingerprints also appeared suitable for strain typing and traceability within a reservoir, indicating its potential for use in cyanobacterial monitoring, as a quality management control. Based on Simpson (D) and Shannon-Wiener (J') indices a high diversity was observed within all species, with Planktothrix agardhii showing the lowest diversity values (D=0.83; J'=0.88) and Aphanizomenon flos-aquae the highest ones (D=J'=0.99). A diagnostic key based on 16S-ARDRA, ITS amplification and ITS-ARDRA for identification purposes is also presented.