Genetic and morphological characterization of Rivularia and Calothrix (Nostocales, Cyanobacteria) from running water

Abstract

In this study, a polyphasic approach was adopted to investigate natural freshwater (river and stream) samples of Rivularia colonies and isolated strains of cyanobacteria with a high degree of trichome tapering (genera Rivularia and Calothrix). Analysis of the phycocyanin (PC) operon and the intervening intergenic spacer (cpcBA-IGS) and 16S rRNA gene sequences were used for genetic characterization. In addition, a molecular fingerprinting method, temperature-gradient gel electrophoresis, which allows sequence-dependent separation of PCR products, was used to assess genotypic diversity in environmental samples and isolated strains. The results showed a high variability of the PC-IGS among the genotypes that was not associated with the morphologies observed. This study underlines the importance of choosing a low-nutrient-content culture medium, especially one with a low phosphorus concentration, for studying typical morphological features of Rivularia for taxonomic purposes. Molecular fingerprinting methods and morphological analyses confirmed the diversity in Rivularia colonial structure and trichome features corresponding to genetic diversity within a single colony. Phylogenetic analysis of cpcBA-IGS was largely consistent with that obtained from 16S rRNA gene sequence analysis and confirmed the high level of divergence between genotypes. The sequences of Rivularia and Calothrix from this study and database sequences showed great heterogeneity and were clearly not monophyletic. The results of this genetic and morphological study of field samples and fresh isolates indicated that the current classification of these genera needs to be revised. INTRODUCTIONHeterocystous cyanobacteria correspond to a monophyletic lineage (Wilmotte & Herdman, 2001) that contains the orders Nostocales and Stigonematales (subsections IV and V) (Rippka et al., 1979;Castenholz, 2001). The genera Rivularia and Calothrix belong to the order Nostocales and the family Rivulariaceae according to traditional classification (Geitler, 1932; Komárek & Anagnostidis, 1989;Whitton, 2002) and to subsection IV by bacteriological classification (Rippka et al., 2001a). The Rivulariaceae are among the most morphologically complex cyanobacteria (Whitton, 1987). They are characterized by tapered trichomes, apart from short phases of hormogonium formation. The mature trichome has a terminal heterocyst, although some species also have intercalary heterocysts, and cell division is largely localized to a region near the heterocyst (Whitton, 2002). Traditional taxonomy (Geitler, 1932) included 12 genera, some of which are widespread and others that have rarely been recorded (Whitton, 1987). Thus, Calothrix, Rivularia and Gloeotrichia can be considered the most representative genera of this group and are the most thoroughly studied. The genus Rivularia Agardh is easily distinguishable in the field by its characteristic development as gelatinous, hemispherical or subspherical colonies containing a large number of filaments, arranged radially or sometimes parallel ...

Scytonematopsis contorta sp. nov. (Nostocales), a new species from the Hawaiian Islands.

“…Additional freshwater Calothrixlike taxa would need diagnosis and one or more new genera. Berrendero et al (2008) noted that one clade of freshwater tapering species in their study belonged in a new genus, but they did not erect the taxon in that paper.…”

Phenotype diversity and phylogeny of selected Scytonema-species (Cyanoprokaryota) from SE Brazil.

“…As follows from the current molecular data, Scytonema is polyphyletic (similarly to other traditional cyanobacterial genera, see e.g., Boyer et al 2002;BerrenDero et al 2008;Zapomělová et al 2011, etc. ) and it will evidently be divided into several generic entities (BohuniCKá et al 2012).…”

Photosynthesis and calcification of the stromatolitic freshwater cyanobacteriumRivularia

“…However, some populations of R. biasolettiana are more intensely calcified than those investigated here and field observations suggest that a continuity of forms may exist, even within the same stream. Recent work by Berrendero et al (2008) employing molecular fingerprinting also indicates a high morphological and genetic diversity within the genus as currently recognized.…”