Crinalium magnum, 1927

Mikhailyuk, Tatiana, Vinogradova, Oksana, Holzinger, Andreas, Glaser, Karin, Samolov, Elena & Karsten, Ulf, 2019, New record of the rare genus Crinalium Crow (Oscillatoriales, Cyanobacteria) from sand dunes of the Baltic Sea, Germany: epitypification and emendation of Crinalium magnum Fritsch et John based on an integrative approach, Phytotaxa 400 (3), pp. 165-179 : 173-174

Placement of Crinalium magnum in the molecular phylogeny of Gomontiellaceae

Molecular phylogenetic analyses based on the 16S rRNA gene revealed close relationship of the strain Hg-6-6 to the other representatives of the family Gomontiellaceae . It once again confirmed the monophyly of this family, with the genus Komvophoron as a sister group and its placement inside Oscillatoriales ( Hašler et al. 2014; Bohunická et al. 2015, see Fig. 1 ). Recently it was also found that representatives of the Gomontiellaceae are closely related with Chamaesiphon Braun ( Kurmayer et al. 2017) that was also shown on our phylogenetic tree (see Fig. 1 ).

However, the position of Crinalium strains on the phylogenetic tree raises a question of relationship between the genera (namely Crinalium and Hormoscilla ). In our research, the original strain of C. magnum Hg-6-6 forms a separate lineage and is nested among strains of both genera. Bohunická et al. (2015) also noted a high molecular similarity of the mentioned genera despite clear morphological differences (flattened versus non-flattened trichomes). The pair-wise nucleotide identity of the 16S rRNA gene of Crinalium strains SAG 34.87, SAG 22.89 and Us-s-6-2, and Hormoscilla strains SAG 1407-1 and CCALA 1054 was 99%. Strains SAG 34.87 and SAG 22.89, representing “ Crinalium magnum ” and C. epipsammum , showed 100% similarity ( Bohunická et al. 2015; Table S3). Despite the fact that calculated levels of pairwise similarity are much higher than that required for the separation of genera ( Stackebrandt & Goebel 1994), the authors came to the conclusion that clear morphological and ecological differences between Hormoscilla and Crinalium “provide a solid basis for retaining their taxonomic resolution in the framework of a polyphasic approach” ( Bohunická et al. 2015: 1045). The inclusion of Hg-6-6 here confirmed that the strains of both genera are closely related (see Table 1 ). Therefore, generic borders inside Gomontiellaceae are still unclear and perhaps generic concept should be clarified in future with more strains included in the analysis. On the other hand perhaps 16S rRNA is not sufficient marker for some closely related cyanobacterial taxa, therefore other genetic markers should be used in order to resolve relationships within Gomontiellaceae .

For better resolution secondary structures of the main informative helices of 16S-23S ITS region of Hormoscilla and Crinalium were used (see Fig. 2 ). These structures are also characterized by similarity. Although some differences are visible among representatives of two genera, Hormoscilla and Crinalium , due to numerous insertions/deletions of base pairs in the last genus. Unfortunately secondary structure of RNA of authentic strain of Crinalium epipsammum (SAG 22.89) was not analyzed since 16S-23S ITS fragment is not publically available. Therefore perhaps analysis of secondary structure of 16S-23S ITS region of all available strains of Gomontiellaceae will give more information for better understanding generic borders of two genera.

Hg-6-6 is genetically (and morphologically, see below) distant from the strain SAG 34.87, which was previously identified as C. magnum (see Fig. 1 ). Some doubts concerning morphological and genetic data regarding the strain SAG 34.87 were already expressed in Bohunická et al. (2015) and discussed below.

Figures

FIGURE 1. Molecular phylogeny of Synechococcales and Oscillatoriales based on 16S rRNA sequence comparisons.A phylogenetic tree was inferred by the Bayesian method with Bayesian Posterior Probabilities (PP), Maximum Likelihood and Neighbor Joining bootstrap support (BP). From left to right, support values correspond to Neighbor Joining, Maximum Likelihood BP and Bayesian PP; BP values lower than 50% and PP lower than 0.8 not shown. Strain in bold represents newly sequenced cyanobacteria. Clade designations follow Osorio-Santos et al. (2014) and Bohunická et al. (2015).

FIGURE 2. Secondary structure of the main informative helices of region 16S-23S ITS of cultured strains of Hormoscilla and Crinalium. All differences between strains are presented in comparison with authentic strain of H. pringsheimii (SAG 1407-1). Variable bases are shown with arrows, places of insertions/deletions of base pairs are marked with arrowheads, homological base pairs among different strains are indicated with dotted lines.