Pegethrix olivacea Mai, Johansen et Bohunická, 2018

Mai, Truc, Johansen, Jeffrey R., Pietrasiak, Nicole, Bohunická, Markéta & Martin, Michael P., 2018, Revision of the Synechococcales (Cyanobacteria) through recognition of four families including Oculatellaceae fam. nov. and Trichocoleaceae fam. nov. and six new genera containing 14 species, Phytotaxa 365 (1), pp. 1-59 : 22

Pegethrix olivacea Mai, Johansen et Bohunická sp. nov.

Diagnosis: ―Morphologically most similar to P. convoluta in the formation of nodules, however, differing from this and other species in the dirty, olive-green coloration of trichomes.

Description:— Colony dark olive-green, hairy, spreading radially, flat and mucilaginous or mounded. Filaments long or short, frequently irregularly bent due to uneven cell division along filament ( Fig. 11a–d ), false branched ( Fig. 11e ), sometimes loosely coiled to form irregular nodules ( Fig. 11d ), 2.0–3.3–(3.7) μm wide. Sheath firm, colorless, usually attached to trichome, occasionally widened ( Fig. 11h ), up to 1.7 μm wide. Trichomes constricted at indistinctly visible cross-walls, cell division along trichomes often irregular, producing cells with variable shape and width ( Figs. 11g –k ), with necridia, 1.9–2.8 μm wide in young trichomes, 2.4–3.5 μm wide in actively dividing trichomes. Hormogonia few-celled ( Figs. 11h–k ). Cells occasionally isodiametric (1.7–2.6 μm long), shorter than wide in meristematic regions (1.1–1.7 μm long), often with a large central granule. End cells typically rounded, but sometimes elongated and/or irregularly shaped ( Fig. 11k ).

D1-D1’ helix similar to that of P. bostrychoides in structure and sequence, 87 nucleotides long, with basal 3’ side loop of 9 unpaired nucleotides (5’-UCAUCCCAA-3’), opposed on the 5’ strand by a single unpaired cytosine residue, with mid-helix region with two unpaired adenine residues at position 14–15, several internal loops at position 32–33/48–49 and 22–25/56–60. Terminal loop having sequence 5’-GAAA-3’ ( Fig. 6b ). Box B helix 36 nucleotides long, bearing 4 nucleotides at terminal loop, and one 5’-A/C-3’ mismatch at position 5/32 ( Fig. 7b ). V2 helix 24 nucleotides long, with terminal loop of 4 nucleotides ( Fig. 8b ). V3 helix 96 nucleotides long, with several internal loops at positions 5–6/92, 10–14/86–88, 18/81–82 and 36–37/62–63, and two mismatches of 5’-G/A-3’ and 5’-A/G-3’ at positions 24/75 and 29/70 respectively. Terminal loop having sequence 5’-GUAA-3’ ( Fig. 9b ).

Etymology:— olivacea (L.): olive-green coloration of trichomes.

Type locality: ―Drip Tank Seep Wall site, Grand Staircase-Escalante National Monument, 37°19’12.79’’N, 111°31’50.59”W, collected on 15 August 2006 by Markéta Bohunická. Sandstone seep wall with small moist area and larger pond below the rock face, within Strait Cliffs Formation, in the GSENM, Kane County, Utah, USA.

Holoype here designated:— BRY 37772!, Herbarium for Nonvascular Cryptogams, Monte L. Bean Museum, Provo, Utah.

Reference strain: ―GSE-PSE-MK46-15A, Algal Culture Collection at John Carroll University, Cleveland, USA.

Taxonomic notes:— P. olivacea is phylogenetically separated from all previously described Synechococcales , for which sequence data exist. Comparisons with previously described Synechococcales but for which no sequence data exist reveal no exact matches to this species, so we conclude that this taxon is a species new to science, not a previously described species that should be a new combination into Pegethrix . Leptolyngbya subtilissima corresponds in part to this taxon, with olive-green coloration, coiled filaments, thin, and colorless and attached sheath; however, filament width is much narrower (1–1.8 μm wide). The zig-zag bent growth form of some trichomes was illustrated in both Planktolyngbya undulata Komárek & Kling (1991: 30) and P. limnetica ( Lemmermann 1898b: 154) Komárková-Legnerová & Cronberg (1992: 23) , but trichome dimensions, color, and benthic versus planktonic habitat are significantly different.

P. olivacea is most similar to P. bostrychoides in the formation of nodules; molecular characteristics such as the presence of a V 2 helix and sequence length of conserved domains within the ITS region, particularly the D1-D1’ helix, V 2 spacer, pre and post Box-B spacer, and V 3 helix ( Table 6). The 16S rRNA gene phylogeny also supports the close relationship between these two species ( Fig. 2 ). However, the species is distinguished from P. bostrychoides in trichome coloration, presence of irregularly-shaped cells, and hormogonia production, as well as nucleotide differences within the ITS region. Color of trichomes and cell characteristics also distinguish P. olivacea from other Pegethrix sp. Compared with other species of Pegethrix , percent dissimilarity based on aligned ITS regions of the species to all other species is in the range of 8%–23% ( Table 8), and the sequence lengths of the ITS between P. olivacea and P. convoluta , P. indistincta and the Antarctic Pegethrix sp. are also very different ( Table 6).

Figures

FIGURE 2. 16S rRNA Bayesian Inference analysis of the filamentous group of Synechococcales cyanobacteria, showing Oculatellaceae. Black polygons represent genera that have been validly described or are named in provision (e.g., “Trichotorquatus”), with length corresponding to the distance from the most basal OTU to the most diverged OTU of the genus. Posterior probabilities for the BI analysis are given above the nodes. Taxa which we consider to be incorrectly named in NCBI or requiring revisionary work are in quotation marks.

FIGURE 6. D1-D1’ stems of species described in Oculatellaceae.The stem structures of genera described previously in other publications (Oculatella, Thermoleptolyngbya, Timaviella) or in publications under provision (Trichotorquatus) are not shown here.

FIGURE 7. Box B helices of species described in Oculatellaceae. The structures of genera described previously in other publications (Oculatella, Thermoleptolyngbya, Timaviella) or in publications under provision (Trichotorquatus) are not shown here.

FIGURE 8. V2 helices of species described in Oculatellaceae. Several species do not have this structure, including Pegethrix convoluta, P. indistincta, Antartic Pegethrix species, Cartusia fontana¸ Kaiparowitsia implicata.

FIGURE 9. V3 helices of species described in Oculatellaceae. All species described have this structure. The V3 helix of Cartusia aeruginosa is missing because we do not have the full length of its ITS region.

FIGURE 11. Pegethrix olivacea. A–D. Irregular filament shapes due to uneven cell division events along trichome. E. Single falsebranching filament. F. Nodule formation. G–K. Irregular cell shape and trichome length, hormogonia few-celled, abundant. Scale bar 10μm in 1000X magnification.