Pegethrix 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 : 17-19

Pegethrix Mai, Johansen et Bohunická , gen. nov.

Description:— Filaments mostly solitary, at times with multiple hormogonia in a common sheath, or with loose nodule formation, with infrequent double and single false branching. Sheath clear, thin and firm to soft and widened, but never diffluent. Trichomes straight, flexuous, or entangled within a sheath into a loose nodule, sometimes spirally coiled, slightly constricted at the crosswalls, with slow gliding motility observed in trichomes lacking sheath, not tapered. Cells mostly shorter than wide, becoming isodiametric to slightly longer than wide before division, without aerotopes, sometimes with granules in cytoplasm; with parietal thylakoids. Apical cells rounded, without calyptra. Involution cells with axillary bud-like structures rare. Reproduction by trichome fragmentation via disintegration at necridia or without the presence of necridia.

Etymology:— Pege (Gr): water, stream or spring; thrix (Gr.): hair

Type species:— Pegethrix bostrychoides Mai, Johansen et Bohunická , sp. nov.

Pegethrix bostrychoides Mai, Johansen et Bohunická , sp. nov.

Diagnosis: ―Differing from other species in the genus based on the frequent formation of spirals; the internal loop near the base of the Box B helix of the ITS region at position 5–6/31–32 ( Fig. 7a ) and unique V2 and V3 helices of the ITS region ( Figs. 8a , 9a ).

Description:— Colony bright blue green, with radial fasciculation, penetrating the agar. Filaments long or short, sometimes forming nodules ( Fig. 10a ), or loosely to tightly spirally coiled ( Figs. 10b–g ), rarely singly ( Fig. 10i ) or doubly false branched ( Fig. 10h ), 2.0–6.0 μm wide (to 14 μm wide at nodules). Sheath firm, colorless, usually attached to trichome, occasionally softer, widened ( Figs. 10b, i–k ), sometimes irregular and stratified ( Fig. 10k ). Trichomes untapered, more or less constricted at the distinctly visible cross-walls, occasionally with tight, regular, screw-like coils ( Fig. 10l ), necridia not observed, 1.5–2.5–(3.0) μm wide. Cells slightly shorter than wide to longer than wide, rarely with a single central granule, with parietal thylakoids, 1.0–3.0 μm long. End cells rounded.

D1-D1’ helix 85 nucleotides long, with basal 3’ side loop of 8 unpaired nucleotides (5’-UCAUCCCA-3’), mid-helix region with two unpaired adenine residues at position 14–15, internal loops at position 22–25/56–60 and at 32–33/48– 49. Terminal loop 5’-GAAA-3’ ( Fig. 6a ). Box B helix 36 nucleotides long, bearing 4 nucleotides at terminal loop, and one small internal loop at position 5–6/31–32 ( Fig. 7a ). V2 helix 24 nucleotides long, with terminal loop of 6 nucleotides ( Fig. 8a ). V3 helix 96 nucleotides long, with several internal loops at position 5–6/92, 10–14/86–88, 18/81–82, 36–37/62–63, with two mismatches of 5’-A/G-3’ and 5’-G/G-3’ at 29/70 and 44/55. Terminal loop sequence 5’-GAGA-3’ ( Fig. 9a ).

Etymology:— bostrychos (Gr.): curl, anything twisted; Latinized to bostrychoides

Type locality: ―Drip Tank Seep Wall site, Grand Staircase-Escalante National Monument ( GSENM), 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.

Holotype here designated:— BRY37770 !, Herbarium for Nonvascular Cryptogams, Monte L. Bean Museum, Provo, Utah.

Isotype here designated: ― BRY 37771!, Herbarium for Nonvascular Cryptogams, Monte L. Bean Museum, Provo, Utah.

Reference strain:— GSE-PSE-MK47-15B, Algal Culture Collection at John Carroll University, Cleveland, USA.

Taxonomic notes:— The coiling pattern is very characteristic and likely key to species identification. Spirulina rosea Crouan & Crouan (1867: 111) ex Gomont (1892: 253) has trichome width and pattern of coiling very similar to this species; however trichome coloration and especially the intensive, obligate motility observed in Spirulina sp. is not observed in this species. Several species of Planktolyngbya have also been described to have such coils, including Planktolyngbya holsatica ( Lemmermann 1904: 306) Anagnostidis & Komárek (1988: 394) , Planktolyngbya bipunctata ( Lemmermann 1899: 133) Anagnostidis & Komárek (1988: 394) , Planktolyngbya circumcreta ( West 1907: 174) Anagnostidis & Komárek (1988: 394) and Planktolyngbya contorta ( Lemmermann 1898a: 202) Anagnostidis & Komárek (1988: 394) . P. holsatica has dimensions that best fit with this species description (filaments up to 3.5 μm wide, trichomes 2.7–3.0 μm wide). All aforementioned Planktolyngbya sp. have homogeneous cell content, with no constrictions at cross-walls except for P. contorta , but this species has cells distinctively longer than wide. All Planktolyngbya sp. were originally described from planktonic communities, and the single species sequenced for this genus is in the Leptolyngbyaceae ( Fig. 1 ). Several Leptolyngbya species described with coiling behavior include, Leptolyngbya protospira ( Skuja 1939: 50) Anagnostidis (2001: 367) and Leptolyngbya spiralis ( Jao 1948: 169) Anagnostidis (2001: 367) . However the identity of this new species as either of the described Leptolyngbya sp. is questionable, as both were described with thinner trichome widths compared to this species ( L. protospira 0.16–1.4 μm wide; L. spiralis 1–1.5 μm wide), with non-granulated cell content, and non-stratified sheaths. L. protospira and L. spiralis are found in either brackish water or marine environments, which additionally suggests that this is a new, undescribed species to science that differs from all previously described taxa in other genera.

P. bostrychoides is distinct from the four other species in this genus which we recognize in this study. It differs morphologically based on the frequent formation of spirals. Sequence identities of the 16S rRNA gene sequences in the genus do not provide evidence of species separation in this genus, with values between species ranging 98.6–99.9% ( Table 7). However, the phylogeny separates the species fairly well ( Fig. 2 ), with P. bostrychoides being sister to P. olivacea . The separation of species is further supported by the large percent dissimilarity of the 16S–23S ITS region (≥8.2%, see Table 8), which several papers have found useful as evidence of cryptic species separation in other cyanobacterial genera ( Erwin & Thacker 2008, Osorio-Santos et al. 2014, Pietrasiak et al. 2014).

Figures

FIGURE 1.16SrRNA BayesianInferenceanalysis ofthefilamentous groupofSynechococcales cyanobacteria,showing Leptolyngbyaceae. Black polygons represent genera that have been described or are named in provision (e.g., “Myxacorys”), 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 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 10. Pegethrix bostrychoides. A. Nodule formation. B. Existence of multiple trichomes within common sheath. C–G. Variation in the degree of filament coiling, from flexuous to spiral coils. H–I. Double false-branches and single false-branches. J–K. Sheath tightly embraces trichome or expands from trichome. L. Heterogeneity in cell shape and trichome width between young and mature trichomes. Meristematic zone of cell division shown on mature trichome. Scale bar 10μm in 1000X magnification.