Tildeniella nuda 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 : 42-44

Tildeniella nuda Mai, Johansen et Bohunická sp. nov.

Diagnosis:— Different from T. torsiva in the occasional presence of swollen cells and much narrower trichome width. Molecularly distinguished by from T. torsiva by secondary structures of the D1-D1’ and Box B helices ( Figs. 6n‒o , 7m ‒n ), as well as by presence of a V2 helix.

Description:— Colony fasciculated, not penetrating the agar, forming a compact mat, with small evenly distributed, rounded clumps of trichomes, bright blue-green. Filaments relatively short ( Fig. 21a ), without false branching. Sheath usually absent, thin, firm and colorless when present, 1.0 – 1.4 μm wide. Trichomes pale blue-green, clearly constricted at the cross-walls ( Figs. 21c–e ), cell division occurring throughout the trichome, 1.0–1.2 μm wide. Hormogonia and necridia absent. Cells always longer than wide, sometimes elongated ( Fig. 21b–c ), with mostly homogeneous content, rarely swollen ( Fig. 21d–e, g–h , at arrows) or with small granules at polar regions of cells, 2.0 – 4.3 (5.1) long. Apical cells cylindrically rounded, sometimes apically swollen ( Fig. 21a, f at arrow).

D1-D1’ helix 65 nucleotides long, basal 3’ unilateral bulge of 7 nucleotides long, with sequence 5’-CAUCCCA- 3’, with mid-helix with two mismatches of C/U and G/A at positions 9/50 and 22/39, one internal loop at position 25/35 – 36 immediately separated from the terminal loop by a 5’-GC:GC-3’ clamp, and two unpaired nucleotides at position 16–17 of the 5’ strand, with terminal loop sequence 5’-AUUUU-3’ ( Fig. 6o ). Box B helix 38 nucleotides long, with one internal loop at position 5/33–34 and one unpaired adenine residue at position 9 of the 5’ strand ( Fig. 7n ). V2 helix 77 nucleotides long, with one small internal loop at position 10–11/68 and one large internal loop at position 24–26/51–55 ( Fig. 8j ). V3 helix not reported here due to short sequence missing the end of the ITS.

Etymology:— nudus (L.): naked, referring to the frequent absence of sheath.

Type locality:— Switzerland, Stansstaad, collected by Zehnder in 1965; found on a wet stone wall.

Holotype here designated:— BRY37782 !, Herbarium for Nonvascular Cryptogams, Monte L. Bean Museum, Provo, Utah.

Reference strain:— Zehnder 1965/U140, Algal Culture Collection at John Carroll University, Cleveland, USA.

Taxonomic notes:— This species is character poor, lacking features useful for recognition such as necridia, hormogonia, coiling or nodule formation, or false branching. Given its lack of features, it could fit a number of species belonging within Leptolyngbyaceae sensu lato Komárek & Anagnostidis (2005). The cell morphology (length to width ratio, dimensions) is similar to most Oculatella species, but T. nuda lacks the characteristic apical cells of that genus. The closest fit is L. hansgirgiana Komárek in Anagnostidis (2001: 374), but this taxon has a complicated taxonomic history. It was first described as Leptothrix tenuissima Nägeli ex Kützing (1849: 265) , then transferred to Hypheothrix tenuissima (Nägeli) Rabenhorst (1865: 77) , and finally to Lyngbya tenuissima (Nägeli) Hansgirg (1891: 346) . However, these were all pre-starting point names (i.e. pre-Gomont 1892, see McNeill et al. 2015). The taxon was validated post-starting point as Lyngbya tenuissima (Nägeli) Hansgirg ex Hansgirg 1892 . When many of the thin simple Oscillatoriales were transferred into Leptolyngbya (Komárek & Anagnostidis 1988) , Plectonema tenuissimum Gardner (1927) was used as the basionym for Leptolyngbya tenuissimum (Gardner) Komárek & Anagnostidis (1988) , and consequently was occupied at the time of further revision, when Nägele’s taxon was given a new name, L. hansgirgiana . Our taxon is a close fit to the protologue in Kützing (0.7 μm wide, blue-green color only, terrestrial), but the description in Komárek & Anagnostidis (2005) has been broadened considerably based on the many subsequent records by multiple authors and is consequently not as apparent a fit. We hesitate to use this taxon with complicated, long history, broadly circumscribed morphology, and absence of sequence data or clear holotype material as the basis for the species name for Zehnder’s strain shown here to belong to Tildeniella , and thus have created a new name.

T. nuda is distinct from other species within the Oculatellaceae by its thin trichomes and high variation in cell length within trichomes. Molecularly, the species is closely related to T. torsiva , with very high similarity in the 16S rRNA gene (99.1% identity, Table 13), and we were not able to compare the percent similiarty in the ITS structure due to sequence truncation of the T. nuda reference strain. However, substantial taxonomic features separate the two species well.

Figures

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 21. Tildeniella nuda. A. Filaments short, Pseudanabaena-like, trichomes not or only slight constricted, connected by somewhat translucent cell wall; B–H. Cells sometimes distinctively elongated, bent or involuted (arrows). Scale bar 10μm in 1000X magnification.