Drouetiella hepatica Mai, Johansen et Pietrasiak, 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 : 33-34

Drouetiella hepatica Mai, Johansen et Pietrasiak sp. nov.

Diagnosis: ―Distinguished from the other species of the genus by its meristematic zones and false branching, and by its wide variability in trichome width.

Description:— Colony brownish or purplish-brown, forming floating, mucilaginous mats in liquid culture. Filaments long or short. Mature filaments 2.8–3.7 μm wide ( Figs. 16a, g–h ), young filaments narrower, 2.3–2.8 μm wide ( Figs. 16b–f ), occasionally with false branching ( Fig. 16a–b ). Sheath firm, colorless, thin to occasionally enlarged ( Figs. 16c–e ) and lamellate ( Fig. 16e ), up to 4.4 μm wide. Trichomes not or slightly constricted at cross-walls, cylindrical, with compacted coils at meristematic zones ( Figs. 16a,g ), 1.5–2.1 μm wide in young trichomes and 1.7–3.0 μm wide in mature trichomes. Hormogonia absent. Cells longer than wide and occasionally elongated, (2.2) 3.1–4.5 μm long, or in meristematic regions isodiametric, 2.0–2.6 μm long, with one central granule present in both young and mature cells. Necridia present ( Fig. 16h ). End cells cylindrical, rounded.

D1-D1’ helix 64 nucleotides long, with 3’ unilateral bulge of 7 nucleotides (5’-CAUCCCA-3’). Mid-helix region with a mismatch at position 24/34–35 immediately separated from the terminal loop by a 5’-GC:GC-3’ clamp, and two mismatches at position 9 (C/U) and 21 (G/A) on the 5’ strand. Terminal loop having sequence 5’-AAUCA-3’ ( Fig. 6f ). Box B helix 34 nucleotides long, with one basal internal loop at position 5/29–30 and one unpaired adenine residue at position 9 of the 5’ strand ( Fig. 7e ). V2 helix 21 nucleotides long, with terminal loop having sequence 5’-AAUAU-3’ ( Fig. 8c ). V3 helix 51 nucleotides long, with one large internal loop at position 10–12/39–41 and one unpaired guanine residue at position 46 on 3’ strand. Terminal loop sequence 5’-UUAG-3’ ( Fig. 9f ).

Etymology:— hepaticus (L.): of or pertaining to the liver, in reference to the dark reddish brown (liver-colored) color of the colonies.

Type locality: ― Slovakia. National Park Slovak Paradise: Waterfall Kaskady, gorge Sucha Bela, collected in 2000 by Bohuslav Uher. Found on subaerial limestone.

Holotype here designated:— BRY37778 !, Herbarium for Nonvascular Cryptogams, Monte L. Bean Museum, Provo, Utah.

Reference strain: ― UHER 2000/2452, Algal Culture Collection at John Carroll University, Cleveland, USA.

Taxonomic notes:— The characteristic coloration of the trichomes is similar to Leptolyngbya cebennensis ( Gomont 1899: 38) Umezaki & Watanabe (1994: 203) , L. carnea (Kützing ex Lemmermann 1910: 206) Anagnostidis & Komárek (1988: 391) and Lyngbya roseola Richter ex Hansgirg (1892: 491) . Trichomes and cell dimensions fit well with Leptolyngbya cebennensis and Lyngbya roseola , although the characteristic of heterogeneity in width of young and mature trichomes as well as the absence of pseudobranches separate D. hepatica from these taxa. L. carnea has granulated cell contents, tortuous trichomes and irregular sheath outlines that match filaments of D. hepatica . However, D. hepatica has wider trichomes, and brownish rather than pinkish coloration. No lamellate sheath was reported in any of the above species.

D. hepatica is distinct from the other named Drouetiella species based on percent dissimilarity of the ITS region, which is>18% ( Table 10). This very well satisfies the criterion for species distinction based on percent dissimilarity of>4.0% ( Erwin & Thacker 2008, Osorio-Santos et al. 2014, Pietrasiak et al. 2014, Bohunická et al. 2015). The closest taxon to D. hepatica is a strain that was named Leptolyngbya frigida ANT.LH 52.2 by the researchers that found it and subsequently reported on it ( Taton et al. 2006, Sabbe et al. 2004). ANT.LH52.2 has high 16S rRNA gene similarity to D. hepatica (99.5% identity), but dissimilarity in the ITS regions between two taxa is well above the 4% level used as evidence of conspecificity. Both taxa have identical domain lengths in the ITS region ( Table 6). The most striking similarity between the two taxa is the near complete similarity of secondary structure of the conserved ITS domains ( Figs. 6–9 ). We do not know the morphology of ANT LH52.2, so a decision as to whether or not to consider it conspecific with D. hepatica must be postponed until more information is available, but the evidence that this strain and associated sequence belong to Drouetiella is unequivocable. It is discussed further under Antarctic Drouetiella sp. above.

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 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 16. Drouetiella hepatica. A.Heterogeneity in trichome width between young and mature filaments, young filaments isodiametric to slightly cylindrical. B–C. False-branching very rare in young trichomes, only single false-branches observered. D–F. Sheath sometimes elongated and lamellate as in (E). G. Rapid cell division in meristematic zones sometimes caused twisted trichomes. H. Frequent necridia occur along actively dividing trichomes. Scale bar 10μm in 1000X magnification.