Spelaeonaias Lamprinou, Christodoulou, Hernández-Mariné et Economou-Amilli, 2016

Lamprinou, Vasiliki, Christodoulou, Maria, Hernandez-Marine, Mariona, Parmakelis, Aristeidis & Economou-Amilli, Athena, 2016, Spelaeonaias gen. nov., a new true-branched cyanobacterium from Cave Vlychada (Diros, Peloponnese, Greece), Phytotaxa 282 (3), pp. 171-185 : 175

Spelaeonaias Lamprinou, Christodoulou, Hernández-Mariné et Economou-Amilli , gen. nov. ( Figs 1–4 )

Morphologically similar to Symphyonemopsis from which it differs in the autapomorphic feature of the subaerophytic ensheathed hormogonia. Under molecular evaluation (16S rRNA analysis) very close to the Stigonematalean strains SA1301 and SP302 (GenBank: HQ917695 and HQ917696 respectively) from the Maltese catacombs but morphologically different.

Description:— Thallus spread in tufts forming woolly mats, dark blue-grey. Sheaths firm, attached to trichomes, not lamellated. Filaments true-branched, commonly with Y-like type of branching, rarely with false branching. Trichomes uniseriate, ± isopolar, with cells shorter or longer than wide, barrel-shaped, cylindrical, slightly and/or distinctly constricted. Heterocytes intercalary and also terminal at the germinating ensheathed hormogonia (hormocytes). Reproduction succeeded by the formation of ensheathed hormogonia that usually grow subaerophytically over the liquid medium. Akinetes not observed.

Etymology: —Spe.lae.o.naias; GR feminine; spelaeon (= cave); naias (pl. naiades), a commonly inhabiting caves freshwater nymph of Greek mythology.

Type species:— Spelaeonaias floccida (Genbank: KY018918)

Figures

FIGURE 1. A–J. LM and SEM micrographs of Spelaeonaias floccida. A. Filaments of Spelaeonaias floccida showing the main filament and the secondary branches. B. Division of an initial cell, giving rise to two cells that change division polarity for the formation of a secondary branch. C. Secondary filament with a necridic cell (nc). D–G. Main and secondary filaments with the characteristic Y-type of branching; heterocytes at arrows. H. Hormogonia with an intercalary heterocyte at arrow. I. A single hormogonium with a terminal heterocyte (arrow). J. Single hormogonium as seen under SEM; the heterocyte (arrow) in a secondary filament is also obvious. Figs A–B from fresh material. Figs C–J from cultures. Scale bars = 10 μm (A–D, F, H, I) and 20 μm (Ε, G, J).

FIGURE 2. A–F. TEM micrographs of Spelaeonaias floccida. A. Longitudinal section showing a septum (s) without intercellular connection between vegetative cells, the outer membrane (om) and the plasma membrane (pm). Note the thick and compact sheath near the cell wall, becoming diffluent externally. the thylakoids are scattered throughout the cyatoplasm forming curled bundles of 2–4 parallel arranged membranes, with phycobilisomes (pb) on their surface. B. Grazing thin section providing a top view of phycobilisomes as stellate structures, associated with thylakoidal membranes; the plasma membrane is followed by a thin layer of peptidoglycan (pl) and an outer membrane (om). C. Carboxysomes (cb) seen as polyhedral bodies. D. Peptidoglycan layer crossed by pore structures (arrow). E–F. Nucleoid regions surrounded by thylakoids and scattered through the cytoplasm; cy = cyanophycin granule. Scale bars = 500 nm (A, C–F) and 100 nm (B).

FIGURE 3. A–D. TEM micrographs of Spelaeonaias floccida showing cell division and mode of branching.A. Filament with short barrel cells showing a general view of dividing cells for branch formation; the oblique division of an initial cell at arrow. B. Oblique section at a particular part of a filament showing one heterocyte (h) with a polar plug of cyanophycin (cy) connected to the adjacent cell by a neck; note the extra wall layer (wl) surrounding the heterocyte. C. Cell division at a certain region of the filament and formation of a new septum (s); D–E. After the first division of the initial cell (ic) the resulting cell (arrow) changes polarity and is further dividing for the formation of a secondary branch. Scale bars = 2 μm (B) and 5 μm (A–D).

FIGURE 4. A–C. Confocal (CLSM) photomicrographs showing filaments of Spelaeonaias floccida covered by sheaths. A. 41 x-y optical sections (z step= 0.13 μm) showing the Y-type of true branching; note the central spaces devoid of fluorescence in the filaments, corresponding to the area of nucleoids. B. 30 x-y optical sections (z step= 0.13 μm) showing a degraded basal cell (dc) promoting a false branching. C. Main filament with secondary branches; division of initial cells (at arrows) implying further formation of secondary branches. Color allocation: DNA nucleic acids labelled with Hoechst 33258, cyan; reflection from minerals, white; autofluorescence of extracellular polymeric substances, green; colocalized autofluorescence of cyanobacteria in the red (phycobilins) and blue channels (chlorophylls), magenta. Scale bars = 10 μm.