Phayaothrix lacustris Tawong & T. Nishimura

Tawong, Wittaya, Nishimura, Tomohiro, Pongcharoen, Pongsanat, Saijuntha, Weerachai, Kucharoenphaibul, Siriwat, Sunpapao, Pathipat, Pongpadung, Piyawat & Ponza, Supat, 2024, Molecular characterization uncovering a novel genus of tapering-filamentous cyanobacteria from Thailand: Phayaothrix lacustris gen. & sp. nov. (Nostocales, Cyanophyta), Phytotaxa 647 (1), pp. 34-52 : 38

Phayaothrix lacustris Tawong & T. Nishimura sp. nov. ( Fig. 1 )

Description: —Macroscopic colonies in the form of mats or crusts, reddish-brown, non-mucilaginous. In liquid culture, growing or forming a turf attached to the sides of the culture tube. Filaments heteropolar or isopolar, straight or flexuous, sometimes twisted, coiled or loop forming at the terminal and middle regions, olive-green to reddish brown, solitary or aggregated to form dense tufted mats, containing one or two trichomes, swollen or widened at basal regions and then gradually tapering toward the end, 7.15–8.38 µm wide at the basal filament, without terminal thin hair-like forming, single or double lateral false branches at a break in the trichome, sometimes with a knotted growth form with intertwined trichomes. Sheath firm in the basal part but distinct in the middle and terminal parts, broader than the trichome width with 0.8–2.14 µm thick, colorless and open at the end. Trichome with spherical or hemispherical heterocytes at the basal region, occasionally forming cylindrical intercalary heterocytes, constricted or unconstructed at the crosswalls, distinct tapering when young, less evidently tapering or untapered when mature, enclosed in a single sheath, sometimes two inside a single widened sheath. Vegetative cell green or reddish-brown, granulated, cylindrical or barrel-shaped, longer than wide in the middle and terminal part of the filament, 4.22–14.25 µm long × 2.29–4.06 µm wide in the terminal zone and 4.28–12.70 µm long × 2.71–5.86 µm wide in the middle region. In the basal part of the filament, cells elongated to rounded, compressed in the older trichomes, 3.36–9.58 µm long × 3.49–9.74 µm wide. Apical cell conical or conical rounded, slightly elongated, sometimes larger than nearby subterminal cells, 2.42–4.88 µm wide. Conical-rounded apical cells of filament possessed terminal heterocytes and became basal heterocytes. Heterocytes single or two in pairs, terminal, intercalary or basal position, pale yellow or yellow coloured, hemispherical or half-rounded, rounded or oblong, one or two pores, 5.08–11.70 µm long × 3.39–9.61 µm wide in the basal position and 4.93–14.02 µm long × 3.50–8.01 µm wide in intercalary position. The newer heterocyte subterminal to the elder or fading cell or developed from cells in the intercalary and terminal regions. Necridic cells green but sometimes purple. Akinetes not observed. Hormogonia straight, short, untapered and sometimes forming heterocytes at one or both sides of terminal cells (isopolar hormogonia). Reproduction by hormogonia, which separate from the trichome, by the formation of necridic cells and which then are liberated from the sheath, sometimes dissociating at heterocytes and separately develop into new trichomes. Cell division in hormogonia or filament in one plane to the longitudinal axis of trichomes in the same sheath.

Holotype: — QBG No.140239, a specimen of strain NUACC09 fixed in 4% formaldehyde, deposited at the Queen Sirikit Botanic Garden Herbarium ( QBG), the Botanical Garden Organization, Chiang Mai, Thailand.

Habitat: —A cyanobacterial mat attached to a surface of rocks in a freshwater lake.

Type locality: —Mueang Phayao, Phayao Province, Phayao Lake ( Kwan Phayao ), Thailand (19°09’51.8”N, 99°53’47.3”E) .

Etymology: —The species name, lacustris (N.L. masc./fem. adj. lacustris, growing by lakes or ponds), refers to the inhabiting origin of the taxon found in the freshwater lake.

Reference strain: —NUACC09.

GenBank number: —16S rRNA and 16S–23S rRNA ITS: LC777623, rbcLX gene: LC777626.

Figures

FIGURE 1. Morphological variability of Phayaothrix lacustris strain NUACC09 using light microscopy. Scale bar 10 µm. (A–C) heteropolar filament without a hyaline hair at the terminal, (D) old filament showing a hyaline sheath and double intercalary heterocyte, (E–G) twist, coil or loop forming at the terminal and middle regions after cell division, (H–I) knotted growth form and undulating filament, (J–K) young growing filament with single branching (arrow), (L) filament with double branching (arrow), (M–N) heterocytes with senescing heterocytes, (O) second heterocyte forming next to an old terminal cell (arrow), (P–Q) various apical cells developing into heterocyte (arrow), (R) filament showing hormogonia (open square) and necridia (asterisk), (S–T) hormogonia forming heterocytes at one or both sides of terminal cells.